Abrasion wear, thermal shock and impact resistance of WC-cemented carbides produced by PECS and LPS

Abstract

The effects of rapid sintering by pulse electric current sintering (PECS), variation in starting WC size (0.1–0.8μm), Ni as a Co binder substitute and TiC, NbC and Mo2C additions on the microstructure, abrasion wear, thermal shock and impact resistance of WC–Co and WC–Ni alloys were studied. Abrasion wear tests were done using a ball-on-disk tribometer, with 100Cr6 steel and silicon nitride balls. Use of PECS gave finer microstructures with poorly distributed binder pools than similar liquid phase sintered (LPS) samples, although large angular WC grains of up to 1μm occurred in the nano (0.1μm) and ultrafine (0.4μm) grades. Addition of 5wt.% NbC to WC–10Co (wt.%) had negligible effect on the WC grain size, while 5wt.% Mo2C to WC–6.25TiC–9.3Ni significantly improved WC grain growth inhibition, leading to increased hardness (from ~13 to >21GPa) and reduced wear rate (from 2.73×10−4 to <8.0×10−5mm3·N−1·m−1), compared to the LPS WC–9.3Ni. Thermal shock and impact resistance were measured using a thermal imaging camera and force gauges while testing the samples as cutting tools on Ti–6Al–4V under aggressive interrupted milling conditions. The LPS samples had better thermal shock and impact resistance, due to their higher fracture toughness (>12.5MPa·m0.5) and B3B transverse rupture strength (>2100MPa), as a result of the larger and better binder pool distribution.