Different effects of Cr3C2 and VC on the sintering behavior of WC–Co materials

Abstract

Cr3C2 and VC are two typical grain growth inhibitors used in producing fine grain microstructure in WC–Co materials. In this investigation, the sintering processes of Cr3C2 and VC doped submicron WC–Co powders were studied by using dilatometry, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and evolved gas analysis (EGA) by Fourier Transform Infrared Spectrophotometry (FT-IR). The combination of these methods can provide a comprehensive understanding of sintering processes of Cr3C2 and VC doped WC–Co powders during heating. Results show that, below 900°C, similar sintering behaviors were observed for both Cr3C2 and VC doped WC–Co powders, showing a wax vaporization process in the range of 200°C to 400°C, and tungsten oxide reduction by carbon occurring around 800°C. Onset of densification begins around 900°C. Differences in sintering reaction and densification were observed above 900°C. First, VC doping shows an outgassing reaction and a clear shrinkage inflection, increase in shrinkage rate, in the dilatometer curve between 900 and 1100°C, while Cr3C2 doping shows only slight outgassing and no shrinkage inflection in the dilatometer response within the same temperature range. Second, Cr3C2 doping shows a strong outgassing reaction in the 1200–1400°C range, which was not evident in the VC doped material. Third, Cr3C2 doping also shows a higher melting temperature than VC doping. Possible mechanisms for these different sintering reactions and resulting sintering behaviors have been discussed in this paper.