Distinction in electrochemical behaviour of Ti6Al4V alloy produced by direct energy deposition and forging

Abstract

The relationship between microstructural characteristics and anodic dissolution behaviour plays a crucial role in the process control of the electrochemical machining technology (ECM). An additive-manufactured Ti6Al4V alloy produced by direct energy deposition (DED) exhibited a finer lamellar α+β structure within the considerably coarser columnar prior-β grains as compared to the traditional forged Ti6Al4V alloy consisting of equiaxed α and transformed β phases. The electrochemical anodic behaviour of DED-produced Ti6Al4V alloy was investigated in a 15-wt.% NaCl solution and compared with that of the forged Ti6Al4V alloy. Electrochemical measurements showed that the DED-produced Ti6Al4V exhibited higher resistance to corrosion and lower electrochemical machinability than did the forged Ti6Al4V alloy. The high phase boundary density, originating from the refinement of constituent phases, increased the stability of the passive film formed on the surface of the DED-produced Ti6Al4V, thereby improving the corrosion resistance, while the high fraction of β phase in the Ti6Al4V deposit decreased the rate of anodic dissolution. The lower composition difference of solutes of DED-produced Ti6Al4V was beneficial to its higher resistance to corrosion. The fine and lath-type α phases led to a competitively high level of microscopic flatness of the Ti6Al4V alloy after the electrochemical dissolution.