High-Performance Ceramics III

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Authors: U. Akin, Harun Mindivan, R. Samur, E.S. Kayali, H. Çimenoğlu
Abstract: In this paper the tribological performance of oxide (Cr2O3, ZrO2CaO and Al203) and combined coatings applied on a commercially pure aluminum sheet were presented. Combined coatings were produced by applying Polytetrafluoroethylene (PTFE) film on the oxide coatings. Among the oxide coatings Cr2O3 exhibited the highest and Al2O3 exhibited the lowest wear resistance, in accordance with their hardness. Combined coatings exhibited superior wear resistance than oxide coatings even at heavy wear testing conditions.
Authors: Erdem Atar, H. Çimenoğlu, E.S. Kayali
Abstract: In the present study tribological performance of ZrN coatings deposited on hardened AISI D2 quality cold work tool steel by arc-Physical Vapor Deposition technique has been examined in as-deposited and oxidized conditions. ZrN coatings were oxidized at 400 oC for various times up to 12 h. Reciprocating wear tests carried out by rubbing Al2O3 balls on the coatings, revealed significant improvement in wear resistance of ZrN coating upon oxidation. Oxidation treatment at 400 oC for 12 h yielded seven times higher wear resistance than as-deposited ZrN coating, beside significant reduction in the wear of counterface (Al2O3 ball).
Authors: Xi Tang Wang, Zhou Fu Wang, Bao Guo Zhang, Cheng Ji Deng
Abstract: Vanadium nitride is produced from V2O5 by carbon-thermal reduction and nitridation. When the sintered temperature is above 1273K, VN can be formed, and the nitrogen content of the products increased with the firing temperature raised, and then is the largest when the sintered temperature is 1573K. The C/V2O5 mass ratio of the green samples is the other key factor affecting on the nitrogen contents of the products. The nitrogen content of the products reaches the most when the C/V2O5 mass ratio is 0.33, which is the theoretical ratio of the carbothermal nitridation of V2O5.
Authors: Jian Ying Gao, Wan Jiang, Gang Wang
Abstract: A combustion front quenching (CFQ) technique was used to investigate the mechanism of selfpropagating high-temperature synthesis (SHS) of MoSi2 from Mo and Si powders. Based on the experimental results, a combination of reactive diffusion and dissolution-precipitation mechanism of the formation of MoSi2 was proposed, and a model corresponding to this mechanism was drawn.
Authors: Zhi Xiong, Gang Wang, Wan Jiang
Abstract: The room temperature fracture toughness and the high temperature DBTT of MoB particle-reinforced MoSi2 composites were investigated using Vickers indentation technique and MSP testing method, respectively. Modified Small Punch (MSP) test is a method for evaluation of mechanical properties using very small specimens, and it’s appropriate for the determination of strength and DBTT. It was found that the approximate fracture toughness of the composite is 1.3 times that of monolithic MoSi2, and its DBTT is 100°C higher than that of monolithic MoSi2 materials. Cracks deflection is a probable mechanism responsible for this behavior.
Authors: Xiao Li Zhang, Jian Feng Yang, Zhen Lin Lu, Zhi Hao Jin
Abstract: It has been reported that formation of Mo(Al,Si)2 phases by the addition of aluminum can improve the mechanical and oxidation properties of MoSi2, however, the constancy of the Mo(Al,Si)2 phase was not explored. In this study, MoSi2 preforms were added with Al whose contents were 1, 5, 10wt%, respectively, and these performs were sintered at 1150°C-1550°C, respectively. These MoSi2 specimens with the Al addition were heat-treated at 1350°C-1550°C in N2 atmosphere. Results showed that single Mo(Al,Si)2 phase existed only when the aluminum content was above 5 wt%. It was difficult to form single Mo(Al,Si)2 phase for the samples with 1wt% Al addition. For the samples with 5wt% Al, only the single Mo(Al,Si)2 phase was formed at 1350°C; and a large number of the tetragonal MoSi2 were re-appeared at 1450°C, 1550°C. For the samples with 10wt% Al addition, the single Mo(Al,Si)2 phase would always formed at individual sintering temperatures. The formation temperature of the single Mo(Al,Si)2 phase was decreased with increment of aluminum content. For the samples composed of the single Mo(Al,Si)2 phase, the Mo(Al,Si)2 phase disappeared gradually and was substituted for MoSi2 and a little of other phases, such as Mo3Al4Si2, by heat treatment at temperatures mentioned above for 40 min. This indicated that the Mo(Al,Si)2 phase was unstable at the temperatures above 1350°C.
Authors: Ningfeng Gao, Fumihito Inagaki, Ryo Sasai, Hideaki Itoh, Koji Watari
Abstract: WC-Co cermet is widely used in industrial applications such as cutting tools, dies, wear parts and so on. It is of great importance to establish the recycling process for the precious metal resources contained in WC-Co cermet, because all these metals used in Japan are imported. In this paper we reported a hydrothermal oxidation technique using nitric acid for the reclamation of WC and Co. The WC-Co cermet specimens with various WC particle sizes and Co contents were hydrothermally treated in HNO3 aqueous solutions at temperatures of 110-200°C for durations of 6-240 h. The Co was preferentially leached out into the acidic solution, while the WC was oxidized to insoluble WO3 hydrate which was subsequently separated by filtration. The hydrothermal treatment parameters such as solvent concentrations, treatment temperatures, holding time were optimized in respect to different kinds of WC-Co cermets. A hydrothermal oxidation treatment in 3M HNO3 aqueous solution at 150°C for 24 h was capable of fully disintegrating the cermet chip composed of coarse WC grains of 1-5 µm in size with 20 wt% of Co as binder. While the more oxidation resistant specimen composed of fine WC grains of 0.5-1.0 µm in size with 13 wt% of Co, was completely disintegrated by a treatment in 7 M HNO3 aqueous solution at 170°C for 24 h. The filtered solid residues were composed of fine WO3.0.33H2O powder and a small amount of WO3. The recovered WO3.0.33H2O powder can be easily returned to the industrial process for the synthesis of WC powder so that the overall recycling cost can be possibly lowered.
Authors: Gang Qin Shao, Xiao-Hua Yu, Xing Long Duan, Wei Feng Zhang, Zhong Lai Yi, Chong Wang, Peng Shun, Xiao Liang Shi
Abstract: The need for WC-Co with improved properties, particularly increased hardness and strength combined with increased ductility and toughness, has focused attention on the development of grades with finer and finer-grained powders and cemented carbides. The aim of this study is to determine the sintering temperature of nanocomposite WC-6Co (wt.%) sample by using an optical microscope under high temperature and a DSC / TG apparatus. The WC-Co sample was prepared from nanocomposite powder by hot-press-sintering at the determined sintering temperature. The phase structure of the powder and sintered samples was investigated. The SEM imaging was performed on fracture surfaces of sintered samples. The density and the HRA of sintered samples were also measured.
Authors: Zhen Ting Wang, Hua Hui Chen
Abstract: Micro-nanostructured WC composite coatings were successfully fabricated by induced heating sintering method on the surface of Q235 steel .The microstructure, micro-hardness and the wear resistance of the composite coatings were studied .The results show that the microstructure of induced heat layer is mainly composed of Ni-based solid solutions and WC particles. And there exists excellent metallurgical bonding between coating and substrate. The wear resistance of micro-nanostructured WC Composite Coatings is increased by 1.5 times on an average as compared with that of micron.
Authors: Hai Long Wang, Rui Zhang, Hong Liang Xu, Hong Xia Lu, Shao Kang Guan
Abstract: In order to improve the interfacial behavior between SiC and Al, a surface layer of Cu was coated on SiC particles. The influence of pH value on the coating process was analyzed. A powder metallurgy method was used to prepare the Al-based metal matrix composites (MMCs). SEM, XRD techniques were used to characterize the sintered compacts. It was found that the optimized pH value during the coating process was 1~2. The specimen showed the maximum density when sintered at 750oC. Inter-metallic compound of Al3.21Si0.47 was detected which contributed to the enhancement at the interface between SiC and Al. The hardness of the composites is improved to 90 MPa.

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