Microstructure And Mechanical Properties Of Multi-sized Porous Thermal Barrier Coatings

Thermal barrier coatings(TBCs)are used in high-temperature components such as gas turbines and aircraft engines,needing both high thermal insulation and well mechanical properties.Thermal insulation can be improved through the increase of coating thickness.While,the inner stresses are increased which will lead to the failure and falling off the of coatings.Pores are often common in thermal sprayed TBCs.Moreover,closed pores are poor conductors of heat,which can significantly reduce thermal conductivity and improve thermal insulation performance.Although the large pores will reduce the resistance ability to deformation in certain,the small pores will relieve the stress of the TBCs in certain.Therefore,multi-sized pores at nano and micro scale were introduced in TBCs to increase the compatibility of deformation resistance with ensuring high insulation performance at the same time.The porous microstructures and mechanical properties of the TBCs with multi-sized pores at nano and micro scale were investigated.TBCs with multi-sized pores at nano and micro scale were prepared through the transplantation of porous structure in the hollow spherical ceramic powder and the collocation of polyethylene as the pore-forming agent.The porous structure distributions were characterized through scanning electron microscopy and three dimensional X-ray scanning microscopy to test the design of multi-sized pores at micro and nano scale in TBCs.The nano-indentation characteristics of TBCs with multi-sized pores at micro and nano scale were simulated under different loads through the finite element software of Ansys.With the increase of the loads,both the modulus and hardness increased firstly and then decreased.The stimulated resluts were similar with the tested ones.The crack initiation and propagation of a thermal barrier coating with multi-sized pores at micro and nano scale were simulated through the indentation of Berkovich indenter on model with pore units including cohesive forces.Due to the existence of pores,cracks initiated after exceeding the strength of ceramics during the impressing.The stress concentrations were reduced with stresses dispersed into pores for the existence of small pores.Moreover,the interfaces between pores and ceramics increased with the increase of pores,which would consume some energies of the cracks propagation and lead to cease of cracks.The large pores were isolated,which would consume propagation energy greatly of the cracks so as to increase the toughness of the cracks.The stimulated toughness was in agreement with the tested one.The resistance to deformation and deformation recovery were characterized through nano indentation.It was found that pseudo-plasticity existed in the stage of resisting deformation and pseudo-elasticity existed in the stage of deformation recovery with the introduce of multi-sized pores at mico and nano scale into TBCs,which finally increased the abilities of resisting deformation and deformation recovery.Compared with the conventional atmospheric sprayed TBCs,the hardness and the modulus of TBCs with multi-sized pores at micro and nano scale can be increased by 20.23%and 39.16%,respectively.The deformation compatibilities of TBCs with multi-sized pores at mico and nano scal were characterized through nano impact.It was found that the deformation compatibility could be increased greatly for the existence of pseudo-plasticity and pseudo-elasticity.The fracture toughness of multi-sized TBCs at micro and nano scale was increased to 1.047 MPa·m0.5 as compared to the conventional atmospheric sprayed TBCs of 0.73 MPa·m0.5.The toughness was increased by 30.28%.