Analysis of the formation behavior and mechanisms of diamond coatings through laser brazing

Research on diamond coatings was conducted using laser heating as a heat source, and the behavior and mechanisms of diamond coating formation were analyzed with the assistance of high-speed cameras. The results show that in the absence of diamonds, the brazing powder's fusion and spreading process can be divided into five stages: powder melting, liquid brazing material aggregation, powder adsorption fusion, wetting and spreading, and coating solidification. The minimum surface tension is located at the center of the weld pool, while the maximum surface tension is found at the weld pool's edges. A surface tension gradient in the weld pool is the main driving force behind its flow. After introducing diamonds into the coating, the formation process of the coating goes through six stages: powder brazing material melting, liquid brazing material aggregation, brazing material micro-powder adsorption fusion, brazing material wetting and spreading, migration of diamonds to the surface of the coating, and coating solidification. During the diamond brazing and coating process, diamonds tend to float along the surface edge of the weld pool. This is primarily due to the interface tension between diamonds and liquid brazing material being much greater than that between diamonds and the solid substrate, along with the combined effects of Stokes force, gravity, buoyancy, Basset force, and others. Additionally, the efficient and low-damage thermal effect of laser transmission during the brazing process helps to prevent overheating damage to the diamonds. This is a significant potential advantage of diamond-enhanced coatings produced through laser brazing.