Heat Treatment Degrading the Corrosion Resistance of Selective Laser Melted Ti-6Al-4V Alloy

Abstract

Ti-6Al-4V alloy produced by selective laser melting (SLM) was reported to exhibit an inferior corrosion resistance compared with the traditionally processed Grade 5 alloy, due to the formation of high-energy metastable α′ martensite with regard to α martensite. This work manipulates the transformation of α′ martensite to α martensite by heat-treatment in SLM-produced Ti-6Al-4V alloy and studies the effect on its corrosion behavior using electrochemical tests and microstructural analysis. The electrochemical results reveal that the heat-treated SLM-produced samples exhibit a higher corrosion rate than the as-received counterparts. The microstructural characterization results show that the acicular α′ martensite vanishes gradually, and a plate-shaped α phase and a lamellar α + β mixture continuously form with enhancing heat-treatment temperature, which increases the grain size. The relation between changes in grain size and corrosion resistance of SLM-produced Ti-6Al-4V has been discussed in detail.