Comprehensive process maps to synthesize high density plasma sprayed aluminum oxide composite coatings with varying carbon nanotube content

Comprehensive process maps have been developed to synthesize “high density” plasma sprayed Aluminum oxide (Al2O3) composite coatings with 0, 4 and 8 wt.% carbon nanotube (CNT) reinforcement. These process maps correlate the key processing parameters such as plasma power, powder feed rate, primary gas flow rate, and stand-off distance to the temperature and velocity of the in-flight particles and finally, to the porosity and microhardness of coatings. Relative importance of each significant process parameters was also investigated by making “Pareto diagrams”. Stand-off distance followed by the plasma power were found to be most sensitive parameters which affects the porosity of the plasma sprayed Al2O3–CNT composite coatings. Process maps showed that CNTs have a significant effect on altering the temperature and velocity of in-flight particles. Higher thermal conductivity of CNTs alters the heat transfer phenomena during the coating build up which assists in densification.