Effects of combining ultrasonic micro-forging treatment with laser metal wire deposition on microstructural and mechanical properties in Ti–6Al–4V alloy

Abstract Ultrasonic micro-forging treatment (UMFT) is a novel grain refinement and properties improvement technique based on plastic deformation and ultrasonic vibration, and it can be applied to the manufacture of large components. The effects of the different amplitudes and loads of UMFT on microstructure and mechanical properties of laser metal wire deposition (LMwD) Ti–6Al–4V alloy were researched in this paper. The microstructural evolution and properties improvement were investigated by means of optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, surface roughness tester, vickers hardness tester and nano indentor. Experimental results showed that amplitudes and loads can significantly affect geometric dimensioning, surface roughness and constituent phases of the deposited layers. The microstructure of un-treated sample consists of epitaxial growth columnar β grains and a certain volume fraction of equiaxed β grains. A large volume fraction of equiaxed β grains appeared in UMFTed samples and the area percentage of equiaxed grain can be controlled by deposition parameters. The evolution of grain morphology should be attributed to recrystallization. Moreover, after UMFT, vickers hardness increased from 360 HV to 520 HV, nano hardness increased by 1.54 times and Young's modulus reached to 170 GPa. The increase of hardness and Young's modulus are likely to be caused by grain refinement.