Phase transformations in Ti-6Al-4V-xH alloys

Microstructures, phases, and phase transformations in Ti-6Al-4V alloy speci mens containing 0, 10, 20, and 30 at. pet hydrogen were investigated using optical microscopy (OM), transmission electron microscopy (TEM), X-ray diff raction (XRD), and microhardness testing. Alloying with hydrogen was achiev ed by holding the specimens in a pure hydrogen atmosphere of different pres sures at 780 degreesC for 24 hours. The phases present in the temperature r ange of 20 degreesC to 1000 degreesC were determined by microstructural cha racterization of the specimens quenched from different temperatures. Increa sing the hydrogen addition from 0 to 30 at. pet lowered the beta-transus te mperature of the alloy from 1005 degreesC to 815 degreesC, significantly sl owed down the kinetics of the beta-to-alpha transformation, and led to form ation of an orthorhombic martensite instead of the hexagonal martensite fou nd in quenched specimens containing 0 pet H. A hydride phase was detected i n specimens containing 20 and 30 at. pet hydrogen. The time-temperature-tra nsformation (TTT) diagrams for beta-phase decomposition were determined at different hydrogen concentrations. The nose temperature for the beginning o f the transformation decreased from 725 degreesC to 580 degreesC, and the n ose time increased from 12 seconds to 42 minutes when the hydrogen concentr ation was increased from 0 to 30 at. pet.