In-situ Observation of Microstructure Evolution of Cold Sprayed CrZrCu Alloy Coating during Heating

Thermal changes of the cold-sprayed CrZrCu coating were studied by differential scanning calorimetry.With the aid of high-temperature laser scanning microscope the in-situ observation of microstructure evolution in annealing process had been made,and the hardnesses of the coating before and after annealing were tested.The results indicate that there were three peaks on the DSC curve of the coating during heating process,which corresponded to deformed stages of recovering process,recrystallization nucleation and grain growth,and particle interface meniscus-disappearing respectively.Microhardness of the coating declined from 159.69 HV to 7757 HV in the first two stages,but kept stable in the third stage which was similar to the integration of particle boundaries in sintering.The microstructure did not change after 350 ℃ annealing,it turned into equiaxed crystal when the temperature increased to 550 ℃,at 900 ℃,grain structure of CrZrCu coating became homogeneous,corresponding to the structure of original powder.