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Session Chairperson: J.E. Benci, Wayne State University, Dept. of Materials Science and Engineering, Detroit, MI 48202
DEFORMATION BEHAVIOUR OF 7075AL/ SICP COMPOSITE DURING MULTIPASS DEFORMATION AT HIGH TEMPERATURES: A. Razaghian, D. Yu, T. Chandra, Department of Materials Engineering, Wollongong University, Wollongong, NSW, 2522, Australia
Hot deformation behaviour of 7075 aluminium alloy containing 15 vol% of SiC particles (average size of 14 am) and the monolithic alloy was studied at 300 and 400°C at constant strain rate of ls-1 under condition of uniaxial compression. The effect of delay between two consecutive passes on the high temperature mechanical strength and microstructural development was examined. The results showed that the fractional softening (%FS) increased in both reinforced and monolithic alloys when the deformation temperature increased from 300 to 400°C, but monolithic alloy showed a slightly higher FS compared to composite under identical deformation conditions. TEM examination revealed that the monolithic alloy and composite contained almost similar substructures after either single or double pass deformation at a given temperature irrespective of interpass hold time. However, some subgrain growth was observed in these materials during holding after deformation at 400°C, but this was not the case at 300°C. The absence of subgrain growth at lower temperature can be attributed to pinning effect by fine dispersions present in the matrix. The structural study also showed that static recrystallization did not occur in these materials during hold time between passes, and the fractional softening occurs mainly due to static recovery.
WEAR PROPERTIES OF PARTICULATE REINFORCED ALUMINUM ALLOYS: Yeong-gi Cho, Su-young Kim, Ikmin Park, Kyungmox Cho, Dept. of Metallurgical Eng. Pusan National University, Pusan 609735, Korea
Wear properties of cast AlSiCp composites were characterized under dry and lubricated conditions. Wear tests were performed employing blockonroller type and pinondisk type machines. Test conditions including applied load, sliding speed and sliding distance were changed for wear tests. Wear behavior was investigated by analyzing worn surfaces and debris, mainly as a function of the sliding speed. Results show that there exist transition speeds at which the minimum wear rate occurs for both dry and lubricated conditions. However the appearance of wear transition is not well defined for the lubricated wear. It was found that SiCp reinforcement affects wear at the low sliding speeds and the softening of Al matrix dominates wear at the high sliding speeds. Main wear mechanism is abrasive wear although some amounts of adhesive wear are observed especially at the high sliding speeds.
FATIGUE CRACK GROWTH BEHAVIOR OF DIECAST AND CAST SiC PARTICULATES REINFORCED ALUMINUM COMPOSITES: Song-Hee Kim, Iee-Jeoung Kim, Department of Materials Engineering, Kangwon National University, Chunchon, Kangwondo, Korea, 200701
The fatigue crack growth rate (FCGR) of SiC particulates reinforced aluminum matrix composites containing 10vol.% and 20vol.% of SiC fabricated by the casting and the die-casting processes have been studied over a wide range of stress intensity factor for various load ratios. The effect of volume fraction of SiC on FCGR was also investigated for the diecast and cast composites. Fracture toughness was found to affect the fatigue crack growth behavior at the higher level of stress intensity factor range; however, at lower level, fatigue crack roughness related with the volume fraction of SiC reinforcement was more responsible for the fatigue crack growth. Diecast composite with 20vol.% of SiC showed the superior fatigue crack propagation resistance at the lower level of AK, but the inferior resistance at the higher level of AK due to the decreased ductility and fracture toughness.
HIGH STRAIN RATE SUPERPLASTICITY OF DISCONTINUOUS FIBER REINFORCED PUR ALUMINUM COMPOSITES: Tsunemichi Imai, Sumito Kojima, Isao Tochigi, Gilles L'Esperance, Bande Hong, Daming Jiang; National Industrial Research Institute of Nagoya, Hirate-cho, Kita-ku, Nagoya 462, Japan; Nagoy Minucipal Industrial Research Institute, 4-3-4 Rokuban-cho, Atsuta-ku, Nagoya 456, Japan; Ecole Polytechnique de Montreal, PO Box 6079, Station A, Montreal (Quebec) Canada; Harbin Institute of Technology, Harbin 150001, China
High Strain Rate Superplasticity (HSRS) of metal matrix composite has a great potential to apply to components and structures in automobile and aerospace industries and even semi-conductor packings since the composites exhibits excellent mechanical, physical and thermal properties. IN90 pure aluminum (Al) alone and AlN/1N90 pure Al composite made by PM method, and -Si3N4w/99.99% pure Al composite fabricated by squeeze casting were hot-rolled after extrusion and the superplastic characteristics were investigated to clarify the deformation mechanism. IN90 Al alone hot-rolled about 773K could produce the m value of more than 0.3 and 300~450% at the strain rate of about 0.01s-1 and at 913~923K and also has threshold stress in the strain rate less than 0.01s-1. -Si3N4w/99.9% pure Al composite exhibits the m value of 0.47 and the total elongation of about 200% at the strain rate of 0.5s-1 and at 903K. The results indicate that the HSRS could occur by grain boundary sliding without interfacial sliding at liquid phase, because the optimum temperature to produce the HSRS is just below incipient melting temperature.
FRACTURE BEHAVIOR OF COBALT COATED Al203 SHORT FIBER REINFORCED 2024 Al COMPOSITE: K.H. Baik*, E.S. Lee, and S. Ahn, Advanced Materials Division, Research Institute of Industrial Science and Technology, San 32, Hyojadong, Pohang, Kyungbuk 790330, Korea; *Dept. of Materials Science, Oxford University, UK
The effect of chemical reaction at coating/fiber interface on the fracture behavior of 2024 Al alloy reinforced with Co coated Al2O3 fibers were investigated. Al2O3 fibers were coated with metallic Co by solgel process using Co acetate compound. The coated fibers were annealed at temperatures ranging from 300 to 1000°C in vacuum to generate interfacial reaction between the Co coating and the Al2O3 fiber. Regardless of the annealing temperatures, a fair amount of solute Co was detected near the Al2O3 fiber surface ensuring the good bonding between the coating and the fiber. AlgCO2 and Co203 phases were formed at high annealing temperatures. SEM fractography of the composite showed the change of fracture behavior as a result of the interfacial reaction. Fiber debonding was frequently observed in the composite rein forced with fibers annealed at low temperatures. On the other hand, the composite with fibers annealed at higher temperatures had improved tensile strength, and showed much smaller dimples around the fibers and relatively less fiber pull-out. In-situ SEM fracture study was performed to understand the micro fractureprocess of the composite.
THE INFLUENCE OF SOLUTIONIZING TIME AND TEMPERATURE ON THE BONDING CHARACTERISTICS AND MICROSTRUCTURES BETWEEN THE PARTICLES AND MATRIX IN COMPOSITES WITH 6061 AND 2014 ALLOYS REINFORCED WITH ALUMINA PARTICLES: Daniel Salas, Javier Ponce, Erica Corral, S.K. Varma, Department of Metallurgical and Materials Engineering, The University of Texas at El Paso, El Paso, TX 79968-0520
The influence of solutionizing time and temperature on the microstructural development and bonding characteristics between the matrix and the particles will be characterized in composites with 6061 and 2014 aluminum alloys reinforced with 0.10, 0.15 and 0.20 volume fractions of Ai2O 3 particles (VFAP) solutionized at 520, 530, and 540°C for different times up to 20 hours to produce various grain sizes after quenching. The different heat treated samples after solutionizing v,/ill be subjected to room temperature tensile fracture at various strain rates (attainable in an Instron tensile testing machine) and the fracture surfaces will be characterized by SEM and related to the UTS. The samples deformed to various true strains will be analyzed in the TEM to determine the influence of solutionizing time on the microstructural development during the deformation. The results on the composites will be compared with similar treatments performed on the alloys in their monolithic forms in order to determine the deformation mechanisms in the composites. This research has been supported by the National Science Foundation through the grant number HRD9353547.
HOT DEFORMATION BEHAVIOR OF (SiCw+SiCp)/AA2124 COMPOSITES: Yeon-Chul Yoo, ByungChul Ko, and Joon Park, Department of Metallurgical Engineering, Inha University, Inchon 402751, Korea
The hot deformation behavior of 15 vol.% (SiCw + SiCP.) reinforced AA2124 composites was investigated by hot torsion tests. The AA2124 Al based composites with different volume fractions of SiCw and SiCP reinforcements were fabricated by the powder metallurgy. Detailed analyses of flow curves and deformed microstructures were made to identify the hot restoration mechanism, such as dynamic recrystallization or dynamic recovery. Also, the dependence of flow stress and ductility on temperature and strain rate was studied. From the flow curves and microstructures of the hot deformed composites, it has been found that dynamic recrystallization was responsible for the hot restoration of the composites. The flow stress of the hybrid composites was higher than that of the monolithic AA2124 alloy. The flow stress and ductility of the hybrid composites were investigated with respect to the ratio of SiCw and SiCP, reinforcements.
ANALYSIS OF RESIDUAL STRESSED IN Ti-ALLOY, SCS-x MMC's BY NANOINDENTATION: K.L. Kendig, R. Gibala, D.B. Miracle, B.S. Majumdar; Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI; Materials Directorate, Wright Laboratory, Wright-Patterson Air Force Base, OH; UES Inc., Dayton, OH
Knowledge of variation of residual stresses aids in prediction of composite deformation and failure. Hardness measurements with high spatial resolution using extremely low load indentations, such as by nanoindentation techniques, may be an indicator of such variation of residual stresses. In this work, nanoindentation was used to determine hardness as a function of radial position from a fiber for a Ti6Al-4V, SCS-6 SiC fiber composite and a Ti-15V-3Al-3Cr-3Sn, SCS-0 SiC fiber composite, each in the as-consolidated condition. Residual stress predictions from a finite element model were compared to the hardness distributions obtained by nanoindentation. A small difference in nanoindentation hardness was found between the two phases of the Ti-6Al-4V matrix in the Ti-6Al-4V, SCS-6 composite, which likely masked any effects of residual stress on hardness. The Ti-15V-3Al-3Cr-3Sn, SCS-0 system was chosen to avoid this complication and to allow more direct correlation between predicted residual stress and nanoindentation hardness.
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