Effect of laser cladding and laser-induction hybrid cladding coatings on the bending properties and fracture behavior of rails

Laser cladding (LC) and laser-induction hybrid cladding (LIHC) technologies, with low dilution, low deformation and high deposition efficiency, have attracted a lot of notices in repairing and hard-facing the full-scale rail. However, the cladded coatings with different microstructure and properties will also affect the bending stress distributions of rails during service, which may lead to the rails' failure and fracture. In this paper, the bending properties and fracture mechanisms of rails deposited by LC and LIHC were studied systemically by the three-point bending tests coupled with finite element method simulations (FEMS). The results indicate that the ultimate bending strength (UBS), fracture strain (epsilon(f)) and fracture work (W) of the specimen by LIHC are about 1.35, 4.28 and 7.70 times of that by LC correspondingly. The dramatically difference is mainly caused by the heat affected zones (HAZs) induced by different technologies. Under the bending stress, both the maximum stress and initial damage of the specimen by LC generate in the HAZ, while the cracks extend intergranularly in HAZ and lead to the rapid overall instable fracture. Oppositely, the initial damage of the specimen by LIHC originates from the surface on the tension side where the maximum stress generates, and the HAZ by LIHC is proved to be able to promote both the bending strength and fracture toughness of the rail. On the other hand, the thickness and properties of the cladded coatings are the main factors affect the bending properties of specimens by LIHC. When the parameters are chosen suitably, both the yielding strengths and UBSs of specimens by LIHC are even higher than that of the rail substrate, which means LIHC can adjust the rail's performances reasonably while prevent the rail from bending fracture.