Simplified model for description of HVOF NiCr coating properties through experimental design and diagnostic measurements

The use of factorial design in process parameter development allowed determination of the contribution of key process variables, such as flame energy (combustion pressure and O₂/F), spray distance, and feed rate, on in-flight particle properties. The significance of each parameter was used to construct a simple model which enabled the description of particles' temperature and velocity. Particles with velocities ranging by as much as 300 m/s and temperatures ranging up to 350°C were used to produce an array of coatings on an in situ curvature sensor enabling the determination of the evolving - during spraying - and residual stress at the end of the process, correspondingly. These diverse particle states combined with the flame impingement on the substrate, resulted in coatings of similar thickness, but significantly different stress states. Real time evolving stresses - during deposition - and coating properties such as, microhardness, modulus, and corrosion behavior were correlated to particle in-flight properties and, via the use of the introduced model, to spray parameters.