| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1989: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1988: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
The improvement of strength of weld heat-affected zone of beta titanium was carried out, and strengthening mechanism was proposed by higher solution treatment, two stage aging treatment and thermo-mechanical heat treatment. 1. Beta titanium alloy has high strength by the aging treatment after solution treatment. The microstructure has consisting of alpha phase and beta phase. As the age hardened beta titanium alloy was welded, the decreasing area of hardness revealed in the heat-affected zone. The fracture occurred in this area. The alpha phase solutionized in the beta phase in the decreasing area. Aging treatment after welding was carried out. The hardness in the heat-affected zone became higher than that of the base metal.
The age hardening characteristics depended on the solution treatment temperature. The age hardening rate accelerated for the specimen solutiontreated at 1573K, in comparison of the normal solution treatment at 1073K. 2.In order to obtain the higher strength and hardness, two stage aging treatment such as 673K+773K aging treatment,and the cold worked after solution treatment and then aging treatment at 673K or 773K were carried out. The increase of hardness was recognize and age hardening accelerated, because of the increasing of the vacancy and dislocation concentration. 3.Effect of the microstructure and hydrogen on the hydrogen-induced cracking was investigated. For the specimen solution-treated, consisting of beta phase, hydrogen solutioned in the beta phase and hydride hardly precipitated. For the age hardened beta titanium alloy, consisting of alpha+beta phase, hydrogen diffused in the beta phase and the diffused in the alpha phase. the hydride precipitated in the alpha phase. These evidences were confirmed by internal friction measurement and transmission electron microscopy.
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