Fatigue damage in a WC-Nickel cemented carbide composite

Abstract

A WC-15.6 wt pct Ni cemented carbide was designed to investigate the response of this type of composite to compressive cyclic loading. The monotonic stress-strain behavior of the material was investigated in compression. Specimens were mechanically conditioned at 20 Hz for 10⁶ cycles using a zero-compression-zero sinusoidal program under stress control. Peak stress was varied in increments from zero to 1900 MPa, where failure was observed. Only modest changes in hardness, fracture toughness and the residual stress of the carbide were noted. On a local scale, however, significant alterations in binder microstructure and dislocation density and distribution were observed by transmission electron microscopy. As cyclic stress levels were raised, increasing numbers of grain-boundary-ledge dislocation sources became operative, leading to precipitate-free bands of intense slip. These bands broadened at the higher stress levels, saturating entire binder phase regions and finally giving way to a change in dislocation arrangements. It is concluded that fatigue damage in this type of composite accrues in the binder in a characteristic manner dictated by short binder-carbide interaction distances and local stress conditions.