工艺参数对压片预置式激光熔覆涂层微观质量的影响

Effects of Process Parameters on Microscopic Qualities of Coatings Formed by Squash Presetting Type Laser Cladding

针对现有粉末预置方法的不足,提出了一种新的粉末预置方法——压片预置法。采用该方法在基体表面上实现了粉末绿色预置,采用不同工艺参数在横流CO2激光器上扫描预置层制备了激光熔覆涂层。使用光学显微镜和扫描电镜观测了涂层的界面结合情况、稀释率和微观组织,分析了工艺参数对压片预置式激光熔覆涂层微观质量的影响。结果表明:在预置涂层厚度一定的情况下,大的光斑直径有利于基体能量的吸收,从而有利于涂层与基体形成冶金结合;当光斑直径相同时,高能低速有利于涂层与基体结合性能的提高。熔覆层的稀释率以1000W/mm为界随功率密度的增大先增后减,但当功率密度大于1000W/mm时能量有效利用率偏低。此外,随着功率密度的减小,熔覆表层枝晶组织呈现出"胞化"特征。因此,对于压片预置式激光熔覆,应尽可能采用大光斑小功率低扫描速度的工艺参数。

A novel powders presetting method, namely squash presetting method, is presented to overcome the shortcomings of existing methods. The presetting of powders on the substrate was environ- mental friendly performed by the method, and laser cladding coatings were prepared by crosscurrent CO2 laser using different process parameters. Status of interracial bonding, dilution and microstructure of the coatings were observed and determined with OM and SEM, and effects of process parameters on microscopic qualities of the coatings were revealed. The results show that big spot diameter is beneficial to the energy absorption of suhstrate in the case of definitive thickness of presetting layer, which promotes the forming of metallurgical bonding between coating and substrate. When spot diameter is same, high power and low scanning speed are beneficial to the improvement of interfacial bonding performance. With the increase of power density, the dilution of cladding layer increases as power density is less than 1000W/mm and decreases as power density is more than 1000W/ram. However, when power density is more than 1000W/mm, the using efficiency of laser energy is in a low level. Moreover, columnar dendrite in the top section of cladding layer changes into cellular microstructure while the power density decreases. Therefore, the parameter with big spot diameter, low power and slow scanning speed should be adopted in squash presetting type laser cladding.