Research on melting behavior of coaxially fed powder in diode laser cladding process

The purpose of this study was to investigate the thermal interaction between coaxially fed powder and diode laser, which is extremely complex and difficult to be detected in thermal real-time monitoring by the infrared camera system. In order to analyze the dynamic melting behavior of the powder, a high-speed camera system was established to capture the melting behavior of a single powder coaxially fed into the laser, which can reflect the entire melting process. There is a transition of “solid → solid-liquid two-phase state → liquid state” after a single powder enters the laser, and the duration and thermophysical behavior in different transition stages are not the same. Different states and duration determine distinct heat absorption effects. Based on high-speed camera detection results, the thermophysical behavior in different characteristic stages of the melting process in single powder was studied to develop a mathematical model, which is able to simulate and predict the temperature and state of the powder about to enter the melting pool. The experimental and simulation results show that (1) for a well-tested powder melting process, where the laser power ranges from 100 to 1500 W, the duration of the powder particle's absorption stage is between 4.41 and 18 ms, the duration of the solid-liquid two-phase state is between 0.52 and 2.63 ms, and the duration of the liquid state is between 4.67 and 13.48 ms. (2) The laser power ranges from 100 to 1500 W, and the temperature of the powder particles as they enter the melt pool ranges from 745 to 3200 °C.