Microstructures and Properties of Submicrometer Carbides Obtained by Conventional Sintering

摘要

Submicrometer carbides (0.2-0.8 μm) are technologically important new materials because they can reach very high hardness with good mechanical resistance and excellent hardness/toughness combinations, making them especially effective for the wear tools market. Sintering of these engineering materials requires a careful process control to reach the maximum densification without damaging irreversibly the grain size, fundamental for reaching the expected properties. Especially for larger wear tools, which are more complex to produce, further know-how regarding sintering optimization is required to improve their quality and consistency. In this work, grades from WC 0.6 urn and WC 0.4 μrn powders, combined with varying contents of 0.7 μm Co powder (from 2 to 12 wt%), were prepared by water technology to reach high-quality powder mixtures. Thermal analyses were performed to obtain the powders shrinkage profile and sintering temperatures. Pressed powder samples were vacuum- and sinterHIP-sintered at different temperatures on industrial furnaces and their relevant properties were analyzed. Some practical aspects, like compaction pressures, carbon content influence on sintered properties were also addressed. Low Co (<6 wt%) grades presented exceptional high hardness levels (>2200HV30) and hardness/toughness ratios (2200HV30/8.7 MPa·m~(1/2)) although requiring special sintering cycles at higher pressures. The data collected in this work will be further used to optimize the sintering and maximize densification of these special grades using HIP -Hot Isostatic Pressing technology.