A comparison of the tribo-mechanical properties of a wear resistant cobalt-based alloy produced by different manufacturing processes

This paper aims to compare the tribo-mechanical properties and the structure-property relationships of a wear resistant cobalt-based alloy produced via two different manufacturing routes, namely sand casting and powder consolidation by Hot Isostatic Pressing (HIPing). The alloy had a nominal wt% composition of Co-33Cr-17.5W-2.5C, which is similar to the composition of commercially available Stellite 20 alloy. The high tungsten and carbon contents provide resistance to severe abrasive and sliding wear. However, the coarse carbide structure of the cast alloy also gives rise to brittleness, and hence this research was conducted to comprehend if the carbide refinement and corresponding changes in the metal matrix caused by changing the processing route to HIPing can provide additional merits in the tribo-mechanical performance of this alloy. The Hot Isostatic Pressed (HIPed) alloy possessed a much finer microstructure than the cast alloy. Both alloys had similar hardness, but the impact resistance of the HIPed alloy was much higher. Despite similar abrasive and sliding wear resistance for both alloys, their main wear mechanisms were different due to their different carbide morphologies. Brittle fracture of the carbides and ploughing of the matrix were the main wear mechanisms for the cast alloy, whereas ploughing and carbide pullout were the dominant wear mechanisms for the HIPed alloy. The HIPed alloy showed significant improvement in contact fatigue performance, indicating its superior impact and fatigue resistance without compromising the hardness and sliding/abrasive wear resistance, making it suitable for relatively higher stress applications. Copyright © 2006 by ASME.