MICROSTRUCTURE, EXCESS SOLID SOLUBILITY, AND ELEVATED-TEMPERATURE MECHANICAL-BEHAVIOR OF SPRAY-ATOMIZED AND CODEPOSITED AL-TI-SICP

In the present study, the microstructure, thermal stability, and elevated temperature mechanical behavior of Al-Ti-SiC(p) metal matrix composites (MMCs) processed by spray atomization and codeposition were investigated. The evolution of the microstructure of the spray-deposited material before and after thermal annealing was studied using X-ray diffractometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and optical microscopy. The thermal stability of the spray-deposited materials was determined by monitoring the changes in hardness after isochronal thermal anneals at various temperatures. The results of X-ray and microanalysis studies revealed the presence of a supersaturated solid solution of Ti in alpha Al in the spray-atomized and codeposited material, with Ti concentrations in the 0. 8 to 1.1 wt pct range. The formation of an extended solid solution was discussed in light of the cooling rates present during atomization and, subsequently, during deposition. Regarding mechanical behavior, the present results suggest that the as-spray deposited and hot extruded Al-Ti matrix is thermally stable up to a temperature of 400-degrees-C and that the excess solid solubility of Ti in alpha Al, resulting from die rapid quench during processing, is maintained up to a temperature of 300-degrees-C. The elevated-temperature mechanical properties of the hot extruded spray-deposited materials were studied following a 100-hour exposure at 250-degrees-C, 350-degrees-C, and 450-degrees-C; the room-temperature mechanical properties were also determined. Results show that the elevated-temperature yield strength of the spray-deposited and extruded materials compared favorably to those of an equivalent alloy made by powder metallurgical materials, were superior to those of the ingot material, but were inferior to those of mechanically alloyed Al-Ti materials. In addition, TEM studies showed no evidence of interfacial reactions at the Al-Ti/SiC(p) interface.