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1.
等通道转角挤压(Equal channel angular pressing, 简称ECAP)可以使镁合金产生较大的塑性变形.通过有限元方法模拟了等通道转角挤压工艺及其相关工艺参数,研究了工件的应变和载荷分布情况,并建立了累积变形结果、微观组织细化和力学性能的数学模型.通过分析得到了晶粒细化和力学性能的关系,对累积变形的特点分析,预测了晶粒细化后的尺寸和力学性能. 相似文献
2.
Kyung-Tae Park Duck-Young Hwang Si-Young Chang Dong Hyuk Shin 《Metallurgical and Materials Transactions A》2002,33(9):2859-2867
A submicrometer-grained structure was introduced in a commercial 5083 Al alloy by imposing an effective strain of ∼8 through
equal channel angular pressing. In order to examine the low-temperature superplastic behavior, the as-equal channel angular
pressed (as-ECAP) samples were tensile tested in the strain rate range of 10−5 to 10−2 s−1 at temperatures of 498 to 548 K corresponding to 0.58 to 0.65 T
m, where T
m is the incipient melting point. The mechanical data of the alloy at 498 and 548 K exhibited a sigmoidal behavior in a double
logarithmic plot of the maximum true stress vs true strain rate. The strain rate sensitivity was 0.1 to 0.2 in the low- and high-strain rate regions and 0.4 in the intermediate-strain
rate region, indicating the potential for superplasticity. At 523 K, instead of the sigmoidal behavior, a strain rate sensitivity
of 0.4 was maintained to low strain rates. A maximum elongation of 315 pct was obtained at 548 K and 5×10−4 s−1. The activation energy for deformation in the intermediate-strain rate region was estimated as 63 kJ/mol. Low-temperature
superplasticity of the ultrafine grained 5083 Al alloy was attributed to grain boundary sliding that is rate-controlled by
grain boundary diffusion, with a low activation energy associated with nonequilibrium grain boundaries. Cavity stringers parallel
to the tensile axis were developed during deformation, and the failure occurred in a quasi-brittle manner with moderately
diffusive necking. 相似文献
3.
4.
V. M. Segal 《Russian Metallurgy (Metally)》2006,(5):474-483
The mechanics of severe plastic deformation (SPD) is considered. Unlike steady-state plastic flows with the continuous evolution of dislocation structures, the SPD-induced microlocalization strongly depends on the deformation mode. The quantitative characteristic of a deformation mode is determined by the distribution of strain rates over the principal directions of a continuum shear and corresponds to the limiting states of pure shear and simple shear. Simple models of SPD mesomechanics demonstrate that a deformation mode affects a transition to localization, localization in shear bands, and rotational localization. The simple shear mode is shown to correspond to the optimum scheme of plastic structure formation, including the development of high-angle boundaries and grain refinement. Various SPD processes are analyzed in terms of simple shear. 相似文献
5.
Y. Y. Beygelzimer V. N. Varyukhin O. V. Prokof’eva 《Russian Metallurgy (Metally)》2013,2013(10):802-806
It is shown that the relative elongation to failure does not reflect the plastic properties of the ultrafine grained materials produced by severe plastic deformation. The use of the relative reduction of area to failure is proved to be more effective in the characterization of their ductility. 相似文献
6.
晶粒尺寸对大塑性变形的两相合金超塑性的影响 总被引:1,自引:0,他引:1
在室温下对共晶铅锡合金( Pb-62% Sn)进行了高压扭转变形( HPT)。采用不同时间的自退火制备不同晶粒尺寸的样品。最长的自退火时间为12天。通过研究这些样品在室温下不同的拉伸行为,从而获得了关于超塑性性能的结果。之后,本文通过将这些结果与等通道挤压( ECAP)获得的样品进行比较,不仅证明了所有样品都具有良好的超塑性,而且具有小晶粒尺寸的样品更容易在大应变速率的条件下获得超塑性。 相似文献
7.
The microstructures and hardening characteristics of Al and Al with dilute additions of soluble and insoluble impurities were
compared during wire drawing at room temperature to true strains (ε
w
) of 4.95. Three stages of microstructure change are observed: formation of a dislocation cell structure; cell boundary sharpening
and cell size refinement; dynamic recrystallization. A minimum effective cell size is reached at an intermediate strain level
corresponding approximately to the onset of dynamic recrystallization. The amounts and types of impurities at levels less
than 1 pct have a great effect on the details of the microstructural changes as well as the hardening characteristics. 99.98
pct pure Al alternately saturates and hardens fromε
w
= 0 to 4.95. Al-0.6 Fe (insoluble) work softens nearε
w
= 3.5. Al-0.2 Mg (soluble) and EC Al (with 0.15 pct soluble and insoluble impurities) both work harden at a diminishing rate
toε
w
≃1.25 then enter a linear hardening stage which persists toε
w
≃5. A linear relation between yield strength and inverse cell size is established for EC Al and Al-0.2 Mg in the cell refinement
strain range; however, the Petch slope is much less than that of similar Al alloys subjected to elevated temperature dynamic
or static recovery. Al-0.6 Fe does not exhibit a consistent linear relation between yield strength and inverse cell size.
These differences can be attributed to the degree of recovery and the interrelation between cell size, cell boundary character
and total dislocation density. 相似文献
8.
Robert A. Ayres 《Metallurgical and Materials Transactions A》1977,8(3):487-492
A considerable enhancement of the tensile ductility in a commercial Al-4 pct Mg alloy is observed during deformation at elevated
temperatures (up to 250°C) and slow strain rates. Total elongations of ∼175 pct at 250°C were obtained compared to 27 pct
at ambient temperature. Much of this ductility was a result of large increases with temperature in the post uniform or diffuse
necking strain. Measurements of strain rate sensitivity,m, as a function of strain, strain rate, and temperature showed thatm near fracture was linearly related to total elongation. The mechanisms controllingm in this Al-4 pct Mg alloy were dynamic strain aging at the lower temperature range and dynamic recovery at the higher temperatures.m was found to be a function of strain only when the relative fraction of dynamic recovery was greater than ∼35 pct. A comparison
ofm as measured in pure aluminum and in the commercial Al-4 pct Mg alloy suggests that Mg additions can significantly increasem during dynamic recovery. 相似文献
9.
S. V. Dobatkin L. L. Rokhlin T. V. Dobatkina N. I. Nikitina I. E. Tarytina 《Russian Metallurgy (Metally)》2011,(7):629-633
The effect of severe plastic deformation and subsequent aging on the structure and properties of cast and hardened magnesium
alloys containing samarium and yttrium is studied. Severe plastic deformation leads to additional hardening both before and
after aging. Hardening is achieved by the formation of nanocrystalline structure in quenched alloys or submicrocrystalline
structure in cast alloys. Severe plastic deformation results in the rapid decomposition of a supersaturated magnesium solid
solution and additional hardening due to the formation of nano-sized particles of hardening phases. 相似文献
10.
11.
S. V. Dobatkin V. V. Zakharov A. Yu. Vinogradov K. Kitagawa N. A. Krasil’nikov T. D. Rostova E. N. Bastarash 《Russian Metallurgy (Metally)》2006,(6):533-540
The possibility of formation of a nanocrystalline structure (with a grain size smaller than 100 nm) in four Al-Mg-Sc alloys with 3.1–5.9% Mg during severe plastic deformation by torsion at a hydrostatic pressure of 6 GPa (high-pressure torsion (HPT)) has been studied. Room-temperature HPT of the alloys is shown to produce a nanocrystalline structure if the magnesium content is more than 4% (in the range 0.16–0.31% Sc). As the magnesium content increases, the grain size decreases and is minimal (40–50 nm) in a 01570 alloy with 5.9% Mg and 0.3% Sc. The structure of the HPT-processed 01570 alloy remains nanocrystalline upon heating to 200°C or at a deformation temperature as high as 200°C. Postdeformation heating is found to cause aging processes. The hardening of all the Al-Mg-Sc alloys is maximal after HPT at 20°C followed by aging at 300°C. 相似文献
12.
Bing Q. Han Farghalli A. Mohamed Enrique J. Lavernia 《Metallurgical and Materials Transactions A》2003,34(1):71-83
In the present study, the mechanical properties of Fe processed via severe plastic deformation (equal-channel angular pressing (ECAP)) at room temperature were investigated for the first time.
The grain size of annealed Fe, with an initial grain size of about 200 μm, was reduced drastically during ECAP. After eight passes, the grain size reaches 200 to 400 nm, as documented by means of
transmission electron microscopy (TEM). The value of microhardness during pressing increases 3 times over that of the starting
material after the first pass and increases slightly during subsequent pressing for higher-purity Fe. Examination of the value
of microhardness after eight passes as a function of post-ECAP annealing temperature shows a transition from recovery to recrystallization,
an observation that resembles the behavior reported for heavily deformed metals and alloys. The tensile and compression behaviors
were examined. In tension, a drop in the engineering stress-engineering strain curve beyond maximum load was observed both
in the annealed Fe and the ECAP Fe. This drop is related to the neck deformation. The fracture surface, examined by scanning
electron microscopy (SEM), shows vein patterns, which is different from the dimples found on the fracture surface of annealed
Fe. In compression, an initial strain-hardening region followed by a no-strain-hardening region was observed in the ECAP Fe.
The yield strength in tension of the ECAP Fe was observed to be higher than that in compression. The strengthening mechanisms
and softening behavior are discussed. 相似文献
13.
The plastic anisotropy resulting from the initial deformation microstructure and various aging treatments applied to several
regions of an AA2090 near-net-shape extrusion has been investigated. Yield behavior was measured by uniaxial compression in
multiple orientations of each region. Two models of the plastic anisotropy were generated: the Taylor/Bishop-Hill model, based
on crystallographic texture, and the plastic inclusion model, developed by Hosford and Zeisloft,[5] which incorporates anisotropic-precipitate effects. In overaged conditions, the Taylor/Bishop-Hill model adequately describes
the observed plastic anisotropy. As the strengthening increment due to second-phase particles increases, there is a concurrent
increase in the magnitude of the precipitate contribution to anisotropy. This anisotropy can not be accurately predicted solely
by crystallographic texture. By incorporation of terms describing the precipitate anisotropy, the plastic inclusion model
correctly predicts the yield strength variation in all regions tested. Examination of the fundamental interaction between
matrix and precipitation strengthening reveals that there is a stronger basis for taking the critical resolved shear stress
(CRSS) of the precipitates as a constant, rather than their effective yield strength. This consideration provides a more consistent
and accurate form of the plastic inclusion model. 相似文献
14.
以热模拟压缩试验的应力-应变数据为基础,根据DMM模型(dynamic materials model,动态材料模型)建立固溶态粗晶GH4169合金的热加工图;结合光学显微镜(OM)及电子背散射衍射(EBSD)分析,确定合金压缩变形的稳定区和失稳区,研究不同变形条件下的微观变形机制,并提出工艺参数范围.结果表明,粗晶GH4169合金在应变速率为10-0.25~1 s-1、变形温度为950~1100℃的条件下发生热加工流变失稳,失稳原因主要与局部塑性流动引发的裂纹有关;粗晶GH4169合金在中、低应变速率区有3个典型的动态再结晶区域,在应变速率为l0-3s-1、变形温度为950℃时局部能量耗散效率(η)的极大值主要与晶界析出δ相对动态再结晶的促进作用以及局部的晶内形核有关;综合考虑能量耗散效率、伸长率和组织状态,建议粗晶GH4169合金的始锻和终锻分别在应变速率为10-2.7~ 10-1.5s-1、变形温度为1087.5~1100℃和应变速率为10-2.5~10-1.5s-1、变形温度为1000~1065 ℃的条件下进行. 相似文献
15.
Thermoelastic martensite and shape memory effect in B2 Base Ni-Al-Fe alloy with enhanced ductility 总被引:5,自引:0,他引:5
A ductile shape memory alloy of the Ni-AI-Fe system has been developed using principles through the control of microstructure.
Addition of Fe to the binary Ni-Al shape memory alloy allows the introduction of a ductile face-centered cubic (fcc) phase
in an otherwise extremely brittle β phase alloy, leading to an improvement in its ductility while retaining its ability to
exhibit shape memory arising from the martensitic transformation of theβ phase to Ll0 structure. It is shown that the transformation temperature in the ternary Ni-AI-Fe alloy can be easily controlled by the
preannealing in the β+ γ region. Experimental results on the effect of different annealing treatments on the microstructures and the shape memory
behavior in this alloy are presented and discussed. 相似文献
16.
Influence of severe plastic deformations on secondary phase precipitation in a 6082 Al-Mg-Si alloy 总被引:2,自引:0,他引:2
M. Cabibbo E. Evangelista M. Vedani 《Metallurgical and Materials Transactions A》2005,36(5):1353-1364
The role of severe plastic deformation on the second-phase stability in a 6082 Al-Mg-Si alloy was studied using differential
scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques. The alloy was fully annealed prior to undergoing
up to six equal channel angular pressing (ECAP) passes using route C. The Orowan strengthening mechanism was calculated on
the basis of TEM inspections for the two hardening second-phase precipitates: Mg2Si and Si. The former had a major tendency to be cut and fragmented by dislocations, while in the latter, a dissolution process
was induced by severe plastic deformation. Accordingly, the second-phase Si particles became progressively less effective
with increasing deformation (i.e., additional ECAP passes). The increase in hardness with the ECAP passes was mostly due to the grain refining mechanism and
to dislocation tangles within the newly formed grains. The expected, though if limited, contribution of second-phase hardening
was prevalently accounted for by the Mg2Si particles. 相似文献
17.
L. L. Rokhlin S. V. Dobatkin T. V. Dobatkina N. I. Nikitina I. E. Tarytina E. V. Tat’yanin M. V. Popov 《Russian Metallurgy (Metally)》2006,(1):80-85
The effect of severe plastic deformation by high-pressure torsion on the structure and properties of aged magnesium alloys containing 2.8–5.5 wt % Sm (the maximum solubility of samarium in solid magnesium is 5.8 wt %) are studied. The severe plastic deformation leads to substantial strengthening caused by the formation of a submicrocrystalline structure along with strengthening caused by the decomposition of a supersaturated magnesium-based solid solution. 相似文献
18.
19.
20.
The mechanisms of alternating severe plastic deformation (SPD) of polycrystalline foils of high-purity aluminum glued on hard
bulk samples are studied on a mesoscale. It is shown that the SPD mechanisms and its self-organization on a mesoscale are
controlled by the field of maximal shear stresses and rotational strain modes caused by the couple-forces. The effect of the
degree of nonequilibrity of the material under SPD on the deformation mechanism is analyzed in terms of the nonequilibrium
thermodynamics of local structure-phase transformations in zones of hydrostatic tension. 相似文献