Papers by Keyword: Cermet

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Authors: Zakiah Kamdi, P.H. Shipway, K.T. Voisey
Abstract: Various research programmes have been conducted examining cermet coatings in relation to wear, corrosion and the combination of both (erosion-corrosion and abrasion-corrosion). Several methods have been employed to deposit cermet coatings, the most common being thermal spraying or hard facing (weld overlaying).The cermet coatings are carbide-sized ranging from 50 150 μm which is larger than abrasive particles which range between 2 to 10 μm. This allows the abrasive particles to interact with the carbide and matrix separately. Understanding the mechanism of this situation is necessary as abrasion maybe caused by a small abrasive. However, carbide sinking caused by this large carbide leads to diverse local carbide distributions and wear rates with a larger standard deviation. Modified micro-scale abrasion tests were performed with a silica abrasive of 2-10 μm particle size distribution and suspended in water. Due to the sinking of carbide particles during the coating process, the ground samples with more carbide on the surface displayed better wear resistance than those with a lower local carbide content. By using a modified micro-scale abrasion wear test, the correlation between local carbide content and wear rate may be determined with a smaller standard deviation. Rolling wear mode was observed due to the lower degree of hardness of the abrasive compared to the hard phase. The wear behaviour is related to the microstructure.
Authors: Li Wei Zhu, Yu Dong Feng, Y. Wang, Z.M. Wang, K. Zhao, X.M. Su, J.W. Qiu
Abstract: Thin films composed of mixtures of metals and dielectric are being considered for use as solar selective coatings for a various applications. By controlling the metal distribution, the solar selective coatings can be designed to have the combined properties of high absorptance, and low infrared emittance. We have studied the preparation of the Al-Al2O3 cermet composite films deposited on the flexible Kapton substrate by pulsed direct current (DC) magnetron sputtering technique. The complex films include infrared reflective layers, interference absorptive layers, and anti-reflective layers. The measurements of the samples show that the spectral absorptance in the region of 0.2~2.5μm and thermal emittance in the region of 2.5~25μm were 92% and 7%, respectively.
Authors: G. Kapelski, A. Varloteaux
Authors: Zheng Guang Zou, Kai Liu, Yu Fang Shen, Zhi Gang Xiao, Fei Long, Yi Wu
Abstract: This work focus on the effects of C vacancy on wetting of Fe to TiC/Fe at the cermet interfaces. We do the whole work using the first-principles density functional theories. The ideal work of adhesion of the pure interface is not big enough, comparing with the expeimental value. Our calculations suggest that the C vacancy at the interface is a very important factor for interface banding of TiC/Fe cermet composite. An adequate quantities of C vacancies at the interface can improve the wetting of TiC/Fe interfaces.
Authors: Rainer Gadow, Andreas Killinger, Andreas Rempp, Andrei Manzat
Abstract: Protective and functional coatings featuring outstanding tribological performance are of general interest for all kinds of industrial applications i.e for high performance automotive and mechanical applications. Thermal spray coating technologies play a key role in fabricating hard layers based on ceramic, metal - ceramic and further multiphase materials. Additional functionality can be achieved by combining these coatings with polymer based top coats with low friction coefficient or anti adhesive behaviour. Combined coatings feature also designed thermophysical and electrophysical properties. Several case studies will be discussed, ranging from automotive applications to paper and printing industry. Thermally sprayed coatings were applied using APS, HVOF and the newly developed HVSFS processes (High Velocity Suspension Spraying) with a special focus on nanoceramic feedstocks. In some applications polymer top coats with dispersed solid phases are applied to enhance functional properties. Special aspects in manufacturing engineering are addressed with particular importance not only of the influence of spray process parameters on coating properties but also of spray torch kinematic and robot trajectories on hardness, residual stress distributions, dimensional tolerances and porosity distributions will be discussed.
Authors: Thomaz Augusto Guisard Restivo, D.W. Leite, Sonia Regina Homem de Mello-Castanho
Abstract: Anodes composed of Ni-YSZ (yttria-stabilised zirconia) cermets are the key material to allow direct biofuel feeding to Solid Oxide Fuel Cell (SOFC) devices due to its internal reforming capability. The main challenge among these materials is related to carbon deposition poisoning effect when C-bearing fuels are feed. The work deals with these issues by alloying Ni with some metals like Cu to conform a multi-metallic anode material. Mechanical alloying (MA) at shaker mills is chosen as the route to incorporate the metal and ceramic powders in the anode material, also leading to better sintering behaviour. A projected cermet material is conceived where a third metal can be added based on two criteria: low Cu solubility and similar formation enthalpy of hydrides regarding Ni. Refractory metals like Nb, W and Mo, seems to fulfil these characteristics, as well as Ag. The MA resulted powder morphology is highly homogeneous showing nanometric interpolated metal lamellae. The sintering behaviour is investigated by conventional dilatometry as well as by stepwise isothermal dilatometry (SID) quasi-isothermal method to determine the sintering kinetic parameters. Based on these tools, it is found the Cu additive promotes sintering to obtain a denser anode and therefore allowing lower process temperatures. The consolidation is achieved through the sintering by activated surface (SAS) method allied to liquid phase sintering process, where the third metal additive also has influenced. The final cermet can be obtained at one sole process step, dispensing pore-forming additives and reduction treatments. The sintered microstructure demonstrates the material is homogeneous and possesses suitable percolation networks and pore structure for SOFC anode applications.
Authors: Setsuo Aso, Hiroyuki Ike, Ken-Ichi Ohguchi, Yoshinari Komastu, Nobuo Konishi
Abstract: Particle reinforcement via the insertion of hard particles is a promising process in materials reinforcing. Particle-reinforced spheroidal graphite martensitic cast iron (SGMC), in which mixed particles of cermet and cemented carbide are dispersed, was achieved by an insertion process. A four-point bending strength test was applied to evaluate the particle composite material. An evaporative pattern process was used on the bending-test specimen to form a composite layer in the central part. Using a combination of three sizes of cermet particles and two sizes of cemented-carbide particles, the bending strength was found to increase with each small-particle combination. The Weibull coefficient m of the four-point bending strength of the particle-reinforced composite material (PRCM) ranged from 4 to 13, and m was large in the specimen with large bending strength.
Authors: Nur Amira Mohd Rabani, Zakiah Kamdi
Abstract: Cemented tungsten carbides have been paid much attention due its better mechanical properties with excellent combination of hardness and toughness characteristics. The hard WC particles in the coating provide hardness and wear resistance, while the ductile binder such as Co and Ni contribute to toughness and strength. WC-17wt.% Co and WC-9wt.% Ni powders have been sprayed by the HVOF method to form coatings approximately 300μm and 150μm thick onto AISI 1018 steel substrate. Both coatings have been prepared and supplied by an external vendor. The coatings were examined using optical microscope (OM), scanning electron microscope (SEM), and X-Ray diffraction (XRD). The hardness of both coatings were also measured using Vickers micro-hardness tester. The microstructure of the coatings has been analyzed and found to consist of WC, brittle W2C phase, metallic W phase, and amorphous binder phase of Co and Ni. It is found that WC-Ni has a higher hardness value compared to WC-Co due to high porosity distribution.
Authors: Helmo Käerdi, Dmitri Goljandin, Priit Kulu, Heikki Sarjas, Valdek Mikli
Abstract: The current paper deals with characterization of TiC−NiMo cermet powders produced by mechanical milling technology. TiC-based cermets scrap was processed by semi-industrial and laboratory disintegrator milling system. Chemical composition, shape and size of produced powders were analyzed. To estimate the properties of recycled cermet powders the sieving analysis, and angularity studies were conducted. The grindability was estimated using specific energy parameter (Es). Considering that viewpoint, the study is focused on angularity studies as the shape of spray powder has considerable influence on spraying efficiency, the quality and reliability of the coating. To describe the angularity of milled powders, spike parameter – quadratic fit (SPQ) was used and experiments for determination of SPQ sensitivity and precision to characterize particles angularity were performed. Uncertainty of measurements demonstrated trustworthiness of results. The standard deviation of SPQ regardless of milling cycles is the same. For use of produced powders as reinforcements in sprayed coatings the technological parameters of powders were studied. Perspective future use of powders as reinforcements in composite coatings as well as abrasives in tooling were demonstrated.
Authors: Wen Ge Li, Guang Jun Zhang, Jun Li
Abstract: WC-Cr3C2 cermet coating on carbon steel was fabricated by laser controlled reactive synthesis method. Effect of diluents is the key factor influencing the cladding process. When the amount of diluents is 30%, the reaction becomes steadily and the smooth coating can be achieved. Observations of the microstructure and phase composition of the sample showed that the coating was a complex phase system which consisted of WC and Cr3C2. In order to improve bond strength of the coating, Ni was selected as additive. The interface morphology showed that the bonding between coating and substrate was metallurgical bonding.
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