Preparation, properties and microstructure of high hardness WC-Co cemented carbide tool materials for ultra-precision machining

Abstract

WC-Co cemented carbides, with low binder content (Co content <4 wt.%), have become prospects as ultra-precision cutting tool materials as a result of their high hardness, which can be ground to a sharp cutting edge when machining tools. In this paper, three cemented carbides, with Co content of 1 wt.%, 2 wt.% and 3 wt.%, were systematically investigated. The mode of preparation, properties, microstructure and ultra-precision turning of these cemented carbides were studied. It has been researched that 0.1 wt.% VC could effectively refine the WC grains to exhibit excellent properties. The optimum sintering temperatures for WC-1Co-VC, WC-2Co-VC and WC-3Co-VC were 1350, 1300 and 1300 °C, respectively. The resultant cemented carbides displayed extremely high hardness (2450, 2377 and 2325 kg/mm2), high relative density (>99%), specific fracture toughness (8.89, 9.01 and 10.17 MPa·m1/2) and transverse rupture strength (1274, 1387 and 1474 MPa). During oxidation, from room temperature to 400 °C, there was a slight reduction in the strength of the cemented carbides with no oxide formed. From 400 to 600 °C, their strength decreased significantly with apparent oxides formed on the surface. At 800 °C, all the cemented carbides experienced a severe drop in strength and massive oxidation on the surface and fracture surface. The cemented carbides were used to make cutting tools used for ultra-precision turning of brass. The surface roughness after machining with the three modified cemented carbide tools, with increasing Co content, were 22, 14 and 17 nm, respectively.