Preparation And Performance Research Of YSZ Ceramic-based Abradable Sealing Coating

With the rapid development of aero engines,there are more and more demands on its efficiency.At present,reducing the gap between the turbine tip and the casing to improve the seaing technology and the engine efficiency is an important method.Therefore,in order to solve the problem of the low efficiency in gas turbine and aerospace engine under the noral working conditions,the study suggests a suitable abradable seal coating for spraying on the surface of the stator and rotor.As a sacrificial coating,abradable seal coating can grately improve the gas closure technology of gas turbines and aerospace engines,it can also improve the overall efficiency and performance of the engine to extend the service life.Therefore,the research and application of the abradable seal coating is a key issue in the worldwide aerospace industry.The paper summarizes the common gas path sealing technology in the aviation industry,and the similarities and differences between different technologies are presented.Meantime,there are some brief introductions and summaries in recent common abrasable seal coating,including domestic and foreign researchments.It mainly focus on the analysis and determination in the composition and ratio of coatings.In performance,the abradable seal coating needs the abradable,a certain strength and hardness to resist the external erosion.In order to meet the contradictory performance of the coating,the paper designed a variety of YSZ ceramic abradable seal coatings,those materials including YSZ,Ni,h BN and PHB.The paper fabricates YSZ ceramic sheets by ball milling and solid phase sintering under the certain conditions,including 8YSZ,9YSZ,10 YSZ and 11 YSZ.Following that,YSZ ceramic blocks are tested and analyzed in morphology and performance.By comparision,the performance of 8YSZ is much better than 9YSZ,10 YSZ and 11 YSZ,including parts of the thermal and mechanical properties.In the subsequent experiments,4%,6%,8% and 10% of the binder phase material Ni are added to 8YSZ via ball milling to prepare 8YSZ ceramic block dopped with Ni.Simarily,the same mass of Ni was added to 9YSZ and 10 YSZ to prepare 9YSZ and 10 YSZ ceramic blocks.Then,the surface,cross-section and performance of YSZ ceramic sheets are tested,the thermal expansion coefficient,hardness and thermal conductivity are analysed.By comparision,when the amount of Ni addition is 4% in 8YSZ,the comprehensive performance is much superior than other YSZ ceramic sheets.Therefore,it is sure that 8YSZ is the based material for preparing the following abradable seal coating.The lubricant h BN,including 4%,6%,8% and 10%,are added to 8YSZ by ball milling method,then 8YSZ ceramic sheets with the h BN addition are fabricated via the solid phase sintering.By observing the molding conditions and surface morphology,it is more suitable to add 4% lubricant h BN in 8YSZ,too much or little h BN does not meet the coating requirements.The 8YSZ ceramic sheets dopped with 4%,6%,8% and 10% pore former PHB are prepared by ball milling and solid phase sintering.The morphology and properties of samples are repectively analysed.According to the cross-sectional morphology,the PHB doping amount is much higher,the porosity of 8YSZ is much higher.And by the comparision of thermal expansion coefficient and thermal conductivity under the different doping amounts,the overall performance is much better in 8YSZ under the addition of 4% PHB.To further study the amount of Ni in 8YSZ,4%,6%,8% and 10% Ni are respectively added to 8YSZ dopped with 4% h BN and 4%PHB.Then,8YSZ-based ceramic blocks with different Ni contents are prepared by solid phase sintering.The surface,cross-section and properties are tested and analysed.It can be determined that the comprehensive performance of the 8YSZ-based cermic blocks are much better when Ni content is 4%,which can be used as a raw material ratio for preparing an abradable seal coating.Single-layer and double-layer coatings are prepared on Fe and 321 stainless steel substrates by atmospheric plasma spraying.In the paper,three kinds of pre-sprayed powders are designed: the first kind is pure 8YSZ powder,the second is 8YSZ powder with 4%Ni,third is 8YSZ powder with the addition of 4%Ni,4%h BN and 4%PHB.One transition layer is Ni Co Cr Al Y alloy powder.Two base materials are Fe and 304 stainless steel respectively.There are 16 kinds of coatings for single and double layer structures involved in this paper.By comparision of porosity,deposition rate,hardness,bond strength,thermal shock resisitance of coatings,it is proposed to add 4%Ni,4%h BN and 4%PHB in 8YSZ powder,and then use plasma spraying technology to prepare an excellent abradable seal coating,which is benefit to improve the pereformance of the engine under working conditions and protect the engine.