Optimisation of the spray parameters for improved microstructural characteristics in the HVOF Sprayed Cr3C2-20(Ni20Cr) coating
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Wear resistance coating of Cr 3 C 2 -20(Ni20Cr) is required to be sprayed through High Velocity Oxy Fuel (HVOF) Spray Process on the compressor disc of aero gas turbine engine. The part is made up of Ti6Al4V alloy. While employing the spray parameters recommended by Original Equipment Manufacturer (OEM) for preliminary deposition trials, microstructural defects in the form of vertical cracks were observed. In order to overcome the above microstructural defects, various efforts were sequentially carried out. The initial approach of preheating the substrate at 120°C is aimed at reducing the thermal gradient between the substrate and coating which exhibited partial success. Detailed investigation involving design of experiment using Taguchi L16 Orthogonal array is employed to study the effect of certain critical parameters such as standoff distance, powder feed rate, hydrogen flow rate and Oxygen flow rate. TOPSIS method is used to establish the optimal coating parameters to achieve the crack free coating with the acceptable hardness, porosity and oxide levels. From the above studies, standoff distance 150mm, feed rate 25 g/min, hydrogen flow rate 470 NLPM and Oxygen flow rate 205 NLPM are optimised for crack free HVOF coating of Cr 3 C 2 -20(Ni20Cr) on Ti6Al4V substrate and the coating microstructure with the required hardness and the oxides & porosity levels in acceptable range is established for actual component manufacturing.
