Combinatorial Effects of the Recipes of the Initial Gas-atomized Powder Sizes on Microstructure and Passivation Characteristics of the SLM-ed Ti-6Al-4V Bulk Alloys

Bulk Ti-6Al-4V alloys have been fabricated by selective laser melting (SLM) in three recipes with different combinations of powder sizes. Combinatorial effects of initial gas-atomized powder sizes on microstructure and corrosion properties of SLM-ed Ti-6Al-4V alloys have been investigated by optical microscopy, X-ray diffraction, electrochemical measurements and surface free energy. The SLM-ed Ti-6Al-4V alloys are composed of acicular & alpha;' martensite and & alpha; phases. Many pinhole defects and twin boundaries exist in the SLM-ed Ti-6Al-4V alloys. According to electrochemical tests and surface free energy calculation, the SLM-ed Ti-6Al-4V alloys with 0 - 53 & mu;m powders have the most positive corrosion potential, the lowest current density and the smallest surface free energy of 20.89 mJ m2. The passive film of SLM-ed Ti-6Al-4V alloys with 0 - 53 & mu;m powders has superior protection ability due to their large thickness. The carrier concentration of SLM-ed Ti-6Al-4V alloys with 0 - 53 & mu;m powders is the lowest by the Mott-Schottky curves. The SLM-ed samples with contact angles higher than 90o are hydrophobic, but the small contact angle of 46.98o reflects the hydrophilic features of as-rolled Ti-6Al-4V alloys. The combinatorial recipe of SLM-ed Ti-6Al-4V alloys with 0 - 53 & mu;m powders is optimal for improvements on the passivation and corrosion resistance.