Crystal orientation, crystallographic texture and phase evolution in the Ti-45Al-2Cr-5Nb alloy processed by selective laser melting

摘要

A TiAl-based alloy, Ti-45Al-2Cr-5Nb (at.%), has been processed by selective laser melting (SLM) using different energy density inputs. The experimental results show that when the energy density input increased from 250 J/mm(3) to 350 J/mm(3), the crystallographic texture varied from a strong (0001) orientation to a combination of (0001), (10 (1) over bar1) and (11 (2) over bar1) orientations. The SLM-processed TiAl alloy are dominated by high-angle (>15 degrees) grain boundaries (HAGBs) and alpha(2) (Ti3Al) phase. The contents of HAGBs and alpha(2) are 92.8% and 90% respectively at the maximum density input of 350 J/mm(3). Moreover, a small amount of gamma (TiAl) and B-2 phases in a range of several hundred nanometers are uniformly distributed within the alpha(2) matrix. The phase evolution mechanism in the SLM-processed TiAl alloy can be as follows: (210)beta transformed to (20 (2) over bar0) alpha(2) and (110) gamma, and then the residual B-2 and the incompletely transformed gamma phase homogeneously distributed in the alpha(2) phase matrix. The orientation relationship between B2, alpha(2) and gamma phases observed via HRTEM can be expressed as: (111) B-2//(1 (1) over bar0) gamma//(11 (2) over bar0) alpha(2). Those observations and discussions provide a deep insight into the microstructure characteristics and phase evolution in the SLM-processed TiAl alloy, and the findings would be a valuable reference for optimizing the energy density input in SLM to fabricate TiAI components with acceptable grain structure and phase compositions. (C) 2016 Elsevier Inc All rights reserved.