Study On Preparation And Properties Of Al-based Abradable Sealing Coatings

Al-based abradable sealing coatings are mainly used in aeroengine fans and low-pressure compressors at temperatures below 450 °C.By preparing a certain thickness of "soft" and easy-scratching coating on the casing wall,the radial clearance between the rotating blades of the engine and the stator casing is reduced.While reducing the air leakage area of the engine,making the compressed air flow better through the gap between the blades,and further improving the fuel thrust-to-weight ratio,when the blades and the coating move relative to each other,it protects important parts by sacrificing the wear of part of the coating.The rotating blades are not subject to a lot of wear,which improves the stability of the engine operation.However,in practical application conditions,Al-based abradable sealing coatings represented by Al/hBN sealing coatings are prone to high coating scraping wear rate,high maintenance frequency,and a large amount of material transfer at the blade tip.Layer grinding is easy to generate large pieces of material peeling off,which increases engine maintenance and repair costs,and also brings a lot of potential safety hazards to the smooth operation of aero-engines.The main research in this paper is as follows: by using the atmospheric plasma spraying process,the Al/hBN sealing coating is optimized in terms of technology;hBN composite powder,to study the comprehensive properties of the coatings after deposition of different powders,such as the Rockwell hardness of the coating surface,the bonding strength,the content of non-metallic components of the coating,and the wear performance at 450 °C.Electron microscope,X-ray diffraction analysis and other means are used to characterize the coating morphology and phase composition,and analyze the microscopic mechanism of coating performance change.The specific research results are as follows:(1)The optimization results of the Al/hBN sealing coating process are as follows: the current is 400 A,the spray distance is 110 mm,the argon flow rate is 35L/min,and the hydrogen flow rate is 8L/min.Among them,the spray distance has a major influence on the mechanical properties of the coating.The reason is that the molten powder particles with high metal phase components fly in the plasma flame for a long time,and the temperature of the metal components decreases faster.The influence of overall hardness and tissue distribution becomes more and more significant.Argon flow has the strongest effect on the retention of non-metallic phase of the coating.Within a certain range,the higher the density of the plasma jet,the lower the heat contained in the unit plasma,the smaller the jet flow rate per unit time,the slower the jet velocity,the lower the degree of burning loss of the non-metallic hBN phase components in the powder,and the higher the retention rate.,the higher the hBN retention ratio of the Al/hBN coating formed after deposition,the more conducive to the improvement and control of the comprehensive wear performance of the coating.(2)Benefiting from the good coating effect of dendritic Cu on Al and hBN in CuAl/hBN powder,compared with Al/hBN coating,CuAl/hBN coating has a smaller hBN burning loss ratio,and the internal The hBN components and pore distribution are more continuous,and the tissue composition is more uniformly dispersed.The bonding strength decreased slightly,and the surface Rockwell hardness increased slightly,but the fluctuation of the hardness value was more stable.In the low linear speed scraping wear test,the CuAl/hBN sealing coating has less mass loss and less mass transfer of the coating on the friction pair.At the same time,the surface topography of the wear scar is more stable,and the wearability is better.(3)The current density mainly controls the plasma spraying power and changes the overall temperature of the flame to achieve the purpose of controlling the melting effect of the powder,thereby affecting the Rockwell hardness of the coating surface.Higher powder melting effect and higher plasma flame enthalpy can improve the overall hardness of CuAl/hBN coating.Argon flow is the most important factor affecting the N retention of the coating.Comparing the K value of argon flow rate to N retention in CuAl/hBN and Al/hBN coatings,it can be seen that CuAl/hBN has better protection effect on non-metallic hBN components than Al/hBN.(4)In the wear experiment at 450℃,the CuAl/hBN coating wears and a mixed transfer layer is formed at the contact surface of the friction pin.With the increase of hBN content,the IQR value of the mass wear ratio first increased and then decreased,the degree of coating wear decreased,the size of the shedding abrasive particles decreased,and the wear behavior showed more adhesive wear and oxidative wear.When the hBN content in the original powder is 20%,the IQR of the CuAl/hBN coating is-0.13%,which has better wearability.At the same time,the research shows that too high hBN content can easily lead to too high local temperature in the contact surface area,resulting in softening of the friction pair material,which is not conducive to the protection of the friction pair.