Effect of hot isostatic pressing on microstructural and mechanical properties of electroplated coatings on SLM-304L stainless steel

Hot isostatic pressing (HIP) is widely used to eliminate internal defects and refine the microstructure of additively manufactured 304L stainless steel produced via selective laser melting (SLM). However, the effects of HIP on SLM-fabricated 304L coatings—particularly those with electrodeposited chromium layers—remain poorly understood and lack systematic investigation. This study systematically examines how HIP post-treatment influences the microstructural evolution, interfacial integrity, and mechanical performance of chromium-electroplated 304L coatings on SLM-built substrates. In particular, 304L stainless steel substrates were first fabricated by SLM, then coated with chromium via electrodeposition, followed by conventional heat treatment and subsequent HIP processing (600 °C, 70 MPa). Comprehensive characterization—including scanning electron microscopy, energy-dispersive x-ray spectroscopy, Vickers microhardness mapping across substrate/coating interfaces, and surface topography analysis—was performed to correlate processing conditions with microstructural features, elemental distribution, hardness gradients, and coating adhesion. Results reveal that after heat treatment alone, the chromium coating exhibits severe longitudinal cracking perpendicular to the substrate, significant surface waviness, and elevated roughness. In contrast, HIP treatment improves surface planarity but induces interfacial delamination at the Cr/304L boundary, suggesting a trade-off between surface consolidation and interfacial thermal–mechanical compatibility. The underlying mechanism is attributed to differential thermal expansion and residual stress relaxation during HIP, which compromises interfacial bonding despite microstructural homogenization within the coating. In contrast, HIP at 1150 °C and 150 MPa promotes excellent surface flatness through the synergistic effects of high temperature and pressure, resulting in a straight, dense, and well-bonded interface between the chromium coating and the substrate. The coating primarily consists of Fe–Cr and Fe–Ni intermetallic compounds, with complete elimination of elemental phase segregation. A maximum microhardness of 501.8 HV0.2 was achieved. This research provides an experimental foundation for optimizing the surface characteristics of SLM-fabricated 304L stainless steel components.