Effect of laser scanning speed on a Ti-45Al-2Cr-5Nb alloy processed by selective laser melting: Microstructure, phase and mechanical properties

Abstract

This work presents a comprehensive study on the laser scanning speed on the microstructure development, phase evolution and nanohardness of a TiAl alloy, Ti-45Al-2Cr-5Nb (at.%), processed by selective laser melting (SLM). The experimental results show that when increasing the laser scanning speed from 500 to 800 mm/s, the average grains size decreases from 7.11 μm to 5.43 μm, whereas the crystallographic texture showing a combination of (0001), (101¯1) and (112¯1) orientations basically remains unchanged. The SLM-processed TiAl alloy is dominated by high-angle (>15°) grain boundaries (HAGBs) and the contents of HAGBs decrease from 91.6% to 86.1% when the laser scanning speed varies from 500 to 800 mm/s. The α2 phase decreases while the γ and B2 phases increase with increasing the laser scanning speed. Moreover, the phase evolution mechanism in the SLM-processed TiAl alloy can be described as follows: (200) β transforms to (202¯0)α2 and (110) γ, and then the residual B2 and the incompletely transformed γ phase randomly distributed in the α2 phase matrix. The nanohardness of the SLM-process TiAl alloy increases from 7.90 ± 0.32 GPa to 9.49 ± 0.46 GPa with increasing laser scanning speed from 500 to 800 mm/s, which is much higher than those of traditionally manufactured counterparts, such as casting parts (4.98 ± 0.10 GPa) and TiB2 reinforced TiAl alloy fabricated by roll bonding (6.73 GPa). With the increase of laser scanning speed from 500 to 800 mm/s, compression properties of the SLM-process TiAl alloy increases from 829.41 ± 24.88 MPa to 1216.16 ± 36.48 MPa.