Complexions at carbide / binder grain boundaries of Re-containing submicron cemented carbide

Abstract

Samples of submicron WC-Co-Re cemented carbide were produced and examined by different techniques. The microstructure of the samples is fine and extremely uniform indicating the strong inhibiting effect of Re with respect to the WC grain growth during liquid-phase sintering. Results of examination of hot hardness at a temperature of 500°C provide evidence for the significantly higher hardness value of the WC-Co-Re cemented carbide in comparison with that of a conventional submicron WC-Co grade. Studies of creep rates of WC-Co-Re and WC-Co cemented carbides at 800°C indicated dramatically improved high-temperature creep-resistance of the Re-containing cemented carbide. Carbide / binder grain boundaries in a FIB lamella prepared from the WC-Co-Re cemented carbide were examined by high-angle annular dark field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy at a high resolution. Rhenium was found to segregate at the grain boundaries forming complexions of 2 to 3 atomic monolayers, which presumably consist of mixed W-Re carbide. Such complexions are believed to suppress the phenomena of grain boundary sliding at elevated temperatures and WC grain growth at sintering temperatures thus dramatically improving the high-temperature creep-resistance of the WC-Co-Re material in comparison with conventional WC-Co cemented carbide.