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101.
The influence of gravity on the solidification microstructure of Al-Al3Ni eutectic alloy was investigated by using a 50-m-long drop tube. It was found that at different growth rates the average inter-rod spacing was always larger under rnicrogravity (μg) than those under normal gravity (lg). Moreover, with increasing growth rate, the spacing difference between lg samples and μg samples reduced progressively. Based on the experimental results and analysis, a physical model was proposed to describe the effect of gravity on the solidification process of eutectic alloy. 相似文献
102.
Low magnetic permeability is an important criterion in selection of the material of construction of beam pipes and vacuum chambers of electron accelerators for safeguarding against distortion of the magnetic field. In the modified design of new 20 MeV/30 mA Injector Microtron for the existing synchrotron radiation sources Indus-1 and Indus-2, AISI 316 LN stainless steel has been identified as the material of construction of its vacuum chamber. Welding of AISI 316LN stainless steel with conventional filler alloys like ER316L and ER317L of AWS A5.9 produces duplex weld metal with 3–8% ferro-magnetic delta ferrite to avoid solidification cracking. The results of the study has demonstrated that GTAW of AISI 316LN SS with high Mn adaptation of W 18 16 5 N L filler produced a crack free non-magnetic weld with acceptable mechanical properties. Moreover, AISI 316LN stainless steel is not required to be solution annealed after the final forming operation for obtaining a low magnetic permeability, thereby avoiding solution annealing of large vacuum chamber in vacuum/controlled atmosphere furnace and associated problems of distortion. Besides Injector Microtron, the study also provides useful input for design of future indigenous accelerators with vacuum chambers of austenitic stainless steel. 相似文献
103.
P. Gurusamy S. Balasivanandha Prabu R. Paskaramoorthy 《Materials and Manufacturing Processes》2015,30(3):381-386
The objective of this investigation is to study the effects of applied pressure on the solidification time and interfacial thermal resistance of A356/10% SiCp during squeeze casting. Samples were prepared for various but constant squeeze pressures up to 130 MPa while maintaining the melt and mold temperatures at 800°C and 400°C, respectively. It was observed that the solidification time was 60 s when no squeeze pressure was applied but it decreased to 42 s when the squeeze pressure was maintained at 130 MPa. The results also showed that the cooling rate increased with squeeze pressure. The solidification time calculated from one-dimensional heat flow theory was found to be close to that obtained from the experimental cooling curves. The interfacial thermal resistance between the mold and the casting was calculated and it decreases when the squeeze pressure increases. 相似文献
104.
Armindo Werlang Filho Bruno Vaz de Souza Carlos Alexandre dos Santos 《Materials and Manufacturing Processes》2015,30(11):1317-1323
This work presents the influence of austempering heat treatment carried out in one-step and two-step processes on the microstructures and mechanical properties of ductile cast iron. The samples were extracted from as-cast pieces and heat treated by austempering. For the one-step process the samples were heated at 910°C for 90 min for austenitization and cooled in salt bath at a temperature of 300°C for 30 min. For the two-step process the samples were cooled from 910°C to 245°C, kept at this temperature for 5 min in salt bath, then heated in another salt bath at a temperature of 300°C for 30 min. The samples were analyzed by optical microscopy and mechanical tests. After the one-step austempering, microscopic analysis of the samples showed ausferrite microstructure matrix and graphite in nodules surrounded by fine pearlite. For the two-step austempering, the presence of ausferrite matrix with graphite in nodules and retained austenite was observed. As to mechanical properties, the results showed that, with the two-step process there was gain (4.7%) in the average hardness and loss (3.5%) in the impact resistance. The microhardness of the ausferrite was 6.2% higher in the one-step austempering when compared to the two-step process. 相似文献
105.
Michael Vynnycky Shigeo Kimura 《International Journal of Heat and Mass Transfer》2007,50(25-26):5204-5214
The transient process of the solidification of a pure liquid phase-change material in the presence of natural convection in a rectangular enclosure is considered both analytically and numerically. One vertical boundary is held at a temperature below the melting-point of the material, the other above; the horizontal boundaries are both assumed adiabatic. A nondimensional analysis of the problem, principally in terms of the Rayleigh (Ra) and Stefan (St) numbers, indicates that some asymptotic simplification is possible for materials often considered in the literature (water, gallium, lauric acid). This observation suggests a way to simplify the full problem when Ra 1 and St 1, giving a conventional boundary value problem for the liquid phase and pointwise-in-space first-order ODEs for the evolution in time of the solidification front. The method is tested against full 2D finite-element-based transient numerical simulations of solidification. In addition, simpler approaches for determining the average thickness of the solid layer, based on boundary-layer and enclosure flow correlations, are also investigated. 相似文献
106.
It is demonstrated experimentally that by using the Council for Scientific and Industrial Research Rheo Casting System and high pressure die casting it is possible to semi-solid process and cast into a shape unmodified Al-Si binary eutectic without a solidification temperature range. Silicon leads the aluminium coupled crystal growth subjected to convection by induction during thermal arrest. The semi-solid structure during thermal arrest is captured after rheo-processing and casting. 相似文献
107.
The macroscopic morphologies and core-shell dimensional accuracy for Al-Bi immiscible alloys were investigated. Irrespective of compositions, the shell always consists of a Bi-rich phase due to surface segregation. With decreasing the superheat degree above the highest critical point of Al-65.5 wt.% Bi alloy, the shell of particles changed from irregular, annular to crescent shapes under the actions of Marangoni motion and gravity. The simulation suggests that the superheating and particle size affect markedly the temperature gradient and cooling rate of droplets, and thus influence the Marangoni and Stokes motions. At a superheat degree of 100 K, a perfect core-shell microstructure of Al-65.5 wt.% Bi particles with a diameter of 0.9 mm was successfully obtained. The dimensional relationship between the core and whole particle could be described by a function of Dcore = 0.9137 Dparticle − 0.0312. 相似文献
108.
Dongmei LiuXinzhong Li Yanqing SuLiangshu Luo Bo ZhangJingjie Guo Hengzhi Fu 《Materials Letters》2011,65(11):1628-1631
Bridgman-type directional solidification experiments have been carried out in Cu-20Sn peritectic alloy. Peritectic coupled growth and banding structures have been observed at low growth rates (1.5 and 2 μm/s) under a temperature gradient up to 40 K/mm. The peritectic coupled growth structure, containing rod dendrite primary α phase plus peritectic β phase, forms initially. As solidification proceeds, peritectic coupled growth is overgrown by banding or island banding structures. The formation of banding structure from coupled growth is explained by a model involving Sn concentration change at nucleation of the secondary phase ahead of the solid/liquid interface. It is found that the competitive growth between the α and β phases also plays a critical role on the formation of banding structures. 相似文献
109.
Shengyin ZhouRui Hu Jinshan LiHui Chang Hongchao KouLian Zhou 《Materials Science and Engineering: A》2011,528(3):973-977
Substantial undercooling ΔT up to 415 K was achieved for Co80Pd20 melt applying molten glass denucleation combined with cyclic superheating. The as-solidified structure as function of ΔT was described concisely. On this basis, dense-regular fault (DRF) ribbons were detected provided if a critical undercooling is surpassed. An integrated analysis of the DRF formation with a model calculation [16] for shrinkage-stress developed in the coherent dendrite network upon rapid solidification was then performed. This confirms that the as-formed DRF originates from a stress-induced deformation, which also plays an important role in understanding the grain refinement occurring upon rapid solidification of undercooled melts. 相似文献
110.
Using self‐made electromagnetic centrifugal casting machine, optical microscopy (OM) and D/max2200pc X‐ray diffraction, the solidification microstructure and phases of as‐cast high speed steel(HSS) roll made by sand casting, centrifugal casting and electromagnetic centrifugal casting were investigated. The experiment results show that the phases of as‐cast high speed steel (HSS) roll are alloy carbide (such as W2C, VC, Cr7C3), martensite and austenite. The centrifugal casting and electromagnetic centrifugal casting can apparently improve the solidification structure of HSS roll. With the increase of electromagnetic field intensity (B), the volume fraction of austenite in the HSS solidification structure increased obviously and eutectic ledeburite decreased, the secondary carbide precipitated from the austenite is more fine and distribution of secondary carbide is more even. 相似文献