Study On Carbon Content Control Of Nano WC-6Co Composite Powder

Nano WC-Co composite powder is the critical raw material in the preparation of ultra-fine cemented carbide and high wear-resistant coating with low porosity. This paper aimed to realizing the industrialization of nano WC-Co composite powder, and focused on the key issue on carbon content control in the preparation of nano WC-6Co composite powder. The powder were characterized by modern material analysis and testing methods, such as SEM, XRD, EDTA titration, infrared absorption, gasometric method, TG-DSC-DTA, etc. Using different sources of tungsten, cobalt and carbon as raw material to prepare solution, WC-6Co composite powder was produced by spray drying, calcination and reduction-carbonization process.In this paper, the phase transformation rule and carbon content control principle in the process of spray drying, calcination and reduction-carbonization were investigated; the effects of critical parameters on the carbon content of the powder were investigated; also several important issues on the industrialization of nano WC-6Co composite powder were discussed. The following conclusions are obtained:1) During spray drying, when the water content of the solution is higher, the carbon content of the W-Co composite powder prepared by calcination is lower; when the carbon concentration of the solution is higher, the apparent density of the prepared precursor composite powder is larger. The solution carbon concentration of 19.76 g / l is the best.2) The main phases of W-Co oxide composite powder prepared by calcination are Co3O4, C, WO3.3) Under the experimental conditions with the precursor powder material thickness of 13 mm and the boat pushing speed of 30 min / boat, the carbon content of W-Co composite oxide powder has a little change; the carbon content of the powder is stable. With N2 flow rate increasing, the carbon content of W-Co composite oxide powder gradually increases. When N2 flow rate increases to 6.5m3/h, the carbon content remains almost the same. The carbon content of W-Co composite oxide powder prepared by calcination should be controlled at about 13.85%wt for the best.4) W-Co oxide composite powder prepared by spray drying and calcination was dry ball-milled. The results show that with the ratio of the ball to powder being 12: 1 and ball-milling time of 4h, the smallest particle size of the prepared powder is 35 nm.5) The effects of reducing and carbonizing W-Co oxide composite powder at different temperatures on the carbon content of W-6Co oxide composite powder were investigated. It has been found that when the carbonization temperature is higher and H2 flow increases, the total carbon content increases, while the η phase content decreases; with boat pushing time increasing, the combined carbon gradually increases, then gets saturated, and ultimately achieves the theoretical carbon content of 5.76%.6) By controlling process parameters during solution preparation, spray drying-calcination and reduction-carbonization, specially controlling the carbon content, WC-6Co composite powder can be prepared with the combined carbon content of 5.76%, low free carbon content of 0.05%, oxygen content of 0.1%, cobalt content of 6.02%, and WC grain size of 82 nm.