Papers by Keyword: Sintering

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Authors: Chun Ming Wang, Si Yu Gao, Su Fen Xiao, Yun Gui Chen
Abstract: In-situ formation of nanometric TiC reinforcements based on Ti matrix composites were researched by a novel preparation method, which including glucose polymers coating and powder metallurgy. The results showed that TiC nanoparticles were homogeneously distributed in Ti matrix, and the as-sintered Ti-TiC composites displayed excellent compressive properties which ultimate compressive strength was 2500 MPa, yield strength was 1450 MPa and strain to fracture was 53 %.
Authors: Helio R. Simoni, Eduardo Saito, Claudinei dos Santos, Felipe Antunes Santos, Alfeu Saraiva Ramos, Olivério Moreira Macedo Silva
Abstract: In this work, the effect of the milling time on the densification of the alumina ceramics with or without 5wt.%Y2O3, is evaluated, using high-energy ball milling. The milling was performed with different times of 0, 2, 5 or 10 hours. All powders, milled at different times, were characterized by X-Ray Diffraction presenting a reduction of the crystalline degree and crystallite size as function of the milling time increasing. The powders were compacted by cold uniaxial pressing and sintered at 1550°C-60min. Green density of the compacts presented an increasing as function of the milling time and sintered samples presented evolution on the densification as function of the reduction of the crystallite size of the milled powders.
Authors: Yun Zhou, Xiao Qing Zuo, Ting Zhang
Abstract: Pure 316L powder is used to mix with an additive to prepare a powder mixed paste. 316L honeycombs were fabricated by extruding the powder mixed paste, then dried and sintered. The volume shrinkage and the apparent density of extruded honeycombs after drying and sintering were measured. The effect of sintering temperature on the volume shrinkage, the apparent density and the structure of honeycombs had been studied. The results show that the volume shrinkage and the apparent density of sintered honeycombs increase with sintering temperature from 1120°C to 1200°C , the volume shrinkage varying from 42% to 57%, and the apparent density from 1.9 to 2.9g/cm3 for 80% solids fraction. The volume shrinkage decreases and the apparent density increases with solid fractions increasing. The structure of sintered honeycombs consists of matrix phase α-Fe(Cr,Ni) , complex compounds of silicon, oxygen and inclusion elements. There is oxide film forming on surface of sintered honeycombs.
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.
Authors: Muziwenhlanhla A. Masikane, Hilda K. Chikwanda, Iakovos Sigalas
Abstract: Over the past years, the blended elemental powder metallurgy (PM) approach has been identified as one of the most promising strategies to reduce the cost of titanium-based components. However, oxygen pick-up, inhomogeneity of the microstructure and chemical composition are sometimes reported for PM parts. This work compares properties of a blended elemental Ti-6Al-4V alloy obtained by sintering under argon gas atmosphere with those of a vacuum cast alloy. Argon was purified by passing it through a series of oxygen and moisture traps prior to being introduced into the sintering furnace. Casting was performed under vacuum (1 x 10-3 mbar). The starting material in both processes was the cold isostaticaly pressed blended elemental (BE) Ti-6Al-4V powder compact. The BE powder was prepared by mixing 60Al-40V master alloy powder with commercial Grade 4 titanium powder (0.377 wt.% O2). The sintered and cast alloys were compared on the basis of oxygen pick-up, density, microstructure, chemical composition and hardness to determine which method is better. Although the BE approach could not eliminate the common challenges associated with powder metallurgy processing of Ti alloys, oxygen pick-up and additional contamination was lower compared vacuum casting. Sintering at 1350°C for 1 h could not achieve full density compared to casting, but the microstructure appeared more homogeneous. Both sintered and cast Ti6Al4V alloys were harder than wrought Ti6Al4V due to a high concentration of interstitial oxygen. The sinterered and sintered plus HIPed Ti6Al4V alloys were softer than as-cast Ti6Al4V due to lower oxygen pick-up and incomplete densification. From the contamination and homogeneity perspective, the BE approach is an attractive technique for processing of Ti6Al4V alloy.
Authors: Yu Niu, Feng Xu, Xiao Fang Hu, Yong Cun Li, Jing Zhao, Zhong Zhang
Abstract: A kinetic Potts Monte Carlo model was used to investigate the microstructural evolution of a three particles configuration during sintering. The a series of peculiar phenomena was observed and analyzed quantitatively, which indicated that even if the particle shape and the contact area are both completely symmetrical, the asymmetric neck growth will arise due to a special particle arrangement. Although the linear relationship between neck size logarithm and time logarithm was consistent with the traditional theory, a slower neck growth rate comparing with that of the two sphere model displayed a result of the asymmetric neck growth. The analysis of the particle rotation was made to confirm the occurrence of the asymmetric neck growth. It was firstly observed that the morphology of the grain boundaries became bevel, and the reason for this morphology was discussed. All the special phenomena have proved that the asymmetric particle arrangement about the contact area can trigger the unstable neck growth.
Authors: Kouichi Yasuda, Tadachika Nakayama, Satoshi Tanaka
Abstract: A mechanical model is proposed to estimate internal stress during sintering of ceramic multiphase laminates. A symmetrical multi-layered laminate is assumed, and one-dimensional elastic analysis is carried out on the change in stress of each layer during sintering, based on the differences in sintering strain, thermal expansion strain and phase transformation strain between the layers. By taking a limit such that the thickness of each layer approaches infinitesimally small, the internal stress expression can be extended into the case of the materials with continuous compositional change (viz. functionally gradient materials).
Authors: Kouichi Yasuda, Pei Ling Lv
Abstract: This paper proposes a model for estimating stress history during sintering of ceramic laminates. A symmetrical 3-layered laminate is assumed, and one-dimensional elastic calculation gives the stress change of each layer during heating, keeping at the sintering temperature, and cooling, respectively. How to get the stress history is actually shown by incorporating data of mechanical and thermal expansion properties of calcined monolayers. The validity of this model is discussed with a preliminary experiment on dense alumina / porous alumina laminates.
Authors: Ali Lahouel, Said Boudebane, Alain Iost, Alex Montagne
Abstract: The aim of this research paper is to fabricate a Fe-TiC composite by a novel and simple manufacturing method. The latter is based on two cumulative processes; a conventional sintering (transient liquid phase sintering) and a hot forging with steam hammer respectively. The blinder phase of the studied simples is varied from carbon steel to high alloy steel using alloying additive powders. The obtained outcomes showed that after the sintering process, the relative density of the performed simples is improved from 86% to 95.8% without any densification process. Otherwise, in order to ensure maximum densification and enhance in addition the solubility of the alloying additives the hot forging process is then applied. Indeed, the final obtained composite product is a TiC-strengthened steel with a relative density around 99% (about 6.5 g/cm3 of density) wherein 30% (wt.) of spherical and semi-spherical TiC particles are homogeneously distributed in the metal matrix.
Authors: Dang Ni Gao, Z.J. Li, H.W. Guo, X.F. Wang
Abstract: Pure eulytite Bi4(SiO4)3 crystals were prepared by high temperature melt cooling method using Bi2O3 and SiO2 as starting materials. In this study, the properties of the samples were characterized by thermo gravimetric (TG),differential scanning calorimeter (DSC), field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The results showed that eulytite Bi4(SiO4)3 was crystallized when high temperature glass-melt were cooled to 943°C and obvious exothermal peak is shown on the DSC curve; and pure eulytite Bi4(SiO4)3 crystals were synthesized by keeping the processing temperature for 8 hours. Bi4(SiO4)3 grains grew larger and the amount of vacancy increased along with the extension of holding time, while Bi4(SiO4)3 grains still presented a structure of partial ordering. Eulytite Bi4(SiO4)3 prepared through melt-cooling method is of high purity and good stability, and can be applied as starting materials of preparation of Bi4(SiO4)3 thin film and high quality Bi4(SiO4)3 macrocrystal.
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