Optimization of process parameters for fabricating functionally gradient WC–Co composites

• We conduct a study to optimize process parameters for fabricating gradient WC–Co.
• Effect of each factor on gradient structure was analyzed through range analysis.
• The significance of each factor was investigated though the analysis of variance.
• The combination of the optimal process parameters was determined.
• WC grains in fine-grained WC–Co are still at the fine grade after heat treatment.

Functionally gradient WC–Co hardmetals not containing η phase with a Co depleted surface layer can be produced by heat treating WC–Co in a carburizing atmosphere. This study investigates the effect of process parameters of carburizing heat treatment, such as time, temperature, volume fraction of methane in carburizing atmosphere, and flow rate of mixed gases on cobalt gradient structure in functionally gradient WC–Co. Taguchi method is used to formulate the experiment layout, and the range analysis and the analysis of variance are employed to determine the optimal process parameter levels and to analyze the effect of parameters on cobalt gradient structure. The results indicate that the order of significance of the parameters on both thickness and amplitude of cobalt gradient is temperature followed by volume fraction of methane, time and flow rate of mixed gases. Both the thickness and the amplitude of the gradients increase with increasing temperature and time, and decrease with increasing volume fraction of methane, and first increase then decrease with increasing flow rate of mixed gases. Finally, the optimal combination of process parameters for fabricating functionally gradient WC–Co composites is determined.