The forming quality of Tungsten-Carbide coatings synthesized in situ by laser remelting

Abstract

The work aimed to improve the forming quality of multi-pass coatings synthesized by laser remelting in situ. The influence-relation model of the overlap rate on surface flatness and dilution rate of coatings was constructed by the single-factor method. The functions of laser power, scanning speed, defocusing distance, and scanning mode on the surface flatness and pore area of remelted coatings were studied by mixed horizontal orthogonal test, and the influence law of process parameters on surface flatness and internal pore area was revealed. Flatness increased first and then decreased with the increased overlap rate. Energy acting on the substrate decreased, and the dilution rate decreased. When the dilution rate was satisfied, the overlap rate corresponding to the maximum value of the flatness fitting curve was 26.7%. The scanning speed and laser power of remelting significantly affected coating flatness and the signal-to-noise ratio of the pore area. The signal-to-noise ratio of flatness to the pore area was positively correlated with laser power and negatively correlated with the scanning speed. When the scanning speed of remelting decreased, the duration of the molten pool increased, and its solidification rate decreased. Therefore, bubbles in the molten pool had sufficient time to overflow, which increased coating flatness and decreased the internal pore area.The optimum process parameters under multi-index optimization of integrated flatness and pore area were as follows using grey relational analysis: the laser power of 1,600 W, scanning speed of 3 mm/s, a defocusing distance of 10 mm, and parallel cladding direction. Sticky powders in the coating disappeared under the optimal remelting process parameters, and flatness and the internal pore area were improved. Maximum hardness was increased from 1,281.7HV to 1,454.2 HV, with an increase of 13.46%. The grain size was small and hardness was improved due to the increased tissue density in the remelting area of the coating.