Modeling GND-induced back stress and its role in tension-compression behavior of ultra-thin metal sheets

This work investigates the effect of small (5 and 10%) cold rolling reductions on the microstructure, crystallographic texture, and hardness of a solution-treated Al-Cu-Li alloy (AA2055). It was found that deformation initiates the intensive accumulation of crystal defects and the formation of a uniform, dense dislocation substructure. This is confirmed by a sharp increase in the density of geometrically necessary boundaries (GNBs) and a significant rise in hardness in the as-rolled conditions. It is shown that deformation intensifies the β-fiber texture components and suppresses recrystallization orientations. The obtained results demonstrate a clear quantitative correlation between the thermomechanical processing parameters, the evolution of the substructure, and the distribution of geometrically necessary dislocations. This provides a scientific basis for optimizing the aging kinetics and achieving an optimal balance of mechanical properties in the AA2055 alloy.

In this work, anisotropic fatigue crack growth rate (FCGR) behaviour in a hot-rolled Mg-3wt%Al-0.5wt%Ce alloy was investigated using compact tension (CT) specimens with notch (an) parallel to the rolling direction (RD) and transverse direction (TD). The FCGR tests were conducted at a constant load ratio (R = 0.1) and maximum stress intensity factor (KMax = 15.6 MPa√m) to investigate the crack closure effect. For both constant R and KMax conditions: (i) the load-displacement curves for every loading cycle were linear for an ∥ to RD and TD, indicating no crack closure; (ii) the FCGR was found to be lower for an ∥ RD than an ∥ TD over the entire stress intensity factor range (ΔK). The hot-rolled sample contained long-aligned Al11Ce3 intermetallic phase within grain boundaries that are elongated along RD. During the FCGR test, {101¯2}〈101¯1〉 extension twins (ET) with lamellae ∼⊥ and c-axis ∼∥ to these elongated intermetallics along RD developed irrespective of the notch orientation. During the loading cycle, these intermetallics along RD generate back-stresses, reducing the in-plane tensile stress ∼∥ and ∼⊥ to crack-tip to ∼0 for an ∥ to RD and TD, respectively. Hence, lenticular ET ∼⊥ and ∼∥, with c-axis ∼∥ and ∼⊥ to crack path activates, leading to trans and inter lamellar crack for an ∥ to RD and TD, respectively, and anisotropic FCGR. Translamellar crack in an ∥ RD reduces the FCGR due to plastic energy dissipation as perceived by comparatively more geometrically necessary boundaries (GNBs). On the other hand, faster FCGR was obtained for an ∥ TD due to interlamellar cracking. Thus, the crack growth through the matrix-ET interfaces was favoured due to strain incompatibility. The Fractography for an ∥ RD shows smaller elongated grooves along crack propagation, which indicates crack arrest. However, larger elongated grooves for an ∥ TD indicated easy crack propagation due to favourable interlamellar crack.

Effect of accumulative hot rolling on the microstructure and mechanical properties of dual-phase titanium alloy consolidated via SPS sintering

ABSTRACT This work investigates the synergy between texture evolution and grain refinement in ultra-low carbon body-centred cubic (BCC) ferritic steel. In this regard, experiments and polycrystal plasticity for ambient compressive deformation in low (up to ϵ≈0.22) and moderate (ϵ≈0.22−0.69) strain regimes were carried out. The tests were interrupted at intermediate strains for microstructure and texture characterisation. It was observed that the change in texture to γ -fibre ( { 111 } ∥ Compression direction ( CD ) ) and the formation of θ -fibre ( { 100 } ∥ CD ) up to ϵ ≈ 0.22 contributes towards lattice bending, resulting in grain size reduction from ∼ 104 ( 23 ) μ m to ∼ 23 ( 6 ) μ m . Simultaneously, crystallite size decreases, and statistically stored dislocations (SSD) and geometrically necessary boundaries (GNB) increase rapidly. Thus, resulting in an abrupt decrease in strain hardening rate (SHR). From ϵ ≈ 0.22 − 0.69 , the γ and θ -fibre broadens and θ -fibre intensity increases. The low GNB density increase indicates insignificant deformation-induced lattice curvature formation within grains, resulting in SSD intensification. Thus, leading to elongated grains with sluggish grain size decrease to ∼ 17 ( 4 ) μ m and a lesser decrease in SHR. The α -fibre could not evolve due to the dispersion of 110 axes along the axisymmetric radial direction due to axial deformation. The polycrystal model could appropriately simulate strain-hardening behaviour and texture evolution.

High strength, ductility and sheet formability by normalizing and quenching of low carbon microalloyed dual-phase steel

Sequence and mechanism of early microstructure evolution in alloy 690TT subjected to fretting corrosion in high temperature pressurized water

Dislocation behavior in Cu single crystal joints under the ultrasonically excited high-strain-rate deformation

Kink mechanism in Cu/Nb nanolaminates explored by in situ pillar compression

The local migration of recrystallization boundaries into spatially varying deformation fields which are typical for metals deformed to low and high strains is investigated using quantitative phase-field simulations. It is found that the average migration velocities as well as the local velocities of the recrystallization boundaries critically depend on the spacing between planar geometrically necessary boundaries (GNBs) which are present in the deformation microstructure. Also the morphology of the deformation field reflecting low and high strain deformation cases strongly affect the migrating boundary during recrystallization. Additional simulations were performed as a function of the two critical parameters- stored energy and GNB spacing - independently. Two regimes are found suggesting that these two parameters are closely linked. Previous experimental results are interpreted based on these novel simulation results.

In recent years, ultrafine-grained steel has been gaining increasing attention as a high-performance material. Accordingly, it is necessary to develop an efficient production method for ultrafine-grained steel. Severe plastic deformation is a critical factor that causes grain subdivision into ultrafine grains less than 1 µm in diameter. In this study, the effects of plastic deformation on the microstructure and static recrystallization of pure iron were studied by comparing orthogonal cutting and rolling. Orthogonal cutting yielded ultrafine grains with a diameter of 0.2 µm. It was found that a high strain rate in the thin shear plane generated during the cutting process caused a uniform subdivision of grains, and this uniform plastic deformation resulted in the uniform recrystallization of grains. In addition, a theoretical model was developed, and it was revealed that the number of recrystallized grains depended on the fraction of a large-misorientation area constructed with geometrically necessary boundaries (GNBs). It was suggested that the cutting process was more advantageous than rolling in producing ultrafine recrystallized grains because cutting could apply severe plastic strain uniformly on a work material, effectively generating GNBs.

Strain-dependence of deformation microstructures in ultra-low-C IF steel deformed to high strains by torsion at elevated temperatures

The present study targets four representative GNBs (Geometrically Necessary Boundaries) in terms of their unified and quantitative evaluations based on the field theory of multiscale plasticity (FTMP). Discrete dislocation dynamics simulations on GNBs 2, 3, 4 and 7, whose details about the consisting dislocations have been experimentally identified and theoretically evaluated by Hong, Winther, et al., are conducted. Applying the FTMP-based duality diagram representation scheme to the formation processes reveals a systematic interrelationship that further governs the stability of the GNBs, i.e., all the GNBs exhibit a common tendency to converge ultimately to a single master curve. This leads us to propose a postulate about the stability/instability criterion that involves their dynamic interactions with external disturbances.

Evolution of nano-laminated structure formed by the thermally-assisted plastic deformation in dry sliding wear

Mechanochemical reaction of Fe–C is achieved in Ni–Cr–Mo steel during surface mechanochemical case carburizing treatment (SMCT) at room temperature. Gradient nano-carbide layers are formed in the surface and near surface up to few microns. The Ni–Cr–Mo steel was treated for 15, 30, 45 and 60 min, respectively, to find out the alteration in microstructure. The surface and cross-sectional microstructures were investigated by Olympus optical microscope (Japan), 6390-A scanning electron microscope and JEOL F-2100 transmission electron microscope (TEM). It is observed that mechanical alloying of carbon in iron lattice is achieved and surface carbon concentration increased from 0.17 to 0.8 wt% with 1 hour of SMCT operation time. The mechanochemical reaction between Fe and C produces Fe3C (cementite) in the surface and undersurface up to 500–800 microns along with nano-particulate on the surface and near surface in 1-hour operation time. It is observed that the carbide cell blocks (CB) and geometrically necessary boundaries (GNB) are produced due to severe plastic deformation created by SMCT operation.

Formation of Σ3{110} incoherent twin boundaries through geometrically necessary boundaries in an Al-8Zn alloy subjected to one pass of equal channel angular pressing

The microstructural origin of work hardening stages

Evolution mechanism of dislocation boundary and characteristic micro-structure of commercial pure titanium during the projectile impact

Formation of nano-laminated structures in a dry sliding wear-induced layer under different wear mechanisms of 20CrNi2Mo steel

Statistical analysis of dislocations and dislocation boundaries from EBSD data