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.

Coating deposition regularity depended on orientation difference in PS-PVD plasma jet

The YSZ coatings are prepared by the plasma spray-physical vapor deposition(PS-PVD)technology based on a specific experimental design.The structure,thickness and growth angle of YSZ coatings on the entire circumferential surface of the cylindrical sample are studied.The results indicated that the structure,thickness and deflection growth angle of YSZ coatings are related to the orientation of deposition location.The numerical simulation of the multiphase mixed fluid near the substrate is carried out and the deposition regularity and mechanism of YSZ coatings prepared by PS-PVD is deduced.The growth rate is related to the local characteristics of the plasma flow field,and is directly proportional to the field pressure and inversely proportional to the field velocity.The growth angle of the coating is generally affected by the flow direction of the plasma jet.Especially,the normal component of velocity vector,V_(norm),mainly affects the speed at which the coating grows vertically upwards.The tangential component of velocity vector,V_(tan),determines the degree that the coating growth direction deviates from the vertical direction.When V_(tan)≠0,the coating forms a fine column with a certain deflection angle and finally develops into an oblique columnar structure.

Mechanical properties and simulated thermal conductivity of biomimetic structured PS-PVD(Gd_(0.9)Yb_(0.1))_(2)Zr_(2)O_(7) thermal barrier coatings

Plasma spray physical vapor deposition(PS-PVD)(Gd_(0.9)Yb_(0.1))_(2)Zr_(2)O_(7)(GYbZ)thermal barrier coatings(TBCs)exhibited better silicate-phobicity than coatings produced by electron beam physical vapor depo-sition.In combination with PS-PVD and ultrafast laser direct writing technology,biomimetic structured GYbZ TBCs,with a triple-scale micro/nano surface microstructure,were obtained.Laser ablating on the PS-PVD GYbZ coating enhanced the surface roughness,improving its wear resistance without increasing the surface hardness.Furthermore,during the laser ablation processing,numerous nanoparticles were deposited in-situ in the gaps between columns of the coating,reducing the coating Young’s modulus.The simulated temperature field and heat flux field demonstrated that the presence of numerous interfaces between small columns of the PS-PVD coatings is beneficial to thermal insulation.However,laser ablation decreased the coating thickness,reducing the thermal insulation by around 20%-30%as compared to its PS-PVD counterpart,suggesting that a moderate increase in the coating thickness should be considered when designing an efficient TBC system.