The effect of volume fractions of .ALPHA. and .BETA. phases in Ti-Al-V alloys on the superplastic behavior.

概要

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Effects of volume fraction of α or β phase on sup3rplasticity was investigated for the Ti-Al-V alloys, whose chemical compositions were on the tie line including that of Ti-6Al-4V at 900°C. The testing temperature was 900°C and the initial strain rates ranged from 6.67×10-5 to 2.50×10-2/s.In spite of wide distribution of the volume fractions of the phases in the alloys, all showed a good superplasticity under certain strain rate conditions. The maximum Superplastic elongation was seen near the equal volume fraction of the two phases for every strain rate. The initial average grain sizes of the alloys which ranged from 4.7 to 7.0μm, were dependent on the volume fraction ratio of the phases and found to be at the minimum near the equal volume fraction. The effect of volume, fraction on the superplastic elongation would be given through the initial average grain sizes which vary with the volume fraction.At an initial strain rate of 6.67×10-4/s, the average grain sizes of the alloys after fracture was about 8μm for all the alloys and were independent of the initial average grain sizes or the volume fractions of the phases in the alloys.At the same strain rate, the strain induced grain growth rate increased with decreasing initial average grain size. The aspect ratio of the phases at fracture converged not to unity, but to a certain value between 1.2 and 1.5 for all the alloys.
The Iron and Steel Institute of Japanの論文