EFFECT OF HYDROGEN ON PHASE-COMPOSITION AND STRUCTURE OF HIGH-TEMPERATURE TITANIUM-ALLOY VT25U

The effect of hydrogen on the phase composition of the VT25U-grade hig h-temperature titanium ahoy or temperatures from 20 to 1000 degrees C was studied. The alloying with hydrogen up to concentrations exceeding 0.4% lends to the formation of ordered alpha(2) phase in the alloy. T emperatures and compositions corresponding to predetermined ratio betw een the volume fractions of beta and alpha phases are established. The hydrogen addition leads to the depletion of beta phase in beta-stabil izing elements (molybdenum and tungsten) at the temperatures of (alpha + beta) field and to the enrichment of alpha phase with aluminum. The volume effects of (alpha --> beta) transformation are calculated for various hydrogen contents in the alloy. Maximum volume misfit between alpha and beta phases corresponds to the temperature of (alpha + beta/ beta) transformation and to maximum hydrogen content.