FRACTURE AT ELEVATED-TEMPERATURES IN A PARTICLE-REINFORCED COMPOSITE

The tensile fracture behavior of a cast and extruded 2014 aluminum all oy metal matrix composite (MMC) reinforced with 10, 15, and 20 vol.% a luminum oxide particles was investigated as a function of temperature between 100 and 300-degrees-C and hold time, and compared with the unr einforced alloy. In addition, the effect of aging condition was invest igated in a 15 vol.% composite tested at 200-degrees-C. At lower tempe rature the composites have higher yield strength and UTS than the unre inforced material, and both decrease with increasing temperature. At h igher temperatures all the materials have similar strength levels. The elongation is lower in the composites, decreasing with increasing lev el of reinforcement and increasing with increasing temperature, except at the highest temperature where all the composites are about the sam e. The microstructural damage in the composites also varies with tempe rature: particle fracture dominates at lower temperatures and interpar ticle voiding is the main damage feature at elevated temperatures. The time at temperature, and hence the degree of overaging, has little ef fect on the observed trends in the composite, in contrast with the unr einforced material where the density of voids decreases with increasin g hold times. The transition temperature where the major damage change s from particle cracking to interparticle voiding increases with volum e fraction and particle size, and decreases with overaging. The cracke d particle density and void density both increase with strain, and the highest rate of increase occurs in the overaged material. In general, the tendency for particle cracking is reduced and for interparticle v oiding is increased by any factor which permits accommodation of strai n by the matrix, such as lower volume fraction of particles, small par ticle size, nonclustered particle distribution, and matrix softening f rom underaging or overaging.