Materials Science Forum Vols. 534-536

Abstract: A theoretical model is applied to the analysis of thermomechanical properties of Al-SiCp FGMs in this study. Functionally graded Al-SiCp composites (Al-SiCp FGMs) consisted with 10 layers gradually changing volume fractions of Al and SiCp were fabricated using the pressureless infiltration technique. Al-SiCp FGMs plates of total thickness of 3mm, 5mm and 7mm with fairly uniform distribution and compositional gradient of SiCp reinforcement in the Al matrix throughout the thickness was successfully fabricated. The curvature of Al-SiCp FGM plates was measured to check the internal stress distribution predicted via a theoretical model for the analysis of thermomechanical deformation. The evolution of curvature and also internal stresses in response to temperature variations could be predicted for the different combinations of geometric thickness of FGM plates. Theoretical prediction of thermally induced stress distribution makes it possible to design FGM structures without any critical failure during the usage of them.

Abstract: Processing of W-Cu graded materials from attritor-milled W-CuO mixtures is described. The powder reduction steps are investigated by TG and XRD analyses and by microstructural observations (SEM, TEM). Sintering of reduced powder with different compositions is analysed by dilatometry. Sintering behaviour of the graded component processed by co-compaction of a 10/20/30wt%Cu multi-layer material is briefly discussed. Liquid Cu migration is observed and smoothes the composition gradient. Perspectives to control this migration are discussed.

Abstract: Austenitic stainless steel has been used as a corrosion resistance material in tough corrosive circumstance. However, austenitic stainless steel has poor wear resistance property due to its low hardness. Tungsten Carbide alloys (WC) are widely used as tooling materials, because of their high hardness and excellent wear resistance property. In this investigation, we apply powder composite process to obtain hard layer of Stainless steel. The composite material was fabricated from planetary ball milled WC powder and SUS316L stainless steel powder and sintered by Pulsed Current Sintering (PCS) method. We also added TiC powder as a hard particle in WC layer. Evaluations of wear properties were performed by pin-on-disk wear testing machine, and a remarkable improvement in wear resistance property was obtained. The weight loss rate of the composite was 1/10 of SUS316L. In addition, it was found that TiC hard particle addition has a positive effect on the wear resistance property. EPMA investigation showed good dispersion of WC hard phase and TiC hard particle with SUS316L matrix.

Abstract: Alloys of Ti-50 at.% Al with (3 and 10)wt.% Si3N4 particles were prepared by a mechanical alloying-spark plasma sintering (MA-SPS) method. The matrix consisted primarily of TiAl, Ti2AlN, TiN. Si3N4 was unstable in the matrix and started to decompose forming a Ti5Si3 reaction layer on the surface of former Si3N4 particles during sintering and heat treatment at 1373 K.

Abstract: Property modification of Ni3Al with alloying addition of Fe and Cr was investigated through MA and subsequent SHS processes. Fe addition brought about high temperature strengthening effect and formed a Ni-Fe compound in the liquid grainboudary phase of Ni3Al structure and Cr addition showed a retarded homogenization. Homogenized Ni3Al composition with Fe and Cr addition by MA and SHS showed better mechanical resistace and deformability in the compression tests at temperatures up to 800°C than the same composition processed by classical PM routes.

Abstract: New light super-heat-resistant powder Ni3Al and NiAl-based alloys (of the Ni-Al-Mo-B, Ni-Al-Fe-La, and Ni-Al-Y2O3 systems), as well as a new technology for preparing and processing them have been developed. The density of the alloys was 7.3-7.5 and ~6 g/cm 3, respectively. The Ni3Al sheets were used to prepare shields for combustion chambers in gas-turbine engines by roomtemperature deformation; the shields are intended for the long-term operation at 1100-1200°C and for the short-term use at 1300°C. The activated NiAl powders alloyed with Fe+La were used to produce sintered complex-shape articles, such as combustion stabilizers in a jet unit of combustion chamber of the gas-turbine installation, heat sources, etc. capable of operating at t≤1500°C under low mechanical stresses. At 1100, 1300, and 1500°C, the 100-h strength of the heat-resistant NiAl- (2-7.5) vol. % Y2O3 alloys subjected to directional recrystallization is 70, 35 and ≥10 MPa, respectively. The vanes, in which the length of recrystallized grain is smaller than the vane length by a factor of 1.5-2, were manufactured from these alloys.

Abstract: Structure and properties of MASHS powder Ti-46Al-8Cr, at. %, have been investigated. The powder is characterized by the multiphase dispersed strengthened structure with coherent precipitates/matrix bonding. Main structural constituents of the powder are titanium aluminides alloyed with chromium: γ-TiAl(Cr), Al0,67Cr0,08Ti0,25 and α2-Ti3Al(Cr). Average powder microhardness is 313 HV0.25. High-quality detonation coatings with high hardness (940-1100 HV) and low porosity (less than 1%) have been obtained from the synthesized powder. The coatings exhibit good oxidation behaviour at 900°C.

Abstract: Five kinds of double stacked 385 (55ⅹ7) filamentary Bi2212/Ag round wires and 55 filamentary tapes with different Ag ratios (silver area/superconductor area) have been fabricated via PIT method, and the effects of Ag ratio and processing factors on critical current density were studied. The effects of the maximum temperature and average filament diameter on critical current density were also studied. The wire of 0.74 mm diameter having Ag ratio 3.7 showed critical current density of 2,218 A/mm2 at 4.2 K, 0 T.

Abstract: We fabricated Bi-2212/SrSO4 composite superconductors by the melt casting process and evaluated the effects of the powder mixing method and melting temperature on their microstructure and superconducting properties. In the melt casting process, the Bi-2212 powders were mixed with SrSO4 by hand-mixing (HM) and planetary ball milling (PBM) and then the powder mixtures were melted at 1100°C~1200°C, solidified, and annealed. We found that the powder mixture prepared by PBM was finer and more homogeneously mixed than that prepared by HM, resulting in more homogeneous microstructure and smaller SrSO4 and second phases after annealing. The critical current (Ic) also varied significantly with the powder mixing method and the melting temperature. The Ic of the annealed rod prepared by PBM was 193 A at 77 K when melted at 1100°C, which is higher than that of the annealed rod prepared by HM (132 A). This enhancement in the Ic value for the former is considered to be due to its more uniform microstructure.

Abstract: We fabricated YBCO film using a TFA-MOD method and evaluated the phase formation, texture evolution, and critical properties as a function of the firing temperatures. In order to enhance the reaction kinetics and to control the formation of the second phases, Y2Ba1Cu1Ox and Ba3Cu5O8 powders were used as precursors (the so called “211 process”), instead of Y-, Ba-, and Cu-based acetate, and dissolved in trifluoroacetic acid (TFA). The films were calcined at 460°C and then fired at 750°C-800°C in a 12.1% humidified Ar-O2 atmosphere. We found that the microstructure varied significantly with the firing temperature; the grain grew further and the film became denser as the firing temperature increased. The textures of all of the films were similar and mainly biaxial. On the other hand, the intensity of the major and minor texture components differed from each other. For the film fired at 775°C, the critical current was obtained to be 39 A/cm-width (corresponding critical current density is 2.0 MA/cm2), which was probably attributed to such factors as the enhanced phase purity and out-of-plane texture, the moderate film density and grain size, and crack-free surface.