Synthesis and thermophysical properties of RETa3O9 (RE = Ce,Nd, Sm,Eu, Gd,Dy, Er) as promising thermal barrier coatings

Thermal barrier coatings (TBCs) are one of the most important materials in gas turbine to protect the high temperature components. RETa₃O₉ compounds have a defect‐perovskite structure, indicating that they have low thermal conductivity, which is the critical property of TBCs. Herein, dense RETa₃O₉ bulk ceramics were fabricated via solid‐state reaction. The crystal structure was characterized by X‐ray diffraction (XRD) and Raman Spectroscope. Scanning electron microscope (SEM) was used to observe the microstructure. The thermophysical properties of RETa₃O₉ were studied systematically, including specific heat, thermal diffusivity, thermal conductivity, thermal expansion coefficients, and high‐temperature phase stability. The thermal conductivities of RETa₃O₉ are very low (1.33‐2.37 W/m·K, 373‐1073 K), which are much lower than YSZ and La₂Zr₂O₇; and the thermal expansion coefficients range from 4.0 × 10^?6 K^?1 to 10.2×10^?6 K^?1 (1273 K), which is close to La₂Zr₂O₇ and YSZ. According to the differential scanning calorimetry (DSC) curve there is not phase transition at the test temperature. Due to the high melting point and excellent high‐temperature phase stability with these oxides, RETa₃O₉ ceramics were promising candidate materials for TBCs.     

Logarithmic decrease of adhesion force with lateral dynamic revealed by an AFM cantilever at different humidities

Adhesion forces between a tipless cantilever and an Au film were determined to investigate the influence of lateral velocity by recording force curves with an atomic force microscope at 20%–90% relative humidities. The sample was moved laterally, forth and back, with a frequency of 0.001–100 Hz and scan distances of 0.8, 8, and 80 μm to achieve a velocity ranging over 7 orders of magnitude. Experimental results show that at low lateral velocities (between 1.6 nm/s and 1–10 μm/s), the adhesion force either increases or decreases or remains stable with the lateral velocity without a certain characteristic trend. However, after a critical velocity, the adhesion force decreases logarithmically with the lateral velocity (between 1–10 and 16,000 μm/s). The decreasing magnitude can be as large as 97.3% of the maximum adhesion force. This decrease is well-explained by the contact time dependence of water bridges formed by capillary condensation.     

Durability of YSZ coated Ti2AlC in 1300°C high velocity burner rig tests

A thermal barrier coating (TBC) system survived 500 hours in aggressive, 1300°C burner rig testing. The yttria-stabilized zirconia (7YSZ) TBC was plasma sprayed on an oxidation-resistant Ti₂AlC-type MAX phase and tested in a jet fuel burner at 100 m/s, using 5 hours cycles. No coating spallation or surface recession was observed; Al₂O₃-scale growth produced a slight 2.4 mg/cm² mass gain. The coating surface exhibited craze-cracked colonies of [111]_flourite textured columns, with no visible moisture attack. The 20 μm alumina scale remained intact under the YSZ face, about twice that producing failure for TBC/superalloy systems. TiO₂ nodules, initially formed on the uncoated backside, were removed, and Al₂O₃ was etched through volatile hydroxides formed in water vapor (~10%). Overall, the test indicated exceptional stability of the YSZ/Al₂O₃/Ti₂AlC system under turbine conditions due in large part to close thermal expansion matching.     

Sintering behavior of a nanostructured thermal barrier coating deposited using electro-sprayed particles

During high temperature service, a series of microstructure and phase evolutions occur in thermal barrier coatings (TBCs), which result in degradation of thermal insulation and durability. In this study, the sintering behavior of an air plasma sprayed 8 wt% YSZ coating deposited using electro-sprayed nanostructured particles (ESP) as feedstock powder was investigated and compared with conventional YSZ coating deposited using hollow spherical powders (HOSP). Due to the distinct asymmetric porous structure formed by nanosized YSZ particles, the ESP powder was partially melted in the plasma jet during the deposition, which resulted in the formation of a nanostructured coating that consisted of porous nanozones and dense zones. The ESP coating not only shows a significantly lower initial thermal conductivity of 0.70 W/mK, but also exhibits a stronger sintering resistance in terms of phase stability and thermal insulation compared to the conventional coating. When subjected to prolonged sintering at 1400°C for 128 hours, the thermal conductivity of the ESP coating would gradually increase to about half that of the HOSP coating at 1.29 W/mK. These differences are ascribed to the interaction among different sintering behavior between nanozones and dense zones.     

Nanoindentation and scratch behaviour of Ni–P electroless coatings

ABSTRACT

In the present paper, the mechanical properties and the scratch failure mechanisms of Ni–P electroless coatings are described. The material microstructure was studied in as-deposited and annealed conditions through SEM and EDS analyses. Nanoindentation measurements on the coatings showed a remarkable hardening due to the crystallization and precipitation behaviour produced by annealing. The scratch tests, conducted by increasing the load during scratch, revealed the coating failure mechanisms in a broad range of applied stresses up to delamination.     

高寒列车转向架防冰涂料的研究

在高寒地区运行的列车转向架部位容易发生结冰现象，这在一定程度上对行车安全造成隐患。对于平滑表面而言，表面的接触角滞后与冰粘附强度呈现线性关系，即接触角滞后越小，冰粘附强度越低。基于这一基础理论，本文意在构建低滞后的光滑涂层，实现涂层的低冰粘附强度，从而达到易除冰的效果。研究选用 HDI三聚体型多异氰酸酯为固化剂，对比了 3种商品化具有低表面能特性的含氟羟基树脂应用于双组分防冰涂料的性能差异，并采用疏水性最强、防冰性能最优的氟硅树脂制备了综合性能优异的高寒列车转向架防冰涂料。     

水性防腐涂料贮存稳定性的研究

由于水性树脂、颜料和填料等多方面的影响,水性防腐涂料在贮存中容易分层、沉淀,在不同体系中添加不同类型的触变剂可以有效地改善产品的贮存稳定性,使之在不同的环境温度下避免分层、沉淀等问题。     

含Mo的PVD涂层结构及其摩擦学特性的研究进展

从含Mo元素的代表性涂层入手,综述了二元、三元再到多元含Mo系列PVD涂层的研究现状和进展,探究了不同元素添加、不同制备参数等对涂层微观结构、力学性能和摩擦学性能等的影响。在涂层组分从二元发展到多元的过程中,改变掺杂元素种类、含量,制备参数会引起涂层微观结构的变化进而提升涂层力学性能和摩擦学性能。涂层性能的改善,有利于增强对机械设备中关键传动零部件的保护,延长机械设备使用寿命,对军工及社会发展具有重大意义。     

Characterisation of the microplasma spraying of biocompatible coating of titanium

This paper presents new results of studying the influence of parameters of microplasma spraying (MPS) of Ti wire on the structure and properties of Ti coatings. Based on the design of the experiment and the results of the SEM study, certain spraying modes were chosen to form the desired composition and structure of the Ti coating.  The dense sublayer (up to 300 µm thick) provides good adhesion to the substrate, and a porous top layer can accelerate the coated implant ingrowth with the bone.  This technology is developed for the manufacture of coated endoprosthesis implants.