Wear-Resistant Cobalt-Base Alloys

Summary

Cobalt-base alloys have enjoyed extensive use in wear-related engineering applications for well over 50 years because of their inherent high-strength, corrosion resistance, and ability to retain hardness at elevated temperatures. Microstructurally, wear-resistant cobalt-base alloys consist of hard particles (Cr₇C₃) dispersed in cobalt-rich (Co > 50%) solid solution matrix alloys (generally Co-Cr-W/Mo). Recent investigations in the Cabot Corporation Technology Laboratories have shown that the adhesive and cavitation-erosion wear characteristics of these alloys are determined by the composition of the matrix alloy and are influenced to a large extent by a strain-induce fee → hep allotropie transformation in the matrix alloy. Further, it has been shown that the cobalt content in the matrix alloy can be decreased to approximately 30% without significantly degrading relevant wear or corrosion properties. Toughness and abrasive wear resistance, on the other hand, are determined primarily by carbide volume fraction and morphology. Large, hypereutectic carbides are generally preferred for good abrasive wear resistance but are detrimental to toughness considerations. The tribological measurements and microstructural correlations associated with these Cabot investigations are summarized and discussed in this paper.