Stray grain suppression and stress control in single-crystal superalloys fabricated by L-DED: A multiphysics analysis of in-situ remelting

Abstract

Laser-Directed Energy Deposition (L-DED) has been demonstrated as a promising pathway for fabricating single-crystal superalloys. However, achieving single track multilayer continuous epitaxial growth remains a formidable challenge due to the complex gas-powder-melt pool multiphase interactions. Existing approaches are often hindered by stray grain formation due to the presence of un-melted powder particles and the complexity thermal histories processes. Moreover, the excessively high computational cost of high-fidelity multiphysics simulations restricts the swift optimization of the process window. To overcome these challenges, this research demonstrates the application of in-situ remelting (ISR) technology in the single-crystal superalloys. By developing a dedicated laser-powder interaction model and a thermal-fluid–solid coupling model, we systematically reveal the regulatory mechanisms of in-situ remelting on thermal gradients, flow characteristics, and stress evolution during single-crystal superalloys fabricate. To address the efficiency bottleneck, a surrogate model based on deep neural networks (ResNet) was developed for the L-DED multi-physics simulation. Key findings demonstrate that the proposed strategy: 1) Eliminates un-melted powder particles interference and optimizes thermal gradients, increasing the single-crystal epitaxial growth zone ratio to over 50 %; 2) Suppresses flow field intensity (>70 % reduction) and vortex effects, thereby mitigating stray grain susceptibility induced by dendrite deflection; and 3) Reduces residual stress in deposited layers by over 25 %, effectively inhibiting high-layer cracking risks. Through this integrated analysis, we establish a robust L-DED process window incorporating flow/stress constraints and achieve the continuous epitaxial growth of a 20-layer DD432 single-crystal superalloy, validated by EBSD.