The present study aims to optimise process parameters for depositing CoCrFeMnNi high entropy alloy (HEA) on carbon steel substrates via four coating processes: cold spray, high velocity oxygen fuel, high velocity air fuel, and laser cladding. A comprehensive literature review was conducted as part of a H2020-funded project ‘FORGE’ on the production of CCA coatings by using the aforementioned processes to establish an experimental framework for the optimisation of process parameters for each deposition techniques. Process parameter development is being conducted in two phases: (1) screening of input variables using L8 Taguchi design matrix, and (2) optimisation of process parameters using Central-composite and Box-Behnken designs. Optimum process parameters for each deposition technique are being decided based on key performance indicators: deposition efficiency, coating thickness per pass, surface roughness, microstructure (including porosity, cracks, interfacial defects/delamination), interfacial adhesion strength, and microhardness. The paper will also attempt to present correlation between processing parameters, microstructure, properties and performance which is one of the key objectives of the ‘FORGE’ project which received funding from the European Union's Horizon 2020 research and innovation programme (Grant agreement 958457).