Evaluation of magnetic properties of WC-10Co hardmetals containing carbide additives for quality control purpose

摘要

In recent years, the interest in improved mechanical properties, high surface finish and long life time requirements of hardmetals has dictated providing of fine grain microstructure. Since, there is no easy and widely agreed available non-destructive method for measuring grain size, magnetic properties measurements may be considered as a most important and empirically non-destructive quality test In this study, WC-10Co specimens were prepared by the usual powder metallurgical route i.e. milling, granulation, pressing and liquid phase sintering. In addition, in some samples, VC was used in conjunction with (Ta, Nb)C as grain growth inhibitor. These materials are added in form of carbide to the WC and Co powder blend in a total amounts of 3 wt.%. It was attempted to provide the same processing conditions, so that the resulting differences in magnetic properties and microstructure were due to variations in sintering temperature or amount of additives. The magnetic properties were determined as related standard. Furthermore, the optical microscopy examinations were performed on sintered specimens to compare predicted magnetic test results with microstructure of samples. According to test results, decreasing sintering temperature and increment of VC additive content enhanced coercive force, H_c, but had no considerable effect on magnetic saturation, M_s. Moreover, the optical microscopy examinations of straight WC-10Co samples indicated on the finer prismatic shape of carbide grams in sintered samples at lower temperature. In samples containing additives as grain growth inhibitors, the percentage bf WC was decreased and the portion of cubic carbides increased. This effect enhanced by increasing VC as the most effective grain-refining additive. The results of the evaluations revealed an acceptable coincide between microstructure and predictions resulted from magnetic properties measurements on investigated hardmetals. This means that the coercivity measurement may provide an indirect method to estimate the grain size of materials tested.