应变能对Al-Cu合金强变形诱导析出相回溶的影响

透射电镜观察表明,Al-4.11%Cu二元合金中θ′相在等径角挤压(ECAP)强变形中发生反复的弯曲变形,形成了亚结构,并从亚结构界面处开始发生溶解,而θ相则发生了折断和破碎,并从破碎θ粒子的尖角处发生溶解。X射线衍射及小角度X射线散射测试结果表明,θ′相粒子随强变形溶解得比θ快,θ′相粒子在尺寸较大时即开始随强变形溶解。热力学分析表明,θ′相在强变形中因为自身的应变增加了系统的应变能和粒子回溶的驱动力,促使其在强变形中的溶解。而θ相的溶解则是因为破碎粒子尖锐菱角表面能的增加造成的。研究表明,析出相粒子应变能与表面能都是强变形诱导析出相粒子回溶的驱动力,尤其是应变能的作用更大。     

Phase and structural transformations in the aluminum amts alloy upon severe plastic deformation using various techniques

The paper presents experimental data on the structure formation in the commercial aluminum alloy of grade AMts subjected to severe plastic deformation using dynamic channel-angular pressing and torsion under high quasi-hydrodynamic pressure in Bridgman anvils. The dependences of the structural characteristics and hardness on the degree, rate, and scheme of deformation have been analyzed.     

Effect of various kinds of severe plastic deformation on the structure and electromechanical properties of precipitation-strengthened CuCrZr alloy

The effect of various kinds of severe plastic deformation (equal-channel angular pressing and quasi-hydrostatic extrusion at 77 and 300 K) on the structural formation of precipitation-strengthened CuCrZr alloy has been studied. A combination of experimental methods has been used. Sputtering by deuterium ions was used as the tool for the layer-by-layer study of the alloy structure. The difference between the sputtering yields of the matrix (copper) and precipitates (Cr and Zr) allowed us to visualize the alloy structure to a total depth of 0.5?1 μm. The effect of severe plastic deformation on the precipitate distribution is considered. It has been shown that the main peculiarity of the microstructure is related to the high density of precipitates enriched in chromium, which completely determine the surface roughness. Their distribution is not related to the grain size. The combination of equal-channel angular pressing and quasi-hydrostatic extrusion was shown to lead to the increase in the microhardness of the CuCrZr alloy to 2300 MPa in the case of low-temperature quasi-hydrostatic extrusion (at 77 K) and to the retained high conductivity. It has been proved that the high anisotropy of precipitate shape, microhardness, and sputtering yield of the CuCrZr alloy is determined by equal-channel angular pressing.     

Sheet metal forming limit prediction based on plastic deformation energy

For sheet metals, the endurance to fracture under different strain paths may be different. Based on plastic deformation energy, the sheet metal forming limit is calculated, and the relationship model between maximum allowable integral value of the general plastic work criterion and the strain path is built. In addition, the strain-hardening exponent, anisotropy coefficient and the initial thickness of the material are also taken into account to consider their effects on forming limit. In order to simplify the process of parameter determination, only uniaxial tension test is used to calculate the material property parameters and necessary limit strain, and the expression of the criterion is determined finally. Then the limit strains under other strain paths between uniaxial tension to equi-biaxial tension are predicted by the criterion combined with numerical simulation of the forming process. The criterion is also applied to limit strain prediction under bilinear strain path.     

The impact of corrosion on the mechanical behavior of steel undergoing plastic deformation

In the present study the influence of the degree of plastic strain, due to various levels of plastic deformation during bending, on the mechanical properties of class BSt 500_s tempcore steel was investigated, under various levels of salt spray corrosion. The resulted mass loss was of realistic levels and comparable to the one created by natural environmental causes. The results showed that even though an increase in plastic deformation resulted in an expected marginal increase in strength properties, it had a negative effect in ductility. The international community has not reached a consensus yet concerning the minimum required bending roll diameter, for stirrup production, which ranges between 4–10 times the diameter of the steel bar to be bent. It was also shown that this combination is crucial since strain fractures were recorded under the minimum required values set by the most current design guide‐lines and design oriented research. The results of this investigation are intended to offer an in depth understanding of the impact of the underestimated factor of corrosion on the mechanical properties of steel undergoing plastic deformation in corrosive environments and to show the need of re‐examination of existing codes.     

Microstructure evolution ofAZ91D induced by high energy shot peening

A nanostructured surface layer was fabricated on a AZ91D magnesium alloy by using a high-energy shot peening（HESP）. HESP induced structure along the depth of the treated sample surface layer was characterized by means of X-ray diffractometer （XRD）, transmission electron microscope（TEM） and high resolution transmission electron microscopc（HRTEM）. The experimental results show that a deformed layer of about 50 μm has formed after HESP treatment and the average grain size increases from about 40 nm in the surface layer to about 200 nm at the depth of 40 μm. The surface nanocrystallization can realize intercoordination of the dislocations slipping and dynamic recrystallization. The nanocrystalline grains have stacking faults and dislocation in their interiors. The microhardness of the top surface is about triplicate that of the coarse-grained matrix.     

The use of severe plastic deformation techniques in grain refinement

Severe plastic deformation (SPD) has emerged as a promising method to produce ultrafine-grained materials with attractive properties. Today, SPD techniques are rapidly developing and are on the verge of moving from lab-scale research into commercial production. This paper discusses new trends in the development of SPD techniques suchas high-pressure torsion and equal-channel angle pressing, as well as new alternative techniques for introducing SPD. The paper also contains a comparative analysis of SPD techniques in terms of their relative capabilities for grain refinement, enhancement of properties, and potential to economically produce ultrafine-grained metals and alloys. For more information, contact Terry C. Lowe, Science and Technology Base Programs, Los Alamos National Laboratory, Los Alamos, NM 87545; (505) 667-7824; fax (505) 665-3199; e-mail tlowe@lanl.gov.     

Effect of preliminary plastic deformation on the destruction of composite material

Togliatti Polytechnic Institute. Volgograd Polytechnic Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 8–10, July, 1989.     

Investigation on plastic deformation mechanism of ultra-coarse cemented carbide based on energy analysis

Microstructure evolution and plastic deformation mechanisms of the ultra-coarse cemented carbide compressed at different temperatures were studied based on designed experiments and a proposed energy model. The cemented carbide compressed at high temperature exhibited larger strain, which resulted from the generation and movement of high density of dislocations in WC grain. The energies stored in WC and Co phases and dissipated by heat energy in the deformation were quantified. The larger energy stored in WC grain than that in Co phase indicates significant contribution of the hard matrix to deformation of the ultra-coarse cemented carbide.     

Surface nanostructures in commercial pure Ti induced by high energy shot peening

The high-energy shot peening (HESP) technique was used to obtain the surface nanocrystalline microstructure for a hcp metal titanium. XRD, SEM and TEM were applied to characterize the microstructure of the surface layer. Large amount of the deformation twins in the surface layer were observed by SEM in the specimens after HESP treatment in a shot-time, and the number of deformation twins both in a single plane and in intersecting planes increases with HESP time, until the twin character disappears completely in the top surface layer, which means that the severe plastic deformation(SPD) occurs on the surface. The XRD analysis results show that after HESP treatmen for 30 - 60 min the surface grain size decreases to nanoscale. According to the TEM images and corresponding diffraction patterns from SPD areas of the 120 min-treatment specimen, the measured grain size near the surface is about 20 - 30 nm. The grain size in deformation layer increases with the depth from the surface, and the nanostructured layer is about 20 μm in depth. Therefore, the surface nanocrystalline and a gradient microstructure from the surface to the matrix are obtained, which results in the micro-hardness decreasing from surface to the matrix gradually.     

塑性变形对铝合金弹性模量的影响

回弹是影响弯曲件精度的主要障碍 ,而弹性模量是影响回弹的重要因素之一。一般工程应用中都把弹性模量作为常数 ,而实际上弹性模量随塑性变形的进展在不断发生变化。为了准确把握弹性模量值在塑性变形过程中的变化规律 ,针对应用广泛的铝合金材料 ,采用静力学实验方法 ,对常用的退火LY12及退火LF2 1铝合金的弹性模量在塑性变形中的变化情况进行了实验研究。得到了弹性模量值随塑性变形程度及加载方式变化的规律 ,并分别归纳为数学模型。     

Effect of preliminary cold plastic deformation on the properties of maraging steels

Conclusion Cold plastic deformation (rolling and forging) increases the strength of quenched maraging steels with no substantial reduction of the ductility. The effect of strain hardening is more evident after subsequent aging, the preliminary cold deformation leading to acceleration of aging processes, which is due to earlier formation of intermetallic phases.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 15–18, September, 1975.     

Resistance of 1201 aluminum alloy to plastic deformation at various strain rates

Conclusion With an increase in the rate of plastic strain there is a change in the resistance of 1201 alloy to plastic deformation, which is revealed in a nontraditional decrease in _0.2 and increase in , and A_p. The characteristics _k and _t increase nonlinearally.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 56–61, August, 1989.     

高能喷丸对铜合金组织与力学性能的影响

用X射线衍射仪、金相显微镜、扫描电子显微镜及显微硬度计对经喷丸处理的Cu-0.8Cr-0.1Zr铜合金试样进行晶粒尺寸、组织形貌、硬度的观测.结果表明,喷丸后的样品表层晶粒尺寸明显细化,横截面表层剧烈变形,硬度呈明显梯度分布,表层硬度高出基体一倍以上.