Effects of residual porosity on the properties of tungsten carbide-cobalt hard alloys

Abstract

1. The transverse rupture strength, fatigue life in cyclic bending, ultimate strength and yield stress in compression, hardness, and impact strength of VK8 hard alloy decrease with increase in porosity. The decrease is exponential, i.e., manifests itself particularly strongly in the range of low porosities. The relationship discovered, which is satisfactorily described by Ryshkewitch's formula, is due to the fact that the probability of appearance of maximum (dangerous) stress concentration varies exponentially as a function of the number of pores per unit volume. 2. A particularly marked decrease in transverse rupture strength, impact strength, and fatigue life is exhibited by VK8 alloy with large pores (>50Μ). Such an alloy is characterized by higher values of yield stress and ultimate strength in compression. With both large and fine pores, the decrease in these characteristics is less pronounced than the decrease in transverse rupture strength, impact strength, and fatigue life in cantilever type cyclic bending. 3. The useful life of a VK8 alloy tool in the turning of cast iron also decreases exponentially with increase in porosity owing to the fall in hardness and strength.