Microstructure and dry sliding wear behavior of ultrafine-grained Co-30 at% Cr alloy at room and elevated temperatures

Abstract

Abstract Co-Cr-based alloys have been widely used as mechanical components where high wear-resistance is required. However, conventional Co-Cr alloys usually have coarse-grained microstructures with phase coexistence of both hexagonal close packed (hcp) e-Co and face-centered cubic (fcc) γ-Co. The wear resistance of the Co-Cr alloys could be further enhanced by grain refinement and exclusion of γ-phase. Here, a Co-30Cr (at%) bulk alloy consisting of ultrafine-grained matrix of e-phase and uniformly dispersed nanoscale precipitates of σ-phase was fabricated by high energy ball milling and spark plasma sintering. Microstructure and dry sliding wear performance against alumina at room temperature and 600\u202f°C were then investigated. The matrix and the precipitates have the average grain size of 227\u202fnm and 16\u202fnm, respectively. Hardness was determined to be 707 HV. The e-Co matrix, ultrafine-grained microstructure and the uniformly dispersed nanoprecipitates enable the alloy with excellent wear resistance. Grain growth of the matrix grain was found as the key factor to be responsible for the increase of wear rate at 600\u202f°C. Subsurface microstructures of the alloy show no significant plastic deformation after wear tests, which is attributed to high hardness of the alloy and very limited slip in hcp system.