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1.
Texture development in magnesium alloy AZ31 was studied by uniaxial compression tests at temperatures, strain rates and final strains ranging from 573 to 773 K, 1.0 × 10−3 to 5.0 × 10−5 s−1 and −0.2 to −1.5, respectively. Fiber texture was formed in all of the deformation conditions. The main component of the texture varied depending on deformation conditions; it appeared about 33–38° away from the basal pole after the deformation at higher temperatures and lower strain rates. This can be attributed to the increased activity of the secondary pyramidal slip system. With a decrease in temperatures and an increase in strain rate, the tilting angle of the main component (compression plane) from the basal pole decreased down to about 20°. Construction of a basal fiber texture was detected after deformations at the lowest temperature and high strain rates.  相似文献   

2.
Tensile deformation was carried out for a mechanically milled and thermo-mechanically treated Al–1.1Mg–1.2Cu (at.%) alloy at 748 K and three nominal strain rates of 10−3, 100, and 102 s−1. Despite the prevailing belief that superplasticity occurs by grain boundary sliding which requires slow strain rates at high temperatures, the maximum elongation was observed at the intermediate strain rate of 100 s−1, neither at the lowest nor the highest strain rates. In order to explain this phenomenon, the true stress–true strain behaviors at these three nominal strain rates were analyzed from a viewpoint of dislocation dynamics by computer-simulation with four variables of the thermal stress component σ*, dislocation immobilization rate U, re-mobilization probability of unlocked, immobile dislocations Ω and dislocation density at yielding ρ0. It can then be concluded that the large elongation (>400% in nominal strain) at the intermediate strain rate is produced by a combination of a very large Ω and a moderate U, resulting in a large strain rate sensitivity m value.  相似文献   

3.
The effects of the process parameters, including deformation temperature and strain rate, on the deformation behavior and microstructure of an Al–4Cu–Mg alloy, have been investigated through isothermal compression. Experiments were conducted at deformation temperatures of 540 °C, 560 °C, and 580 °C, strain rates of 1 s−1, 1×10−1 s−1, 1×10−2 s−1, and 1×10−3 s−1, and height reductions of 20%, 40%, and 60%. The experimental results show that deformation temperature and strain rate have significant effect on the peak flow stress. The flow stress decreases with an increase of deformation temperature and/or a decrease of the strain rate. Above a critical value of the deformation temperature, the flow stress quickly reaches a steady value. Experimental materials A and B have equiaxed and irregular grains, respectively, prior to deformation. The microstructures vary with the process parameters in the semi-solid state. For material B, the irregular grains transform to equiaxed grains in the process of semi-solid deformation, which improves the deformation behavior.  相似文献   

4.
The effect of deformation speed on defect structures introduced into bulk gold specimens at 298 K has been investigated systematically over a wide range of strain rate from ′=10−2 to 106 s−1. As strain rate increased, dislocation structure changed from heterogeneous distribution, so-called cell structure, to random distribution. Also, stacking fault tetrahedra (SFTs) were produced at anomalously high density by deformation at high strain rate. The anomalous production of SFTs observed at high strain rate is consistent with the characteristic microstructure induced by dislocation-free plastic deformation, which has been recently reported in deformation of gold thin foils. Thus, the results of the present study indicate that high-speed deformation induces an abnormal mechanism of plastic deformation, which falls beyond the scope of dislocation theory. Numerical analysis of dislocation structure and SFTs revealed that the transition point of variation of deformation mode is around the strain rate of 103 s−1.  相似文献   

5.
An extruded ZK60 magnesium alloy was processed by equal-channel angular pressing (ECAP) and then tested in tension at elevated temperatures. The results show the alloy is superplastic at a testing temperature of 473 K with an optimum ductility of 1310% when using an initial strain rate of 2.0 × 10−4 s−1. The results demonstrate that optimum superplasticity is achieved at intermediate strain rates and there are decreases in the elongations to failure at both faster and slower strain rates. Microhardness measurements were taken both on the cross-sectional plane and along the axial direction after processing by ECAP. These measurements show the alloy is essentially homogeneous in the as-pressed condition.  相似文献   

6.
Hot flow behavior of boron microalloyed steels   总被引:1,自引:0,他引:1  
This research work studies the effect of boron contents on the hot flow behavior of boron microalloyed steels. For this purpose, uniaxial hot-compression tests were carried out in a low carbon steel microalloyed with four different amounts of boron over a wide range of temperatures (950, 1000, 1050 and 1100 °C) and constant true strain rates (10−3, 10−2 and 10−1 s−1). Experimental results revealed that both peak stress and peak strain tend to decrease as boron content increases, which indicates that boron additions have a solid solution softening effect. Likewise, the flow curves show a delaying effect on the kinetics of dynamic recrystallization (DRX) when increasing boron content. Deformed microstructures show a finer austenitic grain size in the steel with higher boron content (grain refinement effect). Results are discussed in terms of boron segregation towards austenitic grain boundaries during plastic deformation, which increases the movement of dislocations, enhances the grain boundary cohesion and modificates the grain boundary structure.  相似文献   

7.
An apparatus was developed to facilitate application of an electro-thermo-chemical accelerator to high-speed deformation experiments. The apparatus is designed on the principle of sequential collision of elastic bodies. Speeds ranging from 600 to 780 m s−1 were achieved, and estimated strain rate of deformation is 107 s−1. The newly developed apparatus can be applied to various types of accelerators for attaining deformation speeds as high as several km s−1. Transmission electron microscopy of aluminum deformed at high speed by use of the apparatus revealed the formation of very small stacking fault tetrahedra (SFTs). This observation is quite new for aluminum; previously, SFTs had not been observed in aluminum, although deformation had been carried out at strain rates lower than 106 s−1. Use of the apparatus promises to provide new insight into high-speed deformation.  相似文献   

8.
An appropriate parameter, named the heterogeneity parameter, is introduced for quantitatively representing the nature of distribution of deformation-induced dislocations. The parameter assumes values ranging from 0 to 1, the extremes corresponding to homogeneous and heterogeneous distribution, respectively. The parameter can represent distribution of intermediate nature, typified by stochastically random distribution which has a heterogeneity parameter of about 0.35. Heterogeneity parameter is used to analyze variation in dislocation structure in many kinds of metals for a wide range of deformation speed from 10−2 to 107 s−1 in strain rate. The parameter has large values at slow-speed-deformation, and decreases with increasing strain rate, reaching the level of random distribution at a deformation speed of around 104 s−1. Above this strain rate, formation of vacancy clusters increases remarkably. On the basis of these results of analysis, occurrence of dislocation-free plastic deformation during high-speed-deformation is proposed.  相似文献   

9.
Experiments were conducted on a commercial AZ61 alloy to evaluate the potential for achieving an ultrafine grain size and superplastic ductilities through the use of the EX-ECAP two-step processing procedure of extrusion plus equal-channel angular pressing. The results show that EX-ECAP gives excellent grain refinement with grain sizes of 0.6 and 1.3 μm after pressing at 473 and 523 K, respectively. The alloy processed by EX-ECAP exhibits exceptional superplastic properties including a maximum elongation of 1320% after pressing through four passes when testing at 473 K with an initial strain rate of 3.3 × 10−4 s−1. This result compares with an elongation of 70% achieved in the extruded condition without ECAP under similar testing conditions.  相似文献   

10.
We present the analysis of uniaxial deformation of nickel nanowires using molecular dynamics simulations, and address the strain rate effects on mechanical responses and deformation behavior. The applied strain rate is ranging from 1 × 108 s−1 to 1.4 × 1011 s−1. The results show that two critical strain rates, i.e., 5 × 109 s−1 and 8 × 1010 s−1, are observed to play a pivotal role in switching between plastic deformation modes. At strain rate below 5 × 109 s−1, Ni nanowire maintains its crystalline structure with neck occurring at the end of loading, and the plastic deformation is characterized by {1 1 1} slippages associated with Shockley partial dislocations and rearrangements of atoms close to necking region. At strain rate above 8 × 1010 s−1, Ni nanowire transforms from a fcc crystal into a completely amorphous state once beyond the yield point, and hereafter it deforms uniformly without obvious necking until the end of simulation. For strain rate between 5 × 109 s−1 and 8 × 1010 s−1, only part of the nanowire exhibits amorphous state after yielding while the other part remains crystalline state. Both the {1 1 1} slippages in ordered region and homogenous deformation in amorphous region contribute to the plastic deformation.  相似文献   

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