Advances in Microstructure Evolution, Sigma‑Phase Formation, and XRD Analysis of Laser Metal Deposited 316L/430L‑WC Multilayers on GJL after Brake‑Shock Testing

Grey cast iron brake discs remain standard in automotive braking systems due to their favorable thermal conductivity and mechanical strength. However, increasingly stringent environmental regulations, including Euro 7, necessitate enhanced surface durability to reduce particulate emissions and mitigate corrosion‑related degradation. In this context, Laser Metal Deposition (LMD) offers a promising route to engineer wear‑resistant coating systems with tailored microstructures. This study investigates phase formation and microstructural evolution in a 316L/430L‑WC multilayer coating deposited on grey cast iron (GJL) brake discs and subjected to brake‑shock testing to replicate thermomechanical load cycles representative of real braking conditions. X‑ray diffraction (XRD) performed on the interlayer region between the 316L and 430L‑WC layers revealed clear evidence of σ‑phase formation, indicating intermetallic transformations facilitated by thermal cycling. Microstructural characterization using scanning electron microscopy (SEM) and energy‑dispersive spectroscopy (EDS) identified localized enrichment of Cr‑ and Fe‑rich regions that support the XRD‑based interpretation of σ‑phase development. These results provide insights into phase transformations and elemental diffusion in LMD‑fabricated brake‑disc coatings. The findings advance the understanding of thermally induced transformations in multilayer steel systems and support the optimization of LMD coatings for high‑temperature and wear‑intensive applications through advanced analytical evaluation.