Phase Transformation and its Effect on Dry Sliding Wear of Electro-Pressure Sintered Cobalt and Cobalt-Base Composites

Abstract

Room-temperature dry sliding wear behavior of hot-pressure sintered monolithic Co, Co- 20 wt.% CuSn and Co-20 wt.% WC composites were investigated. Wear tests of the materials were carried out using a pin-on-disk wear tester at various loads of 10N-100N under a constant sliding speed condition of 0.38m/s against glass (83% SiO2) beads. Sliding distances were varied with a range of 100m-600m. A scanning electron microscopy was used to examine worn surfaces, cross sections, and wear debris. X-ray diffraction (XRD) was utilized to identify phases of the specimen and wear debris. All specimens exhibited low friction coefficients ranging from 0.12 to 0.4. The sintered Co exhibited distinctive wear that was characterized by shallow dug canals on worn surface, a very thin detaching surface layer, and fine debris. Thermal transformation of the Co specimen from ε (hcp) phase to α (fcc) phase occurred during the wear of the Co, which was inferred from XRD analysis of the wear debris. The transformation was suggested to cause the thin detaching surface layer and the fine wear debris of the sintered Co. The wear of the Co-CuSn composite proceeded by shear deformation of the CuSn particles, while WC particles of the Co-WC composite sustained most of the applied load, which resulted in the low wear rate with fine wear debris of the Co-WC composite.