| A series of thermochemical hydrogenation processing(THCP), in which hydrogen used as a temporary alloying element. The microstructural refinement and mechanical properties of Ti-6Al-4V alloy subjected to various THCP has been investigated. Very fine equiaxed and broken-up structures(BUS) are developed with THCP, and the finest equiaxed structure is developed with post-treatment at 750℃ after hydrogenation at 700℃. The hardness is decreased with increasing temperature with regardless of the structure, and increased with increasing the hydrogen content. Hydrogenated structure showed to the highest value in elongation among hydrogenated initial structures, but showed lower value in tensile properties than Widmansta¨tten structure. In comparing with the tensile properties of equiaxed structure before hydrogenation, hydrogenated equiaxed structure improved in the tensile properties up to 13℃ with small variation in elongation. According to the increment of hydrogen content, the yield strength and elongation of equiaxed structure increased linearly. In case of the hydrogenated structure, the fracture surface of equiaxed structure exhibits ductile fracture mode with very fine dimple pattern, and that of BUS(broken-up structure) had showed dimple mode and facets in some region. The process of thermochemical hydrogenation, post-treatment and dehydrogenation is obtained to far more fine structure than conventionally solution treatment, and in view of mechanical properties, the former processes is found to be effective for achieving a good balance of tensile strength and elongation. |
|
