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1.
《Materials Science & Technology》2013,29(7):935-942
AbstractThe equilibrium partial pressures of vapour species generated in halide activated pack powder mixtures at high temperatures were calculated for a series of compositions using thermochemical analysis tools. The results obtained were applied to identify suitable activators and pack compositions for codepositing Al and Si to form diffusion coatings on nickel base superalloys by the pack cementation process. The calculation results suggested that compositions of the packpowder mixtures activated by CrCl3.6H2O may be adjusted to create deposition conditions favourable for codepositing Al and Si, but, those activated byAlF3or AlCl3 may only deposit Al.A series of coating deposition experiments were also carried out at 1000 ° C and 1100 ° C and the results obtained confirmed that, with adequate control of pack compositions and deposition conditions, codeposition of Al and Si can be achieved with CrCl3.6H2O activated pack powder mixtures. A mixture of elemental Al and Si powders may be used as a depositing source instead of using Al-Si master alloy powders as conventionally recommended. The coatings could be formed either through the inward diffusions of Al and Si or through the outward diffusion of Ni together with other substrate elements such as Cr and Co, depending on the deposition temperature used. Prolonged deposition at 1100 ° C ledtothe formationofa coatingwith amultilayeredstructure consistingofanouter nickelsilicide layerand a middle Simodified NiAl layer followed by a diffusion zone. The pack compositions and deposition conditions may be adjusted to control the microstructure of the coatings formed by the codeposition process. 相似文献
2.
《Materials Science & Technology》2013,29(5):636-639
AbstractNumerical simulation is being increasingly used to improve the existing cooling systems. In order to attain highest quality strand, a two-dimensional dynamic mathematical heat transfer model of billet continuous casting of low carbon steel has been presented. This model can be used to compute the billet temperature distribution and shell thickness, especially it can be used to simulate the solidification process which is caused by frequently variational casting conditions. The fluctuation of measured temperature has been reduced to <10°C with thermal imaging system. The online model can monitor surface temperature and shell thickness in the casting process. So it provides the possibility for the online process control. For the validation of the dynamic model, a lot of billet surface temperature and shell thickness measurement were carried out on an actual casting machine. Finally, the dynamic model has been used for adjusting the operating parameters to improve the casting speed. 相似文献
3.
Study on continuous casting of bulk metallic glass 总被引:1,自引:0,他引:1
Tao ZhangXingguo Zhang Wei Zhang Fei JiaAkihisa Inoue Hai HaoYuejiao Ma 《Materials Letters》2011,65(14):2257-2260
Continuous casting method for massive production of steel, aluminum, copper or other crystalline alloy ingot is a very important industrial technology for its low energy consumption and high productivity. In this study, a new continuous casting method was developed for the massive production of bulk metallic glass ingot with centimeter-scale diameter without length limitation. An intermittent withdrawal procedure was practiced for continuous casting of bulk glassy alloy. The new developed continuous casting method can provide a cooling speed as high as that provided by the stationary mold casting method. A Zr-based glassy alloy rod with a diameter of about 10 mm and length of tens of centimeters was prepared by the continuous casting method for the first time. 相似文献
4.
《Materials Science & Technology》2013,29(11):1350-1353
AbstractInductive heating has distinctive advantages for reheating of billets in continuous casting, but the success of this process requires good understanding of the operation principles and effective control of the process variables. In the present study modelling and finite element simulation are performed for the inductive reheating of continuously cast square billets. Important performance characteristics such as temperature profile, magnetic field distribution and the power absorption have been analysed. Representative temperatures obtained from the simulation are compared with experimentally measured temperatures. The results provide better understanding of the inductive reheating process and key information for process design. 相似文献
5.
《Materials Science & Technology》2013,29(10):1139-1148
AbstractCoating of organic substrates to improve properties has attracted interest because of the potential industrial applications for these materials. Thermal spraying is an attractive coating technology for this purpose owing to its high deposition rate relative to competing processes; however, actual industrial applications remain limited because of poor bonding between the polymeric substrate and the thermal sprayed deposit. Consequently, specific surface preparation of the polymer is required in most cases. In the present study, an innovative surface treatment of a polymeric material allowing subsequent buildup of a plasma sprayed coating is reported. This patented process, known as Pinpro, was successfully applied to coat an organic stereolithography substrate with an AISI 316 stainless steel thick (1 mm) deposit. The process consists in creating a population of surface microcracks in the polymer to provide mechanical anchoring for the steel deposit. Methods of surface preparation were investigated and optimised. The main surface modification mechanisms were elucidated and a phenomenological model of coating buildup on the treated substrate is proposed. 相似文献
6.
利用渗流铸造法制备了直径为6mm的vit106非晶合金与羟基磷灰石(HA)的复合材料,分别采用扫描电镜(SEM)、X射线衍射(XRD)分析了铸态合金的组织形貌和相组成.实验结果表明,铸态合金由非晶组织和HA组成,二者均匀分布,界面结合良好.力学性能实验表明,复合材料的压缩断裂强度为250MPa,最大塑性变形量达到了65%.与目前钛合舷金/20%(体积分数)HA复合材料相比,强度得到了提高;与块体非晶合金多孔材料相比,在相近的强度指标下,具有更高的塑性.由于HA与非晶合金都具有良好的生物相容性,因此这种复合材料在生物移植材料上具有一定应用前景. 相似文献
7.
Extrusion properties of a Zr-based bulk metallic glass 总被引:1,自引:0,他引:1
The extrusion behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 metallic glasses in the supercooled liquid region was investigated. Good extrusion formability was observed under low strain rates at temperatures higher than 395 °C. The metallic glasses were fully extruded without crystallization and failure within the range of T = 395-415 °C under strain rates from 5 × 10− 3 s− 1 to 5 × 10− 2 s− 1, and the deformation behavior of the metallic glasses during the extrusion was found to be in a Newtonian viscous flow mode by a strain rate sensitivity of 1.0. 相似文献
8.
Liang Deng Long Zhang Konrad Kosiba René Limbach Lothar Wondraczek Gang Wang Dongdong Gu Uta Kühn Simon Pauly 《材料科学技术学报》2021,81(22):139-150
Monolithic bulk metallic glass and glass matrix composites with a relative density above 98 % were produced by processing Cu46Zr46Al8 (at.%) via selective laser melting (SLM).Their microstructures and mechanical properties were systematically examined.B2 CuZr nanocrystals (30-100 nm in diameter) are uniformly dispersed in the glassy matrix when SLM is conducted at an intermediate energy input.These B2 CuZr nanocrystals nucleate the oxygen-stabilized big cube phase during a remelting step.The presence of these nanocrystals increases the structural heterogeneity as indirectly revealed by mircrohardness and nanoindentation measurements.The corresponding maps in combination with calorimetric data indicate that the glassy phase is altered by the processing conditions.Despite the formation of crystals and a high overall free volume content,all additively manufactured samples fail at lower stress than the as-cast glass and without any plastic strain.The inherent brittleness is attributed to the presence of relatively large pores and the increased oxygen content after selective laser melting. 相似文献
9.
本文分析了熔体温度、铸造压力和化学成分对非晶合金玻璃形成能力(GFA)与压铸成型性能的影响,并探究两种性能的工艺关联。研究发现:随熔体温度升高,Zr基非晶合金GFA先提高后减小,且合金成分不同,熔体化学成分,局域原子团簇特征和合金实际冷却速率就不同,非晶合金GFA与玻璃稳定性也就存在差异。非晶合金的压铸成型能力随熔体温度和铸造压力升高不断提高,但与GFA存在相互限制的作用:当合金GFA较强时,熔体内原子堆垛密实,粘滞系数较高严重阻碍过冷液流动成形,且玻璃稳定性越好压铸成型性能越差;而当熔体温度过高,非晶合金GFA减弱,过冷液粘度降低时,才能快速提高非晶合金的压铸成型性能。因此,选择最佳的合金成分、优化工艺参数有利于非晶精密结构件成型。 相似文献
10.
《Materials Science & Technology》2013,29(12):1567-1572
AbstractThe 718 steel used for plastic dies is required to be prehardened to 29 – 35HRC. For large sized blocks, it is relatively difficult to additionally guarantee uniform hardness with the greatest hardness difference of 3HRC and without any quenching cracks after heat treatment. In this paper, the transient temperature field and microstructure transformation during the quenching process of large sized blocks of 718 steel have been simulated numerically. Based on the simulation and experimental results, an appropriate quenching process, that is, direct air cooled quenching after austenitising at higher temperatures such as 880 – 930°C, was recommended in order to reach hardness uniformity and avoid quenching cracks. 相似文献
11.
《Materials Letters》2007,61(11-12):2217-2221
Bulk Mg65Cu20Ag5Gd10 metallic glass matrix composites reinforced by SiC particulates were synthesized and characterized. Thermal stability and glass forming ability of the matrix are not significantly affected by the particle addition. Compressive fracture strength of the SiC particulates reinforced composite reached about 963 MPa, a factor of 1.2 higher than monolithic glass. A small quantity of Si atoms diffusion can be detected in the composite, but no reaction layer can be observed. 相似文献
12.
Mustafa Bakkal Erdin Serbest lker Karip in Ali T. Kuzu Umut Karag zel Bora Derin 《先进制造进展(英文版)》2015,3(4):282-291
There are limited studies in the literature about machinability of bulk metallic glass(BMG).As a novel and promising structural material,BMG material machining characteristics need to be verified before its utilization.In this paper,the effects of cutting speed,feed rate,depth of cut,abrasive particle size/type on the BMG grinding in dry conditions were experimentally investigated.The experimental evaluations were carried out using cubic boron nitride(CBN) and Al_2O_3 cup wheel grinding tools.The parameters were evaluated along with the results of cutting force,temperature and surface roughness measurements,X-ray,scanning electron microscope(SEM)and surface roughness analyse.The results demonstrated that the grinding forces reduced with the increasing cutting speed as specific grinding energy increased.The effect of feed rate was opposite to the cutting speed effect,and increasing feed rate caused higher grinding forces and substantially lower specific energy.Some voids like cracks parallel to the grinding direction were observed at the edge of the grinding tracks.The present investigations on ground surface and grinding chips morphologies showed that material removal and surface formation of the BMG were mainly due to the ductile chip formation and ploughing as well as brittle fracture of some particles from the edge of the tracks.The roughness values obtained with the CBN wheels were found to be acceptable for the grinding operation of the structural materials and were in the range of 0.34-0.58 μm.This study also demonstrates that conventional Al_2O_3 wheel is not suitable for grinding of the BMG in dry conditions. 相似文献
13.
《Materials Science & Technology》2013,29(4):475-482
AbstractThe vertical Bridgman directional solidification equipment has been used in several investigations to simulate direct chill casting of wrought aluminium alloys. As a basis for such investigations and alloy developments, it is important to have an understanding of the performance of the furnace used during simulation of the casting conditions. In this investigation the thermal conditions in the furnace have been analysed in detail, both by measurements and by mathematical modelling. The growth characteristics of the furnace, such as gradient, growth rates and cooling rates have been compared to conditions in large ingots. The direct chill casting conditions, which the simulations have been compared to, are casting of slabs of 330 and 600 mm thickness of an aluminium AA3003 type alloy. The results show that the experiments are able to simulate the cooling conditions in the ingots except from the surface zone. Comparisons of the microstructures have been made and a good agreement has been obtained for structure parameters such as grain size and DAS. 相似文献
14.
(Cu42Zr42Al8Ag8)100? x Si x (x?=?0?~?1) amorphous alloy rods of 2–6?mm diameter were prepared by Cu-mold drop casting. The thermal properties, microstructure evolution, and mechanical properties were studied by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), transmission electron microscopy (TEM), hardness test, and compression test. The XRD result revealed that all as-quenched (Cu42Zr42Al8Ag8)100?x Si x alloy rods exhibited a broad diffraction pattern in the amorphous phase. The (Cu42Zr42Al8Ag8)99.5Si0.5 alloy was found to possess the highest glass forming ability (GFA) as well as the best thermal stability among all tested samples. In addition, both its hardness and yield strength were increased by the microalloyed Si content. The fracture strength and the plastic strain of (Cu42Zr42Al8Ag8)99.5Si0.5 amorphous alloy can reach 2000?MPa and 3.5 %. 相似文献
15.
A Zr-based bulk metallic glass (BMG) in situ composite with a designed composition of Zr60Ti14.67Nb5.33Cu5.56Ni4.44Be10 was prepared based on both modifying alloy composition and controlling solidification process. The composite contains high
volume fraction of coarsen bcc β-Zr(Ti, Nb) solid solution. The β phase particles are short rod-like, worm-like, and nearly spherical in morphology rather than typical dendrite structure,
their volume fraction and average diameter were estimated to be about 55% and 20 μm, respectively. The composite displays
a large fracture strain up to 22.3% under uniaxial compression at room temperature. The coarse β phase and its high volume fraction were thought to be responsible for the excellent plastic deformability of the present
composite. 相似文献
16.
Modelling of safety glass for crash simulation 总被引:3,自引:0,他引:3
In this paper, we present a numerical technique to simulate the crash behaviour of laminated safety glass via finite elements. As the main aspect of this work, we consider two coincided elements: a shell element for glass and a membrane element for the hyperelastic PVB-interlayer. We give an overview of hyperelastic models, which are used in crash simulations and investigate the material laws by Blatz–Ko, Mooney–Rivlin and Ogden. The obtained stress–strain curves are fitted by experimental results of the interlayer. For a comparison, we use an one-material-model with piecewise linear plasticity and a laminated glass model assigning material properties to the integration points. As practical applications, we simulate an impact of a sphere into a glass plate and investigate the behaviour of a windscreen during a roof crash. 相似文献
17.
A bulk metallic glass (BMG) with large plasticity was prepared and its fracturing behavior was observed at a strain rate larger than ∼ 10− 3 s− 1 under uniaxial compression. Even in this strain rate condition, the BMG still exhibits an excellent plastic deformability. The BMG exhibits a large elastic limitation of about 2.43% for engineering strain and 2.46% for true strain. The engineering and true plastic strains are 3.05% and 3.18%, respectively, and the maximum compressive strength is 1810 MPa. High dense shear bands appear in the outer surfaces of the failed BMG, of which the fracture surface exhibits melting and subsequently tearing-up signs with low vein height and small droplet, orientating significantly. The fracture angle is about 54°, deviating from the theoretical fracture angle by 9°. These may be related to the unique performance characteristics and the micro-structure of the BMG. 相似文献
18.
《Materials Science & Technology》2013,29(2):166-170
AbstractCu based bulk metallic glasses and composites with tiny crystalline phases embedded in metallic glass matrix have been successfully fabricated by solidification technique in the present work. The formation of crystalline phases and structure inhomogeneity in bulk metallic glasses was characterised. Al is used as the minor alloying element to partly substitute Cu element in 61Cu–34Zr–5Ti. The results show that quarternary 60Cu–34Zr–5Ti–1Al alloy exhibits monoamorphous feature, and 56Cu–34Zr–5Ti–5Al alloy has a few crystalline peaks superimposed on a broad diffraction peak, suggesting that a composite structure forms in certain solidification conditions. To further identify the microstructure of the as cast rod, all samples were characterised by scanning electron microscopy (SEM). Small size phases are found in 2 mm diameter 56Cu–34Zr–5Ti–5Al rod, which has larger plastic deformation. The composition of those crystalline phases is also investigated. All results indicate that the presence of certain phases in metallic matrix benefits the mechanical properties of the as cast bulk metallic glasses. 相似文献
19.
In this paper, the effect of nickel coating on the plasticity of a brittle Fe-based bulk metallic glass (BMG) was investigated. By electrodepositing a nickel coating onto an Fe75Mo5P10C8.3B1.7 BMG, the plasticity of the BMG is shown to increase dramatically from ~ 0.5% to ~ 5.0%. Without reducing the strength of the BMG, the findings demonstrate that the electrodeposited nickel is an effective way to improve prominently brittle BMGs. The increased compressive plastic strain is believed to be attributed to the nucleation, intersection and bifurcation of multiple shear bands due to the exterior impedance of the surrounding coating. 相似文献
20.
Junqing Wang Chao Xu Shifang Su Xuejun Hu Yunfei Jiang Dewei Yu 《Science and Technology of Advanced Materials》2013,14(1):225-230
Modelling and experiment work is carried out for a large stainless steel casting with variable cross-section and a curved surface which is produced by the electric slag remelting casting process. The casting is part of a hydraulic runner generator at a power station of a big river.Mathematical models of the heat transfer and melted rate from an expendable metallic electrode were established. The melted rate is related to some important parameters, such as electric current and voltage, temperature and the flow rate of the cooling water in a crystallizer. Electrode melting, the moving pattern of the melted pool and the slag pool and the melt solidification in the metal pool were simulated.In order to make the enmeshment of the variable curved surface of the casting, a co-operation method of extended constructive solid geometry (CSG) from 9 to 21 uniform geometry with B-Spline surface functions is developed. By this method the guide vane casting is enmeshed. The boundary condition between the steel casting and the crystallizer cooled by water was measured.Based on the above new content the solidification simulation software ESRC3D is developed. Using it to simulate the whole process of ESRC with different parameters, instead of exploring the technological parameters of casting production by the trail-and-error method, the optimized parameters from the simulation for production of the large stainless steel castings with variable cross-section and a curved surface, such as the guide vane castings, have been used to produce them. Economic benefit and good quality of castings are obtained. Guide vane castings are widely applied to the hydraulic runner generator at numerous river power stations. 相似文献