High velocity air fuel-sprayed thick composite coatings for sustainable refurbishment of engineering components: A viable alternative to hard chrome plating

Electrolytic hard chrome (EHC) plating has traditionally been the preferred technique for surface modification and dimensional restoration for rotary shafts used in turbines, pumps, bearing assemblies, and couplings, due to its excellent wear, corrosion, and oxidation resistance. However, the generation of toxic hexavalent Cr⁶⁺ ions during the plating process poses significant environmental and health hazards, prompting the need for sustainable alternatives. In this context, thermal spray technologies, particularly the high-velocity air-fuel (HVAF) spray, have gained attention as a viable substitute to EHC, offering dense, low porosity coatings with minimal in-flight oxidation and excellent mechanical performance. The study focuses on depositing four feedstock powders of NiCr, SS316L, NiCrBSiFeC, and Tribaloy-400 on Ni-Cr-Mo alloy steel to produce a 1-mm-thick coating employing the HVAF technique. The coatings were evaluated through ball-on-disc sliding wear tests under varied loads, followed by detailed FE-SEM, XRD, and EDAX analysis. Results revealed that the Tribaloy-400 coating exhibited superior wear resistance, with a wear rate of 3.06338E-6 mm³/N · m, outperforming EHC plating (4.19325E-6 mm³/N · m) by 1.5 times under accelerated loading conditions. The enhancement is attributed to the presence of hard intermetallic lave phases (Co_xMo_y and Co_xMo_ySi), which reinforce the metal-matrix composite coating, and significantly improve the sliding wear resistance. The findings establish HVAF sprayed Tribaloy-400 as a sustainable alternative to EHC plating for the refurbishment of industrial shafts operating under demanding conditions.