Ni-W合金めっきの高温特性と加熱相変態

概要

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Hot hardness and dilation curves were measured and the associated X-ray studies were conducted on electroplated Ni-W alloys of 40, 44 and 51wt%W during heating at a rate of 1°C/min. The increase in hot hardness started at around 200°C, and softening began at about 600°C. The 44wt%W alloy showed the highest hot hardness-Hv900-between 450°C and 550°C. Along with such well known Ni-W crystals as face centered cubic solid solution, Ni4W and nearly pure tungsten, a new phase was found to be precipitated. For example in 40wt%W alloy, the new phase had a body centered tetragonal structure with a=9.136Å and c=10.268Å±0.038Å, having 74 or more atoms of anomalously small atomic volume in a giant unit cell. Although the new phase appeared first on heating, it was fairly thermally stable and was the predominant precipitate at the peak hardness of the alloys. The origin of the formation of the new phase is discussed, and the precipitation of pure tungsten which was found on heating the 40 and 44wt%W alloys, was experimentally analyzed.
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