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, d R/d X<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 d R/d X<0, subsurface fracture is also pronounced.