Electron Beam Impact on Microstructure and Microhardness of Ti–6Al–4V Titanium Alloy Produced by Wire Electron-Beam Additive Manufacturing Technology and Selective Laser Alloying at Simulation of Electronic-Beam Welding

The microstructure and phase composition of Ti–6Al–4V alloy specimens produced by wire electron-beam additive manufacturing (EBAM) technology and selective laser melting (SLM) method after exposure to an electron beam, simulating electron-beam welding, have been investigated by X-ray diffraction analysis, optical metallography, and transmission electron microscopy. In the electron beam exposure zone of SLM specimens, in contrast to EBAM specimens, it was observed that the transverse dimensions of anisotropic primary β grains and α/α′ phase plates increased and inside α/α′ phase plates, submicrocrystalline α phase grains and nanocrystalline α′′ phase were formed. The different character of microstructure and, accordingly, microhardness changes in the weld zone and heat-affected zone in comparison with the base metal is caused by the different cooling rate of the melt bath in the weld zones of EBAM and SLM specimens. In the SLM specimen, the cooling rate of the melt bath is less than that observed in the EBAM specimen. This discrepancy can be attributed to the fact that due to the finer needle-like α′ martensitic structure, the thermal conductivity in the base metal of the SLM sample is less than that in the base metal of the EBAM sample.