Solidification texture, variant selection, and phase fraction in a spot-melt electron-beam powder bed fusion processed Ti-6Al-4V

Published on Oct 1, 2021in Additive manufacturing7.002
· DOI :10.1016/J.ADDMA.2021.102136
Rakesh R. Kamath1
Estimated H-index: 1
(UT: University of Tennessee),
Peeyush Nandwana19
Estimated H-index: 19
(ORNL: Oak Ridge National Laboratory)
+ 1 AuthorsHahn Choo47
Estimated H-index: 47
(UT: University of Tennessee)
Source
Abstract
Abstract null null The effect of a spot melt strategy on the solidification texture, variant selection, phase fraction, and their variations along the build height was investigated in comparison to a conventional linear melt strategy. Ti-6Al-4V alloy samples were manufactured by an electron-beam powder bed fusion process using two different melt strategies and characterized using high-energy synchrotron x-ray diffraction. The linear and spot melt cases resulted in β null cube and fiber textures, respectively, with the cube/fiber axis nearly parallel to the build direction. The α phase exhibited Burgers orientation relationship (BOR) with the parent β phase for both melt strategies. Although all of the key texture components and the BOR between the α and β phases were consistently observed in both cases along the build height, there were several measurable differences between the two. At the top of the build height, the β null build texture intensity was stronger in the linear case. However, the texture intensity in the linear case decreased gradually from the top to near the substrate, whereas the spot melt case did not show this trend. Moreover, the BOR was examined along the build height and the results showed that there is a distinct variant selection in the spot melt case, unlike the linear case. Specifically, the planar variants sharing null null null null null null ( null null null 1 null null null null null 01 null ) null null null β null null null null null null null || null null null null null ( null 0002 null ) null null null α null null null null null with null null null null null [ null null null 2 null null null null null null null 2 null null null null null null null 2 null null null null null ] null null null β null null null null null and null null null null null [ null 2 null null null 2 null null null null null 2 null ] null null null β null null null null null were the most prominent in the spot melt, but no preference was identified in the directional variants. The β phase fraction was slightly lower in the spot melt case compared to the linear case. In both the cases, the β phase fraction decreased moving towards the substrate but remained significantly higher than that of the powder feedstock. Overall, the novel spot melt strategy produced a more homogeneous microstructure in terms of both the phase fraction and texture across the build height.
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