THE CONCEPT OF EFFECTIVE HARDNESS IN THE ABRASION OF COARSE 2-PHASE MATERIALS WITH HARD 2ND-PHASE PARTICLES

During the abrasion of a coarse two-phase material which contains hard second-phase particles, a brittleness mechanism can frequently coexis t with plastic grooving. By taking R(X) as the abrasion resistance of given material with X as its second-phase volume fraction, the concept of effective hardness, H-eff, gives rise to a modification of the lin ear rule of mixtures as R(X) proportional to (1 - X) H-m + alpha XH(s) , where H-m and H-s are the hardness of pure matrix material and pure second phase, respectively. The parameter a decreases with increasing severity of the brittleness effect. By defining alpha(c) = H-m/H-s, dR /dX < 0 provided that alpha < alpha(c). The SiC abrasion data of a ser ies of Al-Si alloys (with the volume fractions of pro-eutectic Si part icles ranging from 0.023 to 0.219) can be rationalized by the above mo del since R(X) shows a nice linear fit with X. The alpha(c) value of t he test alloys is close to zero. Therefore, as indicated from the wear surface, extensive brittle fracture can occur without deteriorating t he abrasion resistance. For those with dR/dX < 0, subsurface fracture is also pronounced.