Simulation for f.c.c. deformation texture by modified pencil glide theory

Inspired by the pencil glide theory for b.c.c. metal, modified pencil glide theory for f.c.c. metal was proposed, dividing the 12 glide systems of f.c.c. metal into three groups individually composed of eight {111}〈110〉 glide systems around the principal axes X[100], Y[010] and Z[001]. These assumptions yielded two mathematical solutions Ω(3) and Ω(1). In Ω(3), from the three groups with four complete conjugated glide systems composed of, respectively, two glide systems of common 〈110〉 direction, only one group with the maximum plastic work may operate if the requirements are satisfied, otherwise glide systems in Ω(1) where one of the four conjugated glide systems is zero are activated. The model considering the 12 glide systems of f.c.c. as a whole explained many experimentally stable orientations in axisymmetric and rolling deformation. The differences between the two pencil glide theories for b.c.c. and f.c.c. are also discussed with data.     

Multi-scale modeling of low-temperature deformation in b.c.c. metals

The deformation of body-centered cubic (b.c.c.) metals such as W, Ta, and Mo is complicated both by complex deformation mechanisms at the atomic scale and by microstructural variations at the microscale. In this paper, we develop a multiscale model for low-temperature deformation in b.c.c. metals. This model integrates atomic-scale observations into a single crystal constitutive relationship that is implemented in a polycrystal plasticity grain-scale simulation. We determine that the details of deformation at the microscale differ substantially between b.c.c. and f.c.c. metals.     

Computational modeling of f.c.c. deformation textures over Rodrigues' space

The application of novel tools for texture analysis to a systematic examination of f.c.c. deformation textures over Rodrigues' space is reported. Texture is described using an orientation distribution function (ODF), describing the distribution of crystal orientations over a three-dimensional orientation space. In contrast to existing ODF schemes based on series representations of the ODF, the tools proposed are based on a piecewise polynomial finite element representation, permitting the application of existing finite element technology to quantitative texture analysis. Advantages of such an approach are evident in the following, where a finite element scheme for deformation driven ODF evolution, together with the regularity of Rodrigues' space, lead to substantially simplified characterizations of widely examined f.c.c. textures. As a result, interpretation is straightforward, allowing insight into the structures of and relationships between the range of ideal texture components and orientation fibers encountered.     

Simulation of formation of disoriented structures in deformation of f.c.c. materials

It is shown that nuclei of dislocation walls can be formed due to the dynamic loss of stability of a dislocation cluster near the boundaries of a shear zone. A mathematical model is suggested for describing the kinetics of the defect medium that consists of dislocations and dislocation walls. The phase diagrams of dislocation density versus disclination density exhibits various stationary states, namely, a saddle, a stable node, and a limiting cycle of complex structure. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 9–12, April, 1998.     

剪切模式下Ti-1300合金组织及织构演变规律

通过光学显微镜(OM)、透射电子显微镜(TEM)、X射线衍射(XRD)等检测方法,研究等通道转角挤压变形后Ti-1300合金的组织与性能。研究结果表明:Ti-1300合金经过ECAP变形,发生晶粒转动、晶内多系滑移以及晶界处螺型位错与刃型位错的混合位错交错排列的协调作用,致使晶界不能破碎,原始晶界清晰可见,晶内出现大量的相互交错的剪切滑移带,显微组织中存在大量平行细密的板条组织以及位错团、位错胞,位错密度增大,但在整个ECAP变形过程中并未产生形变诱导ω或α″相。织构分析结果表明ECAP变形过程中Ti-1300合金初始(110)■织构逐渐转变为α织构,并形成D织构及立方织构。     

镁合金冷轧板材织构不均匀性分析

用X射线衍射法测量了MB3镁合金冷轧板的表面和心部织构,分析了织构不均匀性产生的原因.结果表明:镁合金薄板冷轧时基面滑移起主要变形作用,而板材表面的剪切应力及可逆轧制方式造成表面织构的"双峰"现象.镁合金板材的织构不均匀性,有利于镁板的进一步冷轧.     

几何因素与摩擦耦合对高纯铝箔剪切织构的影响

采用取向分布函数 (ODF)研究了轧制几何因素、轧制摩擦条件对高纯铝箔轧制织构的影响。结果显示 ,如果轧制摩擦因数大 ,当处于均匀变形几何条件 1相似文献   

Texture evolution in FCC metals from initially different misorientation distributions under shear deformation

We applied the crystal plasticity finite element method (CPFEM) based on a rate sensitivity model to examine the subgrain texture evolution of FCC metals under shear deformation. We used two kinds of microstructure models with the same orientation distribution function (ODF) but different spatial arrangements or misorientation distributions (MDs). One contained a great high frequency around low misorientation angles and the other a great high frequency near high misorientation angles. Different misorientation angles among neighboring crystals caused different interactions among them, particularly at the subgrain scale. The difference in MD affected the evolution of texture and average misorientation angles during deformation. The average misorientation angles of the subgrain boundaries increased with shear strain.     

Effect of the initial texture components of hot-rolled BH steel on the evolution of deformation texture and stored energy during the cold-rolling process

A visco-plastic self-consistent polycrystal model was used to investigate the effect of texture gradients through the thickness direction of hot-rolled bake-hardening steel on the evolution of deformation texture and stored energy during a cold-rolling process. The theoretical texture evolution was in good agreement with the experimental texture evolution, as measured using the electron back-scattering diffraction technique. The VPSC polycrystal model was also used to explain the individual contribution of major texture components to the evolution of deformation texture and stored energy during cold-rolling. The results demonstated that the biased bimodal distribution of stored energy in major texture components contributed to a distinct bimodal distribution of stored energy at the center and surface regions of cold-rolled BH steel.     

Stability of f.c.c. titanium in titanium/aluminum multilayers

Crystal structures of as-sputtered Ti/Al multilayers are studied with special emphasis on the formation of f.c.c.-Ti and the effect of coherency strains on phase stability. The results are rationalized on the basis of a recently proposed thermodynamic model for phase stability in multilayers. In this paper, the thermodynamic model is modified to account for the effect of coherency strains on the phase stability. A new phase stability diagram is proposed for Ti/Al multilayers.     

Interdiffusion in the f.c.c. Phase of Cu-Mn Binary Alloys

Interdiffusion coefficients are calculated in the Cu-Mn binary system from 450 to 925?°C. Starting from the diffusion couples between pure Cu and Mn, the solubility limit of the manganese in copper is determined and the interdiffusion characteristics in the f.c.c. solid solution of Cu-Mn alloys are analysed. The interdiffusion coefficients in this binary system are calculated by the den Broeder method. The interdiffusion coefficients are strongly dependent on the composition: their values lie between approximately 10^?14 and 4?×?10^?9?cm²?s in this temperature range. The Vignes and Birchenall method is used to determine the impurity diffusion coefficients of manganese in pure copper. These coefficients are compared with the tracer diffusion coefficients of Mn⁵⁴ in copper from the literature. Activation energies, which lie from 155 to 180?kJ/mol, are of a vacancy controlled diffusion mechanism.     

Analysis of texture evolution in FCC metals by full constraint and a self-consistent viscoplastic model

The texture evolution of FCC metals during tension, compression and rolling has been analyzed by the full constraint Taylor model and self-consistent model with the large deformation theory of viscoplastic material. The final texture of tension and compression predicted from the initial random texture were similar in both full constraint Taylor and self-consistent models. The final rolling texture of the the full constraint Taylor model was the D-type texture, while that of the self-consistent model was the copper type texture due to lower interaction between single crystals and matrix.     

The Finkelshtain–Rosin effect in deformed f.c.c. steels

Experimental data on effect of plastic deformation on the carbon internal friction peak in austenitic steels (Finkelshtain–Rosin peak) were analysed and it was shown that the general regularity is that peak height increases whereas the peak temperature is rather stable, or decreases. To explain this effect the computer simulation of temperature dependence of internal friction was performed in a model crystal without and with a screw dislocation taking into account long-range C–C and C–Ni interaction and C–dislocation interaction. The last one was calculated by the so-called ‘hybrid’ method. It was shown that the elastic field around a dislocation enhances the asymmetry of metal atom displacements around interstitial atoms and, thus, increases the height of the peak. On the other hand, the weak energy for carbon–dislocation interaction in the f.c.c. lattice does not lead to significant changes in carbon atom energies. Thus, the corresponding value of the activation energy for carbon atom ‘diffusion under stress’ remains nearly the same as for the nondeformed alloy. For the same reason, there is no additional internal peak in austenite, in contrast with the Snoek–Koster peak in ferrite.     

Analysis of texture evolution of cubic metals by isotropic and anisotropic viscoplastic self-consistent models

The texture evolutions of cubic metals during tension, compression and rolling have been analyzed by isotropic and anisotropic self-consistent models with the large deformation theory of viscoplastic material. The final texture components predicted from an initial random texture were the same in both isotropic and anisotropic self-consistent models. The effect of rate sensitivity on the rolling texture component was analyzed. The intensity of the major Copper component of the rolling texture increased with the decreasing of rate sensitivity and the increasing of rolling strain.     

Evolution of shear texture according to shear strain ratio in rolled FCC metal sheets

The shear textures developed in the surface layer by rolling procedures consist mainly of {001}<110> and {111}<uvw> orientations in FCC metal sheets, but the orientation components of shear textures vary with the rolling conditions. That is, either a single orientation component or a mixture of components can be developed depending on the rolling conditions. The purpose of this study is to analyze the various shear deformation textures in rolled FCC metal sheets.     

Rate sensitive analysis of texture evolution in FCC metals

The rate sensitive analysis was used to investigate the texture evolution during plane strain compression and combined deformation (plane strain compression and simple shear). The rate sensitivity of the rate sensitive model affects the orientation density distributions in Euler space and change the major orientations. As the rate sensitivity of the rate sensitive models increases, lattice rotation vectors around major components decreases.     

Structural refinement and deformation mechanisms in nanostructured metals

Deformation mechanisms in metals deformed to ultrahigh strains are analyzed based on a general pattern of grain subdivision down to structural scales 10 nm. The materials analyzed are medium- to high-stacking fault energy face-centered cubic and body-centered cubic metals with different loading conditions. The analysis points to dislocation glide as the dominant deformation mechanism at different length scales supplemented by a limited amount of twinning at the finest scales. With decreasing deformation temperature and increasing strain rate, the contribution of twinning increases.