Laser cladding technology offers an effective repair solution for turbine blades, aircraft landing gears, propellers, and large gears. Typically, these workpieces are fixed to the worktable, after which surface repairs are carried out using the laser cladding head. However, gravitational effects, complex material flow, vaporization, and thermo-physical processes within the melting pool pose challenges in achieving desired shapes and properties, affecting the morphology of the cladding layer and the overall surface quality. Laser remelting, which is a surface post-treatment method, can improve the performance and morphology of a surface without changing the original equipment, thereby saving post-treatment time. This study aims to elucidate the modifications in the laser cladding layer morphology at various tilting angles. Through finite element simulations, we simulate the impacts of substrate tilting angles on the resulting morphology of the laser cladding layer. Furthermore, our investigation aims to identify the optimal location for in-situ remelting by analyzing the distribution of the molten pool velocity and temperature fields. This study involves conducting multi-track experiments to compare the macro-morphology of the cladding layer before and after remelting. We aspire for our findings to serve as a valuable reference guiding the understanding of how in-situ remelting influences morphology modification and microstructure evolution in laser cladding layer on inclined substrates.

This study employed 45 steel substrates and 316L powder materials. A finite element simulation software was used to numerically simulate the laser cladding and in-situ remelting process on inclined substrates. The laser cladding simulation was carried out at different tilting angles, and a tilting angle of 30° was selected for the in-situ remelting simulation. The molten pool velocity and temperature distribution across the three remelting positions were simulated and compared. Subsequently, practical in-situ remelting experiments were performed on tilted laser cladding layers. The changes in the surface morphology of the molten cladding layer before and after remelting were examined using an optical microscope. Mechanical properties were assessed using Vickers hardness testing, friction and wear testing, and three-dimensional profilometry. These analyses were aimed at comprehending the microstructural transformations induced by in-situ remelting.

The morphology of the laser cladding layer on the inclined substrate is significantly affected by gravity. After in-situ remelting, the molten pool tends to flow along the direction of gravity. When the substrate tilt angle is less than 90°, the leading angle is inversely proportional to the substrate tilt angle, whereas the trailing angle is directly proportional. However, when the substrate tilt angle exceeds 90°, the morphology of the molten pool becomes highly unstable. The regular downward-sliding morphology gradually transforms into unpredictable irregular patterns, resulting in splattering and droplet formation (Fig. 4). Numerical simulations of the molten pool velocity field and temperature field during the in-situ laser remelting of the tilted fused cladding show that the optimal remelting position is in the middle of the overlapping region of the cladding tracks (Fig. 6). The primary factor behind this phenomenon is that during remelting, not all the cladding layers on both sides of the laser are fully melted. As the cladding layers on either side of the laser melt, they flow toward the center of the cladding structure. However, the flow of the molten pool encounters resistance from gravity and the existing cladding layers. Consequently, the molten pool bulges upward. Additionally, because of the impact of the laser and powder, a portion of the velocity field forms leftward vortices, whereas another portion of the velocity field increases the height of the molten pool. After remelting, the central region between the two cladding layers exhibits spherical bulges. This effect occurs primarily because a section of the cladding layer is remelted. As the grooves fill with the flowing molten pool, any excess material moves toward the surface of the cladding layer owing to gravitational forces. Given the distance from the center of the heat source, there is an increase in the temperature gradient, accompanied by vaporization of the excess solute. This vaporization lifts the excess material, forming a mass that contracts and solidifies into uniformly sized liquid beads within the molten pool (Fig. 8). The structural changes at the bottom of the cladding layer are minimal compared with the upper portion, where the laser remelting significantly impacts the structure. Consequently, the heat-affected zone from laser remelting primarily concentrates in the upper-middle region of the cladding layer. Observations reveal that the post-remelting dendritic structures at the top of the cladding layer almost vanish. A substantial proportion of the dendritic structures fracture, transforming into equiaxed grains. Furthermore, the grains at the top undergo noticeable refinement (Fig. 9). After laser remelting, an intensified temperature gradient occurs at the molten pool interface, accelerating the crystallization rate. Elevated cooling rates impede grain growth while promoting heightened nucleation, thereby refining the grain structure. Consequently, in-situ laser remelting densifies the cladding layer structure via these mechanisms.

Gravity has a significant impact on the morphology of the cladding layer, and as a result, the cladding layer tends to flow along the direction of gravity after melting. When the tilt angle of the substrate is greater than 90°, the molten pool morphology is extremely unstable. It transitions from the original downward-dripping regular morphology to an unpredictable irregular morphology, often resulting in splashing or even dripping, which substantially damages the morphology of the cladding layer. In-situ remelting in the overlap zone of the cladding channel brings about the most substantial improvement in the surface flatness of the cladding layer. The surface unevenness is reduced significantly, from 0.165 to 0.056, because of remelting. Our results show that the in-situ laser remelting primarily affects the microstructure in the middle and upper parts of the cladding layer. The dendritic crystals at the top of the layer nearly vanish, and a large number of dendritic crystals transform into isometric crystals. After remelting, the height of the cladding layers reduces by 16.1% compared to their pre-melting state, and the roughness significantly decreases by 69.5%. The surface hardness of the cladding layers increases by 70 HV after remelting, accompanied by a 76.3% reduction in wear rate.