The MCrAlY type coatings provide oxidation protection and good adhesion between the ceramic topcoat and the substrate. The high velocity oxy fuel (HVOF) process is currently being introduced to make the bond coats instead of conventional low pressure plasma spraying due to lower cost. In this research, the METJET-III HVOF liquid fuel system was used to produce MCrAlY coatings and the Tecnar DPV2000 was used to investigate in-flight particle temperature, velocity and diameter. To examine the coating-build, the wipe test was used to reveal the particle deformation on the substrate with different spraying parameters and correlated impact behaviour with particle properties. It was found that increasing of total fuel plus oxygen flow rate, percent stoichiometry and stand-off distances did not dramatically change the particle temperature. Increasing of percent stoichiometry and stand off distance led to reduction in particle velocity while increasing of the total fuel plus oxygen flow rate led to increase in the particle velocity. The average particle velocity below 640 m/s seems to make less splat formation than the average particle velocity above 750 m/s. Compiling results of the coating microstructure, the splat formation and the in-flight particle measurements revealed the effect of spraying parameters on the coating characteristics.

An adapted HVOF system has been computationally investigated in order to test the effects of injecting a cooling gas on both the gas phase dynamics and particle behaviour through the system. An existing liquid-fuelled HVOF thermal spray gun is modified by introducing a centrally located mixing chamber. The gas phase model incorporates liquid fuel droplets which heat, evaporate and then exothermically combust within the combustion chamber producing a realistic compressible, supersonic, turbulent jet. The trajectory of each discrete phase powder particle is tracked using the Lagrangian approach, with the inclusion of heating, melting and solidification through each particle. The results obtained give an insight to the complex interrelations present between the gas and particle phases, and demonstrates the usefulness of this modelling approach in aiding the development of thermal spray devices.