Effect of Process Parameters on Microstructure and Crack Sensitivity of Al-Rich NiAl-Cr(Mo) Alloy Single Tracks by Laser-Directed Energy Deposition

Al-rich NiAl–Cr(Mo) intermetallic compound alloy with a higher fraction of β-NiAl phase has attracted increasing attention due to the enhanced hardness and wear resistance. However, the increasing cracking sensitivity becomes the major drawback for additive manufacturing techniques like laser-directed energy deposition (L-DED). In this study, single-track samples of Al-rich NiAl–Cr(Mo) compound alloy (23Ni–52Al–22Cr–2Mo–0.09Hf, at.%) were prepared using L-DED. Laser power, scanning speed, and preheating treatment were optimized to minimize crack density and refine microstructure. Subsequently, crack characteristics, types, and formation mechanisms were systematically analyzed, and the effect of microstructural variations on microhardness was investigated. The results showed that optimizing the scanning speed and laser power reduces the crack density to 0.61 mm/mm2, and preheating treatment significantly reduces the thermal stress, enabling the preparation of crack-free samples. The cracks primarily originate from the bonding interface between the molten pool and the substrate, and the eutectic phase enhances the crack resistance through branching, deflection, and bridging mechanisms. Increasing the laser power only promotes the formation of the eutectic phase, while increasing the scanning speed simultaneously increases the eutectic phase content and refines the microstructure, which are beneficial for crack resistance. Although preheating treatment has a limited impact on microstructure regulation, it significantly reduces thermal stress and inhibits crack initiation. The microhardness is positively correlated with the fineness of the microstructure and the content of the NiAl phase, and its microhardness can reach up to about 680 HV1. This study provides process optimization guidelines for the preparation of highly brittle NiAl-based alloys using L-DED. Graphical Abstract

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