Calculation of high-speed abrasion forces for ceramic coatings based on the Hertzian contact model

Aero engine seal coatings can effectively improve the air tightness of aircraft engines and increase fuel efficiency.However,due to the frictional forces between the blades and the coating,the coating often flakes off,resulting in damage to the blades and causing eco-nomic losses.Therefore,it is necessary to analyze the friction between the blades and the coating.In this paper,three ceramic-based high-temperature seal coatings with different polyphenylene ester contents and a pure Yttria-stabilised zirconia coating were prepared by atmo-spheric plasma spraying(APS).The hardness and modulus of elasticity of the coated surfaces were obtained by hardness and modulus of elasticity tests,and the coatings were subjected to high-speed touch abrasion tests.The Hertzian contact model was used to calculate the maximum normal contact load on the coating during the process.The test values were compared with the theoretical values and it was found that the calculated values were always greater than the test values.In order to make the Hertzian contact model more accurate in calculating the touching and abrasion forces,the contact coefficients in the Hertzian contact model were optimized.Substituting the optimized coeffi-cients into the Hertzian contact model,the results show that the calculated results after optimizing the coefficients are much closer to the test values,with deviations from the test values ranging from 1%to 38%.

Influence of chloride ion concentration on immersion corrosion behaviour of plasma sprayed alumina coatings on AZ31B magnesium alloy

Corrosion attack of aluminium and magnesium based alloys is a major issue worldwide.The corrosion degradation of an uncoated and atmospheric plasma sprayed alumina(APS)coatings on AZ31B magnesium alloy was investigated using immersion corrosion test in NaCl solutions of different chloride ion concentrations viz.,0.01 M,0.2 M,0.6 M and 1 M.The corroded surface was characterized by an optical microscope and X-ray diffraction.The results showed that the corrosion deterioration of uncoated and coated samples were significantly influenced by chloride ion concentration.The uncoated magnesium and alumina coatings were found to offer a superior corrosion resistance in lower chloride ion concentration NaCl solutions(0.01 M and 0.2 M NaCl).On the other hand the coatings and Mg alloy substrate were found to be highly susceptible to localized damage,and could not provide an effective corrosion protection in solutions containing higher chloride concentrations(0.6 M and 1 M).It was found that the corrosion resistance of the ceramic coatings and base metal gets deteriorated with the increase in the chloride concentrations.

Performance of plasma-sprayed CuNiIn coatings and Mo coatings subjected to fretting fatigue

During atmospheric plasma spraying,a cooling process usually plays an important role in the coating quality,especially for the oxidation containment of metallic coatings.CuNiIn and Mo coatings were prepared using atmospheric plasma spraying with different cooling processes.The obtained coatings were characterized in terms of microstructure,microhardness and tensile strengths.The relation between the coating microstructure and their fretting fatigue behavior was emphasized.The results show that the sensitivity of Mo coatings to the cooling process is lower than CuNiIn coatings.The resistance to fretting fatigue is determined by the coating microhardness,correlated with the contents of oxides and pores.The fretting wear mechanisms of both the coatings are galling,third body abrasive wear and material transfer.

Plasma-Sprayed Coating of an Apatite-Type Lanthanum Silicate Electrolyte for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs)

Apatite-type lanthanum silicate was successfully synthesized via a solid state re- action protocol at 1400~C in a vacuum for 4 hours. The powder was synthesized faster and at a lower reaction temperature than by conventional solid state reaction methods. The resulting powder was used in the fabrication of a coating deposited by atmospheric plasma spray （APS） technology. The microstructure of the coating was analyzed by X-ray diffraction and scanning electron microscopy. Heat treatment was found to fully crystallize the coating, increasing its den-sity. The ionic conductivity of the apatite coating was 0.39 （0.054） mS/cm at 850 （700） ℃, and its activation energy was 0.67 eV.

Fabrication and performance of atmospheric plasma sprayed solid oxide fuel cells with liquid antimony anodes

A solid oxide fuel cell(SOFC)with a liquid antimony anode(LAA)is a potential energy conversion technology for the use of impurity-containing fuels.Atmospheric plasma spraying(APS)technology has become a promising LAASOFC preparation method because of its economy and convenience.In this paper,button SOFCs with different cathode materials and ratios of pore former were prepared by the APS method and were operated at 750C.The effect of the cathode structure on the electrochemical performance of the LAA-SOFCs was analyzed,and an optimized spraying method for LAA-SOFCs was developed.A tubular LAA-SOFC was prepared using the APS method based on the optimized spraying method,and a peak power of 2.5 W was reached.The tubular cell was also measured at a constant current of 2 A for 20 h and was fed with a sulfur-containing fuel to demonstrate its impurity resistance and electrode stability.

Wear Resistance and Bond Strength of Plasma Sprayed Fe/Mo Amorphous Coatings

Fe-based and Fe/Mo composite amorphous coatings were deposited on the surface of plain carbon steel substrates by atmospheric plasma spraying （APS）. With increasing the Mo alloy content, the microstructure of the coatings revealed more dense structure. The porosities of composite coating were all less than those of Fe-based coat- ing due to Mo alloy self-bonding performance. The ML10 friction and wear tester was employed to investigate the wear behaviors of the coatings under dry sliding conditions. It was found that the mass loss of the resultant coatings decreased with increasing Mo-based powders into the feedstock. This was attributed to the reduction of the delamina- tions resulting from improved intersplat bond with Mo addition.

Ablation Mechanism of HfC-HfO2Protective Coating for SiC-Coated C/C Composites in an Oxyacetylene Torch Environment

To prevent the C/C composites from ablation, HfC-HfO2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO2 coating were characterized by X-ray diffraction and scanning electron microscopy. The ablation resistance test was carried out by an oxyacetylene torch. The results show that the as-prepared coating is dense with little pinholes and crack free. The elements Hf, C and O were uniformly distributed in the cross-section. After ablation for different time, the mass ablation rate fluctuated along with the change of ablation time. The ablation process of the surface coating could be divided into rapid oxidation and solid state sintering stages. During ablation, an Hf CxOy-HfO2 transitional layer was generated in the coating, which resulted from the active oxidation of Hf C. After cooling, some microcracks were observed on the surface of coating, and the structure of cross-section was broken, which were due to the phase transition of HfO2.