Desirability-Based Multi-Criteria Optimisation of HVOF Spray Experiments

The reduction of the powder grain size is of key interest in the thermal spray technology to produce superfine structured cermet coatings. Due to the low specific weight and a high thermal susceptibility of such fine powders, the use of appropriate process technologies and optimised process settings are required. Experimental design and the desirability index are employed to find optimal settings of a high velocity oxygen fuel (HVOF) spraying process using fine powders (2 − 8 μm). The independent factors kerosene, hydrogen, oxygen, gun velocity, stand-off distance, cooling pressure, carrier gas and disc velocity are considered in a 12-run Plackett-Burman Design, and their effects on the deposition efficiency and on the coating characteristics microhardness, porosity and roughness are estimated. Following an examination of possible 2-way interactions in a 25 − 1 fractional-factorial design, the three most relevant factors are analysed in a central composite design. Derringer’s desirability function and the desirability index are applied to find optimal factor settings with respect to the above characteristics. All analyses are carried out with the statistics software “R”. The optimisation of the desirability index is done using the R-package “desiRe”.