An SDE study of twin-wire electric arc sprayed nickel-aluminum coatings

An analytical and experimental study of the twin-wire electric arc spraying of nickel-aluminum coatings has been performed to demonstrate the suitability of the wire system as a bond coat material for ceramic overcoats in thermal barrier applications, and for spraying a single coat for part refurbishment. Experiments were conducted using a Box-type full-factorial design parametric study. Operating parameters were varied around the typical process parameters (i.e., current, primary and secondary pressure, spray distance) in a systematic design of experiments (SDE) in order to display the range of processing conditions and their effect on the resultant coating. The coatings were characterized by hardness tests and optical metallography. Coating properties were quantified for hardness, porosity, deposition efficiency, and microstructure. The features of the coatings are correlated with the changes in operating parameters. Analytical calculations of the gas and droplet dynamics are presented, which includes molten metal entrainment and droplet breakup models.