Investigation on the fatigue behavior of different extreme high-speed laser cladding materials on the damaged EA4T axle

Surface damage to railway axles intensifies with increasing axle loads and operating speeds. This study evaluates extreme high-speed laser cladding (EHLA) for repairing damaged EA4T axles using five Fe-based alloys (24CrNiMo, AISI 4340, H13, Fe314, and 316L) spanning high-, medium-, and low-alloy categories. The microstructures characteristics, phase compositions, residual stresses, hardness, and elastic modulus of the cladding layers were systematically investigated. Fatigue tests revealed that all repaired specimens exhibited reduced strength compared to smooth ones (370 MPa), primarily due to: (1) epitaxial growth forming stress-aligned coarse columnar austenitic grains, and (2) solidification defects. Among them, high-alloy claddings (316L, Fe314) retained 92-96% fatigue strength (337-359 MPa) through their stable austenitic structure and effective stress transfer to the substrate. In contrast, medium/low-alloy claddings show reduced strength retention (60-81%) from stress concentration due to grain boundary weakening and elastic modulus mismatch (246-253 vs 223 GPa). These findings establish three essential criteria for laser-clad repair axle material selection: (i) austenitic phase stability to prevent deleterious phase transformations, (ii) fine equiaxed grain structure to limit columnar grain growth, and (iii) elastic modulus compatibility with the substrate to ensure optimal stress distribution.