Erosion mechanisms of thermally sprayed coatings with multiple phases

Thermally sprayed coatings are frequently subjected to impacts by small solid particles which induce surface erosion. To identify the physical mechanisms associated with such a material removal process, experimental tests as well as detailed computational analyses of porous coatings containing multiple phases are performed. In the experiments, a gas jet erosion test is conducted to measure material loss of coatings with different mixtures of brittle and ductile phases. The results show higher erosion resistances with small volume fractions of metal phase added to predominantly brittle coatings. Following this outcome, the study is directed toward elucidating the physical mechanisms behind the increased erosion resistance. Here, solid particle impacts are simulated with dynamic finite element analyses where material removals and coating's energy absorption behaviors are closely monitored. Furthermore, parametric study is carried out to quantify effects of cracking resistances and plastic dissipation on the erosion rate. The results reveal synergistic effects of fracture energy and plastic deformation. The combined mechanisms allow greater energy absorptions and enhanced erosion resistance in coatings with mixture of ductile phase. These assessments should offer insights into tailoring coatings with optimized composition of ductile phase to increase their performances. The results are also valuable in understanding foreign object damage (FOD) of coatings.