Effects of machining conditions on some properties of WC-Co based alloys machined by wire electric discharge

摘要

Wire electric discharge machining (WEDM) with A.F. pulse circuit has been applied for precisely machining WC-Co based alloys with high hardness and young's modulus in the wide ranges from rough to finish machining. However, WEDM gives thermal shock to the machined alloys and then deteriorates physical properties of the alloys by introducing some kind of heat affected zone and thermal cracks on the machined alloy surface. Therefore, this study was carried out to investigate the change of some properties of WC-Co based alloys with different Co content and WC grain size by WEDM. The results obtained are as follows: (1) The heat affected zone was composed of W{sub}2C and β WC{sub}(1-x) phases formed by surface decarburization due to thermal effect of WEDM and then the amount of the phases decreased with changing from rough to finish machining and also the increase of Co content in the alloy. (2) Surface residual stress of the alloy changed from compression in the as-ground state to tension by WEDM. (3) Surface roughness of the machined surface which was independent of Co content in the alloy decreased with changing from rough to finish machining and then it showed almost the same as that of the as-ground surface. (4) Bending strength (σ{sub}(mW)) of the alloys after WEDM which was inferior to the strength (σ{sub}(mG)) of the as-ground alloys before WEDM decreased with the decrease of Co content and WC grain size, and also it increased with changing from rough to finish machining and recovered especially in high Co alloys, but not enough in low Co and micro grain alloys. (5) Length of thermal cracks observed on the cross section of the machined alloys decreased with changing from rough to fine machining. The crack length C calculated from the equation of K{sub}(IC) = Y ·σ{sub}(mW)·{the square roots of C} and the thermal shock resistance of the alloys were also discussed.