Finite Element Analysis Of Structure And Thermal Stress Of CuAl/PHB Sealing Coating

Thermal stress is an important factor affecting the service performance and service life of abradable sealing coating.In this paper,the relationship among coating structure,thermal stress and properties was studied with Cu7Al/PHB coating as the research object.Firstly,the finite element analysis software ABAQUS was redeveloped by Python language.Based on the two-dimensional simulation model,the influence of coating structure on cooling instantaneous thermal stress under thermal shock was simulated and analyzed,and the structural design of coating is completed.Secondly,according to the optimized structural parameters,Cu7Al/PHB sealing coating was prepared by atmospheric plasma spraying.The influence of coating structure on coating properties was studied,and the relationship between coating structure and coating properties was clarified.For the coating after structural optimization,a two-dimensional finite element model of blade-casing was established by ABAQUS,and the thermal stress of the coating under scraping condition was numerically simulated.The high-temperature and high-speed abrasion test was carried out by using the abrasion tester.The test results verify the rationality of the structural design of Cu7Al/PHB sealing coating.The simulation results of thermal stress under thermal shock show that porosity is an important factor affecting the distribution of thermal stress.When the top-coating is dense,the thermal stress is mainly concentrated at the coating-substrate interface and the side of the coating.When the top-coating is porous coating,the thermal stress distribution is random and mostly concentrated around the pores.The evolution relationship between the coating structure and the peak stress was obtained.The results show that Ni Al bond-coating can slow down the tensile stress in the coating and help to inhibit the formation and propagation of cracks compared with Cu7Al bond-coating.The peak tensile stress on the side of the coating increases with the increase of bond-coating thickness when the thickness of Ni Al bond-coating is 0.02mm～0.2mm,which raises from 20.77MPa to 24.09MPa.The larger the porosity is,the greater the strain tolerance of the coating is.The peak compressive stress at the coating-substrate interface decreased significantly by 18.76 MPa when the porosity of the top-coating is15vol.%～20vol.%.The peak tensile stress at the coating-substrate interface increases with the increase of pore size when the pore diameter of the top-coating is0.04mm～0.10mm,which raises from 22.25MPa to 32.14MPa.Based on the thermal stress simulation results,coating samples with different structural parameters were prepared by atmospheric plasma spraying.The performance test results show that the bonding strength and thermal shock resistance of sealing coating with Ni Al bonding layer are better than the coating with Cu7Al bond-coating.The thickness of the top-coating has a great influence on the bonding strength and thermal shock resistance.Both of them become worse with the increase of the thickness of the top-coating when the thickness of the top-coating is 0.6mm～1.0mm.The porosity of the top-coating is an important factor affecting the surface roughness,hardness,bonding strength and thermal shock resistance.The surface roughness of the coating increases,the hardness and bonding strength decrease with the increase of top-coating porosity when the porosity of the top-coating is 0～20vol.%.The thermal shock resistance is significantly improved with the increase of top-coating porosity when the porosity of the top-coating is 0～20vol.%,the number of thermal cycles increases from10 to 42.Considering the performance of the coating,the appropriate structure of Cu7Al/PHB sealing coating was determined as follows:bond-coating should be 0.1mm Ni Al coating,the thickness,porosity and pore diameter of Cu7Al top-coating should be0.6mm,20vol.%and 0.06mm,respectively.Based on the scraping condition,the thermal stress simulation and abrasion test of the optimized Cu7Al/PHB sealing coating were carried out.The research results show that the coating surface finish and scraping times are important factors affecting the thermal stress of the coating.The thermal stress of the coating increases with the increase of friction coefficient and blade invasion depth,and decreases with the increase of blade invasion speed.The abradable IDR values of the coating are less than 20%when the feed rate is 10μm·s^-1,50μm·s^-1 and 100μm·s^-1,respectively.The structural system Cu Al sealing coating has good abradable performance,which reflects the rationality of the coating structure design.