Microstructure and mechanical properties of Ti Re alloys manufactured by selective laser melting

In the present study, a commercially pure (CP) Ti and Ti-Re alloys containing 2 and 4 wt% of Re were manufactured by selective laser melting (SLM) and characterized in terms of microstructure, strength and fatigue crack propagation resistance. On the contrary to a homogenous lath-type martensitic alpha' microstructure with no signs of directional solidification observed for CP Ti, the Re addition led to development of columnar prior beta grains oriented along building direction with a much finer acicular alpha' martensite in Ti-Re alloys. The width of martensitic alpha' needles decreased with increasing Re content. Re affected also the formation of different phase constituents. The presence of omega phase precipitates as well as residual undissolved Re particles was noticed in Ti-Re alloys. Ti-Re alloys exhibited also the substantially increased ultimate tensile strength and drastically reduced ductility in comparison to CP Ti. These findings have been discussed in the paper considering the highly refined acicular alpha' martensitic structure, the increased oxygen content as well as the presence of strengthening to phase precipitates in Ti-Re alloys. Finally, the brittleness of Ti-Re alloys caused the deterioration of their fatigue crack propagation resistance.