Observations on the faceted fatigue fracture of cast Co−Cr−Mo alloy used for surgical implants

Abstract

Fatigue crack propagation behavior of cast Co−Cr−Mo alloy used for surgical implants is studied at room temperature with the stress intensity factor range, ΔK, between 20 and$50MPa\sqrt m$, corresponding to a crack growth rate,da/dN, between 10⁻⁵ and 10⁻² mm/cycle. Faceted fatigue fractures are observed to be the dominant fracture features of the alloy under all tested conditions. The characteristics of the faceted fatigue fractures are discussed and identified. The development of facets seems to be a consequence of the low stacking fault energy of the alloy since this results in a dense structure of stacking fault intersections. Grain size has little effect on the occurrence of faceted fatigue fractures in cast Co−Cr−Mo alloy. Modifying the composition of the base alloy with Ni-additions increases the fracture ductility of the alloy.