目的 探索激光熔覆过程中的熔池凝固行为及微观组织演变规律,阐明微观组织与涂层性能之间的关联机制,以实现最优的涂层性能。方法 结合数值模型与实验研究,探究熔池凝固过程中的微观组织演变机理。结果 基于数值模型,分析了熔池的传热行为及演化特征,揭示了熔池尺寸随激光功率升高而增大的规律,熔池长度由2 000 W时的5.13 μm扩大到3 000 W时的7.21 μm。通过提取温度梯度（G）与凝固速度（R）等凝固参数,建立了柱状向等轴转变（CET）图,明确了高激光功率下IN718涂层CET行为的延迟机制。揭示了凝固过程中凝固参数与微观结构之间的关系,并进一步阐明了熔池凝固过程中晶粒生长的机理。晶粒尺寸受控于G×R复合因子,当激光功率由2 000 W增加至3 000 W时,等轴晶面积由19.91 μm2增至35.98 μm2,柱状晶宽度由6.45 μm增至11.33 μm。同时,探讨了晶粒尺寸与显微硬度及耐磨性的关联性。当激光功率为2 000 W时,由晶粒细化引起的组织强化,使涂层的平均显微硬度为408.6HV0.2,相比于3 000 W时涂层显微硬度提升了1.22倍。当激光功率为2 500 W时,获得最佳晶粒类型比例,涂层的摩擦系数曲线最低为0.596。结论 通过调控激光功率在一定程度上影响了涂层微观组织分布及演变规律,从而提升了力学性能。研究结果为制备理想微观组织和性能的涂层提供了理论依据。
Abstract
The work aims to investigate the solidification behavior of the molten pool and the evolution of the microstructure during the laser cladding process, and elucidate the correlation mechanism between microstructural characteristics and coating performance, thereby achieving optimal coating properties. Numerical simulation and experimental approaches were integrated to explore the microstructural evolution mechanism during the solidification process of the molten pool. Based on numerical models, the heat transfer behavior of the molten pool was analyzed, as well as the relationship between molten pool size and the increase in laser power, with the molten pool length increasing from 5.13 μm at 2 000 W to 7.21 μm at 3 000 W. By extracting parameters such as the temperature gradient (G) and solidification rate (R), a columnar-to-equiaxed transformation (CET) diagram was established, which clearly elucidated the delayed mechanism of the CET behavior of IN718 coatings under high laser power conditions. The study revealed the relationship between solidification parameters and microstructure during the solidification process and further elucidated the mechanism of grain growth during the solidification of the molten pool. The grain size was controlled by the G×R composite factor, with an increase in laser power leading to an expansion of the equiaxed grain area from 19.91 μm2 to 35.98 μm2, and the width of the columnar grains from 6.45 μm to 11.33 μm when the laser power increased from 2 000 W to 3 000 W. In addition, the correlation between grain size and microhardness as well as wear resistance was also investigated. At a laser power of 2 000 W, the tissue strengthening caused by grain refinement resulted in an average microhardness of 408.6HV0.2 for the coating, which is a 1.22-fold increase. At a laser power of 2 500 W, the optimal proportion of grain types was achieved, with the coating’s coefficient of friction reaching a minimum of 0.596. By regulating the laser power, the distribution and evolution of the coating’s microstructure can be influenced to a certain extent, thereby enhancing its mechanical properties. The research findings provide a theoretical foundation for the fabrication of coatings with optimized microstructures and properties.
关键词
激光熔覆 /
枝晶转变 /
凝固参数 /
数值模型 /
机械性能
Key words
laser cladding /
dendrite transformation /
solidification parameters /
numerical model /
mechanical properties
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基金
福建省自然科学基金（2026J001999）
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