Description
The kinetics of decomposition of hydrogenated Ti-6Al-4V alloy samples with a martensitic structure were studied. To produce the martensite structure, the samples containing 0, 10, 20 and 30at.% hydrogen were annealed in the beta phase field at a temperature about 30°C above the beta transus temperature and water quenched. Optical microscopy, transmission electron microscopy, X-ray diffraction analysis and microhardness testing techniques were utilized to study the phases and phase transformations and to obtain time-temperature-transformation (TTT) diagrams. The martensite structure consisted of a mixture of hexagonal closed pack (hep) a' and orthorhombic a" martensites. The amount of the orthorhombic martensite a" increased with an increase in the hydrogen concentration. During aging at temperatures below the beta transus, the martensite structure decomposed into a mixture of hep a and body-centered-cubic (bcc) b phases. Some of the b phase re-transformed to martensite during subsequent quenching. The amount of the b phase retained at room temperature increased with an increase in the hydrogen concentration. In the alloys containing 20at.% and 30at.% hydrogen, a hydride phase was also detected. Complete decomposition of the martensite structure in the alloy containing 30at.% H resulted in a fine equiaxed microstructure.