Papers by Keyword: Grain Size

Abstract: In this work, we report the effect of sintering temperature (900°C, 1000°C, 1100°C and 1200°C) on the electrical and magnetotransport properties of polycrystalline La_0.67Sr_0.33MnO₃ (LSMO). Single phase of LSMO hexagonal structure (R-3c) accompanied with minor phases was successfully synthesized by co-precipitation method. With increasing sintering temperature, grain growth was promoted and grain connectivity was improved. It was found that an enhancement of resistivity on smaller grain size was due to larger grain surface over volume (grain boundaries effect). The shifting of the metal-insulator transition (T_MI) to higher temperature was also responsible for observed changes in physical properties. T_MI of 900°C, 1000°C and 1100°C were 232 K, 278 K and 298 K respectively however 1200°C was out of measurement range (higher than 300 K). In summary, CP900 with smaller grain size distribution (~200 nm) displayed the highest resistivity and MR% of -19.2% (at 80 K, 10 kG).

Abstract: The purpose of the paper is to investigate the dependency of various parameters on metal forming process using mathematical models. The incremental sheet metal forming process was studied using Box–Behnken design of experiments along with response from surface methodology analysis. In the study process factors namely feed rate, speed and coolant were analysed to understand the effect on the surface roughness, percentage (%) of thickness reduction, grain size and hardness of the Aluminium (Al) sheet metal, were examined after forming. The surface model analysis predicts that all four responses of the incremental forms show very strong correlation with the experimental results. The optimized process of incremental forming that runs on maintained levels of predicted factors, yield responses very close to that predicted from the model.

Abstract: In order to clarify the influence of milling time on the atomized precursor powders for 9Cr-ODS (Oxide Dispersion Strengthened) steel, the morphology and microstructure of atomized powders and mechanical alloying (MA) powders with different milling time were investigated by scanning electron microscopy (SEM), laser diffraction particle size analyzer, X-ray diffraction (XRD) and Vickers-hardness tester. The experimental results showed that the atomized powders are spherical in shape with the particle size of ~ 47 μm and the grain size of ~ 2 μm. With the increase of MA time, the morphology of MA powders becomes from spherical to lamellar structure, then to equiaxed shape. The mean powder size increases firstly then decreases. The grain size decreases quickly at the initial stage of milling process (0-2 h) then trends to reach a saturation value. The Vickers-hardness increases rapidly at the initial stage of milling, then reaches a saturation value.

Abstract: Microstructure and precipitation of a Ti-Nb microalloyed high-strength steel were studied. The objective of the study is to examine the factors affecting yield strength and the effect of processing temperatures on microstructure and precipitation. The research results indicate that the dominant factors responsible for yield strength are fine ferrite grains and fine-scale carbonitride precipitatates, which are affected by processing temperatures. The influence of reheating temperature on precipitates was analyzed. Moreover, the optimum reheating temperatures is suggested for Ti-Nb microalloyed high-strength steel.

Abstract: Nowdays Barium strontium titanate (BST) can be applied into many fields of engineering. Its properties attracted more researchers to research and apply it into many fields of study. In this work, sol-gel method of preparing barium strontium titanate (BST) has been used. This work was done with 4 different ratio of x with 4 different deposition layers. The main purpose of this work is to investigate the relation between the ratio of barium (Ba) with different deposition layer and the surface of the substrate. Atomic force microscopy (AFM) was used in whole work to investigate the crystalline structure and surface roughness of the BST thin films.

Abstract: In the first part of this article, the SW-CLC (Stoner-Wohlfarth with CLC modification) model is discussed for nanocrystalline magnets, as melt-spun exchange coupled NdFeB. In the second part, the effect of grain size of coercivity for large grain size, above the single domain particle size, is addressed. The Kondorsky law observed for large grain size only can be due to domain wall displacement phenomena, where there is nucleus expansion. There are two main situations, one for nanocrystalline grain size, where the SW-CLC model is obeyed, and other for large grain size, where the coercive field decreases proportionally to the square root of the grain size.

Abstract: Tin tailing sand is one of the residues from tin extraction. Tailing sand for sampling was taken from Batu Gajah, which was one of the active locations in tin mining in Malaysia. The silica content of tailing sand from Batu Gajah is between 95.9 to 98.9%. This research is to determine the effect of grain size by the increasing of water content on the permeability number. Grain size is a major determinant of mould and core permeability and surface finish of the casting. In this research involved the process of conducting the mechanical sieve grading to identify the grain size for this research. Sample was graded into 425 μm, 297 μm and 149 μm. Experiments were conducted according to American Foundrymen Society (AFS) standard of procedures. Cylindrical test pieces dimensioning of Ø50 mm×50 mm in height from various grain sand sizewater ratios bonded with 5wt% clay, were compacted by applying three ramming blows of 6666 g each using Ridsdale-Dietert metric standard rammer. The test pieces were tested for permeability number with Ridsdale-Dietert permeability meter. Grain sand size of 297 μm was discovered has appropriate permeability number with the water content of 4% which is within the requirement as moulding sand.

Abstract: Representative Elementary Volume (REV) is not only a necessary measure for studying heterogeneous pore structure of reservoir rocks but also an important parameter for core-scale numerical modeling. In this paper, we accordingly analyze the REV for different porous media with different grain sizes based on computed tomography (CT) measurement. Our results show that that CT measurement is a relible method for REV analysis and that there is an appropriate linear relationship between grain size and REV.

Abstract: Grain size and lubricating conditions influence material flow behaviours in micro metal forming processes. In this study, the brass (JIS C2700) tubes with 1.1 mm outer diameter and 0.5 mm inner diameter were treated by annealing at 400 °C, 500 °C and 600 °C to obtain various microstructures with the grain sizes of 20 μm, 34 μm and 80 μm, respectively. The treated tubes were machined and grounded to be 0.6 mm length specimens for the experiments of micro forward and backward hollow extrusion. Three lubricating conditions, which were dry, full and punch lubricated conditions, were carried out in the experiments. By comparing the upper cup height and rod length of the extruded specimens with the calibration curves established by finite element simulations, it is possible to estimate the friction factors in the processes. The results show that the dry conditions lead to stronger friction effects and thus larger friction factors. Moreover, the friction factor increased with grain size and stroke for all conditions.

Abstract: Grain size and homogeneity are influence to aluminium properties, Equal channel angular pressing (ECAP) can produce aluminium with ultra fine grain Size (UFG). The grain size is depends on ECAP Dies geometry (Channel angle Φ, Fillet radius ψ) and friction, taguchi method used to find the optimum dies geometry its can produce smaller grain size and homogeny. Modeling done with channel angels 90, 105 and 120°, fillet radius (inside) 1.5, 5,0 and 10 mm ; fillet radius (outside) 1.5, 5,0 and 10 mm and friction 0, 0,025 and 0,05. Modeling used L9 taguchi matrix, the most homogeny dies is ECAP dies with channel angel 105°, fillet radius (inside) 10 mm ; fillet radius (outside) 0 mm and friction 0,025