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.     

Infrared radiative properties of plasma-sprayed BaZrO3 coatings

The room temperature directional-hemispherical reflectance and transmittance spectra of free-standing atmospheric plasma-sprayed BaZrO₃ coatings with different thicknesses were measured in the wavelength range of 0.8–15.0 μm, and the absorption coefficient and scattering coefficient as a function of wavelength were extracted using the modified four-flux model. Results showed that BaZrO₃ is a high scattering, low absorption material at the wavelength <6 μm, where turbine engine thermal radiation is most concentrated. The absorption coefficient of BaZrO₃ starts to increase rapidly at wavelength of 6 μm, indicating that BaZrO₃ is high absorbing and opaque in the long wavelength range. A pronounced absorption peak occurs at a wavelength of 7 μm, and is associated with a BaCO₃ coating impurity. The scattering coefficient of BaZrO₃ decreases with the increase of wavelength in the whole measured wavelength range, caused by the decrease of the relative size of the scattering center compared with the wavelength.     

A comparative study of MoSi2 coatings manufactured by atmospheric and vacuum plasma spray processes

In this work, MoSi₂ coatings were manufactured by atmospheric plasma spraying (APS) and vacuum plasma spraying (VPS) technologies, respectively. Phase composition and microstructure of the coatings were characterized by X-ray diffraction and scanning electron microscopy. Microhardness, void and oxygen content of the coatings were also determined. Oxidation behavior of the coatings at high temperature was examined. The results showed that the surface of VPS-MoSi₂ coating was dense and homogeneous. However, there were many microcracks formed on the surface of APS-MoSi₂ coating. The VPS-MoSi₂ coating also had lower void and oxygen contents, higher Vickers hardness compared with those of APS-MoSi₂ coating. Besides, oxidation resistance of the VPS-MoSi₂ coating was better than that of APS-MoSi₂ at 1500 °C.     

Terahertz dielectric properties of plasma-sprayed thermal-barrier coatings

We investigated the electromagnetic wave transmittance and dielectric properties of yttria partially stabilised zirconia thermal-barrier coatings by terahertz time-domain spectroscopy in which the samples were irradiated by a pulsed THz wave in the frequency range of 0.1-6.3 THz. The coating microstructure was varied by changing the spray conditions and the THz transmittance and dielectric constants were examined as functions of frequency. The coatings exhibited a high transmittance of 20%-80% at frequencies below 0.5 THz and almost zero transmittance above 1.5 THz. The refractive index n for different coatings ranges from 4 to 6, depending on the coating microstructure. For any given coating, n increases to some extent with increasing frequency. Unlike the imaginary part of the dielectric constant, the real part of the dielectric constant is strongly correlated with the porosity of the coatings, which suggests that terahertz spectroscopy may potentially be used to non-destructively evaluate the porosity of ceramic coatings.     

Analysis of phase transformation in plasma sprayed alumina coatings using Rietveld refinement

During plasma spraying of alumina with the stable α phase in the starting powder, metastable phases tend to form in the final coating. This is attributed to the rapid quenching associated with the process. In this paper the weight fraction of metastable phase formed, i.e., stable phase retained, and has been estimated using Rietveld refinement of X-ray diffraction data. This weight fraction depends on the process parameters like standoff distance, primary and secondary gas flow rate, nozzle size, etc., which in turn control particle melting. Under favourable melting conditions the weight fraction of the metastable phases approaches 1.     

氧化铝陶瓷涂层在火电站干除灰系统中的应用研究

利用等离子喷涂设备,采用扫描电镜、X射线衍射仪、显微硬度计和VIDAS图象分析仪等仪器,研究了以镍包铝粉末作为打底层,以NiCrBSi混合不同重量百分比的Al2O3陶瓷粉末作为工作涂层的不同试样的组织和性能特点,得到耐磨性及结合强度较好的金属基氧化铝陶瓷粉末组合,为解决火电站干除灰系统中主要部件的耐冲蚀磨损问题提供了一种可供选择的方法.     

Al-Cu-Cr quasicrystalline coatings prepared by low power plasma spraying

Al-Cu-Cr quasicrystalline coatings were prepared by low power plasma spraying with axially-fed powder systerm. The Al₆₅Cu₂₀Cr₁₅ powders were deposited on AISI 1045 steel substrate at the power ranged from 4.0 to 6.0 kW. The effects of H₂/Ar flow ratio on the phase composition, microstructure and microhardness properties of the as-sprayed coatings were investigated. The XRD results showed that the original powders and as-sprayed coatings contained a predominant icosahedral quasicrystalline phase I-Al₆₅Cu₂₄Cr₁₁ and three minor crystalline phases, including a body-centered cubic α-Al₆₉Cu₁₈Cr₁₃, a monoclinic θ-Al₁₃Cr₂ (i.e. Al₈₃Cu₄Cr₁₃) and a hexagonal ε-Al₂Cu₃. A qualitative analysis on the XRD patterns indicated that the volume fraction of any crystalline phase (α, ε or θ) in the coatings increased, while the quasicrystalline I-phase decreased with increasing hydrogen content in the plasma gas. As H₂/Ar flow ratio increased from 4.8% to 18.8%, the coating hardness increased whilst its porosity decreased, and they reached the maximum (4.98 Gpa) and the minimum (8%) respectively. However, with increasing H₂ content further, the hardness of the coating slightly decreased and its porosity increased because of the excessive vaporization of aluminum at higher plasma energy.     

等离子熔射快速制模中机器人运动轨迹生成方法及实践

在机器人等离子熔射快速制模中,熔射轨迹对熔射皮膜的成形性有重要影响。本文提出了由CAM加工轨迹转化为机器人等离子熔射轨迹的方法,避免了以往通过STL文件生成机器人熔射轨迹的繁琐过程。文章重点介绍了如何将CAM加工轨迹转化为机器人熔射轨迹,并对其进行了仿真与实验验证,结果表明:该方法比原有的由STL文件生成机器人熔射轨迹的方法更简便、灵活,更适应机器人等离子熔射制模成形的要求。     

等离子喷涂氧化铝涂层连通孔的准分子激光表面处理改性

等离子喷涂氧化铝陶瓷涂层由于内部存在孔隙、层迭及层间裂纹等缺陷而呈现出复杂的微观结构。这些典型的微结构特点显著影响着涂层的力学性能。本研究开发了一种等离子喷涂氧化铝涂层的准分子激光表面处理技术以优化石油工业缆绳工具的部件性能。相比于CO2或YAG激光器的液相处理技术,准分子激光工艺采用短波激光,这对陶瓷材料来说就意味着能量主要被表面区所吸收。首先,采用SEM研究了涂层的表面和截面微观结构,并表征了激光处理后表面粗糙度和消融状态。然后采用X射线微观断层成像技术获取了涂层的三维微结构以研究激光处理后涂层的3D孔隙率。最后,借助纳米压痕和电化学阻抗谱方法分别表征了改性后涂层微结构的力学和电学性能。结果表明,准分子激光表面处理技术是一种控制等离子喷涂氧化铝涂层绝缘性能的创新工艺。     

Y-Ba-Cu-O超导涂层的研制

用等离子喷涂工艺制备了 Y-Ba-Cu-O 高临界温度超导涂层,涂层的初始转变温度为101K、零电阻温度为86K。电阻率与磁化率的测量结果表明这种超导涂层具有与烧结超导块体相类似的性能,X 光衍射谱显示出涂层主要由 YBa_2Cu_3O_(?)单相化合物组成。