Integrated thermokinetics and thermomechanics dependent pathways for evolution of cracks in laser additively fabricated tungsten

Abstract

Cracking remains a critical challenge in the Laser Powder Bed Fusion (LPBF) of Tungsten (W) due to its inherent brittleness and the extreme thermal gradients involved in the process. While prior research has explored thermomechanical modeling and experimental observation of cracking in LPBF-processed W, a comprehensive correlation between track-by-track crack evolution and the underlying thermokinetic and thermomechanical phenomena is lacking. This study bridges this gap by integrating thermomechanical simulations with detailed microstructural examinations to systematically characterize crack morphology and behavior in multiscale (single- and multi-track) LPBF experiments. Samples were fabricated using input laser fluences of 10 J/mm², 15 J/mm², and 22.5 J/mm² to evaluate the influence of the process parameters (power, beam diameter, and scanning speed) on crack formation. Microstructural analysis revealed input laser fluence-dependent crack densities and morphologies. Samples produced at 10 J/mm² exhibited extensive cracking (60–65 mm/mm² for single-track, 10–12 mm/mm² for multi-track) with transverse cracks and a dense microcrack network. Increasing input laser fluence to 15 J/mm² reduced microcrack density, while input laser fluence of 22.5 J/mm² resulted in a shift to a single longitudinal crack (14–16 mm/mm² for single-track, 3–4 mm/mm² for multi-track), similar to welding-induced cracks. Track-by-track analysis of thermokinetic and thermomechanical evolution during multiscale LPBF processing coupled with crack evolution is discussed for these varying process parameters. This integrated approach provides a unique physics-based understanding of crack evolution mechanisms in LPBF-processed W, highlighting the critical role of input laser fluence in managing thermal stresses, dictating crack morphology, and offering a pathway for optimized process control.