Dual Mechanisms of Texture Formation for Nickel-Based Superalloys Fabricated Via Laser Powder Bed Fusion

Abstract

Crystallographic preferred orientation (texture) is known to play a crucial role in controlling the anisotropy of the properties in parts of nickel-based superalloys fabricated via laser powder bed fusion (LPBF) processes. Although the feasibility of tailoring the texture via LPBF parameters has been shown, an understanding of the intrinsic impact of LPBF parameters on the mechanisms of texture formation remains unclear. This work aims to determine the mechanism of the heat input influence on the texture formation due to a change the scanning speed. Different intensity textures with <001> parallel to the building direction (BD) are fabricated under different scanning speeds. The strongest texture (MAX = 7.7) is found in the sample with a medium scanning speed (1.0 m/s). This texture intensity is governed by the ability of the columnar dendrites to grow along the BD. The scanning speed is able to tailor this ability via dual mechanisms: (1) alteration of the molten pool size, which changes the overlap ratio of columnar dendrites growing along the BD between adjacent molten pools and (2) modulation of the local solidification condition of the molten pool, which changes the distribution of the columnar dendrites growing along the BD in the single molten pool. The texture intensity is dominated by the molten pool size and the local solidification condition of the molten pool at high and low scanning speeds, respectively. In addition, the anisotropy is evaluated via microhardness. The results show that the degree of anisotropy in the microhardness increases as the texture intensity increases.

Keywords: Texture, anisotropy, IN738LC, Laser powder bed fusion