Microstructures of TC21 alloys after hydrogenation and dehydrogenation

Microstructural evolution and phase transformation of hydrogenated and dehydrogenated TC21 alloys were investigated by optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD peaks of α and β phases after hydrogenation shifted to low angle because of lattice expansion with the solution of hydrogen atoms. Microstructure of TC21 alloy after hydrogenation changed apparently. Compared to the as-received one, the contrasts of equiaxed α phase and transformed β phase under optical microscope were reversed. In addition, XRD and TEM analyses revealed that hydrides and α' martensite precipitated from α and β phases. Bulk of twins and some Ti3Al particles were observed in hydrogenated TC21 alloy, which means that hydrogen led to the redistribution of alloying elements in α and β phase. After dehydrogenation, the microstructure of TC21 alloy was similar to that of the as-received one, which consisted of α and β phases.