Corrosion behavior of air plasma spraying zirconia-based thermal barrier coatings subject to Calcium–Magnesium–Aluminum-Silicate (CMAS) via burner rig test

Three different kinds of thermal barrier coatings (TBCs) — 8YSZ, 38YSZ and a dual-layered (DL) TBCs with pure Y₂O₃ on the top of 8YSZ were produced on nickel-based superalloy substrate by air plasma spraying (APS). The Calcium–Magnesium–Aluminum-Silicate (CMAS) corrosion resistance of these three kinds of coatings were researched via burner rig test at 1350 °C for different durations. The microstructures and phase compositions of the coatings were characterized by SEM, EDS and XRD. With the increase of Y content, TBCs exhibit better performance against CMAS corrosion. The corrosion resistance against CMAS of different TBCs in descending was 8YSZ + Y₂O₃, 38YSZ and 8YSZ, respectively. YSZ diffused from TBCs into the CMAS, and formed Y-lean ZrO₂ in TBCs because of the higher diffusion rate and solubility of Y³⁺ in CMAS than Zr⁴⁺. At the same time, 38YSZ/8YSZ + Y₂O₃ reacts with CAMS to form Ca₄Y₆(SiO₄)₆O/Y_4·67(SiO₄)₃O with dense structure, which can prevent further infiltration of CMAS. The failure of 8YSZ coatings occurred at the interface between the ceramic coating and the thermally grown oxide scale (TGO)/bond coating. During the burner rig test, the Y₂O₃ layer of the DL TBCs peeled off progressively and the 8YSZ layer exposed gradually. DL coatings keep roughly intact and did not meet the failure criteria after 3 h test. 38YSZ coating was partially ablated, the overall thickness of the coating is thinned simultaneously after 2 h. Therefore, 8YSZ + Y₂O₃ dual-layered coating is expected to be a CMAS corrosion-resistant TBC with practical properties.     

纳米陶瓷的热压烧结及超塑成形(英文)

纳米陶瓷具有优良的室温和高温力学性能 ,如较高的抗弯强度、断裂韧性、耐磨性等 ,使其在切削刀具、轴承、高温发动机部件等诸多方面都有广泛的应用。利用纳米陶瓷的超塑性进行成形加工是实现复杂形状零件近净成形的重要手段。本文采用化学沉淀法制备了平均粒径 10nm ,且无硬团聚的 3Y TZP (3%摩尔氧化钇稳定的四方相氧化锆多晶体 )粉体 ,研究了不同密度素坯的热压烧结行为。 3Y TZP毛坯的超塑性拉深试验表明在 14 5 0℃压头速率为 0 2mm·min-1时可以实现半球形件的成形 ,其成形高度达到 5 7mm ;Al2 O3 ZrO2 纳米复相陶瓷的正挤压试验表明 ,这种典型的晶间 /晶内型纳米陶瓷在很高的温度下可以 0 . 5mm·min-1的压头速率进行挤压成形 ,在某种程度上可以满足工业成形的需求 ;Si3 N4 Si2 N2 O复合陶瓷通过烧结锻造可以成形陶瓷齿轮 ,其烧结温度为 16 0 0℃ ,超塑性锻造温度为 15 5 0℃。     

微弧等离子喷涂制备莫来石/金属复合热障涂层

运用微弧等离子喷涂制备了莫来石/金属复合热障涂层.研究了涂层的微观结构、结合强度、隔热性能和抗热震性能.复合涂层结构为莫来石颗粒被"包裹"在金属层片状结构中;涂层的结合强度大于30 MPa.随着涂层中莫来石含量的增加,涂层的隔热性能有所提高,随涂层表面温度的升高,涂层的隔热温度也不断提高,涂层的最高隔热温度为125℃.1 150℃的水淬热震试验表明,基体变形是导致涂层失效的重要原因之一,随着涂层中莫来石含量的增加,涂层的抗热震次数先增加后减小,粉末中莫来石含量为40%的涂层的抗热震性能最好,抗热震次数最多为72次.     

Erosion, corrosion and erosion–corrosion of EB PVD thermal barrier coatings

Electron beam (EB) physical vapour deposited (PVD) thermal barrier coatings (TBCs) have been used in gas turbine engines for a number of years. The primary mode of failure is attributed to oxidation of the bond coat and growth of the thermally grown oxide (TGO), the alumina scale that forms on the bond coat and to which the ceramic top coat adheres. Once the TGO reaches a critical thickness, the TBC tends to spall and expose the underlying substrate to the hot gases. Erosion is commonly accepted as a secondary failure mechanism, which thins the TBC thus reducing its insulation capability and increasing the TGO growth rate. In severe conditions, erosion can completely remove the TBC over time, again resulting in the exposure of the substrate, typically Ni-based superalloys. Since engine efficiency is related to turbine entry temperature (TET), there is a constant driving force to increase this temperature. With this drive for higher TETs comes corrosion problems for the yttria stabilised zirconia (YSZ) ceramic topcoat. YSZ is susceptible to attack from molten calcium–magnesium–alumina–silicates (CMAS) which degrades the YSZ both chemically and micro-structurally. CMAS has a melting point of around 1240 °C and since it is common in atmospheric dust it is easily deposited onto gas turbine blades. If the CMAS then melts and penetrates into the ceramic, the life of the TBC can be significantly reduced. This paper discusses the various failure mechanisms associated with the erosion, corrosion and erosion–corrosion of EB PVD TBCs. The concept of a dimensionless ratio D/d, where D is the contact footprint diameter and d is the column diameter, as a means of determining the erosion mechanism is introduced and discussed for EB PVD TBCs.     

纳米Al2O3粉体材料激光烧结成型基础试验研究

基于激光烧结快速成型技术 ,利用CO2 激光对纳米Al2 O3 粉体材料进行激光烧结成型的试验并用扫描电镜(SEM)和X射线衍射仪等对烧结样品进行分析。结果表明 ,在适当的工艺参数下 ,对Al2 O3 粉体的激光烧结可获得一定形状的、致密的陶瓷块体 ,块体内部晶粒保持在纳米尺度     

Thermal cycling and hot corrosion behavior of a novel LaPO4/YSZ double-ceramic-layer thermal barrier coating

LaPO₄ powders were produced by a chemical co-precipitation and calcination method. The ceramic exhibited a monazite structure, kept phase stability at 1400?°C for 100?h, and had low thermal conductivity (~ 1.41?W/m?K, 1000?°C). LaPO₄/Y₂O₃ partially stabilized ZrO₂ (LaPO₄/YSZ) double-ceramic-layer (DCL) thermal barrier coatings (TBCs) were fabricated by air plasma spray. The LaPO₄ coating contained many nanozones. Thermal cycling tests indicated that the spallation of LaPO₄/YSZ DCL TBCs initially occurred in the LaPO₄ coating. The failure mode was similar to those of many newly developed TBCs, probably due to the low toughness of the ceramics. LaPO₄/YSZ DCL TBCs were highly resistant to V₂O₅ corrosion. Exposed to V₂O₅ at 700–900?°C for 4?h, La(P,V)O₄ formed as the corrosion product, which had little detrimental effect on the coating microstructure. At 1000?°C for 4?h, a minor amount of LaVO₄ was generated.     

Effect of microstructure and temperature on the erosion rates and mechanisms of modified EB PVD TBCs

Thermal barrier coatings (TBCs) have now been used in gas turbine engines for a number of decades and are now considered to be an accepted technology. As there is a constant drive to increase the turbine entry temperature, in order to increase engine efficiency, the coatings operate in increasingly hostile environments. Thus there is a constant drive to both increase the temperature capabilities of TBCs while at the same time reducing their thermal conductivities. The thermal conductivity of standard 7 wt% yttria stabilized zirconia (7YSZ) electron beam (EB) physical vapour deposited (PVD) TBCs can be reduced in two ways: the first by modification of the microstructure of the TBC and the second by addition of ternary oxides. By modifying the microstructure of the TBC such that there are more fine pores, more photon scattering centres are introduced into the coatings, which reduce the heat transfer by radiation. While ternary oxides will introduce lattice defects into the coating, which increases the phonon scattering, thus reducing the thermal conductivity via lattice vibrations. Unfortunately, both of these methods can have a negative effect on the erosion resistance of EB PVD TBCs.This paper compares the relative erosion rates of ten different EB PVD TBCs tested at 90° impact at room temperature and at high temperature and discusses the results in term of microstructural and temperature effects. It was found that by modifying the coating deposition, such that a low density coating with a highly ‘feathered’ microstructure formed, generally resulted in an increase in the erosion rate at room temperature. When there was a significant change between the room temperature and the high temperature erosion mechanism it was accompanied by a significant decrease in the erosion rate, while additions of dopents was found to significantly increase the erosion rate at room and high temperature. However, all the modified coatings still had a lower erosion rate than a plasma sprayed coatings. So, although, relative to a standard 7YSZ coating, the modified coatings have a lower erosion resistance, they still perform better than PS TBCs and their lower thermal conductivities could make them viable alternatives to 7YSZ for use in gas turbine engines.     

Microstructure and mechanical properties of yttria stabilized zirconia coatings prepared by plasma spray physical vapor deposition

Plasma spray physical vapor deposition (PS-PVD) was used to deposit yttria stabilized zirconia (YSZ) coatings with different columnar morphologies by varying the spray distance. Although similar quasi-columnar structures were formed at the spray distances of 600 mm and 1400 mm, the formation mechanisms of particles in the coatings were different. Besides, an electron beam physical vapor deposition (EB-PVD) like columnar coating out of pure vapor was deposited at a spray distance of 1000 mm and the columnar consisted of elongated nano-sized secondary columns. The hardness and Young׳s modulus of the coatings were investigated. Compared to the other two quasi-columnar structures, the EB-PVD like columnar coating exhibited higher hardness (~9.0 GPa ) and Young׳s modulus (~110.9 GPa), mainly due to its low porosity and defect.     

基于纯声子散射模型的梯度阻热涂层热力分析

梯度阻热涂层(由不同混合比的阻热涂层和底层材料组成)可以降低阻热涂层(陶瓷)材料和底层(金属)材料之间因热失配而产生的热应力.结合纯声子散射模型(用于梯度阻热涂层)与傅里叶热传导模型(用于底层),用数值方法求解梯度阻热涂层的温度场和应力场,研究了阻热涂层参数(松弛时间、声子速度)梯度分布对温度场的影响以及阻热涂层力学性能(弹性模量、热膨胀系数)梯度分布对热应力的影响.结果表明:阻热涂层参数梯度分布能明显减小梯度阻热涂层的温度梯度;阻热涂层力学性能梯度分布能降低梯度阻热涂层的热应力,其中热膨胀系数梯度分布的影响明显大于弹性模量梯度分布的影响.