###### Abstract  
As the main mechanical transmission parts, the gears are usually exposed to wear, corrosion, and fatigue; their failure in a poor working environment may cause a huge economic loss and waste of resources. Laser cladding (LC) has been proven to quickly repair parts at good metallurgical bonding performance and has flexible scanning strategies and a wide material selection. Therefore, LC technology can be considered an ideal approach to repairing damaged gear. However, the repair of damaged teeth by LC has not been systematically reported. In this paper, a series of progressive works have been carried out to systematically investigate the repair process of broken gears by LC. Firstly, process parameters, overlapping ratio, and Z-increment for Ni60 powder on 20 CrMnTi were optimized. Secondly, the effects of deposition strategies on morphologies of single-layer and multi-layer multi-tracks were carefully analyzed. Then, the gear repair was successfully realized based on obtained optimized parameters. Finally, the phase composition, microstructure, hardness, and wear properties of the repaired gear tooth were analyzed by XRD, SEM, microhardness tester, and friction and wear tester. The results show that the remanufactured tooth can recover its appearance before breakage. The repaired zone is mainly composed of \(\gamma\)-Ni, Cr\({}_{7}\)C\({}_{3}\), Cr\({}_{23}\)C\({}_{6}\), and CrB phases. The micro-hardness and wear volume loss of the repaired zone is 60.63 \(\pm\) 1.23 HRC and 1674.983 \(\mu\)m\({}^{2}\), which are consistent with those of the other teeth. This study is expected to expand the application of LC technology and provide guidance to engineers in the repair of damaged parts. laser cladding; Ni60 powder; repairing damaged gear; microstructure; microhardness; wear resistance +
Footnote †: journal: Applied Sciences  
Laser cladding (LC) has been applied in various fields [4; 5; 6; 7]. LC is mainly applied to repair and surface strengthening in the fields of aerospace, automotive, petrochemical, metallurgy, and rail transportation. It provides a new option to repair damaged parts, especially important parts, greatly reducing cost and enhancing work efficiency [8]. LC repair technology is a kind of remanufacturing technology, which repairs damaged parts and components using reverse engineering and powder-feed additive manufacturing [9; 10]. LC repair has multiple advantages: low heat input leads to low distortion and low thermal damage in the base substrate, wide material applicability, rapid response to market demand, and a finer microstructure achieved, compared to arc welding, cold spray, and plasma spray [11; 12; 13; 14]. LC repair is regarded as a prospective technology reducing the environmental impact of products by extending their lifespan rather than replacing them. Until now, LC repair technology has gradually been widely applied in different industrial fields. The damaged wheel was repaired by LC. The life evaluation models for repair wheels were established, and the existing railroad wheel damage assessment model was improved. It provides a new idea for the application and maintenance of railroad wheels [15]. The effect of the additive powders B4C and Ti on the damaged carbon steel was studied by adjusting their ratios to obtain mechanical properties with refined organization and good bonding with the substrate. Research shows that 5B4C and the 15 Ti (in wt.%) powder can obtain better morphology, phase composition, microstructure, and mechanical properties [16]. The Ni45 powder was selected to repair 45 steel gear. The laser beam enters from the midpoint of two roots to solve the problem of difficult machining of complex shapes. The hardness and wear resistance of the cladding layer is analyzed to determine that the performance of the cladding layer is better than that of the substrate. However, the optimization of the whole process system is not introduced in detail [1]. A new non-dominated sorting genetic algorithm ii (NSGA-II) to solve the repair model of LC is proposed.