Bending Fracture Strength and Toughness of Ultra Thin WC-Co Alloy Plates Machined by Wire Electric Discharge
Sugimoto Koh-ichi; Nakazawa Kiyoshi; Uchida Sugio; Masuda Setsuya; Niinomi Atsushi; Kobayashi Mitsuyuki
Abstract:Thickness dependence of bending fracture strength and fracture toughness of WC-Co alloy plates of varying WC particle size, machined by wire electric discharge (WED), was investigated in the thickness range of 0.1 to 3 mm. The WED specimens of the alloy with the smaller size WC exhibited a decrease in the bending fracture strength to the extent of one half with the reduction in thickness from 1 mm to 0.1-0.3 mm range. However, the specimens machined by grinding (GR) showed an opposite trend, as observed by a considerable increase in the bending fracture strength with decrease in the thickness. On the other hand, the successive microgrinding of 2mm after the WED machining improved the bending fracture strength to the extent of GR specimens. The fracture toughness of the WED specimens were significantly decreased in a thickness range of 0.1 - 0.3 mm, in the same way as the GR specimens. Also, with lowering in the thickness, the chipping around the corner of reground surface became easier. In the WED specimens, coarsening of WC particle improved the bending fracture strength and the fracture toughness, particularly in the ultra-thin specimens. Key Words:WC-Co alloy, punch, bending fracture strength, fracture toughness, chipping, wire electric discharge, grinding