The concept of effective hardness in the abrasion of coarse two-phase materials with hard second-phase particles

During the abrasion of a coarse two-phase material which contains hard second-phase particles, a brittleness mechanism can frequently coexist 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 linear rule of mixtures as R(X) ∫ (1-X)H _m + αXH _s, where H _m and H _s are the hardness of pure matrix material and pure second phase, respectively. The parameter α decreases with increasing severity of the brittleness effect. By defining α_c=H _m/H_s, dR/dX<0 provided that α<α_c. The SiC abrasion data of a series of Al-Si alloys (with the volume fractions of pro-eutectic Si particles ranging from 0.023 to 0.219) can be rationalized by the above model since R(X) shows a nice linear fit with X. The α_c value of the test alloys is close to zero. Therefore, as indicated from the wear surface, extensive brittle fracture can occur without deteriorating the abrasion resistance. For those with dR/dX<0, subsurface fracture is also pronounced.