Advanced Materials Research Vol. 75

Abstract: To develop novel and advanced thermal barrier coatings, full-scale numerical simulation of plasma-sprayed functionally gradient materials is conducted in this paper, including the prediction of basic parameters at the nozzle exit, simulation of three dimensional simulation of the plasma jet, modeling of the interaction between the plasma jet and the particles, calculation of flight trajectories and temperature history of flying metal and ceramic particles, the interaction between the molten particles and the substrate, as well as the deposition process of the coatings. Various complex phenomena, such as turbulent effects with chemical reactions in the plasma jet, dispersion status of the particles onto the substrate, and the composition distribution of the functionally gradient materials, are fully taken into account. The numerical simulation results are found to be in good agreement with experimental evidence.

Abstract: Carbon ion implantation has often been considered as an additional method to further improve the wear, corrosion and oxidation resistance of hard coatings on tools or machine parts. The present research investigates the effect of carbon implantation on the structural and mechanical properties of the sputter-deposited solid solution Ti-Al-N coatings. The carbon implantation was carried out by using metal vapour vacuum arc ion source (MEVVA) with solid cathode at energies of 5 and 50 keV, and a dose of 6×1017 atoms cm-2. The mechanical and the microstructure properties of the implanted layer were identified by a variety of analytic techniques, such as nano-indentation, x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) etc. Additionally, the wear performance of the samples was evaluated by a typical ball-on-disk tribometer in dry conditions. The results showed that the coatings with high energy carbon implantation exhibited an enhanced hardness. The improved hardness could be attributed to the formation of TiC phase, as indicated in XPS. In the sliding tests, the coatings with the post-treatment of carbon implantation showed an improved tribological property in terms of friction coefficient and wear rate. The friction coefficient could be reduced from 0.6 to 0.1. The coatings had ten-fold better wear resistance than the coating without ion implantation.

Abstract: TiO2 shows a high efficiency in Photocatalysis, however, the recycling of TiO2 is difficult, composite coating is prepared by simultaneous elecroless deposition of NiP and TiO2 on substrates, surface topography and hardness of composite coating are investigated by metalloscope, SEM, EDS and Vickers microhardness; The relation between absorbence of methyl orange and time is researched by 723# spectrophotometer. The results show when TiO2 content in bath is 4g/L, plating speed is most fast and amount to 12.2μm/h, the photocatalytic effect is best. by comparing the microhardness of heat-treated compound coating and the Ni-P alloy coating, the maximum microhardness of the former appears in 500°C and achieves HV1180, and the latter appears in 400 °C and achieves HV950.

Abstract: High velocity oxygen fuel (HVOF) thermal spray coating of micron size (μ) T800 powder has been studied for the durability improvement of sliding machine components. The optimal coating process (OCP), surface properties, friction, wear behavior and adhesion of HVOF T800 coating have been investigated. The temperature dependence of friction coefficient and wear behavior have been studied at 25°C and at an elevated temperature 538°C (1,000°F) for the study of the temperature effects on FC and wear behaviors of the coating and for the application on high speed air bearing spindle which operates with no lubricants. The OCP was determined from the best surface properties of the 16 OCP searching coatings designed by the Taguchi experimental program of four spray parameters with three levels: a hydrogen flow rate (FR) of 38-42 FMR (1 FMR=12scfh=9.44×10-5 m/s), oxygen FR of 65-70 FMR and feed rate of 30 g/min, and a spray distance of 5 inch. Hardness, roughness and porosity observed from the 16 coatings were 560-640 Hv (5488-6272 MPa), 2.2-3.0 μm and 0.01-0.04% respectively. Friction coefficient (FC) decreased from 5.5-7.0 to 4.8-6.0 with increasing the sliding surface temperature from 25°C to 538°C because of the higher lubrication effect of Co oxide debris at the higher temperature. Wear trace of the coating and counter sliding SUS 304 surface decreased to more than a half with increasing the sliding surface temperature from 25°C to 538°C. Tensile bond strength (TBS) and tensile fracture location (TFL) of Ti64 / T800 were 8,770 psi (60.5 MPa) and near the middle of the coating respectively. Bond coat NiCr did not influence on the TBS of the coating. The adhesion between Ti64 substrate and T800 coating (Ti64/T800) was stronger than the cohesion strength 8,770 psi (60.5 MPa) of T800 coating. These showed that Ti64/T800 coating was recommendable for durability improvement coating on high speed spindle of Ti64.

Abstract: Microdrills were deposited by Cr-N based and TiN coatings using a magnetron sputter technique. A flexible printed circuit board was used to evaluate the drilling lives. SEM observation was employed to reveal the wear and local welding. A special pin-on-disc tester was designed to assess the interaction between coatings and against materials. Drilling test indicated that the number of drilling holes increased significantly when the minidrill was coated Cr-N based film than TiN. Failure model of microdrill was studied for cutting this copper rich printed circuit board. Results demonstrated that welding produced between TiN coating and rich copper counter material, but welding did not occur between Cr-N based film and copper material.

Abstract: The aluminum depletion of NiCrAlY bond coat in an air-plasma-sprayed thermal barrier coating (TBC) has been studied by experimental and simulative approaches. Upon thermal exposure, Al depletion regions were observed. The depletion of aluminum is resulting from Al diffusion towards the surface of bond coat and into substrate. A mathematical model of Al depletion was presented. The model is able to explain the observed results in a qualitative way and has been shown that Al depletes within the bond coat by diffusion.

Abstract: Quaternary CrTiAlN hard coatings were deposited by closed field unbalanced magnetron sputtering ion plating technique onto steel substrates, and their structural, mechanical, and tribological properties after heat treatment in air at different temperatures (500-900 oC) were studied and compared by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-indentation, and pin-on-disc (POD) tribometer, etc. The onset temperature of oxidation was determined by thermogravimetric analyser (TGA). The compositional depth profiles before and after the heat treatments were examined by X-ray photoelectron spectroscopy (XPS) in order to study the oxidation mechanism. The experimental results indicate that the CrTiAlN coatings have excellent oxidation resistance and thermal stability, and outperform the traditional hard coatings like TiN and TiAlN in terms of higher oxidation temperature, hardness, adhesion, and wear resistance. It is expected that the CrTiAlN coatings with superior properties should have better performance in dry high speed machining.

Abstract: This paper describes the development of spherical iron-based composite powder with carried alumina abrasive grains made by a plasma spray technique. Carbonyl iron powder (7.2 μm average size) and alumina abrasive grains (0.3 μm average size) are sprayed into the plasma flame from the respective nozzles simultaneously, or their mechanical mixture is directly plasma-sprayed. In case of the composite powder obtained by the direct spray method, the alumina abrasives are well carried on the carbonyl iron particles. However, a plasma current of more than 100 A causes melting and vaporizing of the alumina abrasives;, consequently the carbonyl iron and alumina abrasives are separated. The magnetic abrasive experiments with the composite powder developed are made for SUS304 stainless steel plate, and the result shows that the developed composite powder has high potential abrasive performance.