Controlling mechanical properties of additively manufactured hastelloy X by altering solidification pattern during laser powder-bed fusion

Abstract

Like other manufacturing processes, controlling the microstructure of additively manufactured parts is essential to reach the desirable mechanical properties. However, available reports on the control of as-build microstructure and mechanical properties of Ni-base superalloys during laser powder-bed fusion (LPBF) process are not comprehensive. This article aims at a systematic approach to study the effect of scanning strategies and build orientations on solidification patterns in the printed LPBF Hastelloy X parts. The as-built microstructure (grain size, texture) and mechanical responses (yield strength, ultimate tensile strength (UTS), and elongation) are also presented. Results reveal that the stripe unidirectional scan pattern leads to the largest grain size (>850 μm) with the lowest mechanical strength. These samples also exhibit the strongest crystallographic texture, resulting in a planar anisotropic mechanical response (~22 MPa difference in UTS). On the other hand, the stripe rotation scan strategy (67° rotation) leads to a randomly oriented and finer grain structure (~110 μm) with a higher UTS (~800 MPa) due to grain refinement observed in these samples. In addition, the aspect ratio of the columnar grain structure was observed to influence the mechanical response of these parts. UTS of horizontally printed parts were ~26% more than the vertical parts for the stripe scan strategy (67° rotation). However, changing the solidification pattern (stripe XY with 90° rotation) was observed to reduce this difference to ~18%. These findings can be used to tune the microstructure of as-built LPBF parts to obtain an optimal mechanical behaviour.