Papers by Keyword: Microstructure

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Authors: Xun Luo, Wei Zhao
Abstract: This paper proposed a new 2D method to simulate the microstructure for normal grain growth of polycrystalline materials. In this method, the sample was discretized into geometry points and a straightforward geometric construction was implemented to estimate whether the current point was located at the interior of a certain grown grain. The ceramics material was assumed isotropic; furthermore, the single-phase and two-phase systems without pores were discussed respectively. So each grain core would grow up at the same velocity in all directions until it met another growing core in single-phase systems, while in two-phase systems, there would be two sorts of cores with different growing velocities. The ratio of these different velocities was the key factor of the sample microstructures after sintering. The simulation results and the analysis showed that the proposed method agree well with the experimental observation.
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Authors: Hai Bin Yu, Chuan Zhen Huang, Han Lian Liu, Bin Zou, Hong Tao Zhu, Jun Wang
Abstract: A 3D finite element polycrystalline microstructure model of ceramic tool materials is presented. Quasi-static crack propagation is modeled using the cohesive finite element method (CFEM) and the microstructure is represented by 3D Voronoi tessellation. The influences of cohesive parameters, the ratios of maximum traction of grain boundary to maximum traction of grain on the crack patterns of Al2O3 have been discussed. This study has demonstrated the capability of modeling 3D crack propagation of ceramic microstructure with CFEM and Voronoi tessellation model. It is found that the fracture mode is changed from intergranular to transgranular as the maximum traction of grain boundary is increased.
119
Authors: Yu Liu, Zhi Yu Wen, Li Chen, Xue Feng He, Sheng Qiang Wang
Abstract: This work focuses on the development of a biaxial fully differential capacitive microaccelerometer with a single proof-mass. Its design, optimization and fabrication are discussed in detail. Structure and geometric parameters are optimized by multidisciplinary design optimization, enabling ±1g operating range, 1182Hz resonant frequency, 97 fF/g sensitivity, 4.1mg resolution and 0.68 damping ratio. Silicon-on-glass (SOG) bulk micromachining and inductively coupled plasma (ICP) etching technologies are adopted to fabricate this accelerometer.
148
Authors: She Chuang Wang, Shu Zhu Zhou, Wei Zhen Peng, He Zhuo Miao, Wei Pan
Abstract: The composition, microstructures and properties of the Ti(CN) based cermets have been characterized by using SEM/BSE and energy spectrometer. Results shows that the carbon content of the cermets through N2 and Ar sintering was lower by 0.5% than vacuum sintering and the nitrogen content of the cermets through N2 sintering was higher by 20~25% than the Ar and vacuum atmosphere sintering. When sintered in Ar or N2, the balance between the carbon and nitrogen in the cermets was broken to form a surface defects, which would result in poor properties. The structure of vacuum sintering is more uniform and the properties are better.
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Authors: Haroldo Pinto, Anke Pyzalla, Heinz Hackl, Jürgen Bruckner
Abstract: Recently a new welding technique, the so-called ‘Cold Metal Transfer’ (CMT) technique was introduced, which due to integrated wire feeding leads to lower heat input and higher productivity compared to other gas metal arc (GMA) technique. Here microstructure formation and residual stress state in aluminum CMT welds are characterized and compared to those produced by pulsed MIG- and Laser-hybrid techniques. The results show a small heat affected zone (HAZ) in the MIG weld, the HAZ in the CMT and the laser hybrid welds was not visible by optical and scanning electron microscopy. Compared to the MIG welding the CMT process appears to introduce slightly smaller maximum tensile residual stresses into the weld.
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Authors: P. Kuppusami, T. Dharini, Ajith Kumar Soman, A.M. Kamalan Kirubaharan, Arul Maximus Rabel
Abstract: In this study, a systematic investigation on in-situ sintering behavior of Ni-YSZ (50: 50wt. %) pellets of density of 4.2 (low density) and 4.9 g/cm3 (high density) in ambient and oxygen environment by impedance spectroscopy is presented. X-ray diffraction indicated the formation of cubic phases of NiO and YSZ. The low density pellet sintered for 16 h showed low content of monoclinic phase when compared to high density pellet. The microstructure of the high density pellet revealed finer and homogenous distribution of Ni in YSZ matrix due to longer sintering duration when compared with the low density pellet. AC impedance spectra were recorded for both low and high density pellets during sintering in ambient and oxygen environment in the temperature range 873-1173 K. The results indicate that for both the pellets, the impedance values decreased when sintering temperature increased from 873 to 1173 K in both ambient and oxygen environment. However, the impedance was low while sintering in oxygen atmosphere than in ambient. Besides these observation, impedance of the high density pellet was much lower than that of the low density pellet at all sintering temperature in both ambient and oxygen atmosphere. While the impedance decreased with increasing sintering temperature, the capacitance increased slowly in both the ambient and oxygen atmosphere. The change in the impedance behavior due to grain interior and grain boundaries is explained in relation with the microstructural changes that occur during sintering in different environments.
237
Authors: Peng Lü, Fang Yu, Hong Qiang Ru
Abstract: B4C-Al and B4C-TiB2-Al composites were fabricated by infiltrating aluminum into porous B4C and B4C-TiB2 preforms in vacuum. The effect of TiB2 addition on the microstucture and mechanical properties of the B4C-Al composites were investigated. The flexural strength and the fracture toughness of composite improved greatly as the result of TiB2 addition. The TiB2 addition inhibited the reaction between B4C and Al. The infiltrated aluminum addition was the leading reason for the fracture toughness improvement of the composites. Inter/transgranular fracture mode with many tear ridges and dimples was showing in the fracture surface of the B4C-TiB2-Al composite. The relationships between the microstructures and the mechanical properties of the B4C-TiB2-Al composites were discussed.
255
Authors: Peng Lü
Abstract: B4C-Al and B4C-ZrB2-Al composites were fabricated by infiltrating aluminum into porous B4C and B4C-ZrB2 preforms in vacuum. The effect of ZrB2 addition on the microstucture and mechanical properties of the B4C-Al composites were investigated. The flexural strength and the fracture toughness of composite improved greatly as the result of ZrB2 addition. The ZrB2 addition inhibited the reaction between B4C and Al. The infiltrated aluminum addition was the leading reason for the fracture toughness improvement of the composites. Inter/transgranular fracture mode with many tear ridges and dimples was showing in the fracture surface of the B4C-ZrB2-Al composite. The relationships between the microstructures and the mechanical properties of the B4C-ZrB2-Al composites were discussed.
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Authors: Ning Wang, Jing Wang, Fu Wei Zheng, Yu Min Wu, Bao Rong Hou
Abstract: This paper compares the microstructure and electrochemical properties of the diamond-like carbon films obtained by two different deposition methods - microwave electron cyclotron resonance plasma enhanced chemical vapor deposition (MWECR-PECVD) techniques and electro-deposition – chosen for their low cost and capacity to produce films. The microstructure of the DLC films are investigated by Raman spectroscopy, FTIR spectroscopy, and electrochemical behavior is investigated by potentiodynamic and electrochemical impedance spectroscopy (EIS). Raman spectroscopy indicates that all the films deposited by different techniques show amorphous structure and typical characteristic of DLC film. FTIR spectrum results indicate that these DLC films are a-C:H films. As a result of EIS, the DLC films made by different methods showed obviously different electrochemical characters. The obtained results show that the DLC films deposited using the PECVD methods provided the better results, presenting a high corrosion resistance , high adherence to substrate, and a denser and more uniform surface.
1029
Authors: Khalil Farhangdoost, S. Rahnama
Abstract: A comparison between crack growth rate (da/dN) vs. effective stress intensity range factor (ΔKeff) curve behavior and microscopic and macroscopic fracture surface of commercial Ti-6Al-4V alloy are presented. Three different regimes are correlated with characteristics measured on the fracture surfaces. Three regions can be observed in which part I is rough and darker than others parts known as pre-transition, part II is smooth and light known as transition region and part III is a little darker than part II known as post-transition region. In the present investigation the correlation of fatigue crack growth rate for Ti-6Al-4V and microstructure of fracture surface has been presented.
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