A simplified model for prediction of HVOF NiCr coating properties through experimental design and diagnostic measurements

An empirical model was built for the prediction of HVOF sprayed NiCr in-flight particle properties based on the spraying parameters. The employment of factorial design in process parameter development, allowed determination of the contribution of the key process variables, such as flame energy (combustion pressure and O₂/F ratio), spray distance and feed rate, on the resultant particle velocities and surface temperatures. The significance of each parameter was used to compose a simple model which enabled the description of the particles' in-flight properties. Particles with velocities ranging as much as 300 m/s and temperatures ranging up to 350°C were used to produce a range of coatings on an in situ curvature sensor enabling the determination of evolving and residual stress. These diverse particle states combined with the effect of flame impingement on the substrate, resulted in coatings of similar thickness, but significantly different stress states. Real time evolving stresses -during deposition-, were interrelated to particle in-flight properties and consequently spraying parameters.