Abstract
Previously published results on Al-base alloys and steels have shown that accurate prediction of yield stress and ultimate tensile stress (UTS) is possible from hardness data. The present study was undertaken to see if the relationships were also valid for Ti-base alloys. The intention was to permit exploitation of the economic advantages which would result from a saving in machining cost and in testing time, if the judicious use of hardness testing were to provide data approximately equivalent to that obtained by tensile testing. Rockwell hardness and tensile data obtained in an earlier study on three titanium-base alloys (Ti-13V-11Cr-3Al, Ti-5Al-2·5 Sn, and Ti-6Al-4V) have been augmented with Meyer, Vickers, and Knoop hardness measurements. The tensile data have been analysed to give the work-hardening coefficient n and this has been correlated with (a) the ratios of both yield stress and ultimate tensile stress to Vickers hardness; (b) the Meyer hardness coefficient m; and (c) uniform elongation. While the relationship with (c) was obeyed, the correlations involving (a) and (b) above did not conform to the expected pattern. In addition, the correlation between (a) and (b) was investigated. Again, the expected behaviour was not obtained, although approximately linear correlations were observed for the Ti-13V-11Cr-3Al alloy. An attempt was also made to estimate points along the tensile curve from Meyer hardness data. The agreement was only moderately good for the Ti-13V-11Cr-3Al alloy, and was poor for the other two alloys. After further analysis of the data, the breakdown of the correlation was attributed to a different deformation mechanism, presumably micro-twinning, occurring during hardness testing from that prevailing during tensile testing. This effect also explains, for the materials in the present study, the breakdown of both the relationship between m and n, and the relationships which involve stress/hardness ratios.
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