Effect of Powder Particle Size on Tensile-Compressive Fretting Fatigue Behaviour of EA4T Steel Repaired by Laser Cladding

The surface of high-speed rail wheel axles may attract damage caused by foreign matter during the press-fitting process, which could impact or even reduce the service reliability and safety. This study explored the use of NiCrMo alloy powder particle in three sizes (50, 100 and 150 μm) for laser cladding repair of pre-damaged EA4T steel, the undamaged specimen and repaired specimen were taken as the research object. The article investigates the influence of varying powder particle sizes on the fretting fatigue behavior after material repair through tensile-compressive fretting fatigue repeat tests. The results indicated that the tensile-compressive fretting fatigue S~N curves of the substrates displayed a slanted 'Z-shaped' feature. Despite a slight decrease in fatigue lifespan under the same load conditions of repaired specimens which compared to the substrate specimen, but all of the repaired specimens still showed an overall higher fatigue life in general. The fracture surface of both the undamaged specimens and repaired specimens exhibited a normal transgranular fracture type. Fatigue cracks tilted towards the contact surface direction were visible in the contact damage area after 1×10⁵ cycles. Solidification cracks appeared in the damaged region of the 50 μm particle size specimen result from excessive heat absorption during laser cladding repair process. Shape of all the wear areas appeared as an irregular elliptical, with adhesive wear, oxidation wear, abrasive wear, and delamination being the normal primary damage mechanisms. The wear volume of 50, 100 and 150 μm particle size laser cladding repair specimens were measured at 2.43×10⁶ μm³, 1.94×10⁶ μm³, and 3.29×10⁶ μm³ respectively after 1×10⁵ cycles of fretting fatigue test. After 2×10⁵ cycles of fretting fatigue test, the wear volumes for the same particle sizes powders were 4.32×10⁶ μm³, 3.86×10⁶ μm³, and 5.64×10⁶ μm³. In the case of the 100 μm particle size specimen, there was a slight delamination phenomenon observed in the contact center, resulting in a small wear volume. As the number of cycles about fretting fatigue test increases, the 100 μm particle-repaired specimen crack propagation was delay compared to the 150 μm particle-repaired specimen. Conversely, the 50 μm particle-repaired specimen occurred premature fracture due to the solidification crack propagation. The fatigue lifespan of the 100 μm particle-repaired specimen was relatively longer than the other two kinds of laser cladding repair specimens with 50 μm and 150 μm particle sizes.