Littérature scientifique sur le sujet « Transition Metal Based Intermetallic Alloys »

In order to study the improvement mechanism of transition metal elements on Mg-based hydrogen storage alloys, especially for the structures and properties of hydrogen storage alloy Mg2Ni, Ti and Zn substituted alloys Mg2-mMmNi,Mg2Ni1-nMn (M=Ti and Zn, m, n=0.1667), and their hydrides Mg2NiH4,Mg2-mMmNiH4,Mg2Ni1-nMnH4(M=Ti and Zn, m , n=0.125) have been investigated by first-principles. Through analyzing the results of the crystal structure, electron density distribution and density of states, the changes of structures and properties resulting from the adding of transition metal elements Ti and V of intermetallic Mg2Ni and its hydride Mg2NiH4 were investigated. The results showed that the addition of transition metal elements can reduce the stability of the Mg2Ni system to varying degrees and improve the dehydrogenation dynamics performance. Therefore, it may be considered that the substitution by transition metal elements in Mg-based hydrogen storage alloys is an effective technique to improve the thermodynamic behavior of hydrogenation/dehydrogenation in Mg-based hydrogen storage alloys (HSAs).

Laser cladding is an adequate technique to fabricate Metal Matrix Composite (MMC) layers because of its focused high energy which allows the partial melting of hard ceramic reinforces particles like carbides. Thus, the wettability and gradual transition between metal and particle can be improved. However, metastable or new intermetallic phases can be formed during laser processing due to severe thermal cycle imposed to the clad with unknown properties in some cases. In this work our experience on microstructural analysis of Ti-MMC coatings acquired during the last five years is summarized. Special attention is paid on carbide dilution and secondary carbides formation mechanisms when TiC, SiC, Cr3C2, WC and B4C are mixed with titanium alloys.

RENi5 (RE: rare earth) based alloys have been extensively evaluated for use as an electrode material for nickel-metal hydride batteries. A variety of alloys have been developed from the prototype intermetallic compound LaNi5. The use of mischmetal as a source of rare earth combined with transition metal and Al substitutions for Ni has caused the evolution of the alloy from a binary compound to one containing eight or more elements. This study evaluated the microstructural features of a complex commercial RENi5 based alloy using scanning and transmission electron microscopy.The alloy was evaluated in the as-cast condition. Its chemistry in at. pct. determined by bulk techniques was 12.1 La, 3.2 Ce, 1.5 Pr, 4.9 Nd, 50.2 Ni, 10.4 Co, 5.3 Mn and 2.0 Al. The as-cast material was of low strength, very brittle and contained a multitude of internal cracks. TEM foils could only be prepared by first embedding pieces of the alloy in epoxy.

Platinum (Pt) is a critical element in making electrocatalysts for oxygen reduction reaction (ORR) occurring at the cathode of polymer electrolyte membrane fuel cells (PEMFCs). To address the Pt abundance issue and to enhance Pt catalysis, Pt is often alloyed with another transition metal M (i.e. M = Fe, Co, and Ni). Ordered intermetallic PtM alloys are considered as one of the most promising candidates to achieve both high activity and stability in practical fuel cell applications. The transition metals in ordered intermetallic PtM alloys occupy specific sites, and are stabilized by both metallic and ionic bonding. Ordered intermetallic structures are formed via high temperature (>600 °C) annealing of disordered PtM alloys, as the atomic ordering is a thermodynamically driven process. However, the high temperature annealing inevitably leads to the migration and agglomeration of the nanoparticles forming randomly alloyed particles with poor dispersion and broad size distributions, due to weak adhesions to the carbon support under typical processing conditions. To prevent this coalescence during annealing, protective coating of the nanoparticles with inorganic shells or physical barriers has been suggested. However, these studies were limited to the synthesis of intermetallic nanoparticles on carbon supports at low metal loadings, or require an additional step of removing the coating layer from the surface of the nanoparticles to expose the active sites. Thus, it is essential to develop a general approach that can produce highly dispersed, structurally ordered nanoparticles while achieving controls over the size and size distribution. We propose to use the functionalized carbon supports to control PtM alloy nanoparticle size and prevent nanoparticles from aggregating during the high temperature annealing through improving the metal-support interactions. A strong electrostatic attraction between the negative charge from Pt precursor (PtCl6 2 -) and positive charge from the amino groups (C-NH2+) on the surface of the functionalized carbon will be established during the wet impregnation synthesis. Such bonds will help to make the PtM nanoparticle size smaller and more uniformly distributed over the surface of support. The ordered intermetallic 30 wt.% PtCo/KB-NH2 catalyst demonstrated an average size of 2.7 nm and uniform size distribution. In addition, 30 wt.% PtCo/KB-NH2 catalyst exhibited a mass activity of 535 A/gPt (H2/O2) and a rated power density of 1.05 W/cm2 at 0.67 V (H2/air), meeting the DOE targets.

Nb-silicide based alloys are new ultra-high temperature materials that could replace Ni-based superalloys. Environmentally resistant coating system (s) with αAl2O3 or SiO2 forming bond coat alloys that are chemically compatible with the Nb-silicide based alloy substrates are needed. This paper makes a contribution to the search for non-pesting bond coat alloys. The microstructure and isothermal oxidation at 800 °C of the silicide-based alloy Si-22Fe-12Cr-12Al-10Ti-5Nb (OHC2) were studied. The cast alloy exhibited macrosegregation of all elements. The microstructures in the cast alloy and after the heat treatment at 800 °C consisted of the same phases, namely TM6Si5, TM5Si3 (TM = transition metal), FeSi2Ti, Fe3Al2Si3, (Fe,Cr)(Si,Al), and an unknown phase of dark contrast. The latter two phases were not stable at 950 °C, where the TMSi2 was formed. There was evidence of endothermic reaction(s) below 1200 °C and liquation at 1200 °C. The alloy followed parabolic oxidation kinetics after the first hour of isothermal oxidation at 800 °C, did not pest, and formed a self-healing scale, in which the dominant oxide was Al2O3. The alloy was compared with other alumina or silica scale-forming intermetallic alloys and approaches to the design of bond coat alloys were suggested.

Magnetic intermetallic compounds based on rare earth elements and 3d transition metals are widely investigated due to the functionality of their physical properties and their variety of possible applications. In this work, we investigated the features of the electronic structure and magnetic properties of ternary intermetallic compounds based on gadolinium GdMn1-xTixSi, in the framework of the DFT + U method. Analysis of the densities of electronic states and magnetic moments of ions in Ti-doped GdMnSi showed a significant change in the magnetic properties depending on the contents of Mn and Ti. Together with the magnetic moment, an increase in the density of electronic states at the Fermi energy was found in almost all GdMn1-xTixSi compositions, which may indicate a significant change in the transport properties of intermetallic compounds. Together with the expected Curie temperatures above 300 K, the revealed changes in the magnetic characteristics and electronic structure make the GdMn1-xTixSi intermetallic system promising for use in microelectronic applications.

AlMgTi-based metal–intermetallic laminated composites were successfully fabricated through an innovative dual-step vacuum hot pressing. First, this study prepares the AlTi-based laminated composites by vacuum hot pressing at 650 °C. Then, the researchers place the Mg-Al-1Zn (AZ31) magnesium alloy between the prepared AlTi-based laminated composites at 430 °C for hot pressing. This study investigates the microstructure, phase composition, and microhardness distribution across interfaces of the intermetallics and metal. A multilayer phase (Mg17Al12, Al3Mg2, and transition layers) structure can be found from the diffusion layers between Al and AZ31. The microhardness of the material presents a wavy distribution in the direction perpendicular to the layers; the maximum can be up to 600.0 HV0.2 with a minimum of 28.7 HV0.2 The microhardness gradient of an AlMgTi-based composite is smoother due to the different microhardness of the layers, and reduces the interface stress concentration. The bending strength of AlMgTi-based composites can reach 265 MPa, and the specific strength is 105 × 103 Nm/kg, higher than AlTi-based composites.

Complex metallic alloys (CMAs) are materials composed of structurally complex intermetallic phases (SCIPs). The SCIPs consist of large unit cells containing hundreds or even thousands of atoms. Well-defined atomic clusters are found in their structure, typically of icosahedral point group symmetry. In SCIPs, a long-range order is observed. Aluminum-based CMAs contain approximately 70 at.% Al. In this paper, the corrosion behavior of bulk Al-based CMAs is reviewed. The Al–TM alloys (TM = transition metal) have been sorted according to their chemical composition. The alloys tend to passivate because of high Al concentration. The Al–Cr alloys, for example, can form protective passive layers of considerable thickness in different electrolytes. In halide-containing solutions, however, the alloys are prone to pitting corrosion. The electrochemical activity of aluminum-transition metal SCIPs is primarily determined by electrode potential of the alloying element(s). Galvanic microcells form between different SCIPs which may further accelerate the localized corrosion attack. The electrochemical nobility of individual SCIPs increases with increasing concentration of noble elements. The SCIPs with electrochemically active elements tend to dissolve in contact with nobler particles. The SCIPs with noble metals are prone to selective de-alloying (de–aluminification) and their electrochemical activity may change over time as a result of de-alloying. The metal composition of the SCIPs has a primary influence on their corrosion properties. The structural complexity is secondary and becomes important when phases with similar chemical composition, but different crystal structure, come into close physical contact.

Synchrotron and laboratory-based X-ray imaging techniques have been increasingly used for in situ investigations of alloy solidification and other metal processes. Several reviews have been published in recent years that have focused on the development of in situ X-ray imaging techniques for metal solidification studies. Instead, this work provides a comprehensive review of knowledge provided by in situ X-ray imaging for improved understanding of solidification theories and emerging metal processing technologies. We first review insights related to crystal nucleation and growth mechanisms gained by in situ X-ray imaging, including solute suppressed nucleation theory of α-Al and intermetallic compound crystals, dendritic growth of α-Al and the twin plane re-entrant growth mechanism of faceted Fe-rich intermetallics. Second, we discuss the contribution of in situ X-ray studies in understanding microstructural instability, including dendrite fragmentation induced by solute-driven, dendrite root re-melting, instability of a planar solid/liquid interface, the cellular-to-dendritic transition and the columnar-to-equiaxed transition. Third, we review investigations of defect formation mechanisms during near-equilibrium solidification, including porosity and hot tear formation, and the associated liquid metal flow. Then, we discuss how X-ray imaging is being applied to the understanding and development of emerging metal processes that operate further from equilibrium, such as additive manufacturing. Finally, the outlook for future research opportunities and challenges is presented.

Le but de ce travail est d'étudier expérimentalement l'élaboration des poudres de Ni3Al par mécanosynthèse ainsi que le comportement du produit broyé en fonction de la composition initiale, des conditions et de la durée d'élaboration. L'influence du désordre chimique sur le processus d'amorphisation des métaux à l'état solide est envisagée. Une étude bibliographique, présentée au premier chapitre, a permis de cerner, en partie, les phénomènes conduisant à l'activation des solides par broyage. Pour cela des expériences préliminaires sont effectuées, en deuxième partie, sur un composé modèle (Ni10Zr7) pour déterminer le rôle fondamental des conditions de broyage correspondant aux vitesses des éléments de rotation du dispositif utilisé. Après une étude comparative de deux dispositifs différents, la caractérisation des produits montre que les transformations de phase souhaitées correspondent à des conditions déterminées. Dans la troisième partie, et pour les mêmes conditions de broyage, une étude cinétique est consacrée au comportement, au cours de l'élaboration, d'un mélange de poudres élémentaires de Ni et Al et aussi de ruban de Ni3Al. L'influence d'un agent de contrôle pour prévenir le soudage des produits broyés est aussi considérée. Une similitude dans le comportement des poudres élémentaires et de rubans, après des durées élevées pour certaines conditions de broyage, est établie. Les aspects majeurs relevés dans cette étude sont : la détermination des conditions équivalentes de broyage ; le désordre chimique précède la transition de la phase cristalline à celle amorphe et enfin l'impossibilité de la formation d'une phase complètement ou même majoritairement amorphe à partir du mélange de poudres élémentaires (Al et Ni) et de l'intermétallique (Ni3Al) comme dans le cas de Ni10Zr7

Secondary Al-Si-Cu-Mg based foundry alloys are widely used in automotive industry to particularly produce powertrain cast components mainly due to their good ratio between weight and mechanical properties, and excellent casting characteristics. Presence of impurity elements, such as Fe, Mn, Cr, Ti, V and Zr, in secondary Al-Si alloys is one of the critical issues since these elements tend to reduce alloy mechanical properties. There is an ongoing effort to control the formation of intermetallic phases containing transition metals, during alloy solidification. Although phases formation involving these transition metal impurities in non-grain-refined Al-Si alloys is well documented in the literature, the role of grain refinement in microstructural evolution of secondary Al-Si-Cu-Mg alloys needs further experimental investigations since chemical grain refinement is one of the critical melt treatment operations in foundries. The primary aim of this PhD work is thus defined to characterize the formation of intermetallic phases containing transition metals in secondary Al-7Si-3Cu-0.3Mg alloy before and after grain refinement by different master alloys and contribute to the understanding of the mechanisms underlying the microstructural changes occurring with the addition of grain refiner. Another critical issue related to Al-Si-Cu-Mg alloys is their limited thermal stability at temperatures above 200 oC. The operating temperature in engine combustion chamber is reported to often exceed 200 oC during service. Moreover, a further increase of operating temperature is anticipated due to the expected engine power enhancement in near future, which indicates the necessity for the development of a new creep-resistant Al alloys. Deliberate addition of transition metals is believed to yield a new heat-resistant alloy by promoting the formation of thermally stable dispersoids inside α-Al grains. This study thus also attempted to investigate the effect of adding transition metals Zr, V and Ni on the solidification processing, microstructural evolution and room/high-temperature tensile properties of secondary Al-7Si-3Cu-0.3Mg alloy, one of the most used alloys in automotive engine manufacturing. The influence of transition metal impurities on microstructural evolution of secondary Al-7Si-3Cu-0.3Mg alloy was investigated before and after chemical treatment with different master alloys: Al-10Sr, Al-5Ti-1B, Al-10Ti and Al-5B. The Al-10Zr, Al-10V and Al-25Ni master alloys were used for the experimental investigations of the effects of deliberate additions of transition metals on the solidification path, microstructure and mechanical properties of secondary Al-7Si-3Cu-0.3Mg alloy. Solidification path of the alloys was characterized by the traditional thermal analysis technique and differential scanning calorimetry (DSC). Optical microscope (OM), scanning electron microscope (SEM) equipped with energy-dispersive (EDS), wavelength-dispersive spectrometers (WDS) and electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) equipped with EDS were used to characterize the type, morphology and distribution of the phases precipitated during solidification and heat treatment of the studied alloys. The static tensile properties of the alloys were characterized at room (20 oC) and high temperatures (200 and 300 ºC). Experimental findings indicate that the Sr-modification and grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy with Al-Ti-B can be enough effective despite the presence of transition metal impurities in the material and the variation of pouring temperature. However, the V and Zr (~100 ppm each) available in secondary Al-7Si-3Cu-0.3Mg alloy tended to promote the precipitation of harmful, primary AlSiTi intermetallics during solidification of grain-refined alloy. This implies that more effective optimization of grain refiner addition level in secondary Al foundry alloys can be achieved by considering the role of transition metal impurities, Ti, V and Zr, since the formation of primary AlSiTi particles causes (1) the depletion of Ti needed for effective α-Al grains growth restriction and (2) the formation of casting defects, such as shrinkage, due to their flaky morphology. Iron available in secondary Al-7Si-3Cu-0.3Mg alloy as impurity only formed more desirable α-Al15(FeMn)3Si2 phase in non-grain refined state. After grain refinement by Al-5Ti-1B, Fe was also involved in the formation of more deleterious β-Al5FeSi phase. The TiB2 particles acted as nucleation site for β-Al5FeSi phase. Both higher cooling rate and higher Al-5Ti-1B addition levels tended to promote the formation of deleterious β-Al5FeSi at the expense of α-Al15(FeMn)3Si2 in the alloy refined by Al-5Ti-1B. This implies that rather than the ratio between Mn and Fe, the nucleation kinetics of Fe-rich intermetallics play a decisive role in the selection of competing α-Al15(FeMn)3Si2 and β-Al5FeSi intermetallic phases for the precipitation during alloy solidification. Moreover, grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy by Al-5B showed comparable performance to that of Al-5Ti-1B master alloy, however, without any deleterious influence on the precipitation sequence of Fe-rich phases, i.e. deleterious β-Al5FeSi reaction remained unfavourable during alloy solidification. Experimental findings from the investigations of the effect of deliberate Zr and V addition revealed that Zr and V addition can induce the grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy. While Zr addition yielded the formation of pro-peritectic Zr-rich particles, which are found to nucleate primary α-Al at low undercooling, the effect of adding V can be characterized by the enhancement of the degree of constitutional undercooling. Combined Zr and V addition showed more effective grain refinement level than their individual additions. Majority of both Zr and V added to the alloy were retained inside α-Al matrix during solidification. As a result, limited amounts of Zr and V were rejected to the interdendritic liquid by the growing α-Al dendrites, then forming small-sized and rarely distributed intermetallics. Owing to its low solid solubility in α-Al, nickel available as impurity (~ 200 ppm) or after deliberate addition (0.25 wt.%) in secondary Al-7Si-3Cu-0.3Mg alloy was mainly bound to interdendritic, insoluble intermetallics, such as Al6Cu3Ni and Al9(FeCu)Ni phases. The presence of ~ 200 ppm Ni was sufficient to diminish to a certain extent the precipitation hardening effect of Cu. Interdendritic Zr/V/Ni-rich phases remained undissolved into the α-Al matrix during solution heat treatment. Therefore, the supersaturated transition metals in α-Al solid solution obtained during solidification was only involved in the solid-state precipitation occurring during heat treatment. Unlike Cu/Mg-rich strengthening precipitates that commonly form during aging, the Zr/V-rich precipitates tended to form during solution heat treatment. Other transition metals, such as Mn, Fe, Cr and Ti, which were present as impurities in secondary Al-7Si-3Cu-0.3Mg alloy significantly promoted the formation of nano-sized Zr/V-rich precipitates inside α-Al grains. These thermally more stable precipitates, including novel α-Al(MnVFe)Si, were credited for the enhanced high-temperature strength properties of Al-7Si-3Cu-0.3Mg alloy by ~ 20 %.
Secondary Al-Si-Cu-Mg based foundry alloys are widely used in automotive industry to particularly produce powertrain cast components mainly due to their good ratio between weight and mechanical properties, and excellent casting characteristics. Presence of impurity elements, such as Fe, Mn, Cr, Ti, V and Zr, in secondary Al-Si alloys is one of the critical issues since these elements tend to reduce alloy mechanical properties. There is an ongoing effort to control the formation of intermetallic phases containing transition metals, during alloy solidification. Although phases formation involving these transition metal impurities in non-grain-refined Al-Si alloys is well documented in the literature, the role of grain refinement in microstructural evolution of secondary Al-Si-Cu-Mg alloys needs further experimental investigations since chemical grain refinement is one of the critical melt treatment operations in foundries. The primary aim of this PhD work is thus defined to characterize the formation of intermetallic phases containing transition metals in secondary Al-7Si-3Cu-0.3Mg alloy before and after grain refinement by different master alloys and contribute to the understanding of the mechanisms underlying the microstructural changes occurring with the addition of grain refiner. Another critical issue related to Al-Si-Cu-Mg alloys is their limited thermal stability at temperatures above 200 oC. The operating temperature in engine combustion chamber is reported to often exceed 200 oC during service. Moreover, a further increase of operating temperature is anticipated due to the expected engine power enhancement in near future, which indicates the necessity for the development of a new creep-resistant Al alloys. Deliberate addition of transition metals is believed to yield a new heat-resistant alloy by promoting the formation of thermally stable dispersoids inside α-Al grains. This study thus also attempted to investigate the effect of adding transition metals Zr, V and Ni on the solidification processing, microstructural evolution and room/high-temperature tensile properties of secondary Al-7Si-3Cu-0.3Mg alloy, one of the most used alloys in automotive engine manufacturing. The influence of transition metal impurities on microstructural evolution of secondary Al-7Si-3Cu-0.3Mg alloy was investigated before and after chemical treatment with different master alloys: Al-10Sr, Al-5Ti-1B, Al-10Ti and Al-5B. The Al-10Zr, Al-10V and Al-25Ni master alloys were used for the experimental investigations of the effects of deliberate additions of transition metals on the solidification path, microstructure and mechanical properties of secondary Al-7Si-3Cu-0.3Mg alloy. Solidification path of the alloys was characterized by the traditional thermal analysis technique and differential scanning calorimetry (DSC). Optical microscope (OM), scanning electron microscope (SEM) equipped with energy-dispersive (EDS), wavelength-dispersive spectrometers (WDS) and electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) equipped with EDS were used to characterize the type, morphology and distribution of the phases precipitated during solidification and heat treatment of the studied alloys. The static tensile properties of the alloys were characterized at room (20 oC) and high temperatures (200 and 300 ºC). Experimental findings indicate that the Sr-modification and grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy with Al-Ti-B can be enough effective despite the presence of transition metal impurities in the material and the variation of pouring temperature. However, the V and Zr (~100 ppm each) available in secondary Al-7Si-3Cu-0.3Mg alloy tended to promote the precipitation of harmful, primary AlSiTi intermetallics during solidification of grain-refined alloy. This implies that more effective optimization of grain refiner addition level in secondary Al foundry alloys can be achieved by considering the role of transition metal impurities, Ti, V and Zr, since the formation of primary AlSiTi particles causes (1) the depletion of Ti needed for effective α-Al grains growth restriction and (2) the formation of casting defects, such as shrinkage, due to their flaky morphology. Iron available in secondary Al-7Si-3Cu-0.3Mg alloy as impurity only formed more desirable α-Al15(FeMn)3Si2 phase in non-grain refined state. After grain refinement by Al-5Ti-1B, Fe was also involved in the formation of more deleterious β-Al5FeSi phase. The TiB2 particles acted as nucleation site for β-Al5FeSi phase. Both higher cooling rate and higher Al-5Ti-1B addition levels tended to promote the formation of deleterious β-Al5FeSi at the expense of α-Al15(FeMn)3Si2 in the alloy refined by Al-5Ti-1B. This implies that rather than the ratio between Mn and Fe, the nucleation kinetics of Fe-rich intermetallics play a decisive role in the selection of competing α-Al15(FeMn)3Si2 and β-Al5FeSi intermetallic phases for the precipitation during alloy solidification. Moreover, grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy by Al-5B showed comparable performance to that of Al-5Ti-1B master alloy, however, without any deleterious influence on the precipitation sequence of Fe-rich phases, i.e. deleterious β-Al5FeSi reaction remained unfavourable during alloy solidification. Experimental findings from the investigations of the effect of deliberate Zr and V addition revealed that Zr and V addition can induce the grain refinement of secondary Al-7Si-3Cu-0.3Mg alloy. While Zr addition yielded the formation of pro-peritectic Zr-rich particles, which are found to nucleate primary α-Al at low undercooling, the effect of adding V can be characterized by the enhancement of the degree of constitutional undercooling. Combined Zr and V addition showed more effective grain refinement level than their individual additions. Majority of both Zr and V added to the alloy were retained inside α-Al matrix during solidification. As a result, limited amounts of Zr and V were rejected to the interdendritic liquid by the growing α-Al dendrites, then forming small-sized and rarely distributed intermetallics. Owing to its low solid solubility in α-Al, nickel available as impurity (~ 200 ppm) or after deliberate addition (0.25 wt.%) in secondary Al-7Si-3Cu-0.3Mg alloy was mainly bound to interdendritic, insoluble intermetallics, such as Al6Cu3Ni and Al9(FeCu)Ni phases. The presence of ~ 200 ppm Ni was sufficient to diminish to a certain extent the precipitation hardening effect of Cu. Interdendritic Zr/V/Ni-rich phases remained undissolved into the α-Al matrix during solution heat treatment. Therefore, the supersaturated transition metals in α-Al solid solution obtained during solidification was only involved in the solid-state precipitation occurring during heat treatment. Unlike Cu/Mg-rich strengthening precipitates that commonly form during aging, the Zr/V-rich precipitates tended to form during solution heat treatment. Other transition metals, such as Mn, Fe, Cr and Ti, which were present as impurities in secondary Al-7Si-3Cu-0.3Mg alloy significantly promoted the formation of nano-sized Zr/V-rich precipitates inside α-Al grains. These thermally more stable precipitates, including novel α-Al(MnVFe)Si, were credited for the enhanced high-temperature strength properties of Al-7Si-3Cu-0.3Mg alloy by ~ 20 %.

Nous presentons dans la premiere partie les avantages d'une fusion en levitation pour la preparation de composes intermetalliques terres rares-metaux de transition destines, a l'etude du magnetisme itinerant. Viennent ensuite les caracteristiques techniques du four a levitation que nous avons realise puis des exemples d'applications d'un tel procede d'elaboration. Dans la seconde partie, nous contribuons a l'etude de l'antiferromagnetisme de bande proche de l'instabilite a travers certaines phases de laves rmn#2. Grace aux informations experimentales sur les interactions d'echange extraites des diagrammes de diffraction neutronique et sur l'anisotropie, apprehendee a partir de spectres de resonance magnetique nucleaire, nous proposons un nouvel arrangement des moments magnetiques des atomes de manganese au sein de la structure magnetique du compose ymn#2. Nous discutons des effets de la frustration des interactions d'echange et de la forte anisotropie du manganese dans ce compose. Nous etudions egalement les proprietes magnetiques des composes pseudo-binaires y#1##xtb#xmn#2: la substitution d'atomes de terbium a ceux d'yttrium introduit, en sus de la tres forte frustration des interactions d'echange qui existent deja dans le compose ymn#2, une competition des energies d'anisotropie du terbium et du manganese. Il en resulte un ordre magnetique homogene complexe ainsi que l'apparition d'un ordre a courte distance que nous avons plus particulierement etudie dans le compose tbmn#2. Le terbium joue dans ce cas, le role d'une sonde des correlations de densite d'aimantation du manganese

Etude des composes intermetalliques cecusi, cezn::(5), ceal::(2)ga::(2) et plus particulierement cept::(2)si::(2). Cecusi s'ordonne ferromagnetiquement en dessous de 15,5 k. Les composes de cezn::(5) et ceal::(2)ga::(2) sont des reseaux de kondo presentant une structure antiferromagnetique en dessous de 3,8k et 8,5k respectivement. Description de leur structure magnetique a l'aide d'un vecteur de propagation. Cept::(2)si::(2) est un compose tetragonal de type reseau de kondo non magnetique. Analyse des trois regimes de temperature des proprietes magnetiques. Ce compose est situe entre les fermions lourds et les valences intermediaires

Analyse phénoménologique des processus d'aimantation des composes YCo5 et GDCo5 mettant en évidence une anisotropie des interactions d'échangé Ln-Co liée à l'anisotropie de polarisation des électrons 5d de l'atome Ln. Etude de l'incidence de l'instabilité du magnétisme de bande 3d sur l'anisotropie magnétique dans les phases Ln2Co7 et LnCo3. Etude de l'anisotropie des systèmes à empilement quasi-unidimensionnel LnCo(1-epsilon ). Analyse de la sélection orbitale induite par les intégrales de transfert

Etude du phénomène de valence intermédiaire dans les composés du type CeM2Si2 (m=métal de transition 3d). Mise en évidence d'anomalies lors de l'absorption x ainsi que dans les propriétés magnétiques et de transport. Mesure des seuils d'absorption l(i)ii et classification des composes sur une échelle de valeurs de la valence. Etude des variations thermiques de la valence. L'instabilité de valence a également été mise en évidence qualitativement par des mesures des paramètres de maille.

Etude realisee pour les hydrures cristallins zr#2nih#x (x=2, 1; 3 et 4) et amorphes (x=2,5 et 4,5). On obtient les parametres du diffusion en mesurant la constante de relaxation quadripolaire des spins nucleaires entre 170 k et 470 k. On propose un mecanisme de sauts des atomes d'hydrogene

Etude detaillee de l'evolution de la structure fine des dislocations dans une large gamme de temperature autour du pic de limite elastique (600-700c). Analyse cristallographique de la structure ordonnee l1::(2) et des defauts plans de cette structure. Presentation, a partir de cette analyse, des resultats des simulations atomiques de paroi d'antiphase. Calcul de forme et d'energie de dislocations en elasticite anisotrope. Analyse du mecanisme de formation des defauts d'empilement. Etude, en fonction de la temperature d'essai, de la structure fine des dislocations. Influence d'une variation de composition sur la morphologie des dislocations

by Kwok Chi-Kong = 氧化鋁及鋁-鈦金屬間化合物增強的鋁基複合物的製造和表徵 / 郭智江.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.
Includes bibliographical references.
Text in English; abstracts in English and Chinese.
by Kwok Chi-Kong = Yang hua lv ji lü-tai jin shu jian hua he wu zeng qiang de lü ji fu he wu de zhi zao he biao zheng / Guo Zhijiang.
Acknowledgement --- p.i
Abstract --- p.ii
摘要 --- p.iv
List of tables --- p.v
List of figures --- p.vi
Table of contents --- p.ix
Chapter Chapter 1 --- Introduction --- p.1-1
Chapter 1.1. --- Metal matrix composites (MMCs) --- p.1-1
Chapter 1.1.1. --- Introduction --- p.1-1
Chapter 1.1.2. --- Reinforcements in metal-matrix composites --- p.1-1
Chapter 1.1.3. --- Interface between matrix and reinforcements --- p.1-2
Chapter 1.2. --- Fabrication of metal matrix composites (MMCs) --- p.1-2
Chapter 1.2.1. --- Traditional methods --- p.1-2
Chapter 1.2.1.1. --- Liquid state methods --- p.1-2
Chapter 1.2.1.2. --- Solid state methods --- p.1-4
Chapter 1.2.2. --- In-situ methods --- p.1-5
Chapter 1.3. --- Aluminum based metal matrix composites --- p.1-7
Chapter 1.4. --- Previous works --- p.1-8
Chapter 1.5. --- Works in this study --- p.1-9
Chapter 1.6. --- Thesis layout --- p.1-10
References
Chapter Chapter 2 --- Methodology and instrumentation --- p.2-1
Chapter 2.1. --- Powder metallurgy --- p.2-1
Chapter 2.2. --- Fabrication procedures --- p.2-1
Chapter 2.3. --- Samples to be studied --- p.2-3
Chapter 2.4. --- Instrumentation --- p.2-4
Chapter 2.4.1. --- Differential thermal analyzer (DTA) --- p.2-4
Chapter 2.4.2. --- Argon tube furnace sintering --- p.2-4
Chapter 2.4.3. --- X-ray powder diffractometry (XRD) --- p.2-5
Chapter 2.4.4. --- Scanning electron microscopy (SEM) --- p.2-5
Chapter 2.4.5. --- Three-point bending test --- p.2-5
Chapter 2.4.6. --- Arc melting furnace --- p.2-6
References
Chapter Chapter 3 --- Thermal analysis of Al-Ti02 and Al-Ti02-B203 --- p.3-1
Chapter 3.1. --- Introduction --- p.3-1
Chapter 3.2. --- Results and discussions --- p.3-2
Chapter 3.2.1. --- DTA curve of Al-8.6wt%Ti --- p.3-3
Chapter 3.2.2. --- DTA curve of Al-12.7wt%Ti02 --- p.3-3
Chapter 3.2.3. --- DTA curve of Al-12.7wt%Ti02-5.5wt%B203 --- p.3-5
Chapter 3.2.4. --- DTA curve of Al-12.7wt%Ti02-l lwt%B203 --- p.3-6
Chapter 3.2.5. --- DTA curve of Al-53.6wt%Ti02 --- p.3-7
Chapter 3.2.6. --- "DTA curves of Al-12.7wt%Ti02, 22.3wt%Ti02 and 29.7wt%Ti02" --- p.3-7
Chapter 3.3. --- Conclusions --- p.3-8
References
Chapter Chapter 4 --- Fabrication and characterization of the Al-Ti02 systems --- p.4-1
Chapter 4.1. --- Introduction --- p.4-1
Chapter 4.2. --- Al-12.7wt%Ti02 system --- p.4-2
Chapter 4.2.1. --- Experiments --- p.4-2
Chapter 4.2.2. --- Results and discussions --- p.4-3
Chapter 4.2.2.1. --- XRD spectra --- p.4-3
Chapter 4.2.2.2. --- Microstructural and composition analyses --- p.4-4
Chapter 4.2.3. --- Reaction mechanisms --- p.4-6
Chapter 4.2.4. --- Conclusions --- p.4-8
Chapter 4.3. --- Al-53.6wt%Ti02 system --- p.4-9
Chapter 4.3.1. --- Experiments --- p.4-9
Chapter 4.3.2. --- Sample sintered in tube furnace --- p.4-9
Chapter 4.3.2.1. --- XRD spectra --- p.4-9
Chapter 4.3.2.2. --- Microstructural and EDS analyses --- p.4-10
Chapter 4.3.3. --- Sample prepared by arc-melting method --- p.4-11
Chapter 4.3.3.1. --- XRD spectra --- p.4-11
Chapter 4.3.3.2. --- Microstructural and EDS analyses --- p.4-11
Chapter 4.3.3.3. --- Mechanisms of formation --- p.4-12
Chapter 4.3.4. --- Conclusions --- p.4-14
References
Chapter Chapter 5 --- Characterization of the Al-Ti02-B203 systems --- p.5-1
Chapter 5.1. --- Introduction --- p.5-1
Chapter 5.2. --- Experiments --- p.5-2
Chapter 5.3. --- Results and discussions --- p.5-3
Chapter 5.3.1. --- XRD spectra --- p.5-3
Chapter 5.3.2. --- Microstructural and composition analyses --- p.5-5
Chapter 5.3.3. --- Reaction mechanisms --- p.5-6
Chapter 5.3.4. --- Sample with different contents of B203 --- p.5-7
Chapter 5.4. --- Conclusions --- p.5-8
References
Chapter Chapter 6 --- Flexural strengths of the Al-Ti02 and Al-Ti02-B203 systems --- p.6-1
Chapter 6.1. --- Introduction --- p.6-1
Chapter 6.2. --- Three-point bending test --- p.6-1
Chapter 6.2.1. --- Experiments --- p.6-1
Chapter 6.2.2. --- Results --- p.6-2
Chapter 6.2.3. --- Discussions --- p.6-3
Chapter 6.3. --- Conclusions --- p.6-5
References
Chapter Chapter 7 --- Conclusions and future works --- p.7-1
Chapter 7.1. --- Conclusions --- p.7-1
Chapter 7.2. --- Future works --- p.7-2

Abstract In this chapter, the quantum-based interatomic potentials (QBIPs) developed in Chapters 3–5 for elemental metals are extended to the much larger domain of alloys and intermetallic compounds. The main focus here is on binary systems, but applications to multi-component systems are also considered. Generalized pseudopotential theory (GPT) has been used to develop QBIPs and investigate the trends in cohesion and structure for Mg-Al and transition-metal aluminide (TM-Al) compounds. In this regard, first-principles GPT potentials have been calculated across the entire 3d TM-Al series as a function of TM concentration, together with applications to their binary and ternary phase diagrams in Co-Al, Ni-Al and Co-Cu-Al, as well as a predicted quasicrystal structure in the latter system. Bond-order-potential investigations of 3d transition-metal aluminides have focused on potential development for Ti-Al compounds with applications to dislocation core structure and mobility. An efficient strategy to develop and use model-GPT potentials for pure TM high-entropy alloys is also discussed.

Since the discovery of superconductivity in a high-entropy alloy (HEA) Ti-Zr-Nb-Hf-Ta in 2014, the community of superconductor science has explored new HEA superconductors to find the merit of the HEA states on superconducting properties. Since 2018, we have developed “HEA-type” compounds as superconductors or thermoelectric materials. As well known, compounds like intermetallic compounds or layered compounds are composed of multi crystallographic sites. In a HEA-type compounds, one or more sites are alloyed and total mixing entropy satisfies with the criterion of HEA. Herein, we summarize the synthesis methods, the crystal structural variation and superconducting properties of the HEA-type compounds, which include NaCl-type metal tellurides, CuAl2-type transition metal zirconides, high-Tc cuprates, and BiS2-based layered superconductors. The effects of the introduction of a HEA site in various kinds of complicated compounds are discussed from the structural-dimensionality viewpoint.

Abstract In this chapter, the treatment of thermodynamic properties, phase stability and phase transitions in metals via quantum-based interatomic potentials (QBIPs) is extended to high temperature (high T), including anharmonic vibrational effects in the solid, liquid-state structure and energetics and pressure-temperature phase diagrams. In addition to standard molecular dynamics (MD) techniques, the tools of reversible-scaling MD and variational perturbation theory are introduced to obtain accurate solid and liquid free energies. Respective pair and multi-ion QBIPs from generalized pseudopotential theory (GPT) for the simple metal Mg and from model-GPT for the transition metal Ta are used to illustrate a wide range of high-T solid and liquid applications of interest at both ambient pressure and high pressure. These applications include calculations of the specific heat, thermal expansion coefficient, elastic moduli, shock Hugoniot and melt curve, with detailed comparison to experiment. Also discussed in the case of Ta are large-scale MD simulations of rapid solidification and high-T solid polymorphism.

In this simulation, the permeation of the n-phase precipitation to the Mn2 Fe Al crystallization is induced by the steel casting solidification process by JMatPro. Using the model, the morphological evolution of the Fe and Mn in different percentages was obtained, in which the heated data obtained by simulating casting and extreme heat treatment processes were adopted. This chapter describes a model of the computer model for calculating the phase transition and properties of materials required to predict the deviation during the heat treatment of steel. The current model has the advantage of using a variety of shape memory alloys including medium to high aluminium-based Heusler alloys. Even for an arbitrary cooling profile, a wide range of physical, thermodynamic, and mechanical properties can be calculated as a function of time/temperature/cooling with different proportions. TTT (time-temperature transfer) curves are exported to FE-/FD-based packages to reduce the data distortion of materials. The test results are displayed as a stress-strain diagram.

Abstract In this chapter, the concept of quantum-based interatomic potentials (QBIPs) is introduced as a viable means of extending the predictive power of density functional theory (DFT) quantum mechanics to the much longer length and time scales historically afforded only by simple empirical potentials. In metals and alloys, this extension of DFT is possible because the valence energy bands in these materials are amenable to simplified quantum treatments, leading to reliable expansion of the total energy in terms of weak interatomic matrix elements that define the potentials. In particular, QBIPs derived from first-principles generalized pseudopotential theory can power robust atomistic simulations on both simple- and transition-metal systems involving many millions of atoms. Because of their rigorous quantum origin, the physics content and accuracy of such QBIPs can also be systematically improved, aided by machine learning with state-of-the-art supercomputers where necessary.

Hybrid structures built using Mg/steel are expected to have an increasing impact on the future developments of the manufacturing sector, especially where lightweight structures are required in order to reduce fuel consumption, greenhouse gases and improve efficiency of energy-converting systems. To this end, there is a pressing need for a joining technology to produce effective and low-cost dissimilar Mg/steel joints. Joining of these materials has always been a challenging task for researchers, due to the wide discrepancies in physical properties and lack of metallurgical compatibilities that make the welding process difficult. Based on the existing literature, a successful joint between magnesium alloys and steel can be achieved by inserting an interlayer at the interface or mutual diffusion of alloying elements from the base metal (BM). Thus, intermetallic phases (IMCs) or solid solutions between Mg and the interlayer and also the interlayer and Fe formed at the interface. However, the interfacial bonding achieved and the joints performance depend significantly on the intermediate phase. This paper reviewed the research and progress in the area of joining of Mg alloys to various grades of steel by variety of welding processes, with focus on the techniques used to control the morphology and existence state of intermediate phase and improving the mechanical properties.

Soldering has become an indispensable joining process in the electronic packaging industry. The industry is aiming for the use of environment friendly lead-free solders. All the lead-free solders are high tin-containing alloys. During the soldering process, an intense interaction of metallization on PCB and tin from the solder occurs at the metallization/solder interface. Intermetallic compound (IMC) is formed at the interface and subsequently PCB bond-metal (substrate) is dissolved into the molten solder. In the present study the terms bond-metal and substrate will be used interchangeably and the term 'substrate' refers to the top layer of the PCB which comes in contact with the molten solder during soldering reaction. Thickness of the intermetallic phase formed at the joint interface and amount of substrate lost is critical in achieving reliable solder joints. During the wet phase of soldering process, the IMC does not grow as layered structure; rather it takes the shape of scallops. The growth of scalloped IMC during the solder/substrate interaction entails complicated physics. Understanding of the actual kinetics involved in the formation of IMC phase is important in controlling the process to achieve desired results. This paper presents theoretical analysis of the kinetics involved in the formation of the scalloped intermetallic phase. The intermetallic phase growth is experimentally investigated to support the underlying kinetics of the process. Numerical model has been suggested to translate the physics of the process. The model is based on the basic mass diffusion equations and can predict the substrate dissolution and IMC thickness as a function of soldering time.

Abstract. In this study, the local deformation behavior of the transition zone of thermo-mechanically graded boron steel 22MnB5 and high strength aluminum alloy AA7075 is investigated using an in-situ approach. For this aim, forming tool segments are differentially heated in order to obtain locally tailored microstructures and dissimilar mechanical properties based on the process-induced microstructural phenomena. Material strength distribution is examined by Vickers hardness measurements after thermo-mechanical processing. Tracking of the material- and geometry-dependent local deformation behavior of the resulted transition zone is performed by tensile tests coupled with digital image correlation technique. The experimental results reveal within the transition zone a characteristic reversed S-shape hardness distribution, similar to a sigmoidal curve. The local deformation characterization indicates the occurrence of plastic deformation mainly in the soft zones at the heated forming tools segments, while the harder zones at the cooled tool segments exhibit only an elastic deformation and remain undeformed. By comparing the macroscopic local deformation evolution shortly before failure, absolute strain values up to von Mises = 0.62 and von Mises = 0.28 and a distinct reduction in the area are obtained for 22MnB5 and AA7075, respectively. The occurred plastic strain pattern show the formation of shear bands after a homogenous localization at the necking point.

In this work, computer simulation of mechanical properties such as elastic constants and moduli as well as intrinsic hardness of Al , Al3X and AlX3 having crystal lattice structure of the type L12 is presented. To describe the energy of interaction in metals and alloys, the Sutton-Chen semi-empirical inter-atomic potential was utilized. The simulation was run using the geometry optimization method with the General Utility Lattice Program (GULP) 5.1. From the six different alloys studied, the alloy with highest intrinsic hardness isAlAg3 while with the lowest value for CuAl3. The findings show that Al -based alloys have values of mechanical characteristics that are higher than the pure aluminium metal. The values of mechanical characteristics of the alloys are indirectly proportional to the percentage of aluminium in a given alloy system. The work further confirms that the percentage of aluminium in the alloy systems have significant impact on the mechanical properties.

Shock induced chemical reactions of intermetallics or mixtures of metal and metal-oxides are also used to synthesize new materials with unique phases and microstructures. These materials are also of significant interest to the energetics community because of the significant amount of heat energy released during chemical reactions when subjected to shock and/or thermal loading. Binary energetic materials are classified into two categories— metal/metal oxides and intermetallics. When these materials are synthesized at a nano level with binders and other structural reinforcements, the strength of the resulting mixture increases. Thus, these materials can be used as dual-functional binary energetic structural materials. In this paper, we study the shock-induced chemical reactions of intermetallic mixtures of nickel and aluminum of varying volume fractions of the constituents. The chemical reaction between nickel and aluminum produces different products based on the volume fraction of the starting nickel and aluminum. These chemical reactions along with the transition state are modeled at the continuum level. In this paper, the intermetallic mixture is impact loaded and the subsequent shock process and associated irreversible processes such as void collapse and chemical reactions are modeled in the framework of non-equilibrium thermodynamics. Extended irreversible thermodynamics (EIT) is used to describe the fluxes in this system and account for the associated irreversible processes. Numerical simulations of the intermetallic mixture are carried out using finite difference schemes.

Intermetallic titanium aluminides are recognized as the possibly alloys for high performance aerospace and automobile application. There is an increasing interest of this material due to their extraordinary material properties. The understanding of the machinability of titanium aluminides during various metal cutting processes is very much essential for its wide acceptance over various fields of application. Drilling, with high aspect ratio is a key machining area to be explored because of its complex nature. In the present work, holes were drilled on a titanium aluminide intermetallic alloy with an aspect ratio of 9.37, focusing on the machinability under dry environment using coated and uncoated twist drill. Machinability investigations were evaluated based on the, thrust force, torque, surface integrity, chip morphology, burr formation and performance of the tool. From the results of thrust force and torque, it is revealed that the coated tool doesn’t show any significant advantages over the uncoated tool. The variation of chip shapes was observed as the depth progresses. Small ring shape, uniform and non-uniform roll back burr were observed as the cutting parameters are varied. The adherence of workpiece material on to the tool and various surface defects were observed under all cutting conditions.