Effects of Gas Pressure of Cold Spray on the Formation of Al-Based Intermetallic Compound

In this paper, postannealing of cold-sprayed (CDGS) coatings for intermetallic compounds (IMC) in the matrix at low temperature and dependences of types and dispersion characteristics of intermetallic compounds on spraying pressure condition were investigated. The pressure prior to entering the gas heater was fixed at 0.7, 1.5, and 2.5 MPa. The relatively soft Al has been coated at low gas pressure condition (0.7 MPa) with severe plastic deformation owing to large peening effect. On the contrary, the Al particles coated at the higher pressure (1.5, 2.5 MPa) were not severely deformed. It was concluded that the pressure-controlled peening effects could alter the main route of Al consumption during annealing: eutectic or compounding of intermetallics. The thin and continuous IMC layer was formed at the interface with low pressure condition (0.7 MPa). On the other hand, the thick and discontinuous IMC layer was observed at the higher pressure condition (1.5, 2.5 MPa). Also, many eutectic pores were found in the Al-Ni composite coatings with lower gas pressure condition (0.7 MPa), but far less were found with high pressure environment.