Microstructural evolution of near-β Ti-6Zr-5Fe alloy fabricated by selective laser melting before and after solution treatment

The homogeneity of microstructure and microhardness in different parts of as-fabricated selective laser melting (SLM) and as-solutionized Ti-6Zr-5Fe alloy is presented in this paper. The results show that the as-fabricated SLM alloy has a bigger β phase and finer α phase size in the top part than that in the bottom part due to the reheating treatment during SLM process. However, as-solutionized Ti-6Zr-5Fe alloy mainly consists of β phase in the top part, and the bottom part is mainly comprised of β and α phase in the grain boundary. Apart from the change of phase composition, the β phase size in bottom part is smaller than that in the top part, due to the precipitation of α phase at the grain boundary in the bottom part. The fine α phase in the top part of as-fabricated SLM Ti-6Zr-5Fe alloy results in that the top part has a higher microhardness (518 HV) than the bottom part (394 HV). While, the microhardness becomes almost the same in the top part (482 HV) and bottom part (475 HV) after solid solution treatment. The dissolution of fine α phase in the top part and solution strengthening of Fe and Zr element in the bottom part after solution treatment improve the uniformity of microhardness. This research provides an approach for obtaining the gradient microstructure or gradient property for near-β Ti alloy samples by governing the parameters of SLM technology and solution treatment.