A comprehensive review of thermally sprayed abradable sealing coatings:Focusing on abradability

Modern aero and stationary gas turbine engines have been designed with much higher compressor-pressure ratios and thrust-weight ratios than earlier models,and these ratios are strongly influenced by the hot-running clearances between the rotating and stationary components.The main benefit of reduction in the clearances is efficiency gains,resulting in lowered fuel consumption and polluting gas emissions,with ecological and economic advantages.However,at these undersized clearances,some rubbing interactions are unavoidable,which can be accommodated by applying Abradable Sealing Coatings(ASCs)on the stationary inner surface.This paper reviews the commercially available abradable materials for thermal spraying at various application positions and temperatures.Emphasis is placed on the abradability and wear mechanisms involved.In addition,considering the tendency of SiC/SiC ceramic matrix composites replacing superalloys as hot section components,the future prospect of ceramic abradables based on Environmental Barrier Coatings(EBCs)in turbine stages is summarized and a new concept of"self-degradable ceramics"based on the corrosive steam environment is proposed for the purpose of high-temperature fillerfree abradables.

Corrosion mechanism of CuAl-NiC abradable seal coating system——The influence of porosity,multiphase,and multilayer structure on the corrosion failure

In this study,the corrosion behavior of the CuAl-NiC abradable seal coating system in chloride solution was investigated to systematically research the effect of porosity,multiphase,and multilayer structure on the corrosion failure.Through the composition and structure analysis,the corrosion process of the system was predicted and then verified with mercury intrusion porosimetry,cross-section SEM/EDS analysis,and electrochemical measurements.The results demonstrated that the interphase selective corrosion caused the porosity of the top layer to decrease first and then increase during the corrosion development.The interlayer galvanic corrosion,determined by the pore connectivity,is crucial for corrosion failure.

Homologous layered InFeO3(ZnO)m:new promising abradable seal coating materials

As promising abradable seal coating materials used in high temperature range, the homologous layered InFeO3（ZnO）m （m = 1, 2, 3...20） have attracted great attention. In this short review, we summary the research progress in InFeO3（ZnO）m that were developed in our group. We first introduced a series of conventional abradable seal coating materials as a research motivation. Second, the phase composition and crystal structures of lnFeO3（ZnO）m system were presented. Then, their thermophysical properties, as the most important part, were introduced in detail. At last, the mechanical properties such as hardness, friction coefficient, erosion wear resistance of InFeO3（ZnO）m system were also described. Our summary indicates that InFeO3（ZnO）m sys- tems are promising abradable seal coating materials.

Investigation of high-speed abrasion behavior of an abradable seal rubber in aero-engine fan application

Abradable seal rubber has been widely used in aero-engine fans to improve their efficiency by reducing the clearance between rotating and stationary components. To investigate the high-speed scraping behavior between a vulcanized silicone rubber and a Ti-6Al-4V fan blade and evaluate the abradable performance of seal rubber, abrasion tests were conducted at a blade tip velocity of 50–300 m/s with an incursion rate of 100 lm/s. The influences of the blade tip velocity on the wear mechanism and interaction forces were specially analyzed. It is shown that abrasive wear and pattern wear are the predominant wear mechanisms, and pattern wear can be seen as the emergence and propagation of cracks. With an increase of the blade tip velocity, both of the final incursion depth and wear mass loss of seal rubber exhibit growth trends. The gradual changes of rubbing forces with an increase of rubbing time are the characteristic of abrasive wear, and force curves with unstable mutations are a reflection of pattern wear. At a constant incursion rate of 100 lm/s, the maximum values of interaction forces decrease first and then grow with an increase of the blade tip velocity, and the blade tip velocity of 150 m/s becomes the cut-off point between abrasive wear and pattern wear.