Ultra-fast laser surface treatment of TiAlN pre-coated zircaloy-4 by physical vapor deposition for a dilution-free metallurgical bonding: Process design via a novel re-mesh finite element method approach

Laser surface treatment has emerged as an effective method to enhance the metallurgical bonding between physical vapor deposited (PVD) coatings and metallic substrates, particularly for high-performance nuclear components. In this study, a novel ultra-fast surface treatment process of TiAlN-coated Zircaloy-4 substrates was designed and optimized both experimentally and numerically, i.e., via a three-dimensional fully transient finite element model simulating the temperature evolution in multi-track laser irradiation. A distortion-free remeshing strategy was introduced for the first time, employing a fine spatial resolution in the vicinity of the moving laser spot, i.e., along the scan path to capture sharp thermal gradients and thus the heated zone morphology, while using a coarser mesh in surrounding regions to optimize computational efficiency. Examining the simulated temperature evolution against the experimental observations for the optimized parameters of 100 W laser power and 8000 mm/s scan velocity, the critical interface temperature for metallurgical bonding was ~977°C, corresponding to a single-track bonded width of ~134 µm. This was further validated via multi-track surface treatment experiments, revealing full metallurgical bonding across overlays of up to 125 µm hatch spacing, while exhibiting unbonded gaps for 150 µm hatch spacing. Simulation results, in accordance with experiments, demonstrated that effective localized surface heating with minimal substrate dilution can be obtained via careful tuning of laser processing parameters, which significantly influences the bonded width and coating dilution. The comprehensive methodology introduced provides a reliable basis for optimizing laser surface treatment strategies of ceramic-coated nuclear alloys, as well as large-scale laser surface treatment operations in general.