Tribo-Mechanical Evaluations of Cobalt-Based (Stellite 4) Alloys Manufactured via HIPing and Casting

Abstract

Abstract — Cobalt-based alloys are known for their excellent wear resistance, particularly under high temperature and corrosive environments. However the cast cobalt-based alloys have relatively high brittleness, and low toughness, due to their coarse carbide structure. This paper aims to comprehend if carbide refinement, caused by changing the processing route from sand casting to powder consolidated Hot Isostatic Pressing (HIPing), can improve the tribo-mechanical properties of cobalt-based alloys. The alloy selected for this investigation had a nominal wt. % composition of Co-30Cr-14W-1C, which is similar to the composition of the commercially available Stellite®4 alloy. The Hot Isostatic Pressed (HIPed) alloy had a much finer microstructure than the cast alloy, which showed a typical hypoeutectic dendritic microstructure. Both alloys had similar hardness. Although the cast alloy showed slightly better abrasive and sliding wear resistance than the HIPed alloy due to their coarser eutectic carbides, the HIPed alloy had a significant advantage on the impact toughness and contact fatigue performance. The results of this comparative investigation indicated that the HIPed alloy had an attractive combination of tribo-mechanical properties, i.e. improved impact and fatigue resistance, whilst preserving the high hardness and good wear resistance associated with the cast alloy, making it suitable for relatively higher stress applications.