Internal strain and texture development during twinning: Comparing neutron diffraction measurements with crystal plasticity finite-element approaches

Different approaches to the modeling of twinning are examined within the framework of a crystal plasticity finite-element code. The model predictions are compared with in situ neutron diffraction experiments previously carried out on zirconium and magnesium alloys. The experiments are used to evaluate different model assumptions regarding the stress state inside newly formed twins at inception, as well as different assumptions concerning the interaction between twin and parent grain during subsequent twin growth. In particular the relaxation in some grain orientations that is experimentally observed, and is associated with twin-induced stress relief, can be captured by the model under appropriate assumptions.     

Deformation mechanisms of a 20Mn TWIP steel investigated by in situ neutron diffraction and TEM

The deformation mechanisms and associated microstructure changes during tensile loading of an annealed twinning-induced plasticity steel with chemical composition Fe–20Mn–3Si–3Al–0.045C (wt.%) were systematically investigated using in situ time-of-flight neutron diffraction in combination with post mortem transmission electron microscopy (TEM). The initial microstructure of the investigated alloy consists of equiaxed γ grains with the initial α′-phase of ～7% in volume. In addition to dislocation slip, twinning and two types of martensitic transformations from the austenite to α′- and ε-martensites were observed as the main deformation modes during the tensile deformation. In situ neutron diffraction provides a powerful tool for establishing the deformation mode map for elucidating the role of different deformation modes in different strain regions. The critical stress is 520 MPa for the martensitic transformation from austenite to α′-martensite, whereas a higher stress (>600 MPa) is required for actuating the deformation twin and/or the martensitic transformation from austenite to ε-martensite. Both ε- and α′-martensites act as hard phases, whereas mechanical twinning contributes to both the strength and the ductility of the studied steel. TEM observations confirmed that the twinning process was facilitated by the parent grains oriented with 〈1 1 1〉 or 〈1 1 0〉 parallel to the loading direction. The nucleation and growth of twins are attributed to the pole and self-generation formation mechanisms, as well as the stair-rod cross-slip mechanism.     

On strain gradients and size-dependent hardening descriptions in crystal plasticity frameworks

Strain gradient crystal plasticity models have been quite successful in describing size-dependent deformation. Various formulations have been suggested in the literature involving approaches that vary considerably in principle. In this respect it is important to associate certain classes of material models to specific deformation mechanisms and to investigate possible inherent restrictions. To this end, the scaling relation between dislocation substructures and the order (first order, second order) of strain gradients in the corresponding continuum formulation are discussed. Conclusions for isotropic and kinematic hardening on slip system level and their related orders in the strain gradients are drawn.     

纯钛压缩变形下的晶体塑性有限元分析

考虑滑移和孪晶变形机制,建立描述密排六方结构(HCP)金属力学行为的晶体塑性模型。利用该模型对纯钛在室温下的单向压缩试验进行模拟,模拟结果和实验结果吻合,证明模型具有可靠性;揭示了孪晶体积分数的变化规律、饱和的原因、参数对其的影响,以及速率敏感系数对结果的影响规律。     

高碳含铜TWIP钢TIG焊接头组织与性能

通过单向拉伸试验、显微组织观察、X射线衍射(XRD)和硬度测试对比研究了Fe-20Mn-3Cu-1.38C TWIP钢钨极氩弧焊(TIG)焊接接头固溶处理前后的组织和力学性能. 结果表明,固溶处理前焊缝组织为特定取向的柱状晶,整个焊缝组织晶粒粗大且分布着密集的颗粒状碳化物,热影响区(HAZ)在晶界有大量碳化物析出;固溶处理后,焊缝组织变为等轴晶,碳化物被完全固溶,焊接接头抗拉强度由953 MPa降为870 MPa,断后伸长率由41.85%提高至66.35%,低于母材性能(抗拉强度1 100 MPa,断后伸长率92.25%),但相比固溶处理前,综合力学性能显著提高;两种拉伸试样均断在热影响区,为典型韧性断裂.     

Internal stresses and the mechanism of work hardening in twinning-induced plasticity steels

An analysis of the loading–unloading behaviour of tensile tests of a 22Mn–0.6C (wt.%) twinning-induced plasticity steel shows the development of a very high level of internal stresses concomitant with its peculiar, nearly constant strain-hardening rate. A composite-type strengthening contribution from the increasing volume fraction of twin lamellae offers an explanation for an enhanced internal stress development in this type of materials. Proof of the quantitative significance of the composite-type strengthening requires, however, further study.     

AZ31B镁合金板材中晶界滑移的晶体塑性仿真

建立一种耦合滑移、动态再结晶以及晶界滑移的晶体塑性模型以仿真镁合金的高温变形行为及织构演化.首先,通过实验测量单轴拉伸、压缩后的织构以及显微组织演化,研究AZ31B镁合金在300°C的变形机制.结果发现,动态再结晶在应变小于0.2时起到细化晶粒的作用,之后晶界滑移在变形过程中起显著作用.此外,建立晶界滑移模型来评估由晶...     

孪生诱发塑性钢的研究现状及展望

基于TWIP钢高的强度、好的塑性性能,针对潜在石油工业可膨胀管技术应用背景,对孪生诱发塑性TWIP钢的国内外研究现状、TWIP钢目前的研究方向进行了综述,并提出今后在理论研究方向上的几点设想和展望。     

Similar and dissimilar resistance spot weldability of galvanised DP1000 and TWIP980 steels

Similar and dissimilar combinations of a 1000?MPa galvanised dual phase (DP) steel and a 980?MPa twining-induced plasticity (TWIP) steel were resistance spot welded under different welding parameters. The microstructure, expulsion situation, nugget size and mechanical properties of spot welds were evaluated systematically. The results showed that the differences of microstructure and chemical compositions caused that the weld nugget hardness increases in the order of TWIP/TWIP, DP/TWIP and DP/DP. The lower melting point and heat conductivity of the TWIP steel and the lower electric resistance of the zinc coat on the DP steel caused that the expulsion occurring current increased in the order of TWIP/TWIP, DP/TWIP and DP/DP and under the same welding condition the nugget diameter increased in the order of DP/DP, DP/TWIP and TWIP/TWIP. Furthermore, the tensile shear failure mode and location depends on the nugget size, microstructure and hardness distribution of spot weld.     

Correlation Between Crystal Rotation and Redundant Shear Strain in Rolled Single Crystals: A Crystal Plasticity FE Analysis

The correlation between crystal rotation and redundant shear strain in rolled single crystals was investigated by using the crystal plasticity finite element(CPFE) model in this paper. The deformation in aluminium single crystals of four representative orientations(rotated-Cube, Goss, Copper, and Brass) after rolling and plain strain compression was simulated, and the predictions have been validated by the experimental observations. In the rotated-Cube and Goss, the redundant shear strain and crystal rotation were in the same pattern, alternating along the thickness, while the relation between them was not obvious for the Copper and Brass due to their asymmetrical distributions of activated slip systems. The relations between slip system activation, crystal rotation, and shear strain were investigated based on the CPFE model, and the correlation between shear strain and crystal rotation has been built.     

A study of surface roughening in fcc metals using direct numerical simulation

Grain-scale surface roughening due to plastic straining in polycrystalline aluminum is studied with the aid of a three-dimensional finite-element crystal-plasticity model. An improved understanding of the origin of surface roughening profiles in plastically strained aluminum is sought. Large-scale, Direct Numerical Simulation enables the computation of full-field solutions and the explicit consideration of the deformation of individual crystals as well as of their crystalline texture evolution and interaction with neighboring grains. Simulations are conducted on idealized flat sheet polycrystalline aluminum samples under uniaxial and biaxial loading conditions. The results obtained show that the ensuing surface profiles are controlled by several factors: applied boundary conditions, Taylor factor and shear tendency of the individual grains and the spatial distribution of grain neighborhood orientations. The conditions leading to different ridging profiles, e.g., corrugated and ribbed surface profiles, are discussed.     

On the stress state dependence of the twinning rate and work hardening in twinning-induced plasticity steels

The influence of the stress state on the twinning rate and work hardening is studied in the case of an Fe–Mn–C TWIP steel strained in uniaxial tension, simple shear and rolling. The resulting stress–strain responses exhibit marked differences. The twinning rate, number of activated twinning systems in each grain, twin thickness and transmission of twins across grain boundaries are dependent on the imposed stress state during straining. Relationships between twin features and macroscopic work hardening rate are established.     

退火温度对超低碳烘烤硬化钢织构和固溶元素影响

采用光学显微镜、EBSD测试技术和三维原子探针分别对超低碳烘烤硬化钢的微观组织、织构以及固溶元素进行分析.结果表明,超低碳烘烤硬化钢经过750 ～ 810℃退火后,退火组织均为等轴状的铁素体组织,退火织构主要为{111}有利织构.随着退火温度的增加,其晶粒尺寸和{111}织构的强度都不断增大.烘烤硬化钢板经过退火后碳和磷元素在晶界等缺陷处发生了不同程度的偏聚.通过三维原子探针相应的软件计算得出,固溶在钢中的含碳量随着退火温度的增加而增大.     

Ti3Al单晶塑性变形行为的晶体塑性有限元模拟

基于晶体塑性理论,建立了滑移变形机制下Ti_3Al单晶晶体塑性的细观本构关系,并利用ABAQUS/UMAT用户子程序接口开发本构关系子程序,将其应用于不同取向Ti_3Al单晶的单向压缩模拟。分析不同取向时晶体滑移系的启动情况,以及滑移系启动与取向的相互关系。结果表明:基面滑移系(0001)1120,柱面滑移系{1010}1120和锥面滑移系{1121}1126均被激活,但由于滑移系之间临界剪切应力和施密特因子的不同,各滑移系的启动情况存在显著差异。基面和锥面滑移系的临界剪切应力较大,仅在施密特因子较大时启动;特别是锥面滑移系,其临界剪切应力最大,因而该滑移系只有在压缩轴接近[0001]方向时才被激活。柱面滑移系的启动较为容易,对塑性变形的贡献也最大。同时与实验结果相比较,模拟结果基本与之吻合。     

Simulation of lattice orientation effects on void growth and coalescence by crystal plasticity

A three dimensional rate-dependent crystal plasticity model is applied to study the influence of crystal orientation and grain boundary on the void growth and coalescence. The 3D computational model is a unit cell including one sphere void or two sphere voids. The results of three different orientations for single crystal and bicrystals are compared. It is found that crystallographic orientation has noticeable influences on the void growth direction,void shape, and void coalescence of single crystal. The void growth rate of bicrystals depends on the crystallographic orientations and grain boundary direction.     

理想塑性及线性硬化板材弯曲成形的变薄规律

在板材呈圆弧形弯曲和截面保持平面的基础上 ,对理想塑性板材和线性硬化板材的弯曲变形进行了分析 ,推导出弯曲过程中宽板外表面半径、板料厚度、变薄系数 ,以及应变中性层内移系数随板坯内表面半径变化的理论解 ,并将计算示例与查表法的实验数据作了比较。