Effect of solution heat treatment on microstructure, mechanical and electrochemical properties of hastelloy X fabricated by laser powder bed fusion

Abstract

Laser Powder Bed Fusion (LPBF) technology provides a new way for integral forming and rapid manufacturing of complex components of Hastelloy X, but the parts fabricated by LPBF (LPBFed) inevitably have defects such as micropores, micro-cracks, and residual stress. To eliminate the above defects and further enhance the material properties of the Hastelloy X, solution heat treatment (SHT) was performed on the LPBFed parts. Although SHT can improve material properties, there are many limitations in using traditional machining because of the high hardness of Hastelloy X. So, electrochemical machining (ECM) is used to process LPBFed Hastelloy X parts and has a wide range of applications. Firstly, the optimal SHT process parameters with good comprehensive mechanical properties were obtained by orthogonal experiment, and the influence of the selection of SHT process parameters on the properties of LPBFed samples was discussed. Then, after SHT with optimized process parameters, the elongation after fracture (EAF) increases from 30.0% to 51.3%, and the ultimate tensile strength (UTS) reduces from 798.7 MPa to 732.6 MPa merely. Next, its micro-morphology was observed and analyzed. It can be seen that After the SHT, the grain size increases, and the low-angle grain boundary decreases in the XOY direction, resulting in the decrease of the intergranular area and dislocation densities to reduce the tensile strength. After the SHT, the molten pool boundary disappears in any direction, which greatly improves the plasticity of the part. and the microstructure explains the results of tensile tests. The experimental results show that the material properties of Hastelloy X can be greatly improved by this SHT process, which has great development potential and broad application prospects. Finally, to apply Hastelloy X to the Electrochemical machining (ECM) process, an experimental analysis of the electrochemical passivation performance of LPBFed samples after SHT with optimal parameters was carried out. The experimental results show that after SHT the denseness of the passivation film is improved, the corrosion resistance is enhanced, and the anisotropy of corrosion resistance is reduced. By observing the microscopic morphology of the passivation film, it can be seen that the corrosion products reduced and the number of corrosion pits decreased. This means LPBFed Hastelloy X parts after SHT is significantly improved and meets the ECM processing requirements.