Effects of local heat treatment by electron beam on microstructure and properties of TC4 titanium alloy welded joint

The local heat treatment by electron beam on welded joint of 14.5 mm thick TC4 titanium alloy plate was carried out.Its influence on the microstructure, hardness and tensile properties of electron beam welded joint was investigated.Experimental results show that the crystal grain size of the base metal within the scanning field of local heat treatment grows explicitly after local heat treatment.While it is precipitated and grows along prior-β grain boundary, α phase with a lamellar or acicular appearance grows into β grain from grain boundary.Because local heat treatment decreased the cooling velocity of weld metal, the acicular martensite decomposes β phase and transforms to coarser and shorter α phase, which shows an interwoven pattern.In addition, the hardness profile becomes smoother and differences between heat-affected zone and weld come to be almost eliminated.Integral properties of welded joint are equalized and increased along weld cross-section after local heat treatment.Fracture position of tensile test specimen shifts from the common zone between heat affected zone and base metal to parent metal without undergoing heat treatment.