Academic literature on the topic 'Solidification defects'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the lists of relevant articles, books, theses, conference reports, and other scholarly sources on the topic 'Solidification defects.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Journal articles on the topic "Solidification defects":
1
Elmquist, Lennart, Kaisu Soivio, and Attila Diószegi. "Cast Iron Solidification Structure and how it is Related to Defect Formation." Materials Science Forum 790-791 (May 2014): 441–46. http://dx.doi.org/10.4028/www.scientific.net/msf.790-791.441.
Abstract:
In this work, the meaning of the solidification structure and how it is related to defect formation in grey cast iron will be discussed. The work also confirms observations made earlier. In previous work the formation of shrinkage porosity in grey cast iron cylinder heads was investigated. It was found that the defect is located around solidification units resembling primary austenite grains. The solidification of grey cast iron starts with the formation of primary austenite grains, followed by the eutectic solidification. The primary grains nucleate and grow either as columnar or equiaxed grains, creating a columnar to equiaxed transition between the two zones. Based on the presence of a migrating hot spot, and other characteristics found on the cylinder heads, a geometry was developed that promote the formation of shrinkage porosity. The primary solidification structure, normally transformed during the solid state transformation, was preserved using a technique called Direct Austempering After Solidification (DAAS). After solidification, the samples were cut and prepared for investigation using a Scanning Electron Microscope (SEM) equipped with a detector for Electron Back Scattered Diffraction (EBSD). Individual grains were identified and the primary solidification structure around the defects was revealed. The investigation shows how shrinkage porosity is formed and located between primary austenite grains. This confirms that the primary solidification structure has a large influence on the formation of defects in grey cast iron. The investigation also confirms the correctness of earlier results as well as the validity of the DAAS technique.
2
Nan, Hong Yan, Li Lin Chen, Guo Fa Mi, and Jiao Ma. "Application of Numerical Simulation and Optimization on Tensioner Pulley Bracket." Advanced Materials Research 529 (June 2012): 186–89. http://dx.doi.org/10.4028/www.scientific.net/amr.529.186.
Abstract:
This article is about casting process of tensioner pulley bracket, which includes solidification simulation, mould filling simulation and defect forecast, using ViewCast software. The scale and location of the shrinkage defects were shown in simulation results. Solidification results demonstrated that the casting defects were not eliminated by the casting technology. The optimized scheme was obtained by replacing and adding chills. The optimization scheme was calculated and the simulation results shown that the reasonable casting process was obtained and the process has been proofed by the productive practice.
3
Mooraj, Shahryar, Jiaqi Dong, Kelvin Y. Xie, and Wen Chen. "Formation of printing defects and their effects on mechanical properties of additively manufactured metal alloys." Journal of Applied Physics 132, no. 22 (December 14, 2022): 225108. http://dx.doi.org/10.1063/5.0132137.
Abstract:
Printing defects are known to degrade the performance of additively manufactured (AM) alloys. Thus, a thorough understanding of their formation mechanisms and effects on the mechanical properties of AM materials is critically needed. Here, we take CoCrFeNi high-entropy alloy as a model material and print this alloy by laser powder bed fusion over a wide range of printing conditions. We reveal the processing windows for the formation of different printing defects including lack of fusion (LOF), keyhole, and solidification cracking. LOF and keyholes can be well correlated with insufficient and excessive laser energy density inputs, respectively. Of particular interest, we observe that solidification cracks only emerge at the medium laser energy density region, where the porosity is minimal yet the grain size and misorientation are relatively large. Such observation is rationalized within the framework of Rappaz–Drezet–Gremaud solidification theory. Among the above printing defects, solidification cracks in AM CoCrFeNi result in less degradation of mechanical properties compared with LOF and keyholes due to their different defect densities and resultant capabilities of coalescence. Our work provides fundamental insight into understanding the physical origins underlying the formation of printing defects and their impacts on the mechanical properties of AM metals and alloys.
4
Meshram, Suresh, and Madhusudhan Reddy. "Influence of Tool Tilt Angle on Material Flow and Defect Generation in Friction Stir Welding of AA2219." Defence Science Journal 68, no. 5 (September 12, 2018): 512–18. http://dx.doi.org/10.14429/dsj.68.12027.
Abstract:
Heat treatable aluminium alloy AA2219 is widely used for aerospace applications, welded through gas tungsten and gas metal arc welding processes. Welds of AA2219 fabricated using a fusion welding process suffers from poor joint properties or welding defects due to melting and re-solidification. Friction stir welding (FSW) is a solid-state welding process and hence free from any solidification related defects. However, FSW also results in defects which are not related to solidification but due to improper process parameter selection. One of the important process parameters, i.e., tool tilt angle plays a critical role in material flow during FSW, controlling the size and location of the defects. Effect of tool tilt angle on material flow and defects in FSW is ambiguous. A study is therefore taken to understand the role of tool tilt angle on FSW defects. Variation in temperature, forces, and torque generated during FSW as a result of different tool tilt angles was found to be responsible for material flow in the weld, controlling the weld defects. An intermediate tool tilt angle (1o-2o) gives weld without microscopic defect in 7 mm thick AA2219 for a given set of other process parameters. At this tool tilt angle, x-force, and Z- force is balanced with viscosity and the material flow strain rate sufficient for the material to flow and fill internal voids or surface defects in the weld.
5
Yu, J. K., Q. Yan, and Pin Yang Fang. "Solidification of Aluminum Infiltrated Composites." Materials Science Forum 475-479 (January 2005): 901–4. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.901.
Abstract:
The solidification and defects of Al/SiC and Al/C composites were investigated by directional solidification techniques. The solidification and defects of Al/SiC composites are greatly influenced by temperature gradients, solidification rates, the size of SiC particles and the chemical composition of magnesium, but slightly by the volume fraction of SiC particles and the chemical composition of silicon. The solidification shrinkage feeding of Al/C composites is greatly improved by hybridizing carbon fiber bundles with 3 vol% of SiC particles. A model of the solidification feeding was proposed and the solidification feeding distance was derived according to the preform geometry.
6
Huo, Miao, Chuyue Chen, Hangyue Jian, Wenchao Yang, and Lin Liu. "The Stray Grains from Fragments in the Rejoined Platforms of Ni-Based Single-Crystal Superalloy." Metals 13, no. 8 (August 15, 2023): 1470. http://dx.doi.org/10.3390/met13081470.
Abstract:
Nickel-based single crystal superalloy is the most important material for blade preparation. However, some solidification defects inevitably occur during the process of preparing single-crystal blades through directional solidification. In this study, in order to study the origin of misorientation defects during solidification, a model with rejoined platforms was designed according to the geometry of single-crystal guide vanes. Electron Back-Scattering Diffraction (EBSD) was used to quantify the orientation deviation of the dendrites and identify the solidification defects in the rejoined platforms. The results showed that stray grain defects appeared in the platforms and their misorientation changed gradually, not abruptly. Combined with the simulation results, it was proposed that the stray grains formed as the result of the dendrites fragment, which was induced by solute enrichment in the mushy zone during solidification. Meanwhile, it was accompanied by a obvious dendritic deformation, which was caused by solidification shrinkage stress. This suggested that the fragmentation was induced by multiple factors, among which, the concave interface shape provided favorable conditions for solute enrichment, and the dynamic variability in the local thermal gradient and fluctuations of the solidification rate might play catalytic roles.
7
Korojy, B., L. Ekbom, and H. Fredriksson. "Microsegregation and Solidification Shrinkage of Copper-Lead Base Alloys." Advances in Materials Science and Engineering 2009 (2009): 1–9. http://dx.doi.org/10.1155/2009/627937.
Abstract:
Microsegregation and solidification shrinkage were studied on copper-lead base alloys. A series of solidification experiments was performed, using differential thermal analysis (DTA) to evaluate the solidification process. The chemical compositions of the different phases were measured via energy dispersive X-ray spectroscopy (EDS) for the Cu-Sn-Pb and the Cu-Sn-Zn-Pb systems. The results were compared with the calculated data according to Scheil's equation. The volume change during solidification was measured for the Cu-Pb and the Cu-Sn-Pb systems using a dilatometer that was developed to investigate the melting and solidification processes. A shrinkage model was used to explain the volume change during solidification. The theoretical model agreed reasonably well with the experimental results. The deviation appears to depend on the formation of lattice defects during the solidification process and consequently on the condensation of those defects at the end of the solidification process. The formation of lattice defects was supported by quenching experiments, giving a larger fraction of solid than expected from the equilibrium calculation.
8
Hassan, Mohamed Abubakr, Mahmoud Hassan, Chi-Guhn Lee, and Ahmad Sadek. "Monitoring Variability in Melt Pool Spatiotemporal Dynamics (VIMPS): Towards Proactive Humping Detection in Additive Manufacturing." Journal of Manufacturing and Materials Processing 8, no. 3 (May 29, 2024): 114. http://dx.doi.org/10.3390/jmmp8030114.
Abstract:
Humping is a common defect in direct energy deposition processes that reduces the geometric integrity of printed products. The available literature on humping detection is deemed reactive, as they focus on detecting late-stage melt pool spatial abnormalities. Therefore, this work introduces a novel, proactive indicator designed to detect early-stage spatiotemporal abnormalities. Specifically, the proposed indicator monitors the variability of instantaneous melt pool solidification-front speed (VIMPS). The solidification front dynamics quantify the intensity of cyclic melt pool elongation induced by early-stage humping. VIMPS tracks the solidification front dynamics based on the variance in the melt pool infrared radiations. Qualitative and quantitive analysis of the collected infrared data confirms VIMPS’s utility in reflecting the intricate humping-induced dynamics and defects. Experimental results proved VIMPS’ proactivity. By capturing early spatiotemporal abnormalities, VIMPS predicted humping by up to 10 s before any significant geometric defects. In contrast, current spatial abnormality-based methods failed to detect humping until 20 s after significant geometric defects had occurred. VIMPS’ proactive detection capabilities enable effective direct energy deposition control, boosting the process’s productivity and quality.
9
Khan, Muhammad Azhar Ali. "Simulation Based Mold Design Optimization of a Spring Flap Casting." Solid State Phenomena 305 (June 2020): 178–84. http://dx.doi.org/10.4028/www.scientific.net/ssp.305.178.
Abstract:
The complex nature of metal casting process brings about a need to simulate it before undertaken in a foundry. Casting simulations provide insights on flow of molten metal within the mold, solidification sequence, nature and location of defects etc. Moreover, mold design can be optimized to minimize defects without undergoing physical trials-and-errors as previously practiced in traditional metal casting. This study is based on casting an ASTM A216 WCB steel spring flap for automotive suspension system using a simulation based optimized mold design. The initial and optimized mold designs are simulated in MAGMASoft for mold filling, solidification, stress distribution and defects prediction. The results of simulations and actual castings are found to be in good agreement. It is concluded that simulations are accurate in modeling casting process and in predicting defects followed by their minimization through mold design optimization. The use of auxiliary components in a carefully designed mold can lead to a nearly defect-free and high quality cast product.
10
Xu, Qing Yan, Bai Cheng Liu, Zuo Jian Liang, Jia Rong Li, Shi Zhong Liu, and Ha Llong Yuan. "Modeling of Unidirectional Growth in a Single Crystal Turbine Blade Casting." Materials Science Forum 508 (March 2006): 111–16. http://dx.doi.org/10.4028/www.scientific.net/msf.508.111.
Abstract:
Single crystal superalloy turbine blade are widely used in aero-engineering. However, there are often grain defects occurring during the fabrication of blade by casting. It is important to study the formation of microstructure related defects in turbine blades. Single crystal blade sample castings of a nickel-base superalloy were produced at different withdrawal rates by the directional solidification process and investment casting. There was a difference between the microstructure morphology at the top part of the turbine blade sample castings and the one at the bottom. Higher withdrawal rates led to more differences in the microstructure and a higher probability of crystallographic defect formation such as high angle boundaries at locations with an abrupt change of the transversal section area. To further investigate the formation of grain defects, a numerical simulation technique was used to predict the crystallographic defects occurring during directional solidification. The simulation results agreed with the experimental ones.
Dissertations / Theses on the topic "Solidification defects":
1
Brewster, G. J. J. "Solidification and heat-treatment related defects in single crystal nickel-base superalloys." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596900.
Abstract:
This thesis examines the causes of surface scale, surface inter-dendritic phase formation and surface melting. These effects hinder component inspection and lead to extensive rework operations and component scrap. Surface scale is a region of colouration observed on the external surface of cast components. It has been shown to occur in the solid-state and to result from the differential thermal contraction between the mould and metal, driving separation during the casting process. The regions of the casting that separate from the mould are exposed to the casting atmosphere, resulting in the formation of a thin oxide interference film, or surface scale. The separation of the mould and metal in the solid state can cause the semi-solid ‘mush’ above to contract, resulting in segregated liquid flow towards the surface and a layer of inter-dendritic phases at the surface of the casting. Therefore a close relationship between surface inter-dendritic phase formation and the spatial occurrence of surface scale is observed. After heat-treatment a number of components exhibit ‘blisters’ of melted material at the surface, even in under-solutioned components. Surface melting frequently occurs within the scaled regions of turbine blade components, however the reasons for this were previously not understood. The increased risk of inducing melting of these lower melting point inter-dendritic phases on the surface associated with surface scale rationalizes this observation.
2
Khalajzadeh, Vahid. "Modeling of shrinkage porosity defect formation during alloy solidification." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6155.
Abstract:
Among all casting defects, shrinkage porosities could significantly reduce the strength of metal parts. As several critical components in aerospace and automotive industries are manufactured through casting processes, ensuring these parts are free of defects and are structurally sound is an important issue. This study investigates the formation of shrinkage-related defects in alloy solidification. To have a better understanding about the defect formation mechanisms, three sets of experimental studies were performed. In the first experiment, a real-time video radiography technique is used for the observation of pore nucleation and growth in a wedge-shaped A356 aluminum casting. An image-processing technique is developed to quantify the amount of through-thickness porosity observed in the real-time radiographic video. Experimental results reveal that the formation of shrinkage porosity in castings has two stages: 1-surface sink formation and 2- internal porosity evolution. The transition from surface sink to internal porosity is defined by a critical coherency limit of . In the second and third experimental sets, two Manganese-Steel (Mn-Steel) castings with different geometries are selected. Several thermocouples are placed at different locations in the sand molds and castings to capture the cooling of different parts during solidification. At the end of solidification, castings are sectioned to observe the porosity distributions on the cut surfaces. To develop alloys’ thermo-physical properties, MAGMAsoft (a casting simulation software package) is used for the thermal simulations. To assure that the thermal simulations are accurate, the properties are adjusted to get a good agreement between simulated and measured temperatures by thermocouples.
Based on the knowledge obtained from the experimental observations, a mathematical model is developed for the prediction of shrinkage porosity in castings. The model, called “advanced feeding model”, includes 3D multi-phase continuity, momentum and pore growth rate equations which inputs the material properties and transient temperature fields, and outputs the feeding velocity, liquid pressure and porosity distributions in castings. To solve the model equations, a computational code with a finite-volume approach is developed for the flow calculations. To validate the model, predicted results are compared with the experimental data. The comparison results show that the advanced feeding model can accurately predict the occurrence of shrinkage porosity defects in metal castings. Finally, the model is optimized by performing several parametric studies on the model variables.
3
Zareie, Rajani Hamid Reza. "Development of a three-dimensional multi-scale model to study the formation of solidification defects in fusion welding." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/57601.
Abstract:
One of the long-standing challenges in joining of aluminum alloys is the occurrence of
solidification defects, i.e. hot cracking and porosity, since these defects significantly increase manufacturing costs. This research project investigates the formation of solidification defects through development of a novel and comprehensive 3-D multi-scale and multi-physics numerical study and then application to the GTA welding of the aluminum alloy AA6061. The developed multi-scale model is composed of four different modules: 1) Solidification, 2) Deformation, 3) Fluid flow, and 4) Defect formation. The solidification module numerically reconstructs the 3-D microstructure of semisolid welds using a granular model of solidification. Specifically, a modified Voronoi tessellation algorithm is used to generate an unstructured grid representing the weld microstructure. The reconstructed microstructure contains both columnar and equiaxed grains and varies as a function of welding process parameters. Then, the Scheil equation is used in combination with the temperature field obtained through the Rosenthal equation and the reconstructed 3D microstructure to simulate solidification. This module outputs the evolving 3D structure of the semisolid weld composed of solid grains and a network of micro liquid channels for use by the deformation and fluid flow modules as the simulation geometry. The deformation module analyzes via finite elements the deformation of the semisolid weld due to externally applied strains and self-induced strains such as thermo-mechanical strains and solidification shrinkage in order to obtain local strain rates within the micro liquid channels. The local strain rates outputted by the deformation module feed a fluid flow analysis module in which the pressure field within the semisolid weld is calculated. Finally, the defect formation module uses various defect formation models to link the pressure field and the local strain rates to the formation of solidification defects including micro cracks and hydrogen porosity.Applied Science, Faculty of
Engineering, School of (Okanagan)
Graduate
4
Lantreibecq, Arthur. "Détermination de la nature et de l'origine des défauts cristallins dans le silicium monolike." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30311/document.
Abstract:
Le silicium monolike (ML), est un matériau obtenu par croissance dirigée sur des germes monocristallins et dédié aux applications photovoltaïque. Cette thèse se concentre sur la qualité structurale de ces cristaux de plusieurs centaines de kilogrammes et qui contiennent des défauts dont certains affectent particulièrement le rendement solaire. Le but est de comprendre les mécanismes d'apparition et de multiplication de ces défauts pour pouvoir à terme les inhiber. Comme le développement de sous-joints de grains (SJG), principaux responsables des pertes de rendements photovoltaïques, est potentiellement lié aux contraintes thermomécaniques qui se développent au cours du cycle de fabrication, nous avons simulé numériquement les températures d'un four contenant un lingot sur un cycle complet (fusion, croissance, refroidissement). A partir des valeurs de températures, nous avons pu établir une cartographie des contraintes thermomécaniques ainsi que leur évolution temporelle. En parallèle, nous avons utilisé plusieurs techniques de caractérisations structurales et électriques pour analyser les défauts cristallins et leur répartition dans le lingot, et ce à différentes échelles. Au cours du cycle, un premier maximum de contrainte en fin de chauffe génère des dislocations et des précurseurs de SJG dans le germe, le second en fin de solidification / début de refroidissement mène à l'organisation finale des dislocations du bruit de fond présentes dans tout le lingot. Une fois les SJG apparus, ils s'étendent latéralement au fur et à mesure de la progression de l'interface solide-liquide. Ces sous-joints ont une structure constituée de dislocations sessiles et verticales, qui suivent le front de solidification mais également de dislocations mobiles qui viennent se bloquer sur cette structure préexistante. [...]Monolike silicon (ML Si), is a material obtained by directional solidification on monocrystalline seeds and dedicated to photovoltaic applications. This thesis focuses on the structural quality of these crystals of several hundred kilograms that contain defects that potentially affect the photoelectric yield. The goal is to understand the mechanisms by which these defects nucleate and multiply in order to inhibit them. Since the development of sub-grain boundaries (SGB), which are the main factors for the losses of photovoltaic yields, is potentially related to the thermomechanical stresses that develop during a thermal cycle, we simulated numerically the temperatures of an oven containing an ingot over a complete cycle (fusion, growth, cooling). From the temperature values, we were able to establish a map of the thermomechanical stresses as well as their temporal evolution. In parallel, we used several structural and electrical characterization techniques to analyze crystalline defects and their distribution in the ingot at different scales. During the cycle, a first maximum of stress at the end of the heating stage generates dislocations and precursors of SGB in the seed. The second stress maximum at the end of solidification / start of cooling stage leads to the final organization of background dislocations present in the whole ingot. Once the SGB appear, they extend laterally as the solid-liquid interface progresses. These SGB have a structure consisting of sessile and vertical dislocations, which follow the solidification front and also mobile dislocations that interact with this pre-existing structure. The integration of these mobile dislocations, which can occur just below the solid-liquid interface or during cooling, increases the misorientation of the SGB. [...]
5
Ouaddah, Hadjer. "Study of crystalline defects issued from silicon solidification : effect of impurities and correlation between crystallography, physicochemical and electrical properties." Electronic Thesis or Diss., Aix-Marseille, 2021. http://theses.univ-amu.fr.lama.univ-amu.fr/211214_OUADDAH_370ltw379yep573fxydon897z_TH.pdf.
Abstract:
Une approche expérimentale incluant plusieurs techniques a été utilisée pour caractériser les défauts structuraux issus de la solidification, par imagerie X in situ, et par des techniques complémentaires ex situ pour caractériser la structure de grains, la qualité cristalline et la déformation. La composition et la ségrégation des impuretés ont été corrélées avec la caractérisation des défauts et les propriétés électriques. Les analyses montrent l'influence significative des impuretés légères et métalliques sur la solidification du silicium et sur les propriétés électriques. En présence d'impuretés légères, une fréquence plus élevée de germination des grains est observée, elle est liée à la présence de précipités. La structure de grains résultante est constituée d'une plus grande proportion de macles d'ordre élevé et de joints de grain aléatoires par rapport au cas des échantillons faiblement contaminés. De plus, des déformations locales sont induites par la présence de SiC et sont à l'origine de la formation de sous-joints. Les propriétés électriques sont dégradées en présence d’impuretés légères par rapport au cas des matériaux Si purs. Dans les échantillons contaminés par le Cu, aucun effet significatif sur la structure de grains n'a été mis en évidence. Cependant, les joints de macles Σ3 cohérents qui sont des défauts de haute qualité cristalline peuvent être actifs en présence de Cu. Cette observation a été corrélée à la ségrégation du Cu au niveau de ces joints de grains. Au cours de cette étude, les progrès récents des caractérisations in situ de dynamique de formation des défauts pendant la solidification ont permis d’ouvrir de nouvelles perspectivesAn experimental approach including several techniques was used to characterize structural defects issued from the solidification by in situ X-ray imaging during solidification and by complementary ex situ techniques to characterize and quantify the grain structure, crystalline quality, and deformation. The composition and segregation of impurities were measured in correlation with the defect characterization and correlated to minority carrier lifetime measurements. The analysis shows significant influence of light impurities and metallic impurities on Si solidification and on the electrical properties. In the presence of light impurities, a higher frequency of grain nucleation is observed, it is linked to the presence of precipitates. The resulting grain structure is constituted by a higher proportion of high order twin and of random angle grain boundaries compared to the case of low contaminated samples. Moreover, local deformations are induced by the presence of SiC and are at the origin of SABGs (small angle grain boundaries) formation. The electrical properties are degraded (lower and inhomogeneous minority carrier lifetime) in the presence of light impurities compared to the case of pure Si materials. In Cu contaminated samples, no significant effect on the grain structure was evidenced. However, coherent Σ3 twin boundaries, which are defects of high crystalline quality, can be active in presence of Cu. This observation was correlated to Cu segregation at the level of these grain boundaries. During this study, recent progress concerning the in situ characterization of the defect formation dynamics during solidification allowed to open new prospects
6
Klein, Cândida Cristina. "Segregação de índio em cristais Ga1-xInxSb dopados com telúrio obtidos pelo método Bridgman vertical." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/147761.
Abstract:
Os compostos semicondutores ternários, dentre eles o Ga1-xInxSb, têm sido objeto de interesse de pesquisadores e da indústria microeletrônica devido à possibilidade de ajuste da constante de rede, assim como a correspondente modificação da banda proibida de energia e do intervalo de emissão e absorção óptica, com a variação da fração molar de x. A flexibilidade destas propriedades estruturais torna este composto apropriado como substratos para epitaxias de outros compostos ternários e quaternários, na formação de mono e heterojunções. A maneira mais econômica para obtenção de substratos de materiais semicondutores é através do crescimento de cristais a partir da fase líquida. Porém, os parâmetros que regem a obtenção de lingotes de Ga1-xInxSb com qualidade comercial, a partir da fase líquida, ainda não estão bem definidos. O índio tende a segregar para o líquido, pois seu coeficiente de segregação é menor que a unidade (k < 1), resultando num perfil composicional variado ao longo do lingote. Como os binários GaSb e InSb apresentam configurações de defeitos intrínsecos que originam condutividades de tipos opostos, tipo p e tipo n, respectivamente, a mudança na composição da liga, durante o crescimento, provavelmente resulta na modificação da concentração de cada um destes defeitos. A dopagem com telúrio consiste numa alternativa para minimizar a segregação do índio e diminuir a densidade dos defeitos pontuais, melhorando a qualidade estrutural de cristais de Ga1-xInxSb obtidos através do método Bridgman convencional. Desta forma foram crescidos cristais ternários Ga1-xInxSb, com e sem agitação do líquido durante a síntese, com fração molar inicial de índio de 10% e 20%, alguns deles dopados com 1020 átomos/cm3 de telúrio, pelo método Bridgman vertical. A caracterização estrutural em termos de formação de defeitos lineares, interfaciais e volumétricos foi realizada através de imagens obtidas por microscopia óptica, eletrônica de varredura e de transmissão. A homogeneidade composicional e distribuição de fases foi avaliada através de medidas de espectroscopia por dispersão de energia. Medidas de resistividade e efeito Hall foram utilizadas para a caracterização elétrica, enquanto que a transmitância óptica e a banda proibida de energia foram avaliadas por espectrometria FTIR. Os padrões de difração obtidos através da microscopia eletrônica de transmissão foram utilizados para avaliar a cristalinidade das amostras e determinar o parâmetro de rede. Os resultados obtidos indicam que o telúrio atua de forma compensatória, minimizando a segregação de índio e contribuindo para a homogeneidade composicional e redução de defeitos, principalmente de discordâncias. Além disso, altera a condutividade do Ga1-xInxSb para tipo n, mesmo em frações molares de In inferiores a x = 0,5, diminuindo o número de cargas positivas na rede atribuídas aos defeitos tipo GaSb e VGaGaSb e, desta forma, aumenta a concentração de portadores de carga e reduz a resistividade. Na condição de alta dopagem, reduz a transmitância óptica no infravermelho e aumenta a banda proibida de energia através do efeito Burstein-Moss. A avaliação de cristais de Ga1-xInxSb, dopados e não dopados, crescidos pelo método Bridgman convencional contribuiu para o entendimento do comportamento de dopantes em compostos semicondutores ternários.Ternary compound semiconductors, including Ga1-xInxSb, have been subject of interest of researchers and microelectronics industry because of the possibility of adjusting the lattice constant, as well as the corresponding modification in the band gap energy, and in the optical absorption and emission range, by varying the mole fraction x. The flexibility of their structural properties makes this compound suitable as substrates for epitaxy of other ternary and quaternary compounds, in the formation of mono- and heterojunctions. The most economical way to obtain semiconductor substrates is by crystal growth from the liquid phase. However, the parameters governing the outcoming of Ga1-xInxSb ingots with commercial quality, from liquid phase, are not well defined. Indium tends to segregate to the liquid, since its segregation coefficient is less than the unity (k < 1), resulting in a varied compositional profile along the ingot. As the binary GaSb and InSb have intrinsic defects configurations that originate opposite conductivities, type p and type n, respectively, the change in the alloy composition, while growing, probably results in a modification of the concentration on each of these defects. Doping with tellurium is an alternative to minimize the indium segregation and decrease the density of point defects, therefore improving the structural quality of Ga1-xInxSb crystals obtained through the conventional Bridgman method. Thus, ternary Ga1-xInxSb crystals were grown by vertical Bridgman method with and without stirring the melt during the synthesis, with 10% and 20% initial molar fraction of indium and some of them were tellurium-doped at 1020 atoms/cm3. The structural characterization regarding linear, interfacial, and volumetric defects formation was performed by using images obtained through optical, scanning and transmission electron microscopy. The compositional homogeneity and phase distribution was assessed by energy-dispersive spectroscopy measurements. Resistivity and Hall Effect measurements were used for the electrical characterization, while the optical transmittance and the band gap energy were examined by FTIR spectroscopy. Diffraction patterns obtained by transmission electron microscopy were used to evaluate the crystallinity of the samples and determine the lattice parameter. The results indicate that tellurium acts in a compensatory way, minimizing indium segregation and contributing to the compositional homogeneity and defect reduction, especially in dislocations. In addition, it changes the conductivity of Ga1-xInxSb to n-type, even in mole fraction of In lower than x = 0.5, reducing the number of positive charges on the network assigned to GaSb and VGaGaSb defects, thus increasing the concentration of charge carriers and reducing the resistivity. In high doping condition, it reduces the optical transmittance in the infrared region and increases the energy of the band gap by the Burstein-Moss Effect. The evaluation of Ga1-xInxSb crystals, doped and undoped, grown by the conventional Bridgman method contributed to the understanding of dopants behavior in ternary compound semiconductors.
7
Riberi-Béridot, Thècle. "In situ characterization by X-ray synchrotron imaging of the solidification of silicon for the photovoltaic applications : control of the grain structure and interaction with the defects and the impurities." Electronic Thesis or Diss., Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0412.
Abstract:
Au cours de cette thèse, nous avons étudié in situ la solidification du silicium à l’aide de l'imagerie X-synchrotron. Les deux techniques utilisées lors de la solidification sont la radiographie et la diffraction de Bragg, elles permettent de caractériser: la dynamique des mécanismes de croissance, la cinétique de croissance, la nucléation et la compétition de grains, la déformation du réseau cristallin et les champs de contraintes liés aux dislocations. Ces observations sont combinées avec des caractérisations ex situ pour étudier l'orientation cristallographique, les déformations du réseau cristallin ainsi que les concentrations d'impuretés légères telles que le carbone et l'oxygène.La complémentarité de ces techniques permet d'étudier et de mieux comprendre : les phénomènes physiques liés à la formation de la structure de grain finale. Les résultats concernant la cinétique de croissance de l'interface solide-liquide et des facettes {111}, l'établissement de la structure de grain, l'importance du maclage, l'effet des impuretés légères, le champ de contrainte lié à la croissance et la compétition de grains et les dislocations sont discutés dans le manuscritDuring this thesis, we studied in situ the solidification of silicon with X-synchrotron imaging. The two techniques used during solidification are radiography and Bragg diffraction and they allow characterizing: dynamic growth mechanisms, growth kinetics, grain nucleation and competition, lattice deformation and dislocation related strain fields. These observations are combined with ex situ characterizations to study the crystallographic orientation, the deformations of the crystal lattice as well as the concentrations of light impurities such as carbon and oxygen. The complementarity of these techniques makes it possible to study and to better understand: the physical phenomena related to the formation of the final grain structure. Results concerning the growth kinetics of the solid-liquid interface and of the {111} facets, the establishment of the grain structure, the importance of twinning, the effect of light impurities, the strain field related to growth and grain competition and dislocations are discussed in the manuscript
8
Castro, Roman Manuel de Jesús. "Étude expérimentale et modélisation de la solidification des pièces coulées en fonte à graphite spheroidal : influence de la vitesse de refroidissement et de l'inoculation." Vandoeuvre-les-Nancy, INPL, 1991. http://docnum.univ-lorraine.fr/public/INPL_T_1991_CASTRO_ROMAN_M_J.pdf.
Abstract:
La présente étude porte sur l'influence de la vitesse de refroidissement et du taux d'inoculation sur la structure de solidification des fontes à graphite sphéroïdal. Des modèles de simulation numérique de la solidification sont proposés. Des pièces comportant 5 cylindres de diamètres différents, instrumentés à l'aide de thermocouples, ont été coulées. Les courbes de refroidissement ont été dépouillées par analyse thermique directe et dérivée. La structure des cylindres a été caractérisée par analyse d'images : on a ainsi déterminé la densité surfacique de nodules, leur densité volumique, le taux de graphite et celui de cémentite. Des corrélations entre ces paramètres ont été établies et chiffrées, de même que des corrélations entre les caractéristiques des courbes de refroidissement et les paramètres structuraux des pièces. L'ensemble des corrélations expérimentales obtenues représente un moyen empirique pour décrire l'effet du taux d'inoculation et de la vitesse de refroidissement sur la structure de solidification des fontes. Les différents aspects de la simulation numérique et de la confrontation entre les résultats des calculs et les données expérimentales sont ensuite successivement abordés. La cinétique de solidification est décrite par un modèle qui comporte des lois de germination et de croissance des sphères eutectiques (nodule de graphite plus coquille d'austénite). On présente enfin un modèle amélioré qui considère le dépôt d'austénite hors des sphères eutectiques. La confrontation simulation-expérience montre que le type de modélisation examine permet de décrire l'effet de l'inoculation et de la vitesse de refroidissement sur la structure des pièces coulées. Cette approche peut aider à la rationalisation des connaissances empiriques que l'on a de ces phénomènes en fonderie
9
Riberi-Béridot, Thècle. "In situ characterization by X-ray synchrotron imaging of the solidification of silicon for the photovoltaic applications : control of the grain structure and interaction with the defects and the impurities." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0412/document.
Abstract:
Au cours de cette thèse, nous avons étudié in situ la solidification du silicium à l’aide de l'imagerie X-synchrotron. Les deux techniques utilisées lors de la solidification sont la radiographie et la diffraction de Bragg, elles permettent de caractériser: la dynamique des mécanismes de croissance, la cinétique de croissance, la nucléation et la compétition de grains, la déformation du réseau cristallin et les champs de contraintes liés aux dislocations. Ces observations sont combinées avec des caractérisations ex situ pour étudier l'orientation cristallographique, les déformations du réseau cristallin ainsi que les concentrations d'impuretés légères telles que le carbone et l'oxygène.La complémentarité de ces techniques permet d'étudier et de mieux comprendre : les phénomènes physiques liés à la formation de la structure de grain finale. Les résultats concernant la cinétique de croissance de l'interface solide-liquide et des facettes {111}, l'établissement de la structure de grain, l'importance du maclage, l'effet des impuretés légères, le champ de contrainte lié à la croissance et la compétition de grains et les dislocations sont discutés dans le manuscritDuring this thesis, we studied in situ the solidification of silicon with X-synchrotron imaging. The two techniques used during solidification are radiography and Bragg diffraction and they allow characterizing: dynamic growth mechanisms, growth kinetics, grain nucleation and competition, lattice deformation and dislocation related strain fields. These observations are combined with ex situ characterizations to study the crystallographic orientation, the deformations of the crystal lattice as well as the concentrations of light impurities such as carbon and oxygen. The complementarity of these techniques makes it possible to study and to better understand: the physical phenomena related to the formation of the final grain structure. Results concerning the growth kinetics of the solid-liquid interface and of the {111} facets, the establishment of the grain structure, the importance of twinning, the effect of light impurities, the strain field related to growth and grain competition and dislocations are discussed in the manuscript
10
Banos, Julien. "Modélisation du procédé de refusion à l’arc sous vide : Échanges thermiques et défauts de solidification." Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0117.
Abstract:
Le procédé de refusion à l'arc sous vide (Vacuum Arc Remelting ou VAR en anglais) est employé dans la production d'alliages métalliques à haute valeur ajoutée tels que les alliages de titane ou superalliages base nickel à destination de l'industrie aéronautique. La maîtrise des conditions de solidification constitue un enjeu industriel important pour obtenir des lingots d'une homogénéité chimique adéquate et dépourvus de défauts de solidification. Les travaux présentés dans ce document visent à améliorer la description des échanges thermiques dans un modèle du procédé VAR (SOLAR) et proposer une nouvelle approche pour la prédiction des défauts de solidification de type canaux ségrégés. Dans un premier temps, la description dans le modèle des échanges thermiques entre l'électrode, le lingot, la lingotière et le circuit de refroidissement a été améliorée. Les modifications ont fait l'objet de validation par comparaison des résultats numériques avec des mesures sur des refusions industrielles réelles. Un dispositif expérimental original de mesure de température à la paroi extérieure de la lingotière adapté aux refusions industrielles a été conçu et utilisé lors d'une campagne expérimentale sur site industriel lors de la refusion d'un alliage de titane. Les mesures obtenues ont été confrontées aux résultats numériques de SOLAR. Ces deux activités ont abouti à une première implémentation du phénomène de side-arcing dans le modèle. En parallèle, une approche numérique multi-échelle a été développée pour prédire la formation de canaux ségrégés en fonction des conditions locales de solidification. Une première étude sur un alliage Sn-Pb a été réalisée et un critère mathématique de prédiction a été calculé à partir des résultats. Cette première étude montre un impact du gradient thermique sur la formation de canaux ségrégés bien plus faible que celui généralement considéré dans la littératureThe Vacuum Arc Remelting (VAR) process is used in the production of high-added value metals such as titanium alloys or nickel-based superalloys for the aerospace industry. The control of solidification conditions is an important industrial issue in order to process ingots of adequate chemical homogeneity and free of solidification defects. The work presented in this manuscript aims at improving the description of heat exchanges in a VAR process model (SOLAR) and at proposing a new approach for the prediction of segregated channels type solidification defects. First, the description of the heat exchanges in the model between the electrode, the ingot, the mould and the cooling circuit has been improved. These modifications were validated by comparing the numerical results with measurements from real industrial melts. An original experimental apparatus for measuring the external mould temperature adapted to industrial melts was designed. This apparatus was used during an experimental campaign on an industrial site during the remelting of a titanium alloy. The measurements obtained were compared with the numerical results from SOLAR. These two activities led to a first implementation of the side-arcing phenomenon in the model. In parallel, a multi-scale numerical approach was developed to predict the formation of segregated channels as a function of local solidification conditions. A first study on a Sn-Pb alloy was carried out and a mathematical criterion was calculated from the results. This first study shows a much lower impact of the thermal gradient on the formation of segregated channels than that generally considered in the literature
Books on the topic "Solidification defects":
1
Campbell, F. C., ed. Metals Fabrication. ASM International, 2013. http://dx.doi.org/10.31399/asm.tb.mfub.9781627083089.
Abstract:
Metals Fabrication: Understanding the Basics describes the practices, processes, and procedures used throughout industry to produce metal products and goods. It begins with a review of primary mill processes and the basic steps for making iron, steel, aluminum, and titanium. It then covers nearly every subsequent fabrication process, starting with casting followed by forging, forming, machining, heat treating, finishing, and coating as well as powder-metal part production. The book provides a thorough review of each process, discussing typical implementations, material requirements, design considerations, and common imperfections and defects. It also explains how heat, force, and power generated by production equipment alter the metallurgical and mechanical properties of work in process, bringing practical perspective to many fundamental concepts including solidification, deformation, residual stress, fracture mechanics, wear, and phase transformations. For information on the print version, ISBN 978-1-62708-018-7, follow this link.
Book chapters on the topic "Solidification defects":
1
Perez, Nestor. "Solidification Defects." In Phase Transformation in Metals, 461–518. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-49168-0_10.
2
Mashaal, M., and M. Amar. "Stationnary Cells in Directional Solidification." In Patterns, Defects and Materials Instabilities, 147–57. Dordrecht: Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-009-0593-1_13.
3
Levine, Herbert. "Directional Solidification: Theoretical Methods and Current Understanding." In Patterns, Defects and Materials Instabilities, 123–33. Dordrecht: Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-009-0593-1_11.
4
Cladis, P. E., J. T. Gleeson, and P. L. Finn. "New Instabilities in Directional Solidification of Succinonitrile." In Patterns, Defects and Materials Instabilities, 135–46. Dordrecht: Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-009-0593-1_12.
5
Jamgotchian, H., R. Trivedi, and B. Billia. "Nonlinear Dynamics in Cellular Solidification in Presence of Defects." In Interactive Dynamics of Convection and Solidification, 105–8. Dordrecht: Springer Netherlands, 1992. http://dx.doi.org/10.1007/978-94-011-2809-4_18.
6
Saeedipour, Mahdi, Simon Schneiderbauer, Stefan Pirker, and Salar Bozorgi. "Prediction of Surface Porosity Defects in High Pressure Die Casting." In Advances in the Science and Engineering of Casting Solidification, 155–63. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2015. http://dx.doi.org/10.1002/9781119093367.ch19.
7
Saeedipour, Mahdi, Simon Schneiderbauer, Stefan Pirker, and Salar Bozorgi. "Prediction of Surface Porosity Defects in High Pressure Die Casting." In Advances in the Science and Engineering of Casting Solidification, 155–63. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-48117-3_19.
8
Sabau, Adrian S. "Modeling of Casting Defects in an Integrated Computational Materials Engineering Approach." In Advances in the Science and Engineering of Casting Solidification, 231–40. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2015. http://dx.doi.org/10.1002/9781119093367.ch28.
9
Sabau, Adrian S. "Modeling of Casting Defects in an Integrated Computational Materials Engineering Approach." In Advances in the Science and Engineering of Casting Solidification, 231–40. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-48117-3_28.
10
Eskin, D. G. "Structure and Casting Defects of Aluminum Billets Produced by Direct-Chill Casting." In Advances in the Science and Engineering of Casting Solidification, 73–80. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2015. http://dx.doi.org/10.1002/9781119093367.ch10.
Conference papers on the topic "Solidification defects":
1
Gor, S., T. Hohlweck, D. Fritsche, A. Schacht, N. Wolff, B. Pustal, H. Heinemann, A. Bührig-Polaczek, C. Hopmann, and K. Bobzin. "Potential Use of Plasma Sprayed Heating Coatings in Die Casting and Injection Molding." In ITSC2022. DVS Media GmbH, 2022. http://dx.doi.org/10.31399/asm.cp.itsc2022p0220.
Abstract:
Abstract In metal die casting as well as plastic injection molding, controlling the heat balance during the injection and solidification process can lead to fewer defects and a better component quality. An appropriate cooling channel design for the mold can help to control the solidification to a certain extent. But the heat control achievable by cooling channels is limited due to the high effective thermal mass, and therefore near-cavity energy input is of interest. In this paper, a simulation study is performed demonstrating the use of plasma sprayed ceramic coating as a heating coating at the cavity of the mold. The goal is to apply heat faster and locally focused during the solidification process in metal die casting as well as before the injection phase in plastic injection molding. The heat generation of these ceramic coatings is modelled using experimentally measured values and the effects of this approach on defects such as distortion and hot tearing is discussed.
2
Wielage, B., S. Steinhäuser, W. Milewski, and H. Pokhmurska. "Solidification of Detonation Sprayed Ceramic Coating Melted by CO2 Laser." In ITSC2002, edited by C. C. Berndt and E. Lugscheider. Verlag für Schweißen und verwandte Verfahren DVS-Verlag GmbH, 2002. http://dx.doi.org/10.31399/asm.cp.itsc2002p1020.
Abstract:
Abstract This paper investigates the effect of laser treatment on alumina-TiO2 coatings deposited by detonation spraying. It describes the changes observed in the microstructure and hardness of the remelted layers. The originally lamellar structure is transformed into a fine, pore-free columnar structure in which the grains are oriented perpendicular to the interface between the layer and substrate. The remelted zones contain alpha-aluminum oxide as the main phase and are characterized by high microhardness, although a few defects were observed on the periphery. Paper includes a German-language abstract.
3
Ghosh, S., and J. Choi. "Three-Dimensional Transient Finite Element Analysis for Microstructure Formation and Residual Stresses in Laser-Aided DMD Process." In ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56359.
Abstract:
Despite immense advances in Laser-Aided Direct Material Deposition process, many issues concerning the adverse effects of process parameters on the stability of variety of properties and the integrity of microstructure have been reported. Macroscopic aspects are important in predicting macroscopic defects or optimizing process conditions, while microstructural features such as phase appearance, morphology, grain size, spacing, or micro-defects are certainly no less important in determining the ultimate properties of the solidified product. Traditional solidification theories as applied to castings or related processes are inappropriate in describing solidification in high-energy beam processes involving significantly greater cooling rates. Due to the complexity and nonlinearity of this process, analytical solutions can rarely address the practical manufacturing process. This paper is an attempt towards a methodology of finite element analysis for the prediction of solidification microstructure and macroscopic as well as microscopic thermal residual stresses in this process. The computer simulation which is based on metallo-thermomechanical theory and finite element analysis for coupled temperature, solidification, phase transformation and stress/strain fields can prove to be a very useful tool in predicting the material behavior and optimizing the process parameters to obtain the best material properties. This model would reduce long and cumbersome experimental routes to predict the material behavior under similar loading conditions.
4
Rakita, Milan, and Qingyou Han. "Simulation of Solidification Defects for Prediction of Dross Formation in Aluminum 5182 Remelt Secondary Ingot." In ASME 2009 International Manufacturing Science and Engineering Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/msec2009-84160.
Abstract:
In aluminum recycling about 4% on average is lost on oxidation and dross. However, large percent of remelt secondary ingots (RSI) produce much more dross after remelting. It is rather surprising that no dross can be detected in the RSI, but after remelting some parts of apparently ‘healthy’ aluminum can give up to 80% of dross. This raises question how dross gets formed. Recent research proposes that the formation of dross after remelting of the RSI is closely related to the solidification process in the ingot, specifically the formation of shrinkage porosity, hydrogen porosity, and hot tearing. Under these circumstances, dross comes from oxidized surfaces of those defects. In this paper, simulations of the RSI cooling down show susceptibility of ingots towards shrinkage porosity and hot tearing, which are in accordance with experimental findings. Simulations also show that dross is more likely to form with increased temperature of the mold and increased thickness of the ingot. The only efficient solution for the problem of dross formation, however, seems to be a change in geometry of the mold.
5
Wang, W. B., X. H. Yang, Q. C. Zhang, and T. J. Lu. "Solidification Analysis of Density-Graded Closed-Cell Metallic Foam Under Constant Temperature Boundary Condition." In ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/mnhmt2016-6719.
Abstract:
In the industrial fabrication processes of density-graded closed-cell metallic foams, it is of great importance to control the solidification immediately after foams are formed so as to obtain the final products with well distributed density-graded pores and less defects. This paper presented an analytical work aiming to predict the solidification front of density-graded metallic foam under constant temperature boundary condition. Numerical simulations based on ideal density-graded circular pores demonstrated good agreement with the analytical solutions. The 2D porous morphology of a real density-graded aluminum foam was further reconstructed with microCT, on the basis of which the propagation of solidification front inside this real density-graded foam was numerically investigated. An equivalent shape factor for this real foam was calculated to provide an insight for the influence of different pore shapes on solidification. Compared with other pores, the solidification speed of elliptical pores (a common pore shape in real foams) is moderate, i.e., slower than circular pores but quicker than triangular pores for same porosity.
6
Hossain, Md Shahjahan, Russell Krenek, Hossein Taheri, and Fadwa Dababneh. "Ultrasonic Phased Array Technique for Defect Detection and Sizing in Heavy-Walled Cast Components." In ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-23319.
Abstract:
Abstract Cast metal parts are extensively found in many engineering products such as pump casing and engines. Thermal effects exhibited during metal casting processes, such as solidification can generate defects in the cast components. Effective nondestructive testing (NDT) for detection and sizing of defects in cast parts prevents extra cost and time associated with repair and maintenance. Surface-breaking cracks and porosity are among the common types of defects in large cast components. There are several limitations in using conventional NDT methods for as built cast parts due to surface conditions, coarse-grain structure, and characteristics of potential defects. Ultrasonic adaptive imaging based on the Phased Array Ultrasonic Testing (PAUT) technology is proposed for coarse-grain heavy-walled cast material inspection. The capability of aperture focusing in PAUT provides the opportunity for better imaging results. A comprehensive understanding about the ultrasonic beam focusing and the selection of an appropriate transducer and wedges is necessary for successful defect characterization. Cast aluminum and iron samples having on-purpose made defects were successfully inspected using the PAUT. Unlike conventional techniques, the results indicated that the PAUT is a promising method for inspecting as-built cast parts with rough surface finish conditions. The proposed method helps to decrease the inspection time, machining requirements, and preparation costs. Moreover, the enhanced defect sizing approach provides useful information for repair and maintenance decision making such as amount of material grinding and post-welding procedure.
7
Zhou, J., H. L. Tsai, and P. C. Wang. "Transport Phenomena and Defect Formation in Laser Welding of Zinc-Coated Steels." In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-59286.
Abstract:
Zinc-coated steels are used extensively in the auto industry because they are inexpensive, durable and have high corrosion resistance. Lasers are being used to weld zinc-coated steels due to high welding speed, small seam and narrow heat affected zone. However, it is difficult to laser weld lap-joint zinc-coated steel sheets under a very small gap condition between the metal interfaces since there is a considerable amount of zinc vapor generated. This vapor must be vented out; otherwise it will be trapped in the weld pool leading to different welding defects, such as large voids at the tip of the weld and porosities in the form of small bubbles in the weld. These defects can significantly decrease the strength of the weld. In this paper, a mathematical model and the associated numerical techniques have been developed to study the transport phenomena in laser welding of zinc-coated steels. The volume-of-fluid (VOF) method is employed to track free surfaces. The continuum model is used to handle the liquid phase, solid phase and mushy zone of the metal. The enthalpy method is employed to account for the latent heat during melting and solidification. The transient heat transfer and melt flow in the weld pool during the keyhole formation and collapse processes are calculated. The escape of zinc vapor through the keyhole and the interaction between zinc vapor and weld pool are studied. The aforementioned weld defects are found to be caused by the combined effects of zinc vapor-melt interactions, keyhole collapse and solidification process. By controlling the laser pulse profile, it is found that the keyhole collapse and solidification process can be delayed, allowing the zinc vapor to escape, which results in the reduction or elimination of weld defects.
8
Wang, Deming, Harry S. Whitesell, and Tony Overfelt. "Two-Dimensional Combined Radiation and Conduction Transient Heat Transfer in Directional Solidification." In ASME 1999 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/detc99/cie-9050.
Abstract:
Abstract This paper presents a computer-aided heat transfer simulation method to predict the thermal characteristics of an alloy sample in a special furnace for directional solidification. A two-dimensional transient heat transfer by radiation combined with conduction is developed to calculate the energy exchange between the symmetric furnace and the sample. Control volumes are used to obtain a set of highly efficient finite difference equations for heat conduction and heat radiation with changeable view factors. The simulation results are verified by measurable experimental results. Using the two-dimensional computer simulation model, many thermal properties of the samples can be obtained, such as temperature distribution, solidification velocity, the shapes and positions of the liquid/solid interface and thermal gradient at the interfaces. These are very important to analyze microstructure of casting alloy, avoid casting defects and control casting quality.
9
Fang, Haisheng, Lili Zheng, and Hui Zhang. "Control of Flow Pattern and Solidification Interface Shape in an Induction Heated Czochralski Crystal Growth System." In ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference collocated with the ASME 2007 InterPACK Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ht2007-32288.
Abstract:
Optical crystals grown by Czochralski technique from a solute-rich melt usually suffer defects of melt inclusion or bubble core defects, which severely affect the optical, thermal and mechanical properties of the material. It is well known that the formation of melt inclusion or bubble core is highly related to species distribution in the growth system especially at the solidification interface and the shape of the growth interface. This paper has examined the flow pattern and solidification interface changes by changing the forced convection, e.g., crystal rotation and by changing the natural convection, e.g., inserting a horizontal disk plate. The relative effect of fluid-flow convection modes in the melt associated with crystal rotation rate is represented by a dimensionless parameter, Gr/Re2. Increasing the rotation rate will cause the solid-liquid interface change from the convex shape to concave. When the crystal rotation rate is relatively low and natural convection is strong, Gr/Re2 is large. In this case, the concentration of species pertinent to melt inclusion moves down along the axis of rotation. When the crystal rotation rate is increased, the value of Gr/Re2 decreases. The precipitated composition spreads over the growing interface may then be swiped away from the growth interface by increased crystal rotation. Melt inclusion-free crystals can thus be obtained. The relationship between Gr/Re2 and growth interface shape change is achieved by numerical simulations. The stagnant point location as a function of crystal rotation is also presented, which shows that the stagnant point moves outward by increasing Reynolds number and/or reducing Grashof number. From such understanding, the interface shape and melt inclusion position can then be controlled through control of Gr/Re2 in the growth system. Many times, it is, however, not practical in the experiments to use a high rotation rate for optical crystal growth since high rotation rate will introduce the striation defects. A new design to reduce natural convection is then proposed to improve the effect of crystal rotation and to control the solidification interface shape. Numerical simulations have been performed to demonstrate the possibility of the new design. Results show that such design is very effective and practical to control the melt inclusion and the solidification interface shape.
10
Futas, Peter, Alena Pribulova, Jozef Petrik, Peter Blasko, and Vladimir Sabik. "THE NUMERICAL SIMULATION OF CASTING PROCESS OF CAST MADE FROM AUSTEMPERED DUCTILE IRON (ADI)." In 23rd SGEM International Multidisciplinary Scientific GeoConference 2023. STEF92 Technology, 2023. http://dx.doi.org/10.5593/sgem2023/2.1/s07.14.
Abstract:
Computer simulation has a significant application in the field of metallurgy. It is primarily an issue that deals with the issue of casting. The simulation of casting and solidification makes visible the foundry phenomena that take place in the gating system and the casting when the mold is filled with liquid metal and during its solidification. The article deals with the design of the gating system and the simulation of the filling and solidification of a real casting made of ductile iron. In the next production process, this casting is thermally treated (isothermal hardening) and ADI cast iron is obtained. Ductile iron EN-GJS-700-2 is used in the foundry as the basic material for ADI cast iron. The design of the gating system for a specific casting was designed in the CATIA V5R20 CAD system, and the computer simulation of casting and solidification was realized in the NovaFlow & Solid program. The correct design of the gating system is important mainly because of the resulting internal quality of the casting, the elimination of possible defects (shrinkages, micro shrinkages), as well as the increase in the use of liquid metal.
Reports on the topic "Solidification defects":
1
Asta, M. D., S. H. Davis, D. N. Seidman, P. W. Voorhees, T. M. Pollock, C. F. Woodward, and J. E. Spowart. Defects Associated with Solidification of Melt-Processed Superalloys for the Aerospace Industry. Fort Belvoir, VA: Defense Technical Information Center, June 2009. http://dx.doi.org/10.21236/ada501481.