Experiments and modeling of microstructural and mechanical behaviors of laser-welded Ni-based superalloy at high temperatures

The performance of welded Ni-based superalloys at high temperatures is essential to be evaluated due to their particular service environment for aero-engines and high-speed aircrafts. The tensile properties and related microstructural evolutions such as the carbide precipitate and grain of a laser-welded Ni-based alloy were experimentally and numerically investigated at different temperatures (20, 300, 500, 800 °C). The results show that at room temperature, the strength of the Base Material (BM) was slightly smaller, with a difference of less than 1%, than the Welded Material (WM), which can be attributed to the more uniformly distributed needle-shaped carbide precipitates in the WM than those nonuniformly coarser spherical ones in the BM. While at 300 °C and 500 °C, the strength of WM decreased more obviously compared with that of BM due to the more apparent growth of grain: 13.52% loss in yield strength in WM alloys as compared with BM alloys at 300 °C, and 16.57% at 500 °C. At 800 °C, the strength of BM and WM both decreased to a similar level due to Dynamic Recrystallization (DRX). However, a much higher elongation was observed for the BM than WM (less than 50% of BM), which can be attributed to the enhanced dislocation accumulation capability of the large spherical carbides along grain boundaries on the fracture surface in BM. Furthermore, a unified model considering the welding effects on both microstructures (dislocation, carbides, and grain) and mechanical properties evolutions at different temperatures was developed and validated. Based on this model, the key temperature ranges (20–600 °C) where apparent weakening of strength and uniform plasticity occurs for welded structures were identified, providing a direct guidance for potential structure and process design.