Journal articles: 'Sintering; Powder compacts; Chromium oxide'

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Hrubovčáková, Monika, Eva Dudrová, Eduard Hryha, Margita Kabátová, and Jarmila Harvanová. "Parameters Controlling the Oxide Reduction during Sintering of Chromium Prealloyed Steel." Advances in Materials Science and Engineering 2013 (2013): 1–16. http://dx.doi.org/10.1155/2013/789373.

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Temperature intervals of oxide reduction processes during sintering of the Fe-3%Cr-0.5%Mo prealloyed powder using continuous monitoring of processing-exhaust gas composition (CO, CO2, and H2O) were identified and interpreted in relation to density (6.5–7.4 g/cm3), sintering temperature (1120 and 1200°C), heating and cooling rates (10 and 50°C/min), carbon addition (0.5/0.6/0.8%), type (10%H2-N2, N2), and purity (5.0 and 6.0) of the sintering atmosphere. The progress in reduction processes was evaluated by oxygen and carbon contents in sintered material and fracture strength values as well. Higher sintering temperature (1200°C) and density <7.0 g/cm3resulted in a relative decrease of oxygen content by more than 80%. The deterioration of microclimate purity of inner microvolumes of compacts shifted the thermodynamic equilibrium towards oxidation. It resulted in a closing of residual oxides inside interparticle necks. The reducing ability of the N2atmosphere can be improved by sintering in a graphite container. High density of 7.4 g/cm3achieved by double pressing indicated a negative effect on reduction processes due to restricted replenishment of the microclimate atmosphere with the processing gas. In terms of strength properties, carbon content should not be higher than ~0.45%.

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Pathak, L. C., S. K. Mishra (Pathak), and S. Srikanth. "Sintering characteristics of Y–Ba–Cu oxide–Agx superconductors under argon atmosphere." Journal of Materials Research 17, no. 4 (April 2002): 895–900. http://dx.doi.org/10.1557/jmr.2002.0130.

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Sintering studies on Y–Ba–Cu oxide (YBCO)–Agx (x = 0, 0.6, and 1.0 mol) powder were carried out in argon atmosphere to understand the role of silver addition on the densification behavior of these materials. The increase of sintered densities of the compacts with silver addition in argon atmosphere contradicted our earlier observation on sintering of YBCO–Agx powder compacts in air, where the densities decreased for x > 0.6. Thermogravimetric (TG) studies under argon atmosphere indicate a continuous decrease of mass on heating suggesting an enhanced rate of oxygen removal from the YBCO matrix that facilitated the sintering in argon atmosphere. Sintering studies of YBCO–Agx powder compacts in argon in conjunction with earlier observations in air has substantiated our claim that high-temperature oxygen desorption by the silver from the YBCO matrix to the sintering atmosphere controls the rate of densification for these superconducting composites. However, the apparent activation energies for sintering suggest that the sintering process is controlled by yttrium ion diffusion along bulk and grain boundaries.

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Pathak, L. C., S. K. Mishra, D. Bhattacharya, and K. L. Chopra. "Sintering characteristics of Y–Ba–Cu–oxide–Agx superconductors." Journal of Materials Research 14, no. 11 (November 1999): 4148–56. http://dx.doi.org/10.1557/jmr.1999.0561.

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The sintering characteristics of Y–Ba–Cu–oxide (YBCO)–Agx (x = 0 to 1.2) using thermomechanical analyzer were systematically investigated to understand the sintering mechanism of the metal superconductor composites. The addition of Ag was observed to lower the sintering temperatures, and the apparent densities of the sintered compacts increased with x from 0 to 0.6. A further increase of x above 0.6 decreased the apparent densities of the sintered compacts. The presence of Ag globules in the YBCO–Ag compacts was observed by scanning electron microscopy and energy dispersive x-ray spectroscopy. The apparent activation energies for sintering of the powder compacts were estimated and observed to vary between 900 to 2000 kJ/mol. The formation of AgOx by absorbing oxygen from YBCO and sintering atmosphere possibly controls the sintering and superconducting behavior. Incorporation of Ag into the matrix modifies the weak-link characteristics from superconductor–insulator– normal–superconductor (S–I–N–S) to superconductor–normal–superconductor (S–N–S) type.

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Marina, M., M. Z. M. Zamzuri, M. N. Derman, M. A. Selamat, W. Rahman, and Z. Nooraizedfiza. "Characterization of PM Fe-Cr-Y₂O₃Composites Prepared by Microwave Sintering Technology." Advanced Materials Research 879 (January 2014): 43–50. http://dx.doi.org/10.4028/www.scientific.net/amr.879.43.

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This research is focused on assessing the feasibility of the new and innovative microwave sintering technology for fabricating iron-chromium composites prepared via powder metallurgy route. Accordingly, the microwave sintered iron-chromium compacts was benchmarked against conventional sintered counterparts fabricated in other researches. We also studied the viability of yttria reinforcement to the iron-chromium composites with varying weight fraction from 5 to 20 %. Comparison on the end properties were also being made on the unreinforced iron-chromium matrix (0 wt. % of yttria). The result revealed that the microwave sintered iron-chromium composites possess improved density and micro hardness value. Process evaluation also revealed that microwave assisted sintering can lead to a reduction of 70 % of sintering time when compared to conventional sintering. The micro hardness property of microwave sintered iron-chromium was slightly improved with 5 wt. % addition of yttria, although the density and compressive strength were reduced with increasing content of the ceramic particulates. Most importantly, the study has established the viability of microwave sintering approach used in place of conventional sintering for iron based powder metallurgy composites.

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Sulowski, Maciej, Ewa Lichańska, Paweł Kulecki, Monika Tenerowicz-Żaba, and Anna Staniek. "Dilatometric investigations of Fe – Cr – Mo – C system." ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA 2, no. 2 (December 21, 2018): 1–13. http://dx.doi.org/10.29114/ajtuv.vol2.iss2.79.

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Sintering behavior in high purity nitrogen and mixture of 5% H2-95% N2 of Fe-(Cr)-(Mo)-C system was investigated. The mixtures, differ from chromium, molybdenum and carbon content were prepared in Turbula mixer. Then, using single-action pressing in a rigid die at pressing pressure 400 MPa, green compacts with density level 5.9±0.17 g/cm3 were pressed. Sintering was carried out in a horizontal push rod dilatometer Netzsch 402E at 1120 and 1250°C for 60 min. Heating and cooling rates were 10 and 20°C/min., respectively. After heating, compacts were isothermal sintered at 1120 or 1250°C for 60 minutes an cooled up to 200°C, then isothermally hold for 60 minutes and definitely cooled to the room temperature. Pure nitrogen and mixture of 5% H2-95% N2 were employed as sintering atmospheres. During investigations the influence of isothermal sintering temperature, chemical composition of sintering atmosphere, chromium, molybdenum and carbon content was followed by dilatometry. The aim of investigations was to determine transformation temperatures. It was shown that the dimensional changes occurring during heating and isothermal sintering and the final density of sintered compacts are influenced by sintering parameters and the alloying elements concentration in powder mixture.

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Ahmad, Mohamad Azmirruddin, Fazira Suriani Mohamed Fadzil, Mazlan Mohamad, Mohamad Hasnan Abdul Hamid, and Mohd Asri Selamat. "Microstructure and Mechanical Properties Study of CoCrMo Parts Sintered under Control Atmosphere." Advanced Materials Research 1133 (January 2016): 85–89. http://dx.doi.org/10.4028/www.scientific.net/amr.1133.85.

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Their excellent properties, such as corrosion resistance, fatigue strength and bio-compatibility, made Cobalt-chromium-molybdenum (CoCrMo) were used in total hip and knee replacements and dental devices. The green CoCrMo compacts specimens in rectangle shape were fabricated by powder pressing technique. The effects of sintering temperature and atmosphere on the mechanical properties and microstructure of the CoCrMo compacts which is sintered at 1300°C-1400°C under two different inert gases sintering atmosphere (Ar2/N2H2) were investigated. The experimental results show that the grain boundaries sizes of CoCrMo compact sintered specimen were increased with increasing sintering temperature. The CoCrMo compacts specimens sintered at 1350°C under inert gases N2H2 atmosphere possess highest density (8.096 g/cm3) and hardness (327.1Hv). However, when the compacts specimens are sintered at 1400°C, the density (7.596 g/cm3) and hardness (320 Hv) properties of sintered compact were decreased.

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Rahman, Mujibur M., and A. A. A. Talib. "Effect of Sintering Schedule to the Alloyability of FeCrAl Powder Mix Formed at above Ambient Temperature." Advanced Materials Research 1115 (July 2015): 199–202. http://dx.doi.org/10.4028/www.scientific.net/amr.1115.199.

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This paper presents the outcomes of an experimental investigation on the effect of sintering schedule to the alloyability of FeCrAl powder mix formed through warm powder compaction process. A lab-scale uni-axial die compaction rig was designed and fabricated which enabled the compaction of powder mass at elevated temperature. Iron (Fe) powder ASC 100.29 was mechanically mixed with other alloying elements, namely chromium (Cr), and aluminum (Al) for 60 minutes and compacted at 150°C by applying 130 kN axial loading to generate green compacts. The defect-free green compacts were subsequently sintered in an argon gas fired furnace for different holding times. The sintered samples were then undergone XRD analysis. The results revealed that the alloyability of sintered products were affected by the holding time during sintering. The sample sintered at 800°C for 60 minutes showed the highest intensity of FeCrAl alloy.

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Das, P. "Effect of Temperature on the Sintering Zirconia Based Mixed Oxide Powder Compacts." Solid State Phenomena 8-9 (January 1991): 493–500. http://dx.doi.org/10.4028/www.scientific.net/ssp.8-9.493.

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Das, P., and R. Choudhury. "Further interpretation of sintering data in zirconia-urania mixed oxide powder compacts." Journal of Nuclear Materials 174, no. 1 (November 1990): 76–79. http://dx.doi.org/10.1016/0022-3115(90)90423-k.

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Rahman, Mujibur M., and S. R. Yogaswerarow. "Effects of Compaction and Sintering Temperature to the Alloyability of FeCrCu Powder Mixture." Advanced Materials Research 1133 (January 2016): 264–68. http://dx.doi.org/10.4028/www.scientific.net/amr.1133.264.

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This paper presents the alloyability of FeCrCu powder compacts formed through warm powder compaction route. A lab-scale uni-axial die compaction rig was designed and fabricated which enabled the powder forming at elevated temperature. Iron powder ASC 100.29 was mechanically mixed with other alloying elements, i.e., copper (Cu) and chromium (Cr) as well as carbon (C) as additive for 60 minutes. Green samples were formed at 30°C (room temperature), 100°C, and 180°C through simultaneous upward and downward axial loadings. The defect-free green compacts were subsequently sintered in argon gas fired furnace at 900°C and 1000°C for 60 minutes at a rate of 5°C/minute. The alloyability of the sintered products was analyzed through XRD testing. The compressive strength of the sintered samples was also measured. The results revealed that FeCrCu alloy was formed at different intensity depended upon the forming and sintering temperature. The compressive strength was found to be highest for sample formed at 180°C and sintered at 1000°C.

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Kim, Ji Soon, Young Do Kim, Choong Hyo Lee, Pyuck Pa Choi, and Young Soon Kwon. "Spark-Plasma Sintering of Molybdenum Disilicide." Key Engineering Materials 287 (June 2005): 160–65. http://dx.doi.org/10.4028/www.scientific.net/kem.287.160.

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The effect of milling on the densification behavior of MoSi2 powder during spark-plasma sintering (SPS) was investigated. MoSi2 starting powder with an average particle size of 10 µm was milled to reduce particle sizes to less than 1 µm. Sintering was performed in a SPS facility, varying the sintering temperature from 1200°C to 1500°C. Changes in relative density and the densification rate were measured as a function of temperature. Additionally, the microstructure of sintered compacts was analyzed by means of SEM and EPMA. The sintered density was lower for ballmilled powder compacts (having 94-95% relative density) than for as-received ones (having 94- 98% relative density) despite a higher densification rate of the former in the early and middle stages of sintering. These apparently contradictory results can be explained by a pick-up of oxygen (from 0.3 to 1.8 wt. % O) during the milling process, leading to the formation of silicon oxide and its decomposition into a gas phase at temperatures above 1200°C.

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Marinca, Traian Florin, Bogdan V. Neamţu, Florin Popa, Ionel Chicinaş, and Olivier Isnard. "Composite Powder and Compacts of Iron/Iron Oxide Type Produced by Mechanosynthesis and Reactive Sintering." Solid State Phenomena 216 (August 2014): 29–34. http://dx.doi.org/10.4028/www.scientific.net/ssp.216.29.

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Composite powder of Fe/Fe2O3type was synthesized by mechanical milling using commercially Fe and Fe2O3powders in mass ratio of 35/65. The milling process leads to the powder homogenization, powder activation and formation of some Fe/Fe2O3composite particles. The Fe/Fe2O3composite powder obtained by mechanical milling and the un-milled Fe/Fe2O3mixture were subjected to the reactive sintering procedure in argon atmosphere at 1100 °C for 6 hours. The sintering procedure promotes the reaction of the Fe with the Fe2O3and the result is a sintered composite compact of Fe/Fe3O4/FeO type. The microstructure of the Fe/Fe3O4/FeO sintered composite compacts presents iron clusters in an oxide matrix. A more homogeneous iron clusters size and distribution in oxide matrix is observed in the case of the sintered compact obtained from mechano-activated powder. The X-ray diffraction (XRD), laser particles size analysis (LPSA), optical (OM) and scanning electron (SEM) microscopies techniques were used for the investigations.

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Andrushchik, L. O., O. N. Balakshina, S. P. Oshkaderov, E. P. Severyanina, and V. A. Shvitai. "Character of porosity and structural defectiveness variation in chromium powder compacts during electric-contact sintering." Soviet Powder Metallurgy and Metal Ceramics 26, no. 11 (November 1987): 896–98. http://dx.doi.org/10.1007/bf00794106.

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Fuentes-Pacheco, L., and M. Campos. "Bonding evolution with sintering temperature in low alloyed steels with chromium." Science of Sintering 41, no. 2 (2009): 161–73. http://dx.doi.org/10.2298/sos0902161f.

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At present, high performance PM steels for automotive applications follow a processing route that comprises die compaction of water-atomized powder, followed by sintering and secondary treatments, and finishing operations. This study examines Cr-alloyed sintered steels with two level of alloying. In chromium-alloyed steels, the surface oxide on the powder is of critical importance for developing the bonding between the particles during sintering. Reduction of this oxide depends mainly on three factors: temperature, dew point of the atmosphere, and carbothermic reduction provided by the added graphite. The transformation of the initial surface oxide evolves sequence as temperature increases during sintering, depending on the oxide composition. Carbothermic reduction is supposed to be the controlling mechanism, even when sintering in hydrogen-containing atmospheres. The effect of carbothermic reduction can be monitored by investigating the behavior of the specimens under tensile testing, and studying the resultant fracture surfaces.

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Dehghan-Manshadi, Ali, Nicholas Hoye, Bob de Jong, and Rian J. Dippenaar. "Resistance Heated Pressing (RHP): A Novel Technique for Fabrication of Titanium Alloys." Key Engineering Materials 520 (August 2012): 341–46. http://dx.doi.org/10.4028/www.scientific.net/kem.520.341.

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A novel powder metallurgical technique for the fabrication of titanium alloys has been developed by utilizing a pressure-assisted, resistance-heating sintering technique. In this technique, the high electrical resistance of oxide layers present on the surface of powder particles has been exploited to ensure effective resistance heating of green compacts. Ti-6Al-4V pre-alloyed powders of 100 µm size were compressed while being heated under a variety of conditions of sintering temperature, pressure and time. The outcomes of our experiments have proven that resistance heating can be a very effective means of heating during powder consolidation. The results have indicated that the required sintering time and temperature in the new resistance-heated sintering technique are much reduced in compared to sinter-press and/or hot isostatic pressing techniques, resulting in a refined microstructure with a concomitant improvement in mechanical properties.

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Vos, Frans, Luc Delaey, Marc De Bonte, and Ludo Froyen. "Reactivity in the chromium oxide-calcium fluoride system: An empirical approach." Journal of Materials Research 14, no. 6 (June 1999): 2518–23. http://dx.doi.org/10.1557/jmr.1999.0337.

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The reaction mechanisms observed when sintering loose Cr2O3–CaF2 powder mixtures were analyzed, and the influence of the sintering parameters on the reaction behavior is presented. Using x-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and differential thermal analysis (DTA) measurements, CaCrO4 was shown to be the reaction product when sintering in air. The reaction occurs in two steps: CaF2 transforms to CaO at the Cr2O3–CaF2 interface, followed by a CaO–Cr2O3 interaction, which creates the reaction product. Scanning electron microscopy (SEM) and x-ray fluorescence (XRF) analysis showed an increasing loss of CaF2 with increasing sintering temperature and heating rate, while an opposite evolution of the amount of reaction product was observed.

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Watanabe, R. "Powder Processing of Functionally Gradient Materials." MRS Bulletin 20, no. 1 (January 1995): 32–34. http://dx.doi.org/10.1557/s0883769400048892.

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Powder metallurgical (P/M) processing of FGMs provides a wide range of compositional and microstructural control, along with shape-forming capability. Oxide/metal systems are desirable because this materials combination can be used to easily tailor materials properties. However, there are many problems to be investigated which pertain to each of the processing steps; process innovations will often be required to realize the versatility of this route. In this article, I briefly review the present status of the powder-processing method.Powder metallurgical fabrication of FGMs involves the following sequential steps with a selected material combination of metals and ceramics: determination of the optimum composition profile for an effective thermal-stress reduction; stepwise or continuous stacking of powder premixes according to the predesigned composition profile; compaction of the stacked powder heap and sintering with or without pressurizing. Besides the conventional powder metallurgical routes, a spray deposition method, using mixed powder suspensions and a slurry stacking method, have been developed to form continuously graded stacking. A powder spray stacking apparatus has been devised, which is fully automatic with computer control. Deposited compacts were cold isostatically pressed (CIP) and consolidated by hot isostatic pressing. Their microstructures show that this process provides fine compositional control with desired profiles.Differential temperature sintering by laser-beam heating has been studied to add versatility to the P/M process. The surface of the green compacts is scanned with a laser beam using a predesigned scanning pattern to ensure homogeneous heating over the entire surface.

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Pillis, M. F., Edval G. de Araújo, and Lalgudi Venkataraman Ramanathan. "Effect of Addition of Rare Earth Oxide Concentrates on Oxidation Resistance of AISI 304L." Materials Science Forum 530-531 (November 2006): 99–104. http://dx.doi.org/10.4028/www.scientific.net/msf.530-531.99.

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Rare earth elements are often added to chromium dioxide forming alloys to improve its high temperature oxidation resistance. The rare earths can be also added as oxide dispersions. Significant cost reductions are possible if rare earth oxide concentrates can be used instead of pure rare earth oxides, the former being the precursor to obtaining pure rare earth oxide. In this study the effect of adding pure and concentrates of rare earth oxides to AISI 304L on its oxidation behavior has been evaluated. AISI 304L stainless steel powder compacts containing 2 vol% of pure lanthanum and yttrium oxides or their concentrate were prepared by milling followed by pressing. The compacts were vacuum sintered and isothermally oxidized in air for up to 200h at 900°C. The parabolic rate constants were determined and the reaction products examined using a scanning electron microscope. X-ray diffraction analysis of the reaction products was also carried out. The compacts with pure rare earth oxides and the concentrates exhibited similar oxidation behavior.

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Johari, Nurhaslina, Rosliza Sauti, Noorsyakirah Abdullah, Nurazilah Mohd Zainon, Bakar Meh, Mohd Nizam Abd Jalil, Mohd Bakri Mohd Hijazi, et al. "Physical and Mechanical Properties of Injection Molded Co-Cr-Mo Alloy Powder for Orthopedic Applications." Advanced Materials Research 1133 (January 2016): 80–84. http://dx.doi.org/10.4028/www.scientific.net/amr.1133.80.

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Cobalt-chromium alloys are commonly used for surgical implants because of their high strength, superior corrosion resistance, non-magnetic behavior, and biocompatibility. Cobalt-Chromium-Molybdenum (Co-Cr-Mo) applications include prosthetic replacements of hips. This paper presents the attempt to produce metallic implant using Co-Cr-Mo powder by MIM process, focusing on the effects of different heating rate during sintering process at 1380°C. Co-Cr-Mo powder were mixed homogeneously with palm oil and conventional binders respectively with powder loading 65 vol% and was injection molded using vertical injection molding machine with the nozzle temperature of 160°C to produce green compacts. The binders then was removed by solvent extraction process and sintered in vacuum condition at atmosphere 10-5 mbar at temperature 1380 °C with varied heating rate; 0.5°C/min, 1.0°C/min and 3.0°C/min . Results indicated that sintered density and tensile strength varied from 8.100 gcm-3 to 8.200 gcm-3 and 546.971 MPa to 798.767 MPa respectively. The mechanical properties comply with the international standard (ASTM F75).

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Mahmoud, Morsi M., Guido Link, and Manfred Thumm. "The role of the native oxide shell on the microwave sintering of copper metal powder compacts." Journal of Alloys and Compounds 627 (April 2015): 231–37. http://dx.doi.org/10.1016/j.jallcom.2014.11.180.

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Manchili, Swathi K., Johan Wendel, Eduard Hryha, and Lars Nyborg. "Analysis of Iron Oxide Reduction Kinetics in the Nanometric Scale Using Hydrogen." Nanomaterials 10, no. 7 (June 30, 2020): 1276. http://dx.doi.org/10.3390/nano10071276.

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Iron nanopowder could be used as a sintering aid to water-atomised steel powder to improve the sintered density of metallurgical (PM) compacts. For the sintering process to be efficient, the inevitable surface oxide on the nanopowder must be reduced at least in part to facilitate its sintering aid effect. While appreciable research has been conducted in the domain of oxide reduction of the normal ferrous powder, the same cannot be said about the nanometric counterpart. The reaction kinetics for the reduction of surface oxide of iron nanopowder in hydrogen was therefore investigated using nonisothermal thermogravimetric (TG) measurements. The activation energy values were determined from the TG data using both isoconversional Kissinger–Akahira–Sunose (KAS) method and the Kissinger approach. The values obtained were well within the range of reported data. The reaction kinetics of Fe2O3 as a reference material was also depicted and the reduction of this oxide proceeds in two sequential stages. The first stage corresponds to the reduction of Fe2O3 to Fe3O4, while the second stage corresponds to a complete reduction of oxide to metallic Fe. The activation energy variation over the reduction process was observed and a model was proposed to understand the reduction of surface iron oxide of iron nanopowder.

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Hrubovčáková, Monika, Eva Dudrová, and Margita Kabátová. "Oxide Reduction Processes, Microstructure and Properties of Sintered Chromium Pre-Alloyed Steel." Materials Science Forum 782 (April 2014): 487–90. http://dx.doi.org/10.4028/www.scientific.net/msf.782.487.

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The reduction processes during the sintering of Fe-3Cr-0.5Mo+0.5C pre-alloyed powder using continuous monitoring of exhaust gas composition (CO, CO2, H2O) have been identified and interpreted in relation to the density (6.5-7.4 g/cm3), sintering temperature (1120 and 1200°C), heating and cooling rates (10 and 50°C/min) and type of sintering atmosphere (10%H2-N2, N2), respectively. The progress in reduction processes was evaluated by the change in C and O contents, and fracture strength values as well. The results were compared with metallographic study of microstructure and fractographic observations of fracture surfaces. Higher sintering temperature (1200°C) and low density (<7.0 g/cm3) resulted in a relative decrease in oxygen content by more than 80%. Higher cooling rate (50°C/min) eliminates re-oxidation during cooling. High density of 7.4 g/cm3,achievedby double pressing, indicated to have a negative effect on reduction processes due to restricted replenishment of the “microclimate” atmosphere with the processing gas. Higher O2 content causes weakening of interfaces with residual oxides.

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Geßwein, H., N. Schlechtriemen, J. R. Binder, and J. Haußelt. "Finite-difference model for the reaction sintering of oxide ceramics by direct oxidation of intermetallic powder compacts." Journal of Thermal Analysis and Calorimetry 100, no. 1 (June 19, 2009): 33–42. http://dx.doi.org/10.1007/s10973-009-0188-z.

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Kume, Shoichi, Saruhan Saklar, and Koji Watari. "Consolidation of h-BN/Feldspar Composites in Air." Advanced Materials Research 11-12 (February 2006): 429–32. http://dx.doi.org/10.4028/www.scientific.net/amr.11-12.429.

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Attempts have been made to sinter hexagonal boron nitride (h-BN) by pressureless-sintering in air. In order to achieve this purpose, feldspar has been selected as a sintering aid to produce sintered compacts at a temperature above the melting point of feldspar. Even though h-BN was not wetted by the molten feldspar in nitrogen, the wettability was significantly improved in air. Through the heating process, the h-BN powder disappeared owing to the oxidation of the powder followed by sublimation of the boron oxide. The decomposition of BN was prevented effectively by the presence of molten feldspar in the h-BN/feldspar (30 vol.%) compact. It was shown that h-BN/feldspar composite can be sintered in air under normal pressure, although the bulk density of h-BN/feldspar composites (1.40 to 1.51 g/cm3) was not satisfactory enough.

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Wendel, Johan, Swathi K. Manchili, Eduard Hryha, and Lars Nyborg. "Oxide reduction and oxygen removal in water-atomized iron powder: a kinetic study." Journal of Thermal Analysis and Calorimetry 142, no. 1 (May 9, 2020): 309–20. http://dx.doi.org/10.1007/s10973-020-09724-6.

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Abstract Reduction of oxides during sintering is a prerequisite for the manufacturing of powder metallurgy steels. Inadequate control of the sintering atmosphere may impede sinter neck formation and cause entrapment and growth of oxides in sinter necks, ultimately deteriorating the mechanical properties of sintered components. In this study, the oxide reduction and oxygen removal in water-atomized iron powder was investigated by means of thermogravimetric analysis in pure hydrogen. Two principal mass loss events were recorded, corresponding to the removal of the surface oxide layer at around 400 °C and reduction of internal and stable oxides in the range 600–1350 °C. The apparent activation energies of these mass loss processes were determined by means of kinetic analyses, giving values around 100 kJ mol−1 and 200–400 kJ mol−1, respectively. The validity of the results was asserted using hematite reference samples which displayed good correlation with the reduction of the surface oxide layer, thereby showing that the powder surfaces are covered by an Fe2O3 oxide. The high-temperature mass loss, with no analogy in the reference samples, is believed to originate from a combination of oxygen removal from internal oxides and stable oxide particulates on the surface. Analysis of the oxide reduction in iron powder compacts show a slightly lower activation energy for the oxide layer reduction, indicating an influence of the compaction step on the initial state of the powder and oxide layer. At the same time, the high-temperature mass loss event was shifted to higher temperatures, which is believed to be caused by the increasingly restricted mass transport of reduction products along the pores in the sintered compact.

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Sharipova, A. F., S. G. Psakhie, I. Gotman, M. I. Lerner, A. S. Lozhkomoev, and E. Y. Gutmanas. "Cold sintering of Fe-Ag and Fe-Cu by consolidation in high pressure gradient." Izvestiya Vuzov Tsvetnaya Metallurgiya (Proceedings of Higher Schools Nonferrous Metallurgy, no. 1 (February 22, 2019): 67–74. http://dx.doi.org/10.17073/0021-3438-2019-1-67-74.

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The paper states the results of obtaining Fe—Ag and Fe—Cu dense nanocomposites from composite powders consolidated by cold sintering in the high pressure gradient, as well as from nanosize powders of silver (Ag), iron (Fe) and copper (Cu). The results of mechanical tests conducted on Fe—Ag and Fe—Cu nanocomposites are provided. Nanocomposite powders were obtained by high energy attrition milling of carbonyl iron (Fe) micron scale powder and nanosize silver oxide powder (Ag2O), as well as iron and cuprous oxide (Cu2O) nanopowders. High resolution scanning electron microscopy was used to study the microstructure. Compacts featuring approximately 70 % of full density were annealed in hydrogen atmosphere to reduce silver and cuprous oxides to metals and to remove oxide layers from the surface of iron powder particles. This was followed by cold sintering — consolidation under high pressure at a room temperature. The data on specimen density dependence on pressure in the range of 0,25 —3,0 GPa were obtained. Densities were above 95 % of the full density for all nanocomposites, and close to 100 % of the full density under 3,0 GPa for Ag and Cu powders. High mechanical properties in three-point bending and compression were observed for all nanocomposites. It was found that mechanical properties of nanocomposites are substantially higher as compared with composites obtained from micron scale powders. Higher ductility was observed in Fe—Ag and Fe—Cu nanocomposites as compared with specimens obtained from nanostructured Fe.

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Dyachkova, L. N. "Features of the formation of the structure and properties of powder steels with additives that activate diffusion processes during sintering." Proceedings of the National Academy of Sciences of Belarus, Physical-Technical Series 65, no. 1 (April 6, 2020): 43–53. http://dx.doi.org/10.29235/1561-8358-2020-65-1-43-53.

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Effect of activating the sintering process of powder steel alloyed with nickel or chromium by grinding the initial powders and introducing alkali metal compounds was investigated. The kinetics of grinding the initial iron powders, Cr30, and a mixture of iron powders with 4 % nickel was studied. It is shown that, depending on the hardness of the powder, it is grinded in three or two stages. When grinding more hard powders, there is no stage of intensive deformation of particles and an increase in their size. Crystalline lattice defects resulting from grinding of powders accelerate diffusion processes. This reduces sintering temperature by 100–200 °С compared to the sintering temperature of steels from the initial powders, contributes to a homogeneous structure, reduces porosity by 4–17 %, and increase strength of powder steels by 1.5–1.6 times. The mechanism of the effect of sodium bicarbonate on the acceleration of diffusion of carbon, nickel and chromium into iron has been established. With the introduction of sodium bicarbonate under the action of water vapor, formed upon its decomposition to carbonate, thin oxide films are formed on iron particles, which are actively recovered in a protective-recovering atmosphere during sintering. This leads to formation of a metal contact between the particles, acceleration of the self-diffusion of iron atoms and the diffusion of alloying additives into iron by 5–7 times, depending on the sintering temperature and the amount of added additive. Sodium forms nanodispersed complex compounds of the ferritic type Na3Fe5O9 along the grain boundaries of the iron base, which provide grain refinement and the formation of a homogeneous structure. Changes in the structure of powder steel with the introduction of sodium bicarbonate cause an increase in its strength by 1.5–1.7 times. The results can be used to obtain structural products from alloyed powder steels.

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Zhou, Yun, Yu Jie Du, and Xiao Qing Zuo. "The Microstructure and Characteristic of 410L Stainless Honeycombs Fabricated by Extruding and Sintering." Advanced Materials Research 535-537 (June 2012): 597–600. http://dx.doi.org/10.4028/www.scientific.net/amr.535-537.597.

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Pure 410L powder is used to mix with an additive to prepare a powder mixed paste. 410L honeycombs are fabricated by extruding the powder mixed paste, then dried and sintered. With sintering temperature increasing from 1120°C to1150°C, the density of sintered honeycombs increasing, powder particles bind together and become grains. The structure parameters and properties of sintered honeycombs were obtained by measuring and calculating. Results show that wall thickness 0.13~0.18mm, cell number (1/in2) 350~385, clear cross section (%) 73~80, specific surface Sv(sq m/cu dm）2.68~2.85； specific heat capacity Cp(J/g.K) 0.50~0.56, heat conductivity κ(W/m.K) 11.2~12.5. SEM/EDS analysis shows that the structure of sintered honeycombs consists of matrix phase α-Fe(Cr) and small particles which are complex compounds of silicon, iron and inclusion elements distributed in matrix. Chromium oxide is formed on surface of sintered honeycombs.

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Xie, Guoqiang, Osamu Ohashi, Norio Yamaguchi, Minghui Song, Kazutaka Mitsuishi, Kazuo Furuya, and Tetsuji Noda. "Behavior of Oxide Film at Interface between Particles of Al-Mg Alloy Powder Compacts Prepared by Pulse Electric Current Sintering." Japanese Journal of Applied Physics 42, Part 1, No. 7B (July 30, 2003): 4725–28. http://dx.doi.org/10.1143/jjap.42.4725.

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Ortiz, P., and F. Castro. "Thermodynamic and experimental study of role of sintering atmospheres and graphite additions on oxide reduction in Astaloy CrM powder compacts." Powder Metallurgy 47, no. 3 (September 2004): 291–98. http://dx.doi.org/10.1179/003258904225020747.

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binti Johari, Nurhaslina, Rosdi Ibrahim, Ahmad Nizam bin Abdullah, Muhammad Jabir bin Suleiman Ahmad, and Abdul Rahim Abu Talib. "The Effect of Sintering Temperature on Physical Properties of Sintered Inconel 718 for Potential Aerospace Industry Application." Advanced Materials Research 879 (January 2014): 139–43. http://dx.doi.org/10.4028/www.scientific.net/amr.879.139.

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The most demanding high temperature application requires nickel-based super alloys, named Inconel 718 (IN718) is a precipitation hardenable nickel chromium alloy containing significant amount of iron, niobium and molybdenum along with lesser amounts of aluminium and titanium. The development of IN718 for metal injection molding was already proposed to provide increased resistance to distortion during and prior to debinding. This paper reports on the effects of sintering temperature on physical and mechanical properties of IN718 alloy. IN718 powder (60 vol%) with binder formulation (40 vol%) consists of polyethylene (PE) and palm stearin (PS) were mixed homogeneously and injected to produce green compacts. The binders then was removed and sintered at 1100 °C and 1200 °C for 8 h respectively. During sintering, the debound part is heated, which is allowing densification of the powder into a dense solid followed by elimination of pores. The sample sintered in vacuum condition at atmosphere 10-5 mbar whereby samples sintered at 1100 °C, show the density of 6.806 g/cm3 compared to samples sintered at 1200 °C is 8.186 g/cm3. Super alloy sintered at 1200 °C exhibited better densification rate with lower porosity. The preliminary results indicate that super alloy can be used in the MIM fabrication of nickel based super alloys to produce high-density sintered parts.

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Bell, Nelson S., James A. Voigt, Bruce A. Tuttle, and Duane B. Dimos. "Colloidal processing of chemically prepared zinc oxide varistors. Part II: Near-net-shape forming and fired electrical properties." Journal of Materials Research 19, no. 5 (May 2004): 1341–47. http://dx.doi.org/10.1557/jmr.2004.0180.

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Chemically prepared zinc oxide powders were processed for the production of high aspect ratio varistor components (length/diameter >5). Near-net-shape casting methods including slip casting and agarose gelcasting were evaluated for effectiveness in achieving a uniform green microstructure that densifies to near theoretical values during sintering. The structure of the green parts was examined by mercury porisimetry. Agarose gelcasting produced green parts having low solids loading values and did not achieve high fired density. Isopressing the agarose cast parts after drying raised the fired density to greater than 95%, but the parts exhibited catastrophic shorting during electrical testing. Slip casting produced high green density parts, which exhibit high fired density values. The electrical characteristics of slip-cast parts are comparable with dry-pressed powder compacts.

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Bergman, Ola, Björn Lindqvist, and Sven Bengtsson. "Influence of Sintering Parameters on the Mechanical Performance of PM Steels Pre-Alloyed with Chromium." Materials Science Forum 534-536 (January 2007): 545–48. http://dx.doi.org/10.4028/www.scientific.net/msf.534-536.545.

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Powder grades pre-alloyed with 1.5-3 wt% chromium are suitable for PM steel components in high performance applications. These materials can be successfully sintered at the conventional temperature 1120 °C, although well-monitored sintering atmospheres with low oxygen partial pressures (<10-17-10-18 atm) are required to avoid oxidation. Mechanical properties of the Cralloyed PM grades are enhanced by a higher sintering temperature in the range 1120-1250 °C, due to positive effects from pore rounding, increased density and more effective oxide reduction. A material consisting of Astaloy CrM, which is pre-alloyed with 3 wt% Cr and 0.5 wt% Mo, and 0.6 wt% graphite obtains an ultimate tensile strength of 1470 MPa combined with an impact strength of 31 J at density 7.1 g/cm3, after sintering at 1250 °C followed by cooling at 2.5 °C/s and tempering.

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Baud, S., F. Thévenot, and C. Chatillon. "High temperature sintering of SiC with oxide additives: IV. Powder beds and the influence of vaporization on the behaviour of SiC compacts." Journal of the European Ceramic Society 23, no. 1 (January 2003): 29–36. http://dx.doi.org/10.1016/s0955-2219(02)00070-5.

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Ren, Qiang, Xiu Lan Wu, and Xuan Meng He. "Effects of Adding Form of Additives on the Structure and Properties of High-Purity Alumina Ceramics." Key Engineering Materials 336-338 (April 2007): 1130–32. http://dx.doi.org/10.4028/www.scientific.net/kem.336-338.1130.

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High-purity alumina ceramics was prepared using high-purity α-Al2O3 powder as raw material, nitrates or oxides of magnesium, chromium and copper as additives by a wet ball milling with a later dry pressing forming and normal pressure sintering process. The influence of additives on the sintering temperature, microstructure and bending strength of the prepared alumina ceramics was studies. The results showed that the additive doped with nitrate can be dispersed uniformly in the body with molecule scale, and the oxides obtained by decomposing of nitrates have the higher reactivity. Thus, the nitrate additives have better capacity than oxide additives in reducing the sintering temperature and inhibiting the abnormal grain growth, and the alumina ceramics prepared by adding of nitrate additives have higher density and bending strength.

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Luo, Qiong, Hua Zhi Gu, Ao Huang, and Mei Jie Zhang. "Potash Erosion Resistance of Chromium-Containing Materials." Solid State Phenomena 281 (August 2018): 144–49. http://dx.doi.org/10.4028/www.scientific.net/ssp.281.144.

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Compared with the traditional entrained flow gasifier, coal catalytic gasifier has the advantages of low reaction temperature, high production efficiency and low energy consumption, but it also has higher requirements for potash erosion resistance. Chromium-containing material is commonly used as lining material for gasification furnaces. In this paper, potash erosion resistance of chromium-containing raw materials and products were respectively researched by using powder tabletting sintering and potassium vapor erosion method. The potash erosion resistance are characterized by XRD and SEM. The study show that:(1)There are obvious potassium salt deposition on the surface of chromium-containing raw materials and products after potash erosion experiment. Potash reacts with chrome-corundum and magnesium-chrome spinel to form K2CrO4,and reacts with chromium oxide to form K2Cr2O7at 750°C. (2)Potassium vapor enters into chromium-containing products through pores and leads to crack formation and volume change, which destroy the structure and reduce high temperature volume stability of material.

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Yadava, Yogendra Prasad, and Ricardo Arthur Sanguinetti Ferreira. "Study of Sintering Behavior of Ba₂AlSnO_5.5 Ceramic Powder Compacts as Substrate for Temperature Sensing Devices." Materials Science Forum 591-593 (August 2008): 661–66. http://dx.doi.org/10.4028/www.scientific.net/msf.591-593.661.

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Ceramic components are frequently used as substrates for the production of temperature sensing devices in petroleum industries, in view of their high thermal and electrical resistance and inertness in hostile ambient conditions. Complex cubic perovskite oxide ceramics have a great advantage in terms of their varied physico-chemical characteristics with the substitution of structural elements in the respective formula units. In this context, we have produced Ba2AlSnO5.5 ceramics by solid state reaction process. Structural characteristics, studied by powder x-diffraction, reveal that Ba2AlSnO5.5 ceramic has an ordered complex cubic perovskite structure. Ba2AlSnO5;5 ceramics were sintered in the form of circular discs of 10 and 15 mm diameters and 2 mm thickness, in the temperature 1200 to 14000C by normal sintering process. The microstrutural characteristics were studied by scanning electron microscopy on both polished and fracture surfaces. The SEM micrographs show homogenous surface morphology and particle size distribution. Mechanical hardness of the sintered Ba2AlSnO5.5 ceramics were studied by Vicker´s hardness tests. The results of these studies have been presented and discussed in this work

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Feller, Claudia, Stefan Furche, and Markus Eberstein. "Development and characterization of glass matrix composites as porous coating film of a solid state reference electrode." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2012, CICMT (September 1, 2012): 000200–000207. http://dx.doi.org/10.4071/cicmt-2012-tp46.

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For protection against leaching of the electrolyte reservoir of a solid state reference electrode a porous covering film was prepared and characterized. The porous covering film is based on a glass matrix composite and fired at 400 °C according to the thick-film-based structure of the reference electrode. Based on stability investigations on low sintering glasses in the range of pH 1.68 to pH 9.18 and in various concentrated potassium chloride solutions, a suitable zinc borate glass was selected. Using this glass and Al2O3 or ZrO2 oxide powders, various glass matrix composites were prepared and their sintering behavior was investigated in dependence on the amount of crystalline fraction up to 45 vol%. The shrinkage was measured by heating microscopy of powder compacts of cylindrical shape. In addition composite films on ZrO2 substrates screen-printed and at 400 °C fired were characterized in terms of their porosity by means of micro structural analysis and electrochemical deposition of copper. According to these investigations, suitable composites were selected as porous covering materials for the reference electrode and were tested therefore. The electrochemical characterization showed that the solid-state reference electrodes with porous covering films have a very good performance compared to conventional reference electrodes.

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Imam, M. Ashraf, Arne W. Fliflet, Ralph W. Bruce, C. R. Feng, Chad Stephenson, A. K. Kinkead, and Steven H. Gold. "Recent Advances in Microwave, Millimeter-Wave and Plasma-Assisted Processing of Materials." Materials Science Forum 638-642 (January 2010): 2052–57. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.2052.

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We present results on microwave, millimeter-wave, and millimeter-wave-driven plasma-assisted processing of materials. The research is primarily based on two systems- a 2.45 GHz, 6 kW S-band system and an 83 GHz, 15 kW gyrotron-based quasi-optical system. The S-Band system is used to synthesize nanophase metals, metal mixtures, and metal oxides by our patented continuous microwave polyol process, which has potential for large scale and low cost production. This system is also being investigated to develop techniques for titanium melting and sintering. The 83-GHz system is used for rapid sintering of ceramic powder compacts to produce polycrystalline materials with limited grain growth. An important application is to the development of polycrystalline laser host materials for high power solid-state lasers, where the requirement is for transparency with high optical quality and good lasing efficiency. We are currently investigating solid-state reactive sintering of Nd-doped YAG (Yttrium Aluminum Garnet) from commercial oxide powders. This has thus far yielded translucent samples with good fluorescence lifetime of the lasing state. Techniques for further reducing light scattering by residual pores are being investigated. Finally, the millimeter-wave system is being used in the development of millimeter-wave plasma-assisted diamond deposition, as the quasi-optical system has significant advantages over conventional microwave plasma-assisted diamond deposition systems. The results and implications of this wide range of materials processing experiments are presented and discussed.

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40

Kuznetsov, Maxim V., Ivan P. Parkin, Yuri G. Morozov, and Alexander G. Merzhanov. "Self-Propagating High-Temperature Synthesis of Chromium Substituted Lanthanide – Barium – Copper Oxides, LnBa2Cu3-xCrxO7-y (Ln = Y; La; Nd; Sm and Yb)." Eurasian Chemico-Technological Journal 4, no. 2 (June 30, 2017): 73. http://dx.doi.org/10.18321/ectj521.

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A series of MBa2Cu3-xCrxO7-y (M = Y; La; Nd; Sm and Yb; x = 0, 0.05, 0.15, 0.25) materials were synthesized in air by self-propagating high-temperature synthesis (SHS) involving reaction of stoichiometric mixtures of rare-earth metal (III) oxide, barium peroxide, copper metal, chromium (III) oxide and sodium perchlorate. All the SHS processes were followed by sintering in oxygen at 950 °C for 2h. The products were characterized by SEM, X-ray powder diffraction, UV, superconductive transition temperatures (Tc) and magnetic susceptibility (χ) measurements. X-ray diffraction data showed that single phase orthorhombic (or tetragonal for M = Nd) materials were produced. All series of materials showed a systematic increase in lattice parameters and unit cell volume with chromium content (M = Y: x = 0, V = 174.25 Å3; x = 0.25, V = 175.10 Å3). Thermal stability of all the SHS prepared materials increased with x. Oxygen content of all the samples increased with x, but did not exceed 7.0. Superconductivity transition temperature decreased with chromium substitution in all systems (98-77 K). Magnetic susceptibility decreased with chromium substitution.

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Mansourirad, Nima, Mohammad Ardestani, and Reza Afshar. "Synthesis and characterization of Ag-8 %wt Cr2O3 composites prepared by different densification processes." Science of Sintering 50, no. 3 (2018): 323–35. http://dx.doi.org/10.2298/sos1803323m.

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A novel Ag-8 %wt Cr2O3 composite prepared via powder metallurgy route. Silver and chromium oxides were used as starting powders. The powder mixtures were mechanically milled by a SPEX high energy mill for 5 h. Based on the thermogravimetric analysis (TGA) and X-Ray Diffraction (XRD) results, the milled powders were calcined in an argon atmosphere at 550?C. During calcination, the silver oxide decomposed into silver. The results showed that the Heckel equation was the preferred one for description the cold compressibility of the powders. The calcined powders were consolidated by Press-Sinter-Repress (PSR), Press-Sinter-Repress-Anneal (PSRA) and Spark Plasma Sintering (SPS) processes. The Field Emission Scanning Electron Microscope (FESEM) investigations showed a nearly dense microstructure of the sintered samples. However, the hardness of the pressed-sintered-repressed samples was 81 Vickers which was the highest among the processed specimen. Furthermore, the flexural strength of the PSR and SPS processed samples were 231 and 255 MPa, respectively which were too higher than that of the annealed specimens. The results confirmed the effect of microstructural parameters such as Cr2O3 particle size and processing route on the mechanical properties of the sintered composites.

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42

Shevelev, S. A., and S. A. Ghyngazov. "The Effect of Pressure in Producing Ultrafine Powder Compacts from Zirconium Dioxide Doped with Bismuth Oxide on Compaction Efficiency and Mechanical Properties of the Sintered Ceramics Under Conditions of High-Temperature Sintering." Russian Physics Journal 60, no. 10 (February 2018): 1848–51. http://dx.doi.org/10.1007/s11182-018-1292-y.

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Santos, Silas Cardoso, Orlando Rodrigues Junior, and Leticia Campos. "Microstructure evolution of yttria compacts by powder technology." Current Smart Materials 05 (January 20, 2021). http://dx.doi.org/10.2174/2405465805666210120102315.

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Background: Innovation in ceramic materials relies on processing of powders. Yttria also known as yttrium oxide belongs to rare earths group, which usual form is RE2O3 (RE from La to Lu, including Sc and Y). Due to great end use of RE based materials since agriculture until astronomy, the main economies such as United States of America and European Union addressed REs as critical materials. The aim of this paper is to obtain dense compacts of yttria by powder technology, in which the effect of sintering temperature on samples microstructure is evaluated. Methods: Yttria powders (Y2O3) were used as starting material, being characterized by Photon Correlation Spectroscopy (PCS); X-ray Diffraction (XRD); Scanning Electron Microscopy (SEM). Powder compacts in cylindrical shape formed by uniaxial compaction, followed by hydrostatic compaction were evaluated by means of apparent density. Sintered samples under sintering temperatures from 1350 to 1550ºC were evaluated by SEM, XRD, apparent density, and true density. Results: Cubic C-type yttria powders exhibited mean particle size (d50) of 1.6μm, and morphology like acicular. Powder compacts (diameter x height) of 9.57mm ± 0.01 x 1.53mm ± 0.01 presented mean apparent density of 53.69% (based on free powder density). As sintered samples at 1550ºC, exhibited the most densification 65.0% related to green density and 91.0% related to theoretical density, respectively. Conclusion : Yttria cylindrical compacts with dense microstructure and symmetric dimensions were formed by powder technology from powders with mean particle size of 6.51μm, by compaction methods (uniaxial and hydrostatic), followed by sintering. The most densification of samples was achieved by the sintering condition of 1550ºC for 2h, providing samples with theoretical density of 91%. These results provide useful subsidies to advance toward full densification of ytrria based materials.

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Seeley, Zachary M., Joshua D. Kuntz, Nerine J. Cherepy, and Stephen A. Payne. "Transparent Lu2O3:Eu Ceramics." MRS Proceedings 1341 (2011). http://dx.doi.org/10.1557/opl.2011.1205.

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ABSTRACTWe are developing highly transparent ceramic oxide scintillators for high energy (MeV) radiography screens. Lutetium oxide doped with europium (Lu2O3:Eu) is the material of choice due to its high light yield and stopping power. As an alternative to hot-pressing, we are utilizing vacuum sintering followed by hot isostatic pressing (HIP). Nano-scale starting powder was uniaxially pressed into compacts and then sintered under high vacuum, followed by HIP’ing. Vacuum sintering temperature proved to be a critical parameter in order to obtain highly transparent Lu2O3:Eu. Under-sintering resulted in open porosity disabling the driving force for densification during HIP’ing, while over-sintering lead to trapped pores in the Lu2O3:Eu grain interiors. Optimal vacuum sintering conditions allowed the pores to remain mobile during the subsequent HIP’ing step which provided enough pressure to close the pores completely resulting in fully-dense highly transparent ceramics. Currently, we have produced 3 mm thick by 4.5 cm diameter ceramics with excellent transparency, and anticipate scaling to larger sizes while maintaining comparable optical properties.

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García, D. E., S. Schicker, J. Bruhn, A. Krupp, R. Janssen, and N. Claussen. "Al2O3 Composites Containing Fe, Nb and Zr Aluminides." MRS Proceedings 460 (1996). http://dx.doi.org/10.1557/proc-460-761.

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ABSTRACTA reactive powder-processing technique involving controlled exothermic solid-state reactions between Al and oxides has been used to produce nearly fully dense composites with interpenetrating networks of aluminides and Al2O3. The process consists of the in situ formation of aluminides and Al2O3 from compacts of intensively milled oxide-Al powder mixtures followed by pressureless sintering. The reactions take place usually at temperatures below the melting point of Al. At temperatures >1000°C, the reaction products start to sinter yielding microstructures with very fine and uniform phase distribution. The present paper discuses processing parameters such as attrition milling, heating cycle and atmosphere controlling microstructural development and mechanical properties of Al2O3 composites containing Fe, Nb and Zr aluminides.

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Min, Zheng, Sarwesh Narayan Parbat, Li Yang, Bruce Kang, and Minking K. Chyu. "Fabrication and Characterization of Additive Manufactured Nickel-Based Oxide Dispersion Strengthened Coating Layer for High-Temperature Application." Journal of Engineering for Gas Turbines and Power 140, no. 6 (January 23, 2018). http://dx.doi.org/10.1115/1.4038351.

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Increasing turbine inlet temperature is important for improving the efficiency of gas turbine engine. Elevated thermal load causes severe oxidation and corrosion for base alloy in turbine airfoils. To survive in this extreme high-temperature and harsh oxidation environment, both outside protection like thermal barrier coatings (TBC) and inside air cooling have been applied to turbine blades. Significantly more protection can be achieved if the cooling channels are embedded near surface, constructed partially by the coating system and partially by the superalloy substrate. However, neither the ceramic coating layer nor the metallic bond coating layer in current TBC system can provide structural support to such internal cooling channels. Development of structural bond coating layers consequently becomes one of the key technologies to achieve this goal. The present study proposed a method to fabricate structural coating layers on top of turbine blades with the aid of additive manufacturing (AM) and oxide dispersion strengthened (ODS) nickel-based alloy. ODS powder comprised of evenly distributed host composite particles (Ni, Al, Cr) with oxide coating layers (Y2O3) was subjected to a direct metal laser sintering (DMLS) process to fabricate a desirable structural coating layer above nickel-based superalloy substrates. Systematic experimental tests were carried out focusing on the interface adhesion, mechanical strength, microstructure, and surface finish of the ODS coating layer. Based on characterization results from indentation tests and microscopy observations, an optimal coating quality was obtained under ∼250 W laser power. The selected samples were then characterized under isothermal conditions of 1200 °C for 2000 h. Scanning electron microscope (SEM) observations and energy-dispersive X-ray spectroscopy (EDX) analysis were conducted in different stages of the oxidation process. Results indicated a formation of Al2O3 scale on top of the ODS coating layer at early stage, which showed long-term stability throughout the oxidation test. The formation of a stable alumina scale is acting as a protective layer to prevent oxygen penetrating the top surface. Spallation of part of nickel oxide and chromium oxide is observed but the thickness of oxide scale is almost no change. In addition, the observed adhesion between ODS coating layer and substrate was tight and stable throughout the entire oxidation test. The present study has provided strong proof that additive manufacturing has the capability to fabricate structural and protective coating layers for turbine airfoils.

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Journal articles on the topic 'Sintering; Powder compacts; Chromium oxide'

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