Effects of substrate preheating and processing parameters on the crystallographic texture of Hastelloy X on SX-like Ni fabricated by L-PBF process with flat-top laser beam

This work investigates the effects of substrate preheating and processing parameters on the crystallographic texture of Hastelloy X (HX) deposited on a single crystal (SX)-like Ni substrate using laser powder bed fusion (L-PBF) process. Single- and multi-track experiments together with HX deposited on SX-like Ni substrate, were examined under varying laser powers and scanning speeds, with substrate preheating applied using a flat-top beam. A heat transfer model was employed to simulate the thermal history of melt pool. The results showed that higher laser power and lower scanning speed, combined with substrate preheating, produced larger melt pools and promoted elongated columnar grains formation throughout the Z-direction. Increasing the linear energy density (LED) from 1.5 J/mm to 5 J/mm at substrate preheating of 200 °C reduced the temperature gradient (G) by approximately -16%, as well as the solidification rate (R) and cooling rate (G×R) by -87% and -89%, respectively. These reductions in solidification kinetics promoted coarser primary dendrite arm spacing (PDAS), increasing from ∼1.2 μm to ∼2 μm. Moreover, substrate preheating improved metallurgical bonding and promoted epitaxial columnar growth, resulting in a strong texture extending from the SX-like Ni into the HX layers. Consequently, the multiple of uniform distribution (MUD) increased from 2.5 to 4 under higher energy density (E) with substrate preheating. The findings demonstrate that high E and substrate preheating effectively reduces G, R, and G×R, thereby enhancing texture control and improving process optimization for fabricating SX-like HX structures via the L-PBF process.