Effect of Hydrogen in Axial Suspension Plasma Spraying on the microstructure of TBC and its resistance to CMAS solicitation

One of the major advantages of Plasma Spray Suspension is its versatility in producing very different microstructures. These different microstructures can be achieved by varying the process parameters. The parameters that directly influence the microstructure are those that affect the kinetic and thermal properties of the particles. In the case of ASPS spraying using the Axial III Plus torch, Tarasi et al. have shown that gas flow rates have the greatest influence. In particular, the flow of hydrogen, a diatomic gas, is known to have a significant effect on the in-flight treatment of ceramic particles. In the present study, the effect of hydrogen on the in-flight treatment of particles and therefore on the microstructures was investigated using the Axial III Plus torch. Three microstructures with different morphological aspects (porous to dense), different mechanical properties (microhardness, porosity) and different thermal properties (diffusivity) were obtained. The TBCs were characterized on a thermal gradient CMAS test rig in order to study the effect of microstructure on CMAS attack resistance under thermal gradients. This study showed that increasing H2 results in a densification of the TBC, which prevents CMAS infiltration into the coating and affects the CMAS resistance in the thermal gradient test.