Laser surface modification of plasma sprayed CYSZ thermal barrier coatings

In this study, Inconel 738 LC superalloy coupons were first sprayed with a NiCoCrAlY bond coat and then with a ceria and yttria stabilized zirconia (CYSZ) top coat by air plasma spraying (APS). After that, the plasma sprayed CYSZ thermal barrier coatings (TBCs) were treated using a Nd:YAG pulsed laser. The effect of laser glazing on the microstructure of the coatings was investigated. The microstructures and surface topographies of both as-sprayed and laser glazed samples were investigated using field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). The phases of the coatings were analyzed with X-ray diffractometry (XRD). The microstructural analysis results revealed that laser surface glazing of ceramic top coat reduced the surface roughness considerably, eliminated the surface porosities and produced a network of continuous cracks perpendicular to the surface. XRD patterns also showed that both as-sprayed and laser glazed top coats consisted of nonequibrium tetragonal (T′) phase.     

Evaluation of hot corrosion behavior of plasma sprayed ceria and yttria stabilized zirconia thermal barrier coatings in the presence of Na2SO4+V2O5 molten salt

In this study, substrates of Inconel 738 LC superalloy coupons were first sprayed with a NiCoCrAlY bondcoat and then with a ceria and yttria stabilized zirconia (CYSZ; ZrO₂−25 wt%CeO₂−2.5 wt%Y₂O₃) topcoat by air plasma spraying (APS). Hot corrosion studies of plasma sprayed thermal barrier coatings (TBCs) were conducted in 45 wt%Na₂SO₄+55 wt%V₂O₅ molten salt at 1000 °C for 30 h. The results showed that the coating defects, such as pores and microcracks play important roles as effective paths for the salt penetration in hot corrosion. Based on the results, the reaction between molten salt and stabilizers of zirconia (Y₂O₃ and CeO₂), the formation of YVO₄, CeVO₄ and CeO₂ crystals, the detrimental phase transformation of zirconia from tetragonal to monoclinic due to the depletion of stabilizers and finally, the creation of stresses were recognized to be in the degradation mechanism of CYSZ ceramic coatings in the presence of molten sulfate–vanadate salt.     

Hot corrosion and thermal shock resistance of Dense-CYSZ/YSZ bilayer thermal barrier coatings systems applied onto Ni-base superalloy

Bilayer thermal barriers coatings of Dense Ceria-Yttria-Stabilized Zirconia (D-CYSZ)/Yttria-Stabilized Zirconia (YSZ) were deposited onto Inconel 625 using atmospheric plasma spray (APS). The thickness of the d-CYSZ layer varied (0, 50, 100, and 150 μm), but the total thickness of the system was kept at 300 μm. The thermo-mechanical resistance of the multilayer system was evaluated through thermal shock tests, in which the bilayer systems evaluated exceeded 500 cycles with percentages of delamination of the coating below 20 % of the exposed area and showed higher thermomechanical resistance than a conventional YSZ system. Hot corrosion (HC) resistance of the bilayer system was evaluated using a salt mixture of 32 wt.% Na₂SO₄ and 68 wt.% V₂O₅ at 900 °C. The systems with a d-CYSZ layer showed higher resistance to HC, exhibiting fewer changes into the microstructure and presence of the monoclinic phase despite the presence of vertical cracks in the microstructure.     

氧化铈稳定纳米氧化锆高温性能的研究

等离子喷涂热障涂层技术广泛应用于航空发动机热端部件的高温防护。应用大气等离子喷涂法成功制备了纳米氧化铈氧化钇稳定的氧化锆(CYSZ)涂层,并与常规氧化钇稳定氧化锆(YSZ)涂层在1300℃下热处理10小时,研究高温对两种涂层性能的影响,与常规的YSZ涂层相比,CeO2的掺杂使涂层具有更高的稳定性。经过高温处理,CYSZ涂层的相结构没有发生明显变化。显微形貌结果表明,CYSZ涂层没有产生裂纹缺陷,涂层中纳米区域晶粒度随着温度的升高略有增大,这表明了纳米结构的CYSZ涂层具有更优异的高温稳定性。热循环氧化实验结果证明,CYSZ涂层具有更长的热循环寿命以及优异的高温抗氧化性能。     

Plasma-sprayed nanostructured scandia-yttria and ceria-yttria codoped zirconia coatings: Microstructure,bonding strength and thermal insulation properties

Microstructure, thermal insulation behavior and bonding strength of nanostructured 5%scandia, 0.5%yttria codoped zirconia (5.5 ScYSZ) and 25%ceria, 2.5%yttria co stabilized zirconia (27.5%CYSZ) coatings were investigated. ScYSZ and CYSZ nanostructured granules (as a top coat) and commercial NiCrAlY powder (as a bond coat) were thermal sprayed on an Inconel 738 substrate. The results revealed ScYSZ coating to have higher bonding strength. Nevertheless, due to higher porosity and the presence of local strains, the thermal insulation of nanostructured CYSZ coating was higher than for ScYSZ coating.     

等离子喷涂CeO2-Y2O3稳定ZrO2陶瓷涂层耐高温铁水热震研究

采用等离子喷涂方法在304不锈钢表面制备NiCoCrAlY2O3/(ZrO2+25 %CeO2+3 %Y2O3)耐高温涂层,模拟铸造模具表面的工作环境,涂层在1350 ℃铁水液中加热热震和在炉中大气环境下加热热震后,对涂层组织结构和物相变化进行了对比研究.结果表明:涂层在铁水中热震后,涂层内部的大量裂纹交联在一起,在陶瓷层与粘结层界面靠近陶瓷层一侧出现尺寸近10 μm宽的裂纹,陶瓷层中的部分四方相向单斜相和立方相转变,铁水中部分元素与陶瓷元素发生了扩散并生产新相.     

CeO_2-Y_2O_3-ZrO_2热障涂层的组织结构及隔热性能

为获得孔隙率高、隔热性能好的热障涂层CeO2-Y2O3-ZrO2(CYSZ),采用低温超音速火焰喷涂(LT-HVOF)和大气等离子喷涂(APS)工艺在K4169镍基高温合金表面分别沉积NiCoCrAlYTa粘结层和CeO2、Y2O3共同稳定的ZrO2空心粉CYSZ陶瓷层。通过扫描电子显微镜(SEM)和X射线衍射仪(XRD)对不同喷涂电流(500,600和700A)制备的CYSZ热障涂层和采用传统Y2O3稳定的ZrO2团聚粉7YSZ为陶瓷面层的热障涂层的组织结构进行观察分析,并测定其隔热性能。结果表明:与传统的7YSZ类似,CYSZ涂层主要组成相为四方t相,涂层呈典型层状结构,但相对于7YSZ,空心粉CYSZ涂层存在更多孔隙和微裂纹;在1 150℃时,随着喷涂电流的增大,隔热性能呈降低趋势,CYSZ涂层隔热性能比传统7YSZ涂层隔热性能好。