Influence of post-treatment on the performance of SLM forming 18Ni300 electroplated coatings

To enhance the interfacial bonding performance of chromium coatings on additively manufactured 18Ni300 martensitic aging steel, this study employed hot isostatic pressing (HIP) as a post-deposition surface treatment. A conventional heat treatment was concurrently conducted as the control condition. The microstructure, elemental distribution, phase composition, and microhardness of the coating–substrate interface region were systematically characterized using scanning electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction, and a microhardness tester. The results indicate that the as-deposited pure chromium coating exhibits poor surface flatness. Following conventional heat treatment, the electrodeposited chromium layer underwent complex microstructural evolution, accompanied by transverse network cracking and interfacial delamination. In contrast, HIP treatment at 600 °C/70 MPa preserved both surface and interfacial flatness but resulted in numerous internal pores, indicating insufficient densification. Notably, HIP at 1150 °C/150 MPa yielded substantial improvements: surface flatness was retained; a dense, planar metallurgical bond formed at the coating–substrate interface; coating hardness increased significantly to 406.3–673.1 HV0.2 (±10%); the main phase was Cr0.19Fe0.7Ni0.11; and the monomer Cr phase completely disappeared. These findings confirm that HIP effectively modulates atomic diffusion across the interface—thereby strengthening metallurgical bonding, suppressing crack initiation, and markedly enhancing hardness. This work establishes a promising new technical pathway for optimizing protective surface layers on additively manufactured high-performance alloys.