高抗热震性红外辐射涂料的实验研究

针对红外辐射涂料在不同基体表面上应用时出现的涂层易脱落问题 ,采用正交实验设计对不同配方的过渡金属氧化物系红外辐射涂料进行了涂层高温抗热震性实验研究。优化配方制得的红外辐射涂料既适用于 1Cr18Ni9Ti金属基体又适用于耐火材料基体 ;与国外相关产品相比 ,其抗热震性能更佳。     

Microstructure and fracture toughness of in-situ nanocomposite coating by thermal spraying of Ti3AlC2/Cu powder

The low fracture toughness of ceramic coatings has always hindered their wide application. In this study, an in-situ nanocomposite coating was prepared by the atmospheric plasma spraying of a 50 wt% Ti₃AlC₂-50 wt% Cu mixed powder. The in-situ nanocomposite coating was found to have an unusual microstructure with a nano-micrometre phase synergistic enhancement, which consisted of submicrometre-thick layers of Cu and nanoparticles of Cu(Al), Ti₄O₅, TiO₂, and Al₂TiO₅. Thus, in the spraying process, Al was delinked out of Ti₃AlC₂, forming a large amount of plastic Cu(Al) with Cu. The delinked channel provided a path for Cu to diffuse into Ti₃AlC₂, which a spatial Cu network structure was formed in the coating. The in-situ nanocomposite coating has high fracture toughness and crack growth resistance by a three-point bending test. This paper reports a new method to prepare a high-fracture-toughness composite ceramic coating.     

纳米ZrO2对MgO-CaO材料烧结及抗热震性的影响

在≤0.1mm的MgO-CaO砂中分别加入占其总质量2%、4%、6%和8%的纳米ZrO2,分别经干混、压制成型,1600℃3h煅烧后,检测其体积密度和抗热震性,并进行XRD和SEM分析,以研究添加纳米ZrO2对MgO-CaO材料烧结和抗热震性能的影响及其作用机理。结果表明:添加2%的纳米ZrO2即可显著提高MgO-CaO材料的烧结程度和抗热震性;综合考虑MgO-CaO材料的烧结程度和抗热震性认为,添加6%的纳米ZrO2可使材料获得良好的性能。     

Multilayer gradient rare earth disilicate coating prepared by in-situ melt infiltration and sintering method with high thermal shock resistance on porous Si3N4 ceramics

Dense multilayer gradient rare earth disilicate (γ-Y₂Si₂O₇ /β-Yb₂Si₂O₇ /β-Lu₂Si₂O₇) coatings were in-situ prepared by melt-infiltration /sintering procedure on porous Si₃N₄ ceramics for water resistance. Experimental and numerical simulation methods were used to study their thermal shock behavior. As a control, thermal shock behavior of pure γ-Y₂Si₂O₇ coatings were also compared. FEM results showed that the gradient design of modulus in ceramic coating can effectively avoid the mismatch of mechanical properties between coating layer and internal substrate, reducing the transient thermal stress in each layer during thermal shock. All of the pure γ-Y₂Si₂O₇ coatings were failed after thermal shock tests with ΔT ≈ 1200 ℃. However, when sintering temperature of multi-layer disilicate coatings were higher than 1400 ℃, the water absorption rates after thermal shock were all less than 5%, still showing good waterproof performance. The gradient design of modulus could effectively improve the structural stability of ceramic coatings.     

Thermal failure of thermal barrier coating with thermal sprayed bond coating on titanium alloy

A thermal spray technology high-velocity oxygen fuel (HVOF) was used to deposit NiCoCrAlY as a bond coating between the titanium alloy substrate and top 8 wt% yttria-stabilized zirconia thermal-barrier coating (TBC) deposited by electron beam-physical vapor deposition (EB-PVD). The thermal cycling and isothermal exposure tests were conducted to evaluate the durability of the TBC. Investigations using OM, SEM, EPMA, and XRD revealed that the thermal-sprayed BC makes the TBC more durable in isothermal exposure tests but more short-lived in thermal cycling tests, in comparison to our previous study in which the BC was prepared by EB-PVD. This is because the thermal-sprayed imperfections, such as microcracks and voids, elevate the diffusion resistance and degrade the mechanical properties of the BC, simultaneously. To current TBC systems in which the BC is deposited by HVOF, thermal failure behaviors—such as the formation of the Ti/Al mixture oxides at some individual places in the BC, and the Ti₂Ni gaps formed around the BC/substrate interface—were also discussed.     

The enhanced thermal shock resistance and combustion efficiency of SiC reticulated porous ceramics via the construction of multi-layer coating

SiC reticulated porous ceramic (SRPC) as the key component determined the service life and combustion characteristics of porous burner. The novel multi-layer struts were constructed to synergistically improve the oxidation resistance and infrared radiation of SRPC, including microporous cordierite coating, dense mullite transition layer, SiC skeleton and filling layer. The continuous mullite transition layer significantly improved the resistance to water vapor oxidation of SRPC, also their strength and thermal shock resistance were enhanced because the elimination of strut defects in multi-layer struts. In addition, the microporous cordierite coating generated from the burnt out of pitch increased the burner surface temperature from 764.4 °C to 1061.7 °C, and obviously reduced the CO/NOx emission due to its improved infrared radiation property. Furthermore, the porous cordierite coating enhanced the heat radiation of SRPC, thus increasing the heating rate of the burner from 29.4 °C/min to 33.1 °C/min in the process of water heating.     

炭/陶复合材料的抗热震性能研究

对含石墨的炭／陶复合材料优良的抗热震性能进行了讨论。这种性质与石墨的导热系数大、断裂功高、热膨胀和弹性模量小密切相关。     

金属基耐高温陶瓷涂层抗热冲击性能的研究

为提高金属基陶瓷涂层的抗热冲击性能，以无机胶粘剂磷酸二氢铝、耐磨陶瓷骨料氧化铝、碳化硅和氧化镁混合后涂覆于金属表面制得陶瓷涂层。通过交替加热及冷却试验测试该陶瓷涂层的抗热冲击性能，并与其他人的研究数据进行比较。所得涂层抗热冲击次数超过10次，超过了其他人的实验数据，这是由于涂层与基体在界面处相互扩散形成过渡层。另外，宏观上的机械联锁有利于提高涂层与基体在界面处的结合，从而提高了其抗热冲击性能。     

Microstructure and thermal shock resistance of AlBOw- and BNw-whisker-modified thermal barrier coatings

To improve the crack propagation resistance of YSZ thermal barrier coatings during the thermal cycle, three kinds of thermal barrier coatings were prepared by atmospheric plasma spraying: YSZ, AlBOw-modified YSZ and BNW-modified YSZ. SEM, EDS and XRD were used to analyse the morphology, composition and phase composition of the sprayed powder and coating section. The phase structures of the YSZ, YSZ+AlBOw and YSZ+BNw coatings were t' phase. The cross-section of the coating presents a layered structure with pores inside. The porosity values of the YSZ, YSZ+AlBOw and YSZ+BNw coatings are 10.33%, 14.17% and 12.52%, respectively. The thermal shock resistance of three groups of coatings after 5 min at 1000 °C was analysed. The failure behaviour of the coatings after several thermal cycles was studied. The results show that the thermal shock resistance of the coatings with AlBOw is slightly lower than that of the YSZ coatings. The thermal shock resistance of the BNw coatings is 62.2% higher than that of the YSZ coatings. The whisker inhibits the crack propagation and prolongs the life of the coatings via crack deflection, whisker pull-out and whisker bridging.     

Effect of MgO on thermal shock resistance of CaZrO3 ceramic

In order to improve the thermal shock resistance of CaZrO_3, CaZrO₃ was synthesized by a solid-state reaction method with analytical ZrO₂ and CaCO₃ as raw materials, and MgO as additive. The effects of MgO on Flexural strength at room temperature, thermal shock resistance, XRD and microstructure of CaZrO₃ were characterized. The results show that the grain growth of CaZrO₃ is inhibited and the thermal shock resistance of CaZrO₃ is improved by adding MgO. With the increasing of MgO, the flexural strength at room temperature of samples are improved due to the grain refinement. When the addition of MgO is 8%, the flexural strength at room temperature increases to 270.15?MPa. The thermal shock resistance of samples are improved by MgO deflecting and bridging cracks. When the addition of MgO is 4%, the residual flexural strength of samples is the maximum (26.94?MPa).     

Improved thermal shock resistance of SiCnw/PyC core-shell structure-toughened CVD-SiC coating

In-situ SiC nanowire (SiCnw)/pyrolytic carbon (PyC) core-shell structures were introduced to mainly improve the thermal shock performance of chemical vapor deposition (CVD)-SiC coating on carbon/carbon (C/C) composites. The microstructure, phase composition, and mechanical properties of the CVD-SiC coating toughened by SiCnw/PyC core-shell structures were studied as well. The results show that the introduction of SiCnw/PyC core-shell structures can effectively alleviate the mismatch of coefficient of thermal expansion (CTE) between SiC coating and C/C substrate, thus enhancing the thermal shock resistance of the coating. Furthermore, the increased numbers of interfaces in the SiC coating owing to the addition of core-shell structures are beneficial to the mechanical properties of the coating after thermal shock test.     

微弧氧化陶瓷膜的性能研究

微弧氧化是一种新兴的金属材料表面陶瓷化处理技术。利用微弧氧化技术在纯铝和LY12铝合金表面制得陶瓷膜，推导出膜层厚度的计算公式，研究了陶瓷膜的硬度、耐蚀性、孔隙率、电绝缘性和热稳定性。结果表明，微弧氧化陶瓷膜层各项性能优异，具有很好的应用前景。     

Heat treatment effect on coating shock resistance of thermal barrier coating system with different types of bond coat

The effect of heat treatment, growth of the TGO layer, oxidation of bond coat, and the impact of the presence of two bond coats on the TBC's thermal shock resistance has been investigated experimentally. TGO oxide layers were created with two-time heat treatment of 12 and 24 h at 1000. Then the thermal shock test was performed on the APS/APS and HVOF/APS/APS samples. The results show that the use of two BCs and the presence of a thin TGO layer has a good effect on TBC performance. The presence of two BC layers increased the shock resistance by an average of 37.2%. 12 h heat treatment caused a 14.0% and 17.4% shock resistance increase in samples with the HVOF/APS/APS layer and APS/APS layer, respectively. 24 h heat treatment decreased the samples' performance by 6.7% and 10.2% for samples with two BC and one BC, respectively.     

Thermal shock resistance of thermal barrier coating with different bondcoat types and diffusion pre-coating

This paper investigates the resistance of two types of thermal barrier coatings and compares their behavior with common coatings. Coatings’ layers in the first and second target sample were fabricated as HVOF/APS/APS (two bondcoats and one topcoat) and APS/APS (one bondcoat and topcoat) with diffusion pre-coating, respectively. Also, to accurately compare the behavior of these two types of coatings with conventional coatings used in gas turbines, this paper explored the resistance of three types of coatings applied as APS/APS, HVOF/APS, and HVOF coatings against thermal shock. In order to create shock loading, five types of laboratory samples were heated under regular cycles and cooled down with water. During the experiment, the sample changes caused by thermal shock loading were investigated through visual inspections. Then, after the experiment, the SEM images were leveraged to inspect the changes. In addition, changes in the structure of coating layers and their degradation process were studied. The results show that using two bond layers increases the resistance and life of the coating against heat shock by up to 1.40 times. Among the samples with one band coat, the sample with a diffusion coating applied under the BC showed the best performance. The sample life increased by 1.25 times compared to the common APS/PAS coating.     

Thermal shock resistance of rare-earth doped in-situ SiAlON reinforced h-BN matrix ceramics under vacuum thermal cycling

In-situ SiAlON reinforced BN-matrix ceramics were prepared by hot pressing sintering, and the effects of different rare earth oxides on the thermal shock resistance of the materials were investigated. The effects of rare earth oxides on the phase composition, microstructure, bending strength, thermal properties and thermal shock resistance of the composites were studied. The results show that the phase composition and bending strength of ceramics with different rare earth oxides had no obvious change. However, the influence on the thermal expansion coefficient of the material was notable. The thermal expansion coefficient of the ceramics with CeO₂ increased by 24.6% compared with Sm₂O₃ in the test temperature range. After 50 cycles of thermal shock at Δt = 1150 °C, the residual strength of ceramics with CeO₂ was down to 157.1 MPa, decreased by 40.6% compared with the one tested in room temperature. And the Sm₂O₃-added ceramics reduced by 34.7%–167.1 MPa after thermal shock. The decrease of the residual strength of ceramics is mainly caused by the internal stress generated by the mismatch between the growth of quartz and SiAlON phase in the matrix and the thermal expansion coefficient of the matrix. However, no macro cracks were observed on the surface of the samples after thermal shock.     

Changes in thermal conductivity and thermal shock resistance of YSZ-SiO2 suspension plasma spray coatings according to various raw material particle sizes

Recently, a technique for improving the thermal efficiency of automotive engines has received considerable attention, namely the application of thermal insulation coatings to automotive engine components to reduce heat loss. This study presents thermal shock resistance and related microstructural changes and thermal properties of 8 wt% yttria-stabilized zirconia (8YSZ)/SiO₂ multi-compositional thermal insulation coatings with suspensions of various particle sizes, when subjected to suspension plasma spray. After 10,000 cycles of thermal shock testing of the coatings, it was found that different degradation behavior related to the different microstructure of the coatings was influenced by the particle sizes of the suspension. The thermal conductivity of the coatings was significantly reduced by increasing the distribution of the unmelted particles within the coating.     

Improvement in thermal shock resistance of gadolinium zirconate coating by addition of nanostructured yttria partially-stabilized zirconia

Gadolinium zirconate (Gd₂Zr₂O₇, GZ) as one of the promising thermal barrier coating materials for high-temperature application in gas turbine was toughened by nanostructured 3 mol% yttria partially-stabilized zirconia (YSZ) incorporation. The fracture toughness of the composite of 90 mol% GZ-10 mol% YSZ (GZ–YSZ) was increased by about 60% relative to the monolithic GZ. Both the GZ and GZ–YSZ composite coatings were deposited by atmospheric plasma spraying on Ni-base superalloys and then thermal-shock tested under the same conditions. The thermal-shock lifetime of GZ–YSZ composite coating was improved, which is believed to be mainly attributed to the enhancement of fracture toughness by the addition of YSZ. In addition, the failure mechanisms of the thermal-shock tested GZ–YSZ composite coatings were discussed.     

Effect of TGO thickness on the thermal barrier coatings life under thermal shock and thermal cycle loading

Effect of thermally grown oxide (TGO) thickness on thermal shock resistance of thermal barrier coatings (TBCs) and also their behavior under a cyclic loading (including aging at maximum temperature) was evaluated experimentally. In order to form different thicknesses of TGO, coated samples experience isothermal loading at 1070?°C for various periods of times. Heat-treated samples were heated to 1000?°C and cooled down rapidly in water from the substrate side using a mechanical fixture. The life of samples was investigated as a function of TGO thickness. Furthermore, by performing an experiment the simultaneous effect of the TGO growth and thermal expansion mismatch– on the failure of thermal barrier coatings was evaluated. The results demonstrated that the presence of TGO with a thickness of 2–3?µm has a positive effect on the resistance against thermal shock.     

Enhanced thermal shock resistance of low-carbon Al2O3-C refractories with direct CVD synthesis of nano carbon decorated oxides

Novel low carbon Al₂O₃-C refractories were prepared through adopting chemical vapour deposition (CVD) synthesized nano carbon decorated Al₂O₃ powder. The phase compositions, microstructures, mechanical properties and thermal shock resistance of Al₂O₃-C refractories were characterized and evaluated. The results show that the morphologies of nano carbon composites are mainly dominated by the concentration of catalyst. Specifically, the growth of MWCNTs is preferred with a Ni²⁺ concentration at 0.1?mol/L, while higher concentrations e.g. 0.3?mol/L would stimulate the formation of nano-onion like carbon. With the introduction of nano carbon decorated Al₂O₃ additives, the residual strength after thermal shock can reach 12.4?MPa, which is much higher than the 2?wt% nano carbon black containing specimens (6.4?MPa). The enhanced thermal shock resistance should be attributed to that the nano onion-like carbon reduces the cohesion between the matrix and the Al₂O₃ particles and decreases the thermal expansion coefficient.     

High thermal-conductivity rGO/ZrB2-SiC ceramics consolidated from ZrB2-SiC particles decorated GO hybrid foam with enhanced thermal shock resistance

Graphene derivative materials exhibit excellent mechanical and thermal properties, which have been extensively used to toughen ceramics and improve thermal shock resistance. To overcome the thermal agglomeration of graphene oxide (GO) during heating and drying process, ZrB₂-SiC particles decorated GO hybrid foam with uniformly anchored ceramic particles was synthesized by electrostatic self-assembly and liquid nitrogen-assisted freeze-drying process. Densified rGO/ZrB₂-SiC ceramics with varying microstructure, thermal physical and mechanical properties were obtained by adjusting the content of decorated ceramic particles. Although the flexural strength of rGO/ZrB₂-SiC ceramics have an attenuation compared with that of ZrB₂-SiC ceramic, the thermal conductivity, work of fracture and thermal shock resistance are greatly improved. rGO/ZrB₂-SiC ceramics exhibit delayed fracture and increasing R-curve behavior during the crack propagation. The novel preparation technology allows for the well dispersion of rGO in ZrB₂-SiC ceramics and can be easily extended to other ceramic or metal materials systems.