Papers by Keyword: Mechanical Milling

Abstract: Carbon dioxide (CO₂) is one of the greenhouse gases (GHG) and the concentration is much more higher than other GHG gases. Based on the prediction, about 285.73 million tonnes will be emitted in year 2020 with the main contributors are from power generation, manufacturing industries, transportation and residential sector [1]. This research focused to study the effect of pressure on the CO₂ absorption with Malaysia steel slag using mechanical stirrer. The steel slag is collected from one of steel industry located in Pasir Gudang Johor Malaysia and characterized to investigated the chemical composition. The reaction between CO₂ absorption and the slag was investigated by using different speed and weight. The initial pressure was set at 101.3 kPa which equivalent with 1 atmospheric pressure. The behavior of the reaction between CO_2, and ground sample was investigated by measuring the change in the CO₂ pressure inside the mechanical stirrer. It was found that the CO₂ pressure decreased as soon as the stirrer started and continuously decreased till bout 270 t/min stirring time.

Abstract: The effect of Ni or Zr addition to Ti-Cu alloy was studied on the microstructure evolution during mechanical milling regarding to dependence of the amorphous transformation on the various composition elements. The microstructure of initial crystalline alloys and the remained phases after few hours of milling were investigated. The milling process lasted to the full amorphization of the powders. The results show that amorphous Ti₄₈Cu₄₂Ni₁₀ and Ti₄₈Cu₄₂Zr₁₀ powders are obtained after 13 h and 14 h of milling.

Abstract: Through many years, conventional material developments have emphasized on microstructural refinement and homogeneity. However, "nanoand Homogeneous "microstructures do not, usually, satisfy the need to be both strong and ductile, due to the plastic instability in the early stage of the deformation. As opposed to such a “nanoand homo-“microstructure design, we have proposed “Harmonic Structure” design. The harmonic structure has a heterogeneous microstructure consisting of bimodal grain size together with a controlled and specific topological distribution of fine and coarse grains. In other words, the harmonic structure is heterogeneous on micro-but homogeneous on macro-scales. In the present work, the harmonic structure design has been applied to SUS304L austenitic stainless steel via a ball milling process and a large size (50 mm in diameter) SPS sintering process. At a macro-scale, the harmonic structure SUS304Lcompacts exhibited significantly better combination of strength and ductility, under quasi-static tensile loadings, as compared to their homogeneous microstructure counterparts. High temperature tensile tests revealed that they also indicated high strength at elevated temperatures.

Abstract: This paper presents the novel microstructure design, called Harmonic Structure, which gives structural metallic materials outstanding mechanical properties through an innovative powder metallurgy process. Homogeneous and ultra-fine grain (UFG) structure enables the materials high strength. However, such a “Homo-“ and “UFG” microstructure does not, usually, satisfy the need to be both strong and ductile, due to the plastic instability in the early stage of the deformation. As opposed to such a “Homo-and UFG“ microstructure, “Harmonic Structure” has a heterogeneous microstructure consisting of bimodal grain size together with a controlled and specific topological distribution of fine and coarse grains. In other words, the harmonic structure is heterogeneous on micro-but homogeneous on macro-scales. In the present work, the harmonic structure design has been applied to pure metals and alloys via a powder metallurgy route consisting of controlled severe plastic deformation of the corresponding powders by mechanical milling or high pressure gas milling, and subsequent consolidation by SPS. At a macro-scale, the harmonic structure materials exhibited superior combination of strength and ductility as compared to their homogeneous microstructure counterparts. This behavior was essentially related to the ability of the harmonic structure to promote the uniform distribution of strain during plastic deformation, leading to improved mechanical properties by avoiding or delaying localized plastic instability.

Abstract: Silicon nitride with 50 mass zirconia ceramic matrix composites were processed by mechanical milling (MM) followed by spark plasma sintering (SPS). Two different of Si₃N₄ particle shapes for create harmonic microstructure were investigated. The microstructure of Si₃N₄-ZrO₂ with initial Si₃N₄ shape is like coin/flakes after MM for 144 ks was failed to create the harmonic microstructure after SPS. With another sphere shape of Si₃N₄ after MM for 144 ks, the harmonic microstructure could be formed after SPS. Thus, the initial powders shape of Si₃N₄ have an effect in the formation of harmonic microstructure could be fully achieved. The highest mechanical properties of Si₃N₄-ZrO₂ are on the powders with mechanical milling time for 144 ks. The Si₃N₄ ceramic with homogeneous fine grains of ZrO₂ dispersed on its surface was obtained, and the mechanical properties were improved. The Vickers hardness obtained on 144 ks is 1031 MPa and the bending strength is 262 MPa. The main factors explaining the improvement in the mechanical properties of Si₃N₄-ZrO₂ are considered to be the porosity decrease caused by the particles shape and appropriate condition of powder processing i.e. MM and SPS.

Abstract: A high density nanoscale clusters of Y–Ti–O exhibit superior creep strength and potential for high resistance to radiation damage. X-Ray Diffraction is used to determine the formation of the complex nanoclusters (NCs). The formation of Y₂TiO₅ NCs takes place during heat treatment of mechanically milled (MM) titanium and Yttria, and also it forms the mixture of Y₂Ti₂O₅ and Y₂Ti₂O₇ NCs during the high temperature soaking of MM iron, MM titanium and yttria. The microstructure of the hot consolidated mixture of MM iron, MM titanium and yttria were obtained through scanning electron microscopy (SEM). The back scattered electron mode is used to show the contrast between different elements in the microstructure. The increase in soaking temperature increases the size of the nanocluster, which decrease the volume fraction and number densities. A large population of nanoclusters precipitates during the heat treatment at high soaking temperature.

Abstract: Nanocrystalline/nanosized magnetite - Fe₃O₄ powder was obtained by mechanical milling of well crystallized magnetite obtained by ceramic method starting from stoichiometric mixture of commercial hematite - Fe₂O₃ and iron - Fe powders. The mean crystallites size of the magnetite is decreasing upon increasing the milling time down to 6 nm after 240 minutes of milling. After 30 minutes of milling an undesired hematite phase is formed in the material. The amount of this phase increases upon increasing the milling time. In the early stage of milling (up to 30 minutes) the existence of nanometric particles (mean size below 100 nm) is noticed. The d₅₀ median diameter decreases first (up to 5 minutes of milling) and after that, an increase follows for milling times up to 120 minutes. Saturation magnetization decreases upon increasing the milling time and is more difficult to saturate. X-ray diffraction, laser particle size analysis and magnetic measurements have been used for powder characterization.

Abstract: The evolution of the Al₂O₃/Ni (25% vol. Ni) composite powders, during the milling and the stability of the composite phases were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX). SEM images show a high level of homogenization of the Ni and Al₂O₃ phases for milling times larger than 120 minutes. The X-ray study indicates no reaction between the two phases. The crystallite grain size decreases with the milling time for both phases.

Abstract: Fe/Fe₂O₃ composite powders were obtained by mechanical milling of iron and hematite up to 120 minutes in a high energy planetary ball mill. The particles size decreases by mechanical milling upon the formation of the Fe/Fe₂O₃ composite particles. After 120 minutes of milling the median particles size is at 7.2 μm. The Fe/Fe₃O₄ type composite were obtained by reactive sintering in argon atmosphere at 1100 °C of the Fe/Fe₂O₃ composite powders milled for 60 and 120 minutes. After sintering a FeO-wüstite residual phase is formed and this phase is eliminated by applying a subsequent annealing at a temperature of 550 °C. The sintered compact before and after annealing is composed by a quasi-continuous iron matrix in which are embedded iron oxides clusters (Fe₃O₄ and FeO before annealing and Fe₃O₄ after annealing). The iron oxide clusters are analogous with the Widmanstatten structure observed in steels before and after annealing. The materials have been investigated using laser particle size analysis, optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction.

Abstract: Novel bio-composites were synthesized by plasma current activated sintering from the Ti-35Nb-2.5Sn/HA powders ball-milled for 12 h. The aim of this study was to investigate the effects of HA content (5, 10 and 15 wt%) on sintering properties, microstructure and compression properties of Ti-35Nb-2.5Sn/HA bio-composites. Results indicated that sintering rate decreased slightly with the increase of HA content. The phases of sintered composites were mainly˰ڂ˽̤̹˼˰̘̑˼˰Ca₃(PO₄)₂(TCP), TiO₂, CaTiO₃ and Ti_xP_y. The grain size of sintered composites reduced with the increasing of HA content, and sintered composites with ultra fine grains were fabricated finally. The compression test showed that all the sintered composites had low elastic modulus and high compression strength. The elastic modulus of Ti-35Nb-2.5Sn/15HA sintered composites was 22GPa with a high strength of 877MPa.