激光熔覆纳米Al_2O_3的粉末冶金件的表面组织

Microstructure of powder metallurgy material surface layer modified by laser cladding nano-Al_2O_3

运用纳米Al2O3作为粉末冶金件的表面改性材料,通过激光熔覆试验对粉末冶金件进行了表面改性。分析了激光熔覆的凝固过程,运用金相显微镜和扫描电镜对粉末冶金材料的表面改性层组织进行了观察,并对改性层不同组织的形成因素进行了研究。结果表明:熔覆后材料组织分为熔覆层区、界面结合区、基体区。从熔覆层到基体密度呈现由密向疏变化。激光熔覆组织主要受涂层成分及含量、工艺参数、形状控制因子G/υ(温度梯度/凝固速度)的影响,而形状控制因子又决定于工艺参数。当光带矩形光斑尺寸为15mm×2mm时,最佳功率为2.5kW,最佳扫描速度为90mm/min。

The nano-Al_2O_3 and the laser cladding were chosen respectively to serve as the surface modification material and processing technology for the powder metallurgy pieces. The solidification process of the laser cladding layer was investigated and the microstructure of the modification layer was observed by means of the metallograph and SEM. The factors affecting the formation of the different structures of the modification layer were studied. The observed microstucture can be divided into 3 zones, i.e., the cladding zone, the transition zone, and the base body zone, their densities decrease gradually from the cladding zone to the base body. The microstructure of the laser cladding surface is affected by the composition and the content of the coating, processing parameters and the shape factor G/υ(temperature gradient/solidification rate) which itself is decided by the processing parameters. When the sizes of the rectangular laser spot are 15 mm×2 mm,the optimal power is 2.5 kW, and the optimal scanning speed is 90 mm/min.