Understanding The Fatigue Behavior Of WC-Co Based Cemented Carbide And Stress Analysis Method

Cemented carbides, which are called industral tools, are indispensable tool and structural materials in modern industral and new technology field. With the rapid development of the synthetic man-made diamond industry, wire rolling, precision mould manufacturing, the demand for improved performance cemented tungsten carbides is requires. Fatigue and fracture are the major failure mechanisms for cemented carbides. So far, the mechanical behavior is mainly characterized by hardness and bending strength. In practical applications, hard metal components may be subjected to repeated impact or cyclic loading. So dynamic strength propertied are important for hard metal. Therefore knowledge about the behavior of this material under cyclic loads is also required. Although compound mechanical, thermal and environmental condition applies in real service, no much has been reported on the effect of compound testing condition on hard metal life. The aim of the present work is to investigate the fatigue life and the microstructure properties of WC-Co hard metals under compound fatigue conditions.In mechanical fatigue conditions, the fatigue effect is strongly dependent on the stress amplitude. At high stress level, material’s fatigue life is more corresponding to its hardness, however, at low stress level, the fatigue life increases with increasing binder content. Fatigue cracks grow alone grain boundaries and in binding phases. After cyclic loading, WC particles and binders separate, this debonding causes pore and micro.cracks formed. The pore and crackle connected to accelerate the crack growth and eventually lead to material fracture. In Co binders, stacking fault and phase transformation occurred during fatigue process, precipitated phases are also found. Ni-Cr additive in Co binder can effectively increase the stacking fault, hinder the expansion, and suppress the occurrence of Co phase transformation.Compared with mechanical fatigue, in thermal-mechanical fatigue conditions, fatigue life reduces in the same stress amplitude. The main reasons are:(1) a loose oxide layer forms on the sample surface, which reduce applied force area of samples;(2) in high temperature, mechanical properties of alloy will decline. This reduction is more obvious at low stress level. This is because sample suffers more temperature damage when its fatigue life is longer. YGR alloys show almost the same fatigue life in thermal-mechanical fatigue conditions as well as just mechanical fatigue conditions. Only in the case of low stress level fatigue life reduces slightly. Which cofirms that Ni and Cr additions can increase the high temperature fatigue resistance.Typical thermal fatigue crack incluse three stages:crack initiation, crack propagation and fracture. And the crack appears first quick back slow trend, which is different with crack in mechanical fatigue condition. High binder content alloys express lower crack propagation rate, compared with corresponding low binder content alloys. Cemented carbides show better fatigue resistance in500℃(?)20℃ranges compared with700℃(?)20℃. Add Ni and Cr in the Co binder is helpful way to improve the crack initiation life.During thermo-corrosion fatigue, mechanisms account for the influence of the corrosive environment on the fatigue response of the cemented carbides is complex. It can be seen from the given formula that many factors interactions contribute simultaneously to crack propagation. High binder content alloys exhibit lower crack propagation rate, compared with corresponding low binder content alloys. Low binder content alloys conduct better crack propagation resistance in acid environment than in neuter and alkali solution. Co-Ni-Cr binder alloys show better crack propagation resistance in corrosion environment.The effect of cryogenic treatment on the fatigue and mechanical properties of cemented carbides has been investigated in this paper. The results show that after cryogenic treatment, the samples are characteristics of the enhanced mechanical properties, wear resistance and fatigue resistance. The change of the properties is highly dependent on the soaking time, and2h is the best process parameter, which could be ascribed to the change of residual stressed and martensitic phase transformation of Co binder during the cryogenic treatment.This paper introduced a method of detecting the quality of anvils made of cemented tungsten carbide used in cubic high-press apparatus. The qualitative standard of anvils was established by means of the finite element method, and subsequent it was being used in batches.