Effects of electron beam heat input mode on microstructure of Ti-6Al-4V

The welded joints obtained on the condition of different electron beam (EB) heat input mode were studied by means of optical microscope, scanning electron microscopy, transmission electron microscopy and microhardness measurement. The results indicate that the heat input energy and distribution pattern have an important effect on the size of the weld grain. The weld microstructure was uniform with the grain size of 350 μm when medium heat input E=48.0 kJ/m was utilized. With the increment of heat input, coarse needle-like α+β phase and martensite of weld metal were transferred from unidirectional long needle to multi-directonal short needle morphology and dislocation density was enhanced although less than that of the base metal. Microhardness distribution in weld zone with different EB heat input was greatly different which was possibly attributed to different phase volume and distribution formed metastale. When E=48.0 kJ/m, the joint microhardness distribution was uniform (404-480 HV).