超高速线光斑激光熔覆不锈钢涂层显微结构及性能研究

Microstructure and Properties of Stainless Steel Coatings by High Power Ultra-high Speed Linear Spot Laser Cladding

目的设计超高速线光斑激光熔覆送粉喷嘴,在极高的熔覆效率和极低的搭接率下制备不锈钢熔覆涂层,对比研究圆光斑及线光斑下的熔覆涂层的微观组织结构及性能。方法基于送粉喷嘴流场及粉末粒子运动轨迹的模拟研究,设计超高速线光斑激光熔覆专用送粉喷嘴。在此基础上,以27Si Mn为基体,采用1mm×10 mm线光斑,在10%搭接率、熔覆效率4.5 m^(2)/h下,采用超高速线光斑激光熔覆FeCr合金薄涂层;作为对比,采用超高速圆形光斑(2 mm)激光在0.2 m^(2)/h熔覆效率下熔覆FeCr合金涂层。采用SEM、XRD对比分析线光斑/圆光斑涂层微观组织结构与涂层显微硬度。结果通收束角度为25°~27°的单流道送粉喷嘴可得到分布均匀、飞行速度适中的粉末束流。对比研究超高速线光斑及圆光斑激光熔覆涂层可知,相同扫描速度下2种光斑制备的涂层均较为致密,无裂纹与气孔,由熔覆层底部到熔覆层表面均呈现出平面晶—柱状晶—等轴晶的变化趋势,线光斑和圆光斑涂层硬度在700~800HV,线光斑下的熔覆层硬度分布更加均匀,表面粗糙度Ra可低至<4μm,搭接率可低至10%,熔覆效率可达4.5 m^(2)/h,远高于圆光斑激光下的熔覆效率。结论2种光斑模式下的涂层微观组织、相组成及硬度相当,但超高速线光斑激光熔覆层表面光洁度更高,表面粗糙度更低,熔覆效率可达圆光斑的20倍。

Ultra high speed linear spot laser cladding is of great potential to effectively deposit thin metal coatings at an ultra-high speed to be applied to different industrial fields.However,the quality of the cladding layer depends on the design of the linear spot laser cladding powder feeder head design and the optimization of processing parameters.The objective of this study is to design a powder feeding nozzle for ultra-high speed linear spot laser cladding,examine the cladding efficiency and overlapping rate of the ultra-high speed linear spot laser cladding,and the microstructure and properties of the cladded FeCr-based alloy coating in comparison with those by circular spot laser cladding.The simulation method based on the simulation of flow field and particle trajectory within the powder feeding nozzle is used for optimizing the design of a special powder feeding nozzle for ultra-high speed linear spot laser cladding.FeCr alloy thin coating was prepared by the ultra-high speed linear spot laser cladding using 1 mm×10 mm line spot on 27SiMn substrate at 10%overlapping rate and cladding efficiency of 4.5 m^(2)/h.FeCr alloy coating was also prepared by the ultra-high speed circular spot laser cladding using 2 mm circular spot under the cladding efficiency of 0.2 m^(2)/h for comparison.The microstructure of FeCr alloy coatings prepared by both linear spot and round spot laser cladding was analyzed by SEM and XRD.The microhardness of the coatings was also compared.Results show that uniform powder particle distribution and moderate particle flight velocity were obtained through the single channel powder feeding nozzle with a beam angle of 25°-27°.The comparative study shows that ultra-high speed linear spot and circular spot laser cladding coatings present dense microstructure without cracks and pores.The plane crystals followed by columnar crystals and equiaxed crystals are observed from the bottom of cladding layer towards the surface of cladding layer.The hardness of the coatings cladded by linear spot and circular spot laser claddings is 700-800HV.However,the hardness distribution in the linear spot laser cladded coating is more uniform.Moreover,the surface roughness of FeCr alloy coating by ultra-high speed line spot laser cladding can be as low as Ra<4μm.The overlapping rate can be as low as 10%,and the cladding efficiency of the linear spot laser cladding is much higher than that of circular spot laser cladding.In this study,it can reach 4.5 m^(2)/h.As the conclusion the ultra-high speed linear spot laser cladding can prepare a dense thin coating with high surface finish.The microstructure,phase composition and hardness of the coating are similar to those by the circular spot laser cladding.However,the primary surface roughness of the ultra-high speed laser cladded coating is lower than that of spot laser cladding,and the cladding efficiency can reach 20 times that of the circular spot laser cladding.