2-STEP AGING TREATMENT FOR LOWERING OF SU SCEPTIBILITY TO HYDROGEN EMBRITTLEMENT OF TI-15V-3CR-3SN-3AL ALLOY

A special aging treatment has been developed to decrease the susceptib ility to hydrogen embrittlement in high-strength Ti-15V-3Cr-3Sn-3Al al loys. Hydrogen embrittlement tests were carried out with CT specimens under a constant loading condition. Hydrogen was occluded into the spe cimens with a cathode charging method during the tests. The formation of fracture-resistant precipitate-free zones and the precipitation of an adequate amount of alpha phases in beta grains are found to be effe ctive in preventing the hydrogen embrittlement and in retaining a high strength. A two-step aging treatment is proposed to obtain this desir ed microstructure. After the first aging for a short time, the precipi tate-free zones form and a small fraction of the alpha precipitates ex ists within the grains. After the secondary aging at a lower temperatu re, the specimens contain a high fraction of the precipitates within t he grains while still retaining the precipitate-free zones. This proce ss makes it possible to obtain the desirable mechanical properties of the present alloy.