Interface Debonding and Spalling of Si‐Al Coatings on Railway Turnouts

ABSTRACT To address the abnormal spalling of silicon‑aluminum coatings on high‑speed railway turnout slide bed plates in service, this study systematically investigates the coating interface bonding behavior and spalling mechanism via mechanical tests, microstructure characterization, and electrochemical measurements using failed field components. Results show that the spalling is a typical coating‑substrate interface debonding failure. With an average adhesion strength of 7.92 MPa, which satisfies the industry acceptance requirement of ≥ 5 MPa and lies within the typical range (5–12 MPa) of arc‐sprayed Al‐Si coatings on steel, the coating is nonetheless bonded to the substrate merely by mechanical interlocking without effective metallurgical bonding; interfacial and internal pores are the core triggers of the failure. Dominated by the Al 9 Si phase, the coating retains the expected dual anti‐corrosion capability. This work reveals that the early spalling is an interfacial fatigue‐debonding failure: although the static bonding strength is qualified, the fatigue resistance of the mechanically interlocked interface is insufficient for the long‐term multi‐field coupled service conditions of turnouts.