A STUDY ON IMPROVEMENT OF STRENGTH IN WELDS OF ULTRA HIGH STRENGTH BETA TITANIUM ALLOY.

对β钛焊接热影响区强度的提高进行了研究，提出了采用高固溶处理、两级时效处理和热机械热处理的强化机制。1.经固溶处理后再进行时效处理的β钛合金具有较高的强度。显微组织由α相和β相组成。随着时效硬化贝塔钛合金的焊接，热影响区出现了硬度下降的区域。骨折发生在这一地区。α相固溶于衰减区的β相中。焊接后进行时效处理。热影响区的硬度高于母材，时效硬化特性取决于固溶处理温度。与1073K的常规固溶处理相比，1573K固溶处理的样品时效硬化速度加快。2.为了获得较高的强度和硬度，进行了673K+773K两级时效处理，并在固溶处理后进行冷加工，然后在673K或773K进行时效处理。由于空位和位错浓度的增加，合金的硬度显著提高，时效硬化加快。3.研究了显微组织和氢对氢致裂纹的影响。固溶处理的样品由β相组成，氢溶解在β相中，氢化物几乎没有析出。时效硬化的β钛合金由α+β相组成，氢在β相中扩散，氢在α相中扩散。氢化物析出于α相中。内耗测量和透射电子显微镜证实了这些证据。

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.