A comparative study of laser direct metal deposition characteristics using gas and plasma-atomized Ti–6Al–4V powders

This research presents a comparative study of the characteristics of laser direct metal deposition (LDMD) using two types of Ti–6Al–4V powder. Ti–6Al–4V powders prepared using the gas-atomization (GA) and the plasma rotating electrode (PREP) processes were first analyzed using laser diffraction, scanning electron microscopy and micro computed tomography. A 1.5 kW diode laser with a coaxial deposition head was then used to deposit a number of thin-wall structures at a range of processing parameters from each of the powders. The deposited structures were characterized using optical microscopy, scanning electron microscopy, X-ray diffraction and micro computed tomography (MicroCT). The results show some potential benefits of using PREP powder in laser direct metal deposition. PREP powder has a higher deposition rate and deposits show lower intralayer porosity and lower surface roughness. In both cases, deposits of Ti–6Al–4V exhibit a unique epitaxial prior beta grains microstructure that transforms to alpha lathes and retained beta during cooling. X-ray diffraction results show that the overall microstructure is α + β and not martensitic. The lamellar α + β phase spacing (Sα+β) increases with laser power but seems unaffected by variation in the mass flow rate of the powder. Micro hardness of the laser deposited Ti–6Al–4V is dependent on the lamellar α + β phase spacing (Sα+β) and PREP powder deposits show lower micro hardness than GA powder deposits.