Impact-Angle-Dependent Thermo-Erosive Degradation of Partially Oxidized HVOF NiCr and Mo–25(NiCrBSiFe) Coatings: An Experimental and DQM-Based Analysis

In this study, experimental and differential quadrature method analyses of the decomposition of NiCr and Mo–25(NiCrBSiFe) coatings sprayed onto Ti–31 alloy by the high-velocity oxy-fuel (HVOF) process as a function of impact angle have been performed. The composition of coatings, impact angle, and test temperature effects on the volumetric erosion loss have been systematically studied. The results indicate that for both coatings erosion loss increases as with increasing temperature, the thermal softening of the coating matrix and oxidation assisted material removal play the major role. The erosion rate increased with increasing impact angle, with the maximum erosion observed at 90∘ , followed by 60∘ , while the lowest erosion rate was recorded at 30∘ . The behaviour of Mo–25(NiCrBSiFe) coating is characterised by significantly lower erosion loss throughout the entire testing range when compared to NiCr and is believed to be due to its Mo-rich composite composition and its greater hardness, load-bearing capacity and resistance to temperature-induced plastic deformation. The eosion trends are adequately captured by the proposed approach, as can be seen by the good correlation with the experimental results, particularly from the Differential Quadrature Method (DQM)-based numerical predictions. The study offers a mechanistic explanation of the thermo-erosive degradation of coatings obtained with the HVOF process, and proves that the Mo–25(NiCrBSiFe) system appears to be a promising material for developing a protective coating for Ti–31 alloy for severe erosive and high-temperature conditions.