宽带光束与同轴粉末流耦合规律及熔覆层成形特征

Coupling Rules Between Broadband Beam and Coaxial Powder Flow and Forming Characteristics of Cladding

利用高功率宽带平顶光束进行熔覆试验,采用高速摄像机和图像处理软件,建立了宽带光束-同轴粉末流耦合模型,研究了不同送粉器粉盘转速和载气流量下激光束与同轴粉末流的耦合特性和规律,并通过金相显微镜和体视显微镜分析不同光粉耦合形态下熔覆涂层的成形特征与规律,构建了光粉耦合特性与熔覆层成形的关系。结果表明:在载气流量不变的条件下,随粉盘转速增加,粉末流与激光束的耦合位置逐渐由宽带光束内变成宽带光束外,粉末流汇聚点焦距增大,汇聚直径先增大后保持不变;在基体处的区域由焦柱粉流区变为环状粉流区,熔覆层宽度略减小,高度和接触角增大,粉末利用率先增大后减小,稀释率减小。在粉盘转速不变的条件下,随载气流量增加,粉末流与激光束的耦合形态不变,粉末流位于宽带光束外,粉末流汇聚点焦距先增大后减小,汇聚直径先增大后保持不变;在基体处的区域由环状粉流区变为焦柱粉流区,熔覆层宽度先增大后减小,高度和接触角先增大后保持不变,粉末利用率先增大后减小,稀释率减小。当粉盘转速为1.2 r/min,载气流量为4 L/min时,能够获得较好的成形质量。

High-power and broadband-flat laser beam was applied for cladding experiments. Using high-speed camera and image processing software, a coupling model of broadband beam and coaxial powder flow was built to investigate coupling rules with different disk revolutions and carrier gas flows. The whole process was characterized by metallographic microscope and stereo microscope. The results show that, when the carrier gas flow is kept the same, with the increase of the disk revolution, the coupling position of the laser beam and powder flow gradually changes from the inside to the outside of the broadband beam.The focal length of the powder confluence point becomes larger at first, and then remain unchanged as well as the diameter. The geometry of the base area changes from the focus-powder spot to the ring-powder spot, and the width of the cladding layer slightly decreases, while the height and contact angle increase. In this condition, the powder using efficiency first increases then decreases, and the dilution rate is reduced. When the disk revolution is kept the same, the coupling position of the laser beam and powder flow was unchanged with the increase of the carrier gas flow. Powder flow is located outside ofthe broadband beam. Focal length of aggregation point of powder first increases and then decreases. Diameter increases first and then remains the same. Base area is from the ring-powder spot to the focus-powder spot. Width of cladding layer first increases and then decreases. Height and contact angle increase first and then remain the same. Powder using efficiency first increases then decreases, and the dilution rate is reduced. The best performance can be achieved when the disk revolution is 1.2 r/min, and the carrier gas flow is 4 L/min.