Fracture Toughness - Fatigue Sensitivity Relationship for PM Tool Materials: Cemented Carbides and High Speed Steels

摘要

The fracture and fatigue behavior of different tool materials processed by powder metallurgy (PM) is investigated. The materials studied included several hardmetal grades with different microstructural combinations of ductile binder content and carbide mean grain size, and a high speed steel. Mechanical characterization involves fracture toughness as well as fatigue crack growth (FCG) behavior under distinct load ratios. Experimental results indicate a more pronounced dependence of FCG kinetics on K_(max) than on ΔK. However, the prevalence of K_(max) over ΔK as the controlling fatigue mechanics parameter, decreases as fracture toughness increases. The results are discussed taking into consideration effective ductility effects on the fatigue sensitivity of the materials studied, the latter defined as the ratio between FCG threshold and fracture toughness. The analysis allows to establish the fracture toughness - fatigue sensitivity relationship determined for these hard PM tool materials as intermediate between those exhibited by ductile metallic- and brittle ceramic-like materials.