最终形变热处理工艺对Al-5.2Mg-3.1Zn(wt.%)铝合金组织性能的影响

本文深入研究了最终形变热处理工艺对Al-5.2Mg-3.1Zn铝合金组织性能的影响。通过维氏硬度测试研究了变形工艺对最终形变热处理最终时效工艺的影响。通过金相观察和透射电镜观察发现经过最终形变热处理的板材内部存留大量的位错结构和纤维状组织,且其含量取决于板材的变形工艺。通过板材的力学性能和晶间腐蚀性能研究发现：(1)变形温度的提高会降低板材的强度,但会提高板材的延伸率;而变形量的作用则恰恰与之相反;(2)提高变形温度和变形量都有利于提高板材的抗晶间腐蚀性能。     

Effect of low-temperature rolling on the structure of copper

The influence of rolling at a liquid-nitrogen temperature on the microstructure of commercially pure copper has been investigated by the methods of transmission electron microscopy (TEM) and automated analysis of electron backscatter diffraction (EBSD) patterns. It has been established that the process of the structure formation was sufficiently complex and included a geometric effect of deformation, recrystallization, twinning, and fragmentation. It is shown that upon deformation to 50% the structure evolution was controlled by the Taylor-Polanyi principle. However, it was established that at larger reductions the formation of grain structure was determined by the competition between the geometric effect of deformation and recrystallization. The contribution of twinning and fragmentation to the structure formation was insignificant in the entire interval of deformations investigated. The recrystallization, apparently, was caused by the warming up of the sample to room temperature after low-temperature rolling.     

Structure and microhardness of chromium-zirconium bronze subjected to severe plastic deformation by dynamic channel-angular pressing and rolling

Bulk samples of chromium-zirconium bronze have been subjected to severe plastic deformation by two methods, namely, high-strain-rate dynamic channel-angular pressing (DCAP) and quasistatic deformation by rolling. After deformation and additional aging using metallography and electron microscopy, the structure has been investigated and the microhardness of the samples has been measured. It has been shown that the high-strain-rate deformation by DCAP is of a periodic character. It has been established that, in the investigated bronze subjected to DCAP, in four passes, the structure of dynamic polygonization is predominantly formed, which is accompanied by processes of aging. Upon the rolling, cells of deformation origin and a structure with randomly distributed dislocations and numerous extinction contours are formed.     

Effect of the degree of deformation on the structure and thermal stability of nanocrystalline niobium produced by high-pressure torsion

The effect of the degree of deformation by high-pressure torsion (using five and ten revolutions of anvils) on the structure of niobium and its thermal stability under annealing has been studied using transmission electron microscopy. By deformation with five revolutions, nanocrystalline niobium with a grain size of about 100 nm has been produced, but increasing degree of deformation (using ten revolutions of anvils) has not resulted in a further structure refinement. Besides, the structure obtained at the higher degree of deformation is more imperfect and exhibits lower thermal stability. In the first case (deformation with 5 revolutions of anvils), structure recovery processes have been observed in niobium at 400–600°C, and only at 700°C intense recrystallization accompanied by an increase in the grain size by an order of magnitude occurred; after deformation with ten revolutions of anvils, the structure is thermally unstable already at 500°C, and after annealing at 600–700°C it becomes completely recrystallized. Along with studying structure evolution, changes in the micro-hardness have been investigated and a correlation between this parameter and specific features of the structure has been established.     

Effect of cold plastic deformation on the structure of granular pearlite in carbon steels

Carbon steel with a structure of granular pearlite has been investigated by methods of scanning electron microscopy and transmission electron microscopy as a function of the degree of cold deformation. It has been shown that with increasing degree of deformation the microstructure of the ferritic constituent changes regularly from dislocation to cellular and to microbanded. It has been established that the structural state of the granular pearlite is stable upon deformation to 50%. An increase in the carbon concentration in the ferrite occurs. Fragmentation of carbide particles into blocks and their subsequent dissolution hawe been observed upon deformation exceeding 50%. Fine-dispersed globular carbides are formed in the ferrite matrix.     

Electron-microscopic examination of microstructural changes in structural martensitic steel after low-cyclic fatigue tests

Microstructural changes in a structural martensitic steel upon low-cyclic fatigue (LCF) deformation have been investigated. The micromechanics of plastic deformation and accompanying effects have been studied at the scale of martensite laths and packets with the aid of transmission electron microscopy (TEM). It has been shown that with increasing LCF deformation, changes in both the morphology and the internal structure of martensite occur. The changes are manifested in the form of a refinement of the structural units of martensite. It has been revealed that in the limits of a packet the fatigue deformation occurs inhomogeneously. However, the laths of the same orientation are deformed equally and almost simultaneously. The influence of the dimensions of former austenite grains and orientation of packets on the LCF process has been considered. The mechanics of the fatigue plastic deformation on the nano-, meso-, and microlevels and the processes that accompany this deformation have been studied.     

Superplastic behavior of magnesium-based Mg-10 wt % Gd alloy after severe plastic deformation by torsion

Characteristic features of superplastic behavior of Mg-10 wt % Gd alloy with an ultrafine-grained structure produced by severe plastic deformation by high-pressure torsion have been considered. The ultrafine-grained structure has been studied by transmission electron microscopy and X-ray diffraction. The optimum temperature-strain-rate regime of superplastic deformation of the ultrafine-grained alloy and the magnitudes of the strain-rate sensitivity parameter of the flow stress have been determined.     

Severe cryogenic deformation of copper

The method of automated analysis of electron backscatter diffraction (EBSD) patterns has been employed for the characterization of the structure of copper obtained using severe plastic deformation by shear under high pressure under cryogenic conditions. It has been established that severe cryogenic deformation leads to a considerable refinement of the structure to a grain size of 0.2 μm. Based on an analysis of the texture data and misorientation spectrum, it has been concluded that it is the 111<110> dislocation slip that was the main mechanism of plastic flow and that the contribution from twinning was very small. It has been shown that the evolution of the grain structure was mainly determined by elongation of initial grains in the direction of macroscopic shear and their subsequent fragmentation.     

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 本文利用Gleeble 3800热模拟机多轴大变形系统，对管线钢进行了几组不同热变形制度的多道次大应变热压缩试验，配合控轧后冷却速度，得到了1~2 μm的超细晶组织。通过金相显微镜观察，扫描电镜观察及透射电镜分析，研究其微观组织形态、精细结构特征、析出相特征，从中找出不同热变形参数变化对其微观组织的影响及析出物析出的影响规律。     

The effect of dispersoids on the grain refinement mechanisms during deformation of aluminium alloys to ultra-high strains

The effect of fine dispersoids on the mechanisms and rate of grain refinement has been investigated during the severe deformation of a model aluminium alloy. A binary Al–0.2Sc alloy, containing coherent Al₃Sc dispersoids, of ∼20 nm in diameter and ∼100 nm spacing, has been deformed by equal channel angular extrusion to an effective strain of ten. The resulting deformation structures were quantitatively analysed using high-resolution electron backscattered diffraction orientation mapping, and the results have been compared to those obtained from a single-phase Al–0.13Mg alloy, deformed under identical conditions. The presence of fine, non-shearable, dispersoids has been found to homogenise slip, retard the formation of a cellular substructure and inhibit the formation of microshear bands during deformation. These factors combine to reduce the rate of high-angle grain boundary generation at low to medium strains and, hence, retard the formation of a submicron grain structure to higher strains during severe deformation.     

Structure and mechanical properties of Ni-Cu-Ti-Zr composite materials with amorphous phase

The structure of specimens of Ni-Cu-Ti-Zr alloys with an amorphous phase has been examined by X-ray diffraction, as well as by transmission and scanning electron microscopy. Mechanical characteristics of the alloys have been determined using universal testing machines. Transformation-induced plasticity has been found to exist. The specimens demonstrate a good combination of strength and plasticity owing to both the composite effect of a heterophase structure and the dynamic martensitic transformation that develops during deformation.     

Deformation behavior of a niobium single crystal upon loading by spherically converging shock waves

Methods of X-ray diffraction, optical metallography, scanning and transmission electron microscopy, and microhardness measurements have been used for a layer-by-layer examination of the structure of a niobium single crystal after loading by spherically converging shock waves. It has been found that after loading the sample acquires a polycrystalline structure in the most part of its volume. It has been revealed that the basic mechanisms of high-strain-rate plastic deformation of the niobium single crystal are slip and the formation of a vortex structure through the development of deformation localization bands and the simultaneous formation and expansion of an internal cavity. The method of loading used in the study does not lead to the formation of adiabatic shear bands in niobium single crystals.     

FINE STRUCTURE VARIATION OF 18R MARTENSITE UNDER DEFORMATION IN POLYCRYSTALLINE CuZnAl AI JOY

The transmission electron microscopy has been used to investigate the fine structure variationof 18R martensite under deformation in a polycrvstalline CuZnAl shape memory alloys.Ithas been found that the strain is gabined by the reorientation of martensite variants in the ini-tial deformation stage.In addition to the result of optical microscopy studies,however,thereorientation is often incomplete and the interfaces among the prior variants still remain.A lotof twins will appear in martensite under enormous deformation,and the twin plane is(001)phane of martensite lattice.The dislocations has also been observed in some regions.In thiscase,the martensite will lose its thermoelasticitv and the shape memory effect will bedamaged.     

Evolution of the structure of V95 aluminum alloy upon high-pressure torsion

The effect of the degree of deformation upon torsion under quasi-hydrostatic pressure on the structural and phase transformations in the V95 alloy has been studied by the methods of electron microscopy and X-ray diffraction. It has been found that, upon severe plastic deformation, a nanocrystalline structure with a hardness of 2.5 GPa is formed. The nanostructure with a minimum average grain size of 55–80 nm is being formed at e = 5.5–6.4. It has been shown that during dynamical strain aging at e ≥ 4.8, a hardening metastable phase MgZn₂ precipitates from the supersaturated α solid solution, and the quantity of this phase increases with increasing degree of deformation.     

Effect of severe plastic deformation on the formation of the nanocrystalline structure and the aging of the multicomponent aluminum-lithium alloy with small additions of Sc and Mg

Effect of severe plastic deformation and subsequent low-temperature annealing on the structural and phase transformations, which are realized in the alloy 1450 on the base of the Al-Li-Cu-Zr system with additives of Sc and Mg has been studied by electron microscopy. The possibility of obtaining a nanocrystalline recrystallized structure in the alloy investigated has been established. It has been shown that its uniformity and dispersiveness depend on the degree of deformation and on the regime of annealing and are determined by the density distribution of particles that are precipitated upon the decomposition of the supersaturated solid solution. The transition of the alloy from microcrystalline to submicrocrystalline or nanocrystalline state changes its phase composition, morphology, and mechanism of nucleation of the precipitated phases and makes it possible to minimize structural factors that exert negative effect on the alloy plasticity.     

Features of plastic deformation of electrospark coatings and ways for improvement of their strength characteristics at friction

Analysis of the structural state of surface metal layers after their electrospark doping (ESD) and subsequent surface plastic deformation (SPD) has been performed. The structure levels and their scale ranging within 20–10³ nm have been determined. Applying the methods of X-ray structure analysis and electron microscopy, it has been found that the linear defect density after ESD and after ESD + SPD is practically identical; this allowed suggesting that the basis for the mechanism of plastic deformation of electrospark coatings is collective motion of dislocations, that is, rotational processes. Some ways of formation of stable and more homogeneous structures of electrospark coatings with required properties have been analyzed and proposed.     

Influence of warm deformation on the formation of a fragmented structure in low-carbon martensitic steels

Methods of optical metallography and scanning and transmission electron microscopy were used to investigate the structure of low-carbon steels of martensitic classes VKS-7 and VKS-10 subjected to warm rolling or upsetting at temperatures of 600 and 700°C (in the α state) and 800°C (in the γ state). It has been shown that the deformation by rolling at 600°C to degrees of 40 and 60% does not lead to the destruction of the lath structure of the initial martensite; an increase in the rolling temperature to 700°C and of the degree of deformation to 80% favors the development of recrystallization in situ. It has been found that, upon warm deformation by upsetting, recrystallization occurs at lower temperatures than in the case of the warm rolling. It has been shown that warm deformation by upsetting at a temperature of 700°C leads to the formation of a fragmented structure with a high fraction of ultrafine grains with a size less than 2 μm.     

Nanocrystallization process and mechanism in a nickel alloy subjected to surface severe plastic deformation

Bulk components made of a Ni-base C-2000 alloy with a face-centered cubic crystal structure and a very low stacking fault energy have been severely plastically deformed at the surface region to attain a grain size gradient ranging from nanocrystalline at the surface to coarse grained in the bulk. The evolution of microstructural characteristics has been studied as a function of the processing time employing a variety of analytical techniques, including extensive conventional and high-resolution transmission electron microscopy analyses. The thickness of the nanocrystalline surface layer is found to increase with the processing time. Deformation twinning is ubiquitous and occurs at the earliest stage of deformation and the deepest region of the material where plastic deformation has taken place in the surface severe plastic deformation process. A grain-refinement mechanism led by deformation twins and complemented by dislocation activity has been put forth to explain the nanocrystallization of the coarse-grained material employed in this investigation.     

Effect of spherically converging shock waves on phase and structural state of quenched Al-4 wt % Cu alloy

Optical metallography, scanning and transmission electron microscopy, and microhardness measurements have been used to perform a layer-by-layer study of the structure of a quenched Al-4 wt % Cu alloy subjected to loading by spherically converging shock waves. It has been established that, when using this mode of loading, the high-strain-rate plastic deformation of this alloy occurs via intragranular dislocation slip. No bands of localized deformation at the grain boundaries, twins, and adiabatic shear bands are formed. Highstrain-rate plastic deformation leads to the dissolution of Guinier-Preston zones.     

Influence of megaplastic deformation on the structure and hardness of Al–Cu–Mg alloy after aging

Methods of electron microscopy and X-ray diffraction have been used to investigate structural and phase transformations in the aluminum alloy of grade A2024 (Al–4.5 Cu–1.37 Mg–0.61 Mn–0.07 Si–0.27 Fe–0.02 Zn–0.02 Ti (wt %)) after aging and deformation by shear under high quasi-static pressure. It has been shown that the combination of two-stage aging with megaplastic deformation leads to the refinement of the structure to a nanolevel and to strengthening of the alloy (to an increase in the microhardness to 3000 MPa). The values of true deformation at which the deformation-induced dissolution of the particles of the strengthening S phase occurs have been determined.