Abstract
The mechanisms during pressureless sintering of TiB2 with 0–50 wt.% Ni were analysed by differential dilatometry after mechanical alloying with hard metal beads. Three main stages of sintering could be identified by means of the changing dilatation rate. The first interval (200–600 °C) comprises reactions with oxygen and moisture (H3BO3, B2O3 formation, melting, evaporation). The second stage (600–700 °C) is governed by solid state sintering and reactions of Ni and/or Co with TiB2 yielding Ni3B, Ni2B, the corresponding Co-compounds and the ternary ω-phase of W2NiB2-type. The third main shrinkage interval is due to liquid phase sintering (987–1640 °C) and is accompanied by a significant weight-loss. Both precipitation of ω-phase as well as a (Ti,W)B2 solid solution in form of a core-shell structure are responsible for a grain growth retardation and the homogeneous microstructure. The results explain well all features reported in the corresponding literature while encountering the role of WC, too.
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