Solidification Microstructure of Laser Additive Manufactured Ti-6Al-2Zr-2Sn-3Mo-1.5Cr-2Nb Titanium Alloy

Solidification microstructure of powder fed laser additive manufactured Ti. 6Al. 2Zr. 2Sn. 3Mo. 1.5Cr. 2Nb titanium alloy was investigated. The results showed that by deliberately increasing the powder feed rate, partially melted powders were retained at the top of the molten pool, which can promote heterogeneous nucleus. Thus, each cladding layer is composed of two regions: (i) randomly orientated cellular structure region caused by partially melted powders at the top of each cladding layer; and (ii) epitaxial cellular structure region adjacent to the fusion line. Usually, randomly orientated cellular structure region was totally remelted for a wide range of process conditions. The remelting effect ensures the continuity of epitaxial growth of cellular structure and leads to the formation of columnar β grains. In order to obtain equiaxed grains the scanning velocity and powder feed rate should be carefully selected to enlarge the randomly orientated cellular structure region.