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1.
《粉末冶金学》2013,56(2):124-134
AbstractWater atomised Cu–Cr–Zr alloy powders were consolidated by inverse warm extrusion and by the commercial continuous rotary extrusion method, Conform. Those alloys consolidated by inverse warm extrusion exhibited enhanced mechanical properties compared with their respective Conform extruded counterparts, when tested at both room and elevated temperatures. The processing parameters adopted in the inverse extrusion experiments resulted in products which retained enough amounts of solutes in solid solution, which in turn, led to improved mechanical properties after aging. Conversely, the excessive adiabatic heat generated in the Conform machine eliminated the saturation effect produced by rapid solidification, negating any possible further improvement on the mechanical properties by aging. The mechanical properties of an inverse extruded Cu–2.8Cr–0.39Zr (at.-%) alloy at temperatures above 450°C were higher than those strengths reported for Cu–Be alloys and comparable to that of Cu–Ta and Cu–Nb composites. Therefore, rapidly solidified Cu–Cr–Zr alloys can be possible candidates for replacing such alloy systems for high temperature applications. 相似文献
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Premkumar M. K. Lawley A. Koczak M. J. 《Metallurgical and Materials Transactions A》1992,23(1):3219-3230
Prealloyed rapidly solidified Al-Fe-Ni alloy powder with dispersoid volume fractions of 0.19, 0.25, and 0.32 FeNiAl9 was produced by air atomization. The powder was degassed, canned, and consolidated to full density by vacuum hot pressing and extrusion or by direct extrusion. Microstructures in the alloy powder and consolidated material were characterized by means of optical, scanning (SEM), and transmission electron microscopy (TEM) and constituent phases identified by X-ray diffraction. The coarsening kinetics of the FeNiAl9 dispersoid were moni- tored by differential scanning calorimetry (DSC) and by quantitative metallography. Atomized powders exhibited two scales of microstructures: optically featureless regions and regions with a coarse dispersoid morphology. Within the featureless regions, there are three morphologies, namely, a fine uniform precipitate microstructure, a cellular microstructure, and an eutectic microstructure. The only dispersoid observed in the atomized powders and consolidated material was FeNiAl9). The two scales of microstructure were retained after consolidation, and after hot extrusion, the typical microstructure consisted of a recovered matrix structure with a grain size of 0.2 to 0.3 μm and equiaxed intermetallics of average diameter 0.1 μm. The microstructure was resistant to coarsening up to approximately 370 °C. Coarsening kinetics in this alloy system were consistent with a grain boundary diffusion model (activation energy 146 kJ/mol) and were not appreciably affected by dispersoid volume fraction. 相似文献
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《粉末冶金学》2013,56(1):46-49
AbstractUnder normal condition the cooling rate in a spray deposition process is too low to form 8009 aluminium alloy. In order to increase the cooling rate, overspray 8009 aluminium alloy powders were added. The effects of adding overspray powder on microstructures and mechanical properties of the spray deposited 8009, with and without addition of the overspray powders, were studied. It is shown that adding proper content of overspray powders significantly improves the mechanical properties of the spray deposited 8009 alloy. The mechanism involved in modification of the microstructures and the mechanical properties of the spray deposited 8009 alloy produced with the overspray powder addition approach was discussed. 相似文献
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Two nanostructured aluminum powder alloys (supersaturated Al4.5Cu prepared by mechanical alloying, and Al3.0Fe0.42Cu0.37Mn
rich in precipitates and prepared by rapid solidification via gas atomization) were consolidated into bulk material under various processing conditions via hot extrusion. The microstructural modifications and mechanical properties of the consolidated alloys as a function of the
extrusion conditions were investigated and are discussed here. The effect of pre-existing precipitates from nonsupersaturated
alloy is shown to be more effective for controlling grain growth during consolidation. The increase in the extrusion load,
with a concomitant increase in the extrusion rate and decrease in temperature, is shown to lead to microstructural modifications.
The differences in mechanical properties measured by compressive tests are also discussed in association with the extrusion
parameters. Furthermore, suggestions are given for rationalizing the extrusion rate and temperature for the consolidation
of nanostructured aluminum powder alloys via hot extrusion. 相似文献
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M. K. Premkumar A. Lawley M. J. Koczak 《Metallurgical and Materials Transactions A》1992,23(12):3219-3230
Prealloyed rapidly solidified Al-Fe-Ni alloy powder with dispersoid volume fractions of 0.19, 0.25, and 0.32 FeNiAl9 was produced by air atomization. The powder was degassed, canned, and consolidated to full density by vacuum hot pressing
and extrusion or by direct extrusion. Microstructures in the alloy powder and consolidated material were characterized by
means of optical, scanning (SEM), and transmission electron microscopy (TEM) and constituent phases identified by X-ray diffraction.
The coarsening kinetics of the FeNiAl9 dispersoid were monitored by differential scanning calorimetry (DSC) and by quantitative metallography. Atomized powders
exhibited two scales of microstructures: optically featureless regions and regions with a coarse dispersoid morphology. Within
the featureless regions, there are three morphologies, namely, a fine uniform precipitate microstructure, a cellular microstructure,
and an eutectic microstructure. The only dispersoid observed in the atomized powders and consolidated material was FeNiAl9. The two scales of microstructure were retained after consolidation, and after hot extrusion, the typical microstructure
consisted of a recovered matrix structure with a grain size of 0.2 to 0.3 μm and equiaxed intermetallics of average diameter
0.1 μm. The microstructure was resistant to coarsening up to approximately 370 °C. Coarsening kinetics in this alloy system
were consistent with a grain boundary diffusion model (activation energy 146 kJ/mol) and were not appreciably affected by
dispersoid volume fraction. 相似文献
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AbstractThe feasibility of producing room temperature superplastic Zn–Al alloys by hot extrusion of gas atomised powders has been investigated. Commercially pure zinc, and Zn–8wt-%Al and Zn–28wt-%Al binary alloys were gas atomised; the resulting powders were cold compacted into cylindrical billets and extruded to form consolidated rod. Two extrusion temperatures (200 and 300°C) were used, chosen to lie on either side of the invariant (eutectoid) temperature of 275°C. It has long been established that in conventional cast alloys rapid quenching from above this temperature is required to produce a microstructure having superplastic properties. (It was anticipated that the 300°C extrusions would contain quantities of near equilibrium eutectoid and thus be unlikely to deform superplastically. The 200°C extrusions were expected to exhibit a non-equilibrium structure that might have potential in terms of superplastic deformation.) The microstructures of the extrudates were investigated by transmission electron microscopy and the mechanical properties established by room temperature tensile testing and Charpy impact testing. PM/0502 相似文献
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The effects of the rare earth element yttrium(Y) and hot extrusion on the microstructure and mechanical properties of A356 alloy were investigated by mechanical properties testing and microstructure observation. The results indicate that the addition of Y improves the microstructure of the as-cast alloy. The distribution of primary α-Al is uniform and orderly. The long needle-like eutectic Si phases and β-Fe phases turn to strips and short rods. When the content of Y increases to 0.2 wt%, the mean diameter of aAl(40.3 μm) and the aspect ratio of the eutectic Si phase(2.3) reach the minimum values, which are68.9% and 86.1% lower, respectively, than that of the alloy without Y addition. Under extrusion stress, the shape of the eutectic Si phase is changed from long rod-like to near grain-like after solution treatment.The size of the eutectic Si phase is significantly reduced. The needle-like β-Fe phases are squeezed and broken. The mechanical properties of the as-extruded alloy are significantly improved compared to the as-cast alloy. When the rare earth content is 0.2 wt%, the ultimate tensile strength, hardness and elongation of the alloy reach the maximum values, which are 328.2 MPa, 110.4 HV and 21.3%, respectively, and increase by 42.01%, 37.71% and 481.91%, respectively, in comparison to the as-cast alloy without Y addition. 相似文献
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Nishtha Gupta B. Ravisankar S. Kumaran T. Srinivasa Rao 《Transactions of the Indian Institute of Metals》2012,65(4):381-386
In this study, mechanically alloyed Al-2024 and Al-2024/Al2O3 powders are densified by conventional sintering and by equal channel angular pressing (ECAP) with and without back pressure. The powder was encapsulated in an aluminium can for consolidation through ECAP. The properties obtained in the compacts by conventional sintering route and by ECAP are compared. The effect of conventional sintering and ECAP on consolidation behaviour of powder, microstructure, density and hardness is discussed. Room temperature back pressure aided ECAP results in nearly full denser (97?% of its theoretical density) compact at room temperature. Nano Indentation technique was used to determine the modulus of the consolidated compacts. 相似文献
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采用雾化法制得ZK60合金粉末,并用掺胶法制备ZK60合金棒材,研究热挤压后ZK60合金的微观组织、相组成及力学性能.结果表明:合金粉末主要由α-Mg固溶体构成,呈枝晶与等轴晶混合组织,晶粒尺寸5~10μm;在后续热挤压过程中粉末之间结合良好,晶粒进一步细化,同时合金基体中大量析出MgZn_2球形纳米颗粒;经T5(175℃保温12h)热处理后,析出相密度呈增加趋势.挤压变形后材料的屈服强度(σ_(0.2))、最大抗拉强度(σ_(UTS))和伸长率(δ)分别为286.3MPa、337.7MPa及5.6%;随后T5处理可进一步提高强度((σ_(0.2))=300.1MPa,σ_(UTS)=340.5 MPa),增加塑性(δ=12.3%). 相似文献
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《粉末冶金学》2013,56(4):380-385
AbstractIn this paper, the use of a microwave plasma method for the synthesis of aluminium nitride nanopowders is described. The powders were consolidated to near theoretical densities using the unique rapid consolidation technique, plasma pressure consolidation (P2C), developed by MMI. Rapid consolidation of nanopowders is an ideal requirement for better mechanical and thermal properties in the consolidated part, as it retains the fine microstructure preventing anomalous grain growth. Microwave plasma synthesis resulted in aluminium nitride nanopowders (85–200 nm), which were consolidated to near theoretical density using P2C in <5 min without sintering additives. The effect of yttria (3 wt-%) as a sintering additive on the thermal conductivity (TC) of aluminium nitride was also evaluated and compared with TC values obtained from additive free AlN consolidated samples. 相似文献
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《粉末冶金学》2013,56(4):203-209
AbstractPrealloyed Ti–6Al–2Sn–4Zr–2Mo titanium alloy powders made by a rotating electrode process were consolidated by three techniques: hot isostatic pressing (HIP), hot explosive compaction (HEC), and hot rolling (HR), to optimize the processing parameters in order to obtain fully dense compacts and the desired microstructures and mechanical properties. Room-temperature tensile properties show that all three techniques are capable of giving full density and mechanical properties equivalent to or better than wrought properties. Control of processing parameters which may require another step of deformation such as rolling gives more reliability for HIP and HEC compacts. Metallography and scanning electron microscopic studies on fractured tensile specimens revealed the presence of both metallic and non-metallic inclusions in the compacts. The control of such contaminations during manufacturing as well as processing is necessary for good mechanical properties. PM/0181 相似文献
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《粉末冶金学》2013,56(3):232-238
AbstractThe influence of microstructure on the mechanical properties of starch consolidated super solidus liquid phase sintered AISI type M3/2 high speed steel powder has been evaluated. Hardness measurements, Rockwell C indentation and scratch testing were used to evaluate the mechanical properties and light optical microscopy and scanning electron microscopy were used for post-test characterisation. The results show that it is possible to starch consolidate and sinter large particle size high speed steel powder to obtain microstructures with high mechanical strength. However, the results show a strong correlation between the as sintered microstructure and the resulting mechanical properties and illuminate the importance of having a dense and isotropic microstructure in order to meet engineering requirements in demanding applications. Consequently, the failure mechanisms observed during indentation and scratch testing can be related to residual pores, present in the low temperature sintered samples, and a coarse microstructure with eutectic carbides, present in the high temperature sintered samples. 相似文献
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研究了热挤压温度、挤压比、挤压速度、挤压前预处理对FGH96镍基粉末高温合金微观组织的影响规律,确定了获得晶粒尺寸小于10 μm的超塑性细晶组织的热挤压方法。研究结果表明,热等静压后FGH96合金发生了再结晶,实现了粉末的完全致密化成形,但晶粒大小极不均匀,且存在明显的原始颗粒边界(PPB)缺陷。采用热挤压前预处理工艺在确保合金晶粒不长大的同时,又可使γ'相粗化,显著降低热挤压变形抗力。随着挤压温度的升高,合金晶粒尺寸呈长大趋势。挤压温度为1 080 ℃时,获得平均晶粒小于10 μm的完全再结晶超塑性组织,挤压温度继续升高,晶粒尺寸将明显长大。随着挤压比的增大,挤压载荷明显增大,采用大于6∶1的挤压比,有利于获得平均晶粒小于10 μm的完全再结晶超塑性组织。载荷随热挤压速度的升高而增大,在保证合金组织为细晶的条件下,应尽量选择较低的挤压速度。由于在热挤压过程中合金已发生了完全的动态再结晶,未观察到明显的取向,力学性能测试结果也表明沿着挤压方向和垂直于挤压方向的性能相当,说明不同挤压方向的微织构对性能没有明显影响。 相似文献
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During hot extrusion, the microstructure and resultant mechanical properties of materials are subjected to considerable change
due to adiabatic local heat generation. In this work, strain, temperature distributions, and microstructural changes resulting
from the hot extrusion of Ti-6A1-4V alloy were studied using visioplasticity methods, thermal calculations, and optical microscopy.
The results were correlated to the microstructural behavior during hot deformation. Billets 62 mm in diameter were heated
to either 950 °C(α + β region) or 1100 °C(β region) and extruded at the extrusion ratios of either 6 or 12. Visioplasticity calculations show that, in the deformation
zone, strain is relatively high at the surface of the billet and gradually decreases with depth. Estimated strains of a bar
extruded at 950 °C with the extrusion ratio of 12 are 3.5 at the surface and 2.5 at the center, respectively. But the estimated
temperature at the surface is lower than that at the center. As a result, microstructures of the bar were bi-modal structure
at the surface and acicular transformed structure at the center. A bar extruded at 950 °C with an extrusion ratio of 6 had
all bi-modal microstructure. The strain distributions of bar extruded at 1100 °C were similar in nature to those at 950 °C.
M. ISHII formerly with Hikari Research and Development Laboratory. 相似文献
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Dongming Liu Yuhong Xiong Troy D. Topping Yizhang Zhou Chris Haines Joseph Paras Darold Martin Deepak Kapoor Julie M. Schoenung Enrique J. Lavernia 《Metallurgical and Materials Transactions A》2012,43(1):340-350
In this study, nanostructured Al 5083 powders, which were prepared via cryomilling, were consolidated using spark plasma sintering
(SPS). The influence of processing conditions, e.g., the loading mode, starting microstructure (i.e., atomized vs cryomilled powders), sintering pressure, sintering temperature, and powder particle size on the consolidation response and
associated mechanical properties were studied. Additionally, the mechanisms that govern densification during SPS were discussed
also. The results reported herein suggest that the morphology and microstructure of the cryomilled powder resulted in an enhanced
densification rate compared with that of atomized powder. The pressure-loading mode had a significant effect on the mechanical
properties of the samples consolidated by SPS. The consolidated compact revealed differences in mechanical response when tested
along the SPS loading axis and radial directions. Higher sintering pressures improved both the strength and ductility of the
samples. The influence of grain size on diffusion was considered on the basis of available diffusion equations, and the results
show that densification was attributed primarily to a plastic flow mechanism during the loading pressure period. Once the
final pressure was applied, power law creep became the dominant densification mechanism. Higher sintering temperature improved
the ductility of the consolidated compact at the expense of strength, whereas samples sintered at lower temperature exhibited
brittle behavior. Finally, densification rate was found to be inversely proportional to the particle size. 相似文献
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研究了挤压温度和挤压比对Ti-6Al-4V钛合金挤压型材显微组织、织构及力学性能的影响.挤压温度在相变点Tβ以上150~350℃、挤压比λ为25~85范围内时,型材动态再结晶均已完成,形成均匀的魏氏组织.型材的晶粒随挤压温度的降低和挤压比的提高而细化.型材织构在挤压比较低(λ=25)时强度较弱且为随机分布;当挤压比增加时,织构增强并有形成(1219)面纤维织构的趋势;当挤压比提高至85时,形成完整的(1219)面纤维织构.由于织构与晶粒细化的共同作用,使不同挤压条件下得到的Ti-6Al-4V钛合金型材综合力学性能比较稳定,即强度差异均不大于35 MPa,且延伸率和断面收缩率差值均不超过3%. 相似文献
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《粉末冶金学》2013,56(4):276-287
AbstractAluminium alloy AA 5083 [Al–4·4Mg–0·7Mn–0·15Cr (wt-%)], powder was ball milled in liquid nitrogen via the cryomilling method to obtain a nanocrystalline (NC) structure. Samples of the powder were hot vacuum degassed to remove interstitial contaminants, then consolidated by hot isostatic pressing (HIPing) at six temperatures (from 0·46Tm to 0·89Tm), before being high strain rate forged (HSRF) to produce plate material. The microstructure was analysed at the different processing stages. The compressive properties of the as HIPed material, plus tensile properties of the final product were studied. Despite grain growth during HIPing, an ultrafine grain (UFG) structure was retained in the consolidated material, which consequently had increased strength over conventionally processed AA 5083. As the HIP temperature was increased, the density increased. Strength changes were minimal in compression and tension with varying HIP temperature, once near full density was attained at 275°C (~0·64TM). Yield strength data indicate negligible variation in the grain size of the materials. 相似文献