Improving corrosion resistance of additively manufactured Ti6Al4V titanium alloy by post heat treatment

Abstract

Additive manufacturing (AM) is a developing manufacturing method and has become an advanced one for producing unique and complex shaped parts. This method is promising for manufacturing of titanium alloys, as it allows to significantly reduce the costs of titanium parts compared to conventional manufactured methods. In this work, the effect of post heat treatment on the microstructure evolution and corrosion resistance of AM titanium alloy in a hydrochloric acid solution was studied by comparing it with a conventional manufactured one (wrought). As AM was chosen selective laser melting method which performed by 3D Metal Tech company (Ukraine). The corrosion resistance was studied by electrochemical and immersion test according to ASTM G 31-72 standard. The results obtained via corrosion tests show that the anti-corrosion properties of AM titanium alloy was worse than for the wrought one, which was explained by the presence of a non-equilibrium metastable martensitic phase and residual stresses in AM titanium alloy. Microstructural results showed that post heat treatment led to the reduction of the non-equilibrium phase martensitic α′, relief of residual stresses, and formation of the β phase, which has higher corrosion resistance. These changes lead to an improvement of the corrosion resistance of AM titanium alloy and result in the performance comparable to that of conventional wrought titanium alloy. These results indicate that the selective laser melting method of AM accompanied by the post heat treatment processes can be used to produce AM Ti6Al4V parts in comparison to wrought ones.