Mechanical Properties of Multi-Sized Porous Thermal Barrier Coatings at Micro and Nano Scales after Long-Term Service at High Temperature

Atmospheric plasma-sprayed multi-sized porous structures in thermal barrier coatings (TBCs) were constructed with hollow spherical (HOSP) 8YSZ powders and polypropylene pore formers. The mechanical properties of the multi-sized TBCs were investigated through the nanoindentation method as comparations of the as-sprayed coating and those serving at 1100 °C for a long-term. The results showed that the introduction of the multi-sized pores into TBCs could lead to the decrease of the hardness and modulus as well as the increase of fracture toughness. The hardness and modulus of the coating increased, and the fracture toughness of the coating decreased with the prolongation of the serving times at high temperatures. The mechanical properties of the coating became stable after 60 days’ serving at 1100 °C. The hardness, elastic modulus and fracture toughness of the TBCs increased to 6.51, 7.79, 10.04 GPa and 126.36, 135.13, 145.22 GPa as well as 1.049, 1.157, 1.255 MPa·m0.5, respectively, corresponding to the multi-sized porous TBCs with 0%, 10% and 15% PP powders. The nano-size pores disappeared gradually in the multi-sized TBCs during serving at 1100 °C. The macropores deposited between the ceramic particles penetrated with little diffusion and were not easy to disappear. The introduction of a multi-scale pore structure into the TBCs could improve the stress-strain tolerance of the TBCs.