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

Peihu Gao,Dan Zhao,Minxian Liang,Yongchun Guo,Shengcong Zeng,Wei Wang,Zhong Yang,Jianping Li,Can Jin,Bo Zhang,Lu Jia,Baiyang Chen,Yongqing Lu

doi:10.3390/coatings12020165

Peihu Gao, Dan Zhao + Show 11 more

Open Access

https://doi.org/10.3390/coatings12020165

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Abstract

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.

Highlights

The research, development and manufacturing capabilities of gas turbines and aero engines play an important role in the standard in the advanced industrial manufacturing level of a country [1]
With the serving time was extended at high temperatures, the nanopores and the pores formed around the boundaries of the deposited particles gradually disappeared, and the micron-sized macropores connected with each other
In Thakarea’s work, the 8YSZ thermal barrier coating had a fracture toughness of 0.55 MPa·m0.5 [43]

Summary

Introduction

The research, development and manufacturing capabilities of gas turbines and aero engines play an important role in the standard in the advanced industrial manufacturing level of a country [1]. Zirconia will undergo a phase transition from high temperature to low temperature, especially the transition from tetragonal phase to monoclinic phase [7,8,9], which will be accompanied by 5–7% volume expansion [10], resulting in high stress and cracks in the TBCs during thermal cycling. Through the mutual cooperation of micro- and nanopores, their respective advantages can be exerted so that the coating has better comprehensive mechanical properties [15] Pore formers, such as polypropylene (PP), polyether-ether-ketone (PEEK), high-density polyethylene (HDPE), polymethyl methacrylate (PMMA), mesocarbon-microbead (MCMB) carbon powder and so on, could be used to prepare porous TBCs with microns or tens of microns closed pores to adjust the properties of the TBCs [16]. It will be helpful to improve the comprehensive mechanical properties of the TBCs with constructed pores

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