1,721,011 research outputs found
Microstructures of binderless tungsten carbides sintered by spark plasma sintering process
No full textPure WC was sintered by spark plasma sintering (SPS) process for a binderless cemented carbide application. The relative density of spark plasma sintered WC was over 98% when the SPS temperature was 1700 degreesC under 50 MPa pressure. Grain growth of WC could be suppressed with full densification by shortening sintering time. When the initial WC powder size was varied from 0.57 to 4.06 mum, the sintered density decreased with decreasing WC powder size. However, WC with an initial powder size of 0.57 mum could be sintered to densification by addition of free carbon. The higher amount of surface oxide in the finer WC powder is considered to have caused decarbonization during the sintering process. For WC powders of 4.06 mum, abnormal grain growth occurred when the sintering time was over 1 min if the sintering temperature was over 1700 degreesC. Also, with the sintering temperature and sintering time where no abnormal grain growth occurred, abnormal grain growth occurred by addition of carbon. This result shows that the abnormal grain growth in WC sintered by SPS process can be controlled by carbon addition. The abnormal grain growth in sintered WC somewhat increased fracture toughness by crack deflection. (C) 2003 Elsevier Science B.V. All rights reserved
Analysis and modeling of residual stress in diamond thin film deposited by the hot-filament chemical vapor deposition process
No full textThe effect of microstructure on residual stress in diamond thin film was investigated. The diamond thin film was deposited by the hot filament chemical vapor deposition process with hydrogen/methane precursor gas and followed by annealing at 1150 degreesC For 1-30 min. The residual stresses of the diamond thin film were measured by Raman spectroscopy. A model to estimate the residual stress was proposed on the basis of grain boundary relaxation mechanism and microstructural analysis of diamond thin film. It is confirmed that the residual stress in diamond thin film is proportional to a microstructural factor, 1/ [D(f + 1)](1/2). where D is the grain size of diamond and f is the volume ratio of nondiamond carbon/diamond
Fabrication of nanocrystalline WC powders by mechanical alloying of elemental powders
No full textTungsten carbides have been widely used for wear resistant materials in forms of cemented carbides with binder and binderless cemented carbides. Nanocrystalline WC powders were fabricated from elemental powders of W and carbon black by mechanical alloying process. The transition of microstructure and phases in powders during the mechanical alloying process were analyzed by XRD, XPS and TEM. The grain size of W was continuously decreased with increasing the milling time and reached to a constant value of about 20nm after 2hours of mechanical alloying. WC phase was start to be formed after 10 hours of mechanical alloying. The XRD analysis showed that the full conversion into WC phase was obtained after about 24 hours of mechanical alloying. The mechanical alloying process could be divided into 4 steps - cell formation, nanocrystalline W grain formation, WC formation initiation and fully reacted to WC - based on the analysis of microstructure and constituent phases. The grain size of WC synthesized by mechanical alloying was was much finer than that fabricated by spray conversion process
Microstructure and mechanical properties of WC-10Co cemented carbides sintered from nanocrystalline spray conversion processed powders
No full textMechanical properties and microstructure of nanocrystalline WC-10Co cemented carbides were investigated. The nanocrystalline WC-10Co cemented carbide powders were manufactured by reduction and carbonization of the nano-crystalline precursor powders which were prepared by the spray drying process the of solution containing ammonia meta-tungstate (AMT) and cobalt nitrate. The WC powders which diameter were about 100 nm mixed homogeneously with Co binder phase and were sintered at 1375°C under the pressure of 1 mtorr. In order to compare the microstructure and mechanical properties with the nanocrystalline WC-10Co, commercial WC powders with diameters of 0.57-4 μm were mixed with Co powders, and were sintered at the same condition with that of nanocrystalline powders. TaC, Cr3C2 and VC of varying amounts were added into nanocrystalline WC-10Co cemented carbides as grain growth inhibitors. To investigate the microstructure of Co binder phase in the WC-10Co cemented carbides, a Co-W-C alloy was fabricated at the temperature of sintering process for the WC-10Co cemented carbides. The hardness of WC-10Co cemented carbides increased with decreasing the WC grain size following the Hall-Petch type relationship. The fracture toughness of WC-10Co cemented carbides increases with increasing the HCP/FCC ratio of Co binder phase by HCP/FCC phase transformation
Mechanical properties of WC–10Co cemented carbides sintered from nanocrystalline spray conversion processed powders
No full textMechanical properties and microstructures of nanocrystalline WC-10Co cemented carbides were investigated. The nanocrystalline WC-10Co cemented carbide powders were manufactured by reduction and carbonization of the nanocrystalline precursor powders which were prepared by spray drying process of solution containing ammonia meta-tungstate (AMT) and cobalt nitrate. The WC powders were about 100 nm in diameter mixed homogeneously with Co binder phase and were sintered at 1375 degreesC under a pressure of 1 mTorr. In order to compare the inicrostructures and mechanical properties with those of nanocrystalline WC-10Co. commercial WC powders in a diameter range of 0.57-4 mum were mixed with Co powders, and were sintered at the same conditions as those of nanocrystalline powders. TaC, Cr3C2 and VC of varying amount were added into nanocrystalline WC-10Co cemented carbides as grain growth inhibitors. To investigate the microstructure of Co binder phase in the WC-10Co cemented carbides, Co-W-C alloy was fabricated at the temperature of sintering process for the WC-10Co cemented carbides. The hardness of WC-10Co cemented carbides increased with decreasing WC grain size following a Hall-Petch-type relationship. The fracture toughness of WC-10Co cemented carbides increases with increasing HCP/FCC ratio of Co binder phase by HCP/FCC phase transformation. (C) 2001 Elsevier Science Ltd. All rights reserved
Mechanical properties of WC-10Co cemented carbides sintered from nanocrystalline spray conversion processed powders
No full textGeneralized shear-lag model for load transfer in SiC/Al metal-matrix composites
No full textThe load-transfer efficiency of reinforcement, in cylindrical forms in metal-matrix composite (MMC), was analyzed based on the shear-lag model. Both the geometric shape and alignment of reinforcement were considered. The stress transferred to a misaligned whisker was calculated from differential equations based on the force equilibrium in longitudinal and transverse directions. A new parameter, defined as effective aspect ratio, was used to indicate the load-transfer efficiency of misaligned reinforcement. The effective aspect ratio was formulated as a function of aspect ratio and misorientation angle of reinforcement in MMC. A probability density function of misorientation distribution was used to estimate the strengthening effect of all misaligned whiskers distributed in the matrix. Considering the contributions of both effective aspect ratio and misorientation distribution on load-transfer efficiency, a generalized shear-lag model was proposed to explain the mechanical anisotropy of discontinuous reinforced MMC
Sintering behaviour and microstructures of carbides and nitrides for the inert matrix fuel by spark plasma sintering
No full textZirconium carbide, titanium carbide, zirconium nitride and titanium nitride. which are promising candidates for the ceramic matrix of inert matrix fuel (IMF) to transmute long-lived actinides were sintered using the spark plasma sintering (SPS) technique. Dy2O3(20 wt%) was added as a surrogate for Am2O3 and the sintering behaviours of Dy2O3 dispersed carbide or nitride matrix composites were compared with that of the matrix. The spark plasma sintering conditions consisted of a rapid heating rate of 75 K min(-1) and a very short holding time of 1-4 min at maximum temperatures ranging from 1773 to 2000 K. Dy2O3 dispersed carbides and nitrides with about 80%, of theoretical density were obtained by spark plasma sintering with a rapid heating rate and a short dwelling time. When Dy2O3 was added to the matrix, the shrinkage of the carbide or of nitride composites was initiated from a lower temperature than its matrix material during the heating stage. In the case of TiC and TiN, microstructural observation exhibited that Ti is soluble in dysprosium oxide and densification is enhanced around the oxide phase. (c) 2006 Published by Elsevier B.V
Characterization of Carbon Nanotube/Cu Nanocomposite Processed by using Nano-sized Cu Powders
No full text- …
