Effect of Stand-off Distance on the Microstructure of Suspension Plasma Sprayed YSZ
Thermal barrier coatings(TBCs)are usually prepared by air plasma spraying(APS)technology and electron beam-physical vapor deposition(EB-PVD)process.However,these two processes cannot balance two following advantages of insulation performance and strain tolerance simultaneously,which will restrict the coating in different applications to some extent.In recent years,the suspension plasma spraying(SPS)with three electrodes has attracted much attention from Chinese and foreign researchers because of its advantages of high energy plasma,nano powder feeding spraying,and a large amount of microporous structure.Suspension plasma spraying technology can contribute to flexibly columnar crystals,inside which layered structures in nano size can also be pertained,resulting in both advantages of insulation and thermal shock resistance characteristics.Therefore,in this work,β-(Ni,Pt)Al coatings was prepared on the surface of DZ411 high-temperature nickel-base superalloy by electrodeposition and gaseous aluminisation treatment.Subsequently,a kind of suspension was prepared with a nano-sized yttria stabilization zirconia(YSZ)into a mixed solution of distilled water and alcohol.Then,8YSZ thermal barrier coatings were sprayed by AXIAL Ⅲ suspension plasma spraying equipment with high energy plasma,in order to obtain the cauliflower-like structure,which was the effective integration of columnar and nano-layered structure.The effect on microstructural changeable regularity of the 8YSZ thermal barrier coatings was systematically explored at different stand-off distance between spraying gun and substrates,e.g.,90 mm,95 mm,100 mm,and 105 mm.Scanning electron microscopy(SEM)and X-ray diffraction(XRD)devices were used to analyze the microstructure of as-deposited and annealed YSZ ceramic coatings at different stand-off distance.The results showed that the YSZ thermal barrier coating obtained by this kind of suspension plasma spraying technology exhibited a cauliflower-like structure.All the sprayed YSZ thermal barrier coatings presented a single non-equilibrium t'ZrO2 phase with the grain structure in micro-nano size.As the stand-off distance between the spray gun and the substrate increased,the crystallinity of the obtained YSZ thermal barrier coating became better due to the longing time of flying powder in high-energy plasma.The surface roughness gradually increased due to the decreased impact force of high-energy plasma with the increasing stand-off distance,and the size of cauliflower-like particles gradually increased.Moreover,the number of internal nano-sized pores in the YSZ thermal barrier coating gradually increased,which could enhance the thermal insulating capability of coatings.After annealing at 1 100℃,the YSZ thermal barrier coating exhibited multiform kind of peeling behavior in varying degrees,interfacial peeling between the YSZ and β-(Ni,Pt)Al coatings,as well as the long-range overlapping behavior of transverse and longitudinal cracks for striking over tens of micrometers across the inner side of YSZ thermal barrier coatings.Finally,only the YSZ thermal barrier coating with a stand-off distance of 105 mm did not have the highest number of micro-nano holes,but also exhibited no obvious coating peeling phenomenon after annealing,due to the adequate thermal melting in the high-energy plasma and lower thermal stress during plasma spraying.A cauliflower like thermal barrier coating is obtained by three-electrode plasma spraying nano YSZ suspension.The effect of different stand-off distances on the microstructure of the coating is investigated.The increase in coating thickness results in good crystallization,high porosity,fewer cracks,and good thermal stability of the coating/substrate interface.
万方数据
维普
