| As the key component of aircraft,turbine engine plays an important role in the field of aerospace.In order to improve the conversion efficiency of turbine engine,thermal barrier coating technology should be used to improve the service temperature of its hot end components.The turbine blade in the combustor has a bad service environment.According to the aerodynamic/performance/control requirements,the blade structure is usually designed as a complex geometry.On the complex surface,the deposition form and microstructure of the coating will be different with the change of the surface relationship.These differences often affect the service performance of the coating on the turbine blade,resulting in premature functional degradation or even failure of the coating,which is seriously related to the performance and service life of the turbine blade and even the engine as a whole.In order to explore the influence of complex surfaces on the structure/properties and deposition mechanism of coatings,plume like coatings were deposited on three typical surfaces(concave surface/convex surface/tip)by plasma spraying physical vapor deposition(PS-PVD).The obtained coatings were characterized by high-precision nanoindentation,transmission electron microscopy and computer numerical simulation.The main conclusions are as follows(1)When the coating is deposited on the convex surface substrate,the micro-morphology of the coating does not change greatly except for the coating near the corner area,and only the overall tilt phenomenon of the coating appears,with the tilt angle ranging from 9°to 18°.The coating thickness decreases with the increase of spray angles,the lowest is?159.2?m,and the highest is?284.4?m.The results show that the porosity of the coating can be increased significantly by the convex surface relationship up to 21.3%.Nanoindentation results show that the hardness of the coating increases gradually from the bottom to the top,which is consistent with the law when the substrate is flat,but the average hardness of the coating(919.59 N/mm~2)is lower than that of the flat substrate(1007.5 N/mm~2).Combined with the results of numerical simulation,it is concluded that the growth of the coating on the convex surface is driven by not only the growth driving force along the normal of the substrate,but also the lateral migration driving force perpendicular to the normal of the substrate due to the migration of particles,which is the key factor affecting the morphology of the coating.(2)The concave substrate has a significant effect on the coating morphology,especially near the top of concave arc surface,the coating presents a sparse atypical columnar crystal structure,and with the increase of spraying angle,the coating gradually recovers to the typical columnar crystal morphology.In the same way,the coating on the convex surface is inclined in the range of 8°?20°.The coating thickness first decreases and then increases with the enhanced spray angles.The maximum coating thickness is?200.1?m and the minimum is?159.6?m.The closer to the top of the concave arc,the higher the porosity of the coating,up to 32.4%.The nanoindentation results show that the hardness of the coating in this area is different from that of the flat and convex surface coatings,and the hardness of the rapid growth layer in the middle is much lower than that of the top and bottom.The simulation results show that the arc top of the concave surface is impacted by irregular plasma turbulence in many directions,while the other areas of the concave surface are impacted by jet turbulence,and the turbulence degree decreases with the increase of spraying angle.(3)For the coating deposited on the tip sample,the single columnar crystal grows perpendicular to the tangent direction of the corner plane,and the overall structure of the coating shows the radial diffusion phenomenen.The average thickness of the coating(309.8?m)is higher than that of the plat substrate,and the porosity(10.1%)is not different from that of the plat substrate.The nanoindentation results show that the average hardness of the coating on the tip sample is 978.15 N/mm~2,which is consistent with the coating deposited on the plat substrate.The simulation results show that the plasma jet velocity at the tip is high.At this time,more gas atoms will flow through the substrate and be absorbed in unit time.Therefore,the coating at the tip structure grows well and gets higher thickness.(4)After 60 times of water quenching experiments,some less obvious pitting pits began to appear in the central area of the basin.With the progress of water quenching experiments,the pitting pits of the coating in the basin area gradually expanded.After 90 times,the pitting pits expanded to a certain extent and then interconnected,resulting in small-scale coating spalling.After 130 times of water quenching,the coating in the central area of the blade basin changed from small-scale spalling to large-scale spalling,and the spalling coating accounted for 40%of the total coating in the basin area.However,only slight cracks appeared on the back of the blade in 130 times water quenching experiments,and the tip area remained well.It is found that uneven hardness distribution,low Young's modulus and high creep coefficient are the main factors leading to early failure of the coating. |
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