Studies On The Preparation Process And Protective Properties Of The Cold Spray Copper Alloy Coatings

Cold gas dynamic spraying (CGDS) process is a new surface engineering technology. In the spraying process, the coating is deposited through plastic deformation of metallic spray particles in a completely solid state with high velocity impact. It has attracted serious concern for its advantages: low spraying temperature, absence of phase transition and oxidation, low porosity level, dense microstructure, good adherence to the substrate, and so on.In this paper, the characters of cold-sprayed copper coating, cold-sprayed Cu-20wt%Al₂O₃ composite coating, cold-sprayed Cu-20wt%SiC composite coating, and cold-sprayed Cu-50wt%SiC composite coating were studied through XRD analysis, SEM, micro-hardness, combination test, wear resistance test and anticorrosion experiment. Furthermore, the effect of vacuum heat treatment on the microstructure, micro-hardness and wear-resistance of the four kinds of coatings are investigated.Studies showed: as-deposited coatings presented the dense microstructure, low porosity; little or no oxidation phenomenon. Thickness of the coatings has no obvious effect on the combination strength and tribological property. By potentiodynamic polarization curves tests and EIS tests, the cold-sprayed copper coating showed good corrosion resistance and the corrosion rate of coatings retained a low level with immersion time.After heat treatment, the cold-sprayed copper coatings present a far different property from that of the as-sprayed coatings. In a certain range of heat treatment temperature (500℃or less), the bonding strength of the coatings significantly increased with the heat treatment temperatures increasing: from the cold-sprayed 6MPa to about 45MPa after heat treatment, but the micro-hardness decreased obviously: from 132.94Hv0.2 cold-sprayed to 41.8Hv0.2(HT500℃). At annealing temperature of 300℃, stress relief annealing plays an important role in the cold-sprayed copper coating, and there is no evident macrostructure change. At this annealing temperature, the micro-hardness decreased evidently, and the combination strength increased. Apparent recrystallization can be seen clearly at 500℃, and the combination strength reaches the maximum 44.6MPa. The micro-hardness decreased with the growth of the annealing temperature.The mental/ceramic coatings were successfully prepared by CGDS. In the composite coatings, the structure is denser, the Al₂O₃ and SiC reinforce particles balancing spread in the coating, and the micro-hardness of the composite coatings increased evidently. For the as-sprayed composite coatings, such factors as ploughing and abrasive wear could determine the sliding process.After heat treatment, the composite coatings present far different properties from that of the as-sprayed composite coatings. At annealing temperature of 300℃, stress relief annealing takes an important role in the cold-sprayed composite coatings, and the micro-hardness decreased evidently. Apparent recrystallization and grain growth occurred at 500℃. When the annealing temperature was 700℃, the recrystallization was evident, and the micro-hardness reach the minimum.In the wear-resistance tests, the tribological mechanisms of the three kinds of composite coatings are different. For the cold-sprayed Cu-20wt%Al2O3 composite coating, the abrasive wear takes an important role in the sliding process to the as-sprayed composite coating and the low temperature (300℃and 500℃) annealed composite coatings. At the annealing temperature of 700℃, such factors as abrasive wear and adhesion wear play a dominant role. In the wear resistance tests of as-sprayed Cu-20wt%SiC composite coating and HT300℃Cu-20wt%SiC composite coating, the abrasive wear is the dominant wear type. At the annealing temperature of 500℃and 700℃, the abrasive wear and adhesion wear play an important role in the sliding process. With the content of the reinforce particle of SiC increasing, such factors as abrasive wear and fatigue wear play a dominant place in the as-sprayed composite coating and all the annealed composite coatings.