The Influence Of Different Stress Ratios On Fatigue Behaviour Of WC-Co Cemented Carbides

Cemented carbides, with a series of excellent physical and chemical properties, arewidely used in construction, machinery, metallurgical and petrochemical fields. Fatigueis a main reason for the fracture of this kind of cemented carbides. Except for themicrostructure and composition of materials, the fatigue behavior is also influenced bythe service conditions, such as stress ratio, frequency, temperature and environment.And researched the fatigue performance of cemented carbides has important significance.The blend strength and fracture toughness of cemented carbides with different binderphase content and composition were tested. The three point bending fatigue behavioursof WC-Co cemented carbides under cyclic loading at two different stress ratios(R=0.1and0.5) were investigated. And the blend strength after different stress ratio fatigueloading was also investigated. Main conclusion are as follows:(1) With the increase of Co content, the blend strength increases firstly and thendecreases, the flexural strength of the alloy with the Co content of15mass%reach2808MPa, cemented carbides with complex binder phase (Co+Ni+Cr) exhibit lowerblend strength than that of pure Co cemented carbides. For power powder metallurgydefects，the blend strength exhibit large dispersion. Weibull statistics can be well usedto analyze the strength of cemented carbides. And the fracture toughness wasincreasing with Co content, for the alloy with the30%Co content with highest fracturethough which reached26.4MPa·m1/2.cemented carbides with complex binder phase (Co+Ni+Cr) exhibit higher facture toughness than that of pure Co cemented carbides.(2) Cemented carbides exhibit a strong fatigue under cyclic loads at the stress ratiosof0.1,0.5. The lifetimes decrease with increasing stress in the cyclic loading. TheFatigue life related with the bend strength, stress ratio and component.With the increaseof Co content, the fatigue sensitivity decreases firstly and then increases, Co phase besubstituted by Ni and Cr can decrease the fatigue sensitivity.(3) With the increase of stress ratio, the fracture mode from brittle fracture toductile fracture and the fatigue sensitivity of cemented carbides decreases. This trend ismore significant with high co content cemented carbides. Under R=0.1loading，cemented carbides with complex binder phase.(5) Compared with the initial states, significant plastic deformation characteristicswere seen in stress-strain curves of some high Co alloys after experienced1×106cyclesat the stress ratio of0.1. And after cyclic loads, the blend strength decreased compared with initial states, the degradation is more remarkable for high Co content cementedcarbides, low stress ratio loading and pure Co content cemented carbides. And comparedwith the initial states, after R=0.1loading causes most decrease in the mean blendstrength from2419MPa to2287MPa for for the cemented carbides with the30%Cocontent.