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

Post-annealing of cold-sprayed (CDGS) Al based composite coatings produces several intermetalllic compounds (IMC) in the matrix useful for many anti-wear applications. Dependence of types and dispersion characteristics of these compounds on spraying pressure was investigated. Typically, in this study, air is the only transporting gas for raw powders. The pressure prior to entering the gas heater was fixed at 0.7, 1.5, and 2.5 MPa and the temperature of gas through the nozzle was 280 ^oC, respectively. 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 MPa, 2.5 MPa) were not severely deformed. During post-annealing, the thin and continuous IMC layer was formed at the interface between Al coating and Ni substrate with low pressure condition (0.7 MPa). In 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) and low post-annealing temperature because of large peening effect. Conclusively, not only simple collision, but peening takes meaningful role for whole plastic deformation process, in turn, quantity and quality of nonequilibrium defects facilitating next stage of IMC formation during post-annealing. Furthermore, these massive defects in the cold sprayed coatings can be controlled by gas pressure.