Heterogeneous layered structure in thermal barrier coatings by plasma spray-physical vapor deposition

The unique columnar structure endows thermal barrier coatings(TBCs)prepared by plasma spray-physical vapor deposition(PS-PVD)with high thermal insulation and long lifetime.However,the coating delamination failure resulting from an intra-column fracture(within a column rather than between columns)is a bottleneck in the solid dust particle impact environment for aero-engine.To clarify the intra-column fracture mechanism,a basic layer deposition model is developed to explore a heterogeneous weak-to-strong layered structure formed by a local transient in-situ deposit temperature.During the PS-PVD,an in-situ deposit surface is continuously updated due to constantly being covered by vapor condensation,showing a transient temperature,which means that the in-situ deposit surface temperature rises sharply in short period of 0.2 s of depositing a thin layer during a single pass.Meanwhile,the increasing temperature of the in-situ deposit surface results in an experimentally observed heterogeneous weak-to-strong structure,showing a continuous transition from a porous weak structure at the bottom region to a dense strong structure at the top region.This structure easily makes the intra-column fracture at the porous weak region.The results shed light on improving TBC lifetime by restraining the intra-column fracture.

Plasma spray-physical vapor deposition toward advanced thermal barrier coatings:a review

Plasma spray–physical vapor deposition(PS–PVD)is a unique technology that enables highly tailorable functional films and coatings with various rare metal elements to be processed.This technology bridges the gap between conventional thermal spray and vapor deposition and provides a variety of coating microstructures composed of vapor,liquid,and solid deposition units.The PS–PVD technique serves a broad range of applications in the fields of thermal barrier coatings(TBCs),environmental barrier coatings(EBCs),oxygen permeable films,and electrode films.It also represents the development direction of high-performance TBC/EBC preparation technologies.With the PS–PVD technique,the composition of the deposition unit determines the microstructure of the coating and its performance.When coating materials are injected into a nozzle and transported into the plasma jet,the deposition unit generated by a coating material is affected by the plasma jet characteristics.However,there is no direct in situ measurement method of material transfer and deposition processes in the PS–PVD plasma jet,because of the extreme conditions of PS–PVD such as a low operating pressure of*100 Pa,temperatures of thousands of degrees,and a thin and high-velocity jet.Despite the difficulties,the transport and transformation behaviors of the deposition units were also researched by optical emission spectroscopy,observation of the coating microstructure and other methods.This paper reviews the progress of PS–PVD technologies considering the preparation of advanced thermal barrier coatings from the perspective of the transport and transformation behaviors of the deposition units.The development prospects of new high-performance TBCs using the PS–PVD technique are also discussed.

Regional characteristic of 7YSZ coatings prepared by plasma spray-physical vapor deposition technique

7 YSZ coating was prepared by plasma sprayphysical vapor deposition(PS-PVD) technique based on a specific experimental design.The microstructure and deposition properties of 7 YSZ coating along the radius of plasma jet were investigated in detail.Results show that the coating presents regional characteristic in the radial direction,which could be divided into three typical zones:In Zone Ⅰ,the coating is all composed of columnar structures with cauliflower structure,and the coating properties including the surface roughness and deposition efficiency(DE) are almost stable;in Zone Ⅲ,the coating is made up of solid particles,droplet and gas phase mixed without columnar structures;Zone Ⅱ is between Zone Ⅰ and ZoneⅢ, in which there are columns with domed top and small particles.Based on experiment results,a model on the state and distribution of particles in plasma jet was proposed to clarify the regional characteristic.This study is helpful to comprehend and control coatings deposition by PS-PVD technique.

A comparison between novel Gd_(2)Zr_(2)O_(7)and Gd_(2)Zr_(2)O_(7)/YSZ thermal barrier coatings fabricated by plasma spray-physical vapor deposition

Spherical Gd_(2)Zr_(2)O_(7)hollow powders with a mean size of 8.8μm were fabricated as feedstock for thermal barrier coatings(TBCs)by spray-drying.The single-ceramic-layer(SCL)Gd_(2)Zr_(2)O_(7)TBCs and double-ceramic-layer(DCL)Gd_(2)Zr_(2)O_(7)/YSZ TBCs with quasicolumnar structure were successfully fabricated by plasma spray-physical vapor deposition(PS-PVD).Tensile and water-quenching tests were applied to evaluate TBCs performances.The results show that adhesion strength of SCL Gd_(2)Zr_(2)O_(7)TBCs and DCL Gd_(2)Zr_(2)O_(7)/YSZ TBCs is36.5 MPa and 15.4 MPa,respectively.The delamination of SCL Gd_(2)Zr_(2)O_(7)TBCs and DCL Gd_(2)Zr_(2)O_(7)/YSZ TBCs in the tensile test takes place at the middle and bottom of Gd_(2)Zr_(2)O_(7)layer,respectively,due to relatively lower fracture toughness of Gd_(2)Zr_(2)O_(7)layer.After 40 cycles of water-quenching test,DCL Gd_(2)Zr_(2)O_(7)/YSZ TBC surface keeps relatively intact,while SCL Gd_(2)Zr_(2)O_(7)TBC surface shows 20%visible destroyed regions,which demonstrates that DCL Gd_(2)Zr_(2)O_(7)/YSZ TBCs have a better thermal shock resistance than SCL Gd_(2)Zr_(2)O_(7)TBCs.The cracks in the SCL system propagate near thermally grown oxide(TGO)due to thermal mismatch and TGO growing stress,while cracks in the DCL system propagate in the Gd_(2)Zr_(2)O_(7)layer due to its relatively lower fracture toughness.

不同制备工艺参数对PS-PVD-8YSZ涂层微结构及性能的影响

作为新型热障涂层工艺制备技术,等离子物理气相沉积(PS-PVD)射流具有高能高速等特性,涂层沉积时存在扰流作用导致涂层微结构及性能的显著影响。为了减少圆柱体工装扰流作用,掌握工艺参数对涂层微结构的基本影响规律,采用平面工装系统研究不同PS-PVD工艺参数下,如喷涂电流、送粉量、喷枪摆动及样品旋转参数等对涂层微结构的影响规律。研究结果表明:送粉量和喷枪-样品相对运动参数对涂层微结构影响较大,可快速实现涂层微结构的调控;喷涂电流的变化通过柱状晶尺寸和冷凝纳米颗粒含量等方面影响涂层微结构,涂层显微硬度随喷涂电流增大而降低;喷涂沉积距离的影响较小,喷涂距离增大使沉积效率和柱状晶发散生长程度降低,冷凝纳米颗粒含量提高,同时涂层显微硬度呈现先降低后升高的趋势。JL-11NP粉末表现出宽幅工艺范围内准柱状结构的获得能力,进一步掌握低沉积电流工艺条件下基于气-固-液三相复合沉积的影响规律。开展了低电流工艺参数条件下PS-PVD涂层的微结构调控及沉积机制研究,研究成果可为兼顾隔热和寿命、抗冲蚀的涂层性能结构优化及调控奠定良好基础。

Al-modification for PS-PVD 7YSZ TBCs to improve particle erosion and thermal cycle performances

Plasma spray-physical vapor deposition(PS-PVD)as a novel process was used to prepare feather-like columnar thermal barrier coatings(TBCs).This special microstructure shows good strain tolerance and non-line-of-sight(NLOS)deposition,giving great potential application in aero-engine.However,due to serious service environment of aero-engine,particle erosion performance is a weakness for PS-PVD 7YSZ TBCs.As a solution,an Al-modification approach was proposed in this investigation.Through in-situ reaction of Al and ZrO2,anα-Al2O3 overlay can be formed on the surface of 7YSZ columnar coating.The results demonstrate that this approach can improve particle erosion resistance since hardness improvement of Al-modified TBCs.Meanwhile,as another important performance of thermal cycle,it has a better optimization with 350-cycle water-quenching,compared with the as-sprayed TBCs.