Investigation on laser cladding Fe-based gradient coatings with hierarchical enhanced wear resistance on U75V railway steel

This study focused on the multilayer laser cladding of 15–5 precipitation hardening (PH) steel coating on U75V railway steel for improved surface performance. The effect of pearlitic substrate dilution action with high carbon content on microstructures and wear performance of PH steel coating with four deposited layers was investigated. Results showed that each cladding layer consisted of a similar multiphase mixture of martensite, retained austenite, and NbC carbides in the case of stepwise changes in chemical compositions induced by dilution effects. The wear resistance of the multilayered PH steel coating is closely related to the deposited layer number, reflected in a gradient increase in the wear rate with the increasing cladding layers. A comparative analysis against the U75V substrate showed substantial wear rate reductions of approximately 95 % and 4.5 % in the first and fourth layers, respectively. Besides, the cross-sectional microstructures were analyzed in detail to reveal the underlying friction-induced microstructural evolution of the gradient coating. The refinement of martensite laths controlled by dislocation reaction and the friction-induced austenite to martensite transformation was responsible for the superior wear resistance. The current experimental results could provide a new strategy for designing hierarchical enhanced wearable gradient coating for surface modification in railway components.