Search Results (12)

Owing to the differences in crystallographic orientations among individual grains, dislocation structures in polycrystals are inherently inhomogeneous from grain to grain. Since intergranular incompatibility is inevitable during plastic deformation, it may consequently lead to unpredictable plastic strain localization, which in turn facilitates the initiation of fatigue crack. Therefore, to elucidate the mechanisms underlying inhomogeneous deformation in polycrystals, this study systematically examines the fatigue-induced dislocation structures in polycrystalline SUS316L stainless steel. We then directly compare them with those in copper single crystals to clarify the dependence of the dislocation structures on crystallographic orientation. SEM characterization demonstrates that high plastic strain near grain boundaries promotes the formation of secondary cell bands (CBs) overlapping the primary CBs, which is attributable to the simultaneous activation of multiple-slip systems under high plastic strain amplitudes. In addition to strain localization, competition among candidate secondary slip systems strongly governs the dislocation structures. Notably, a new type of deformation band (DB) on the (010) plane is identified in a non-coplanar double-slip-oriented grain, a feature not observed in single crystals, indicating that polycrystals accommodate plastic strain through distinct mechanisms. Detailed dislocation structure analysis provides theoretical guidance for mitigating fatigue crack initiation through the manipulation of dislocations. Full article

Al-Mg-Li alloy is an ideal lightweight structural material for aerospace applications due to its low density, high specific strength, and excellent low-temperature performance. This study examines the mechanical properties and microstructural evolution of Al-Mg-Li alloy subjected to cryogenic and room temperature cold rolling, which induces large plastic deformation. Compared with room temperature rolling, cryogenic rolling significantly reduces surface cavity formation, thereby enhancing the alloy’s rolling surface quality. After cryogenic rolling by 80% and subsequent natural aging, the yield strength of artificially aged Al-Mg-Li alloy reaches 560 MPa, delivering a 60% increase compared to the traditional T6 state with a slight reduction in elongation from 6.5% to 4.6%. The specific strength achieves 2.23 × 10⁵ N·m/kg, outperforming conventional Al-Cu-Li and 7xxx-series Al alloys. The depth of intergranular corrosion decreases from 100 µm to 10 µm, demonstrating excellent corrosion resistance enabled by the new method. Transmission electron microscopy reveals that finely distributed δ′ (Al₃Li) is the primary strengthening phase, with high-density dislocations further enhancing strength. However, coarsening of δ′ (from ~2.9 nm to >6 nm) induced by ensuing artificial aging results in coplanar slip and reduced elongation. Lowering the post-aging temperature inhibits δ′ coarsening, thereby improving both strength and elongation. Our results provide valuable insights into optimizing the properties of Al-Mg-Li alloys for advanced lightweight applications. Full article

In order to investigate the effect of fissure inclination on the mechanical properties, deformation, and crack evolution of the surrounding rock in the roadway, uniaxial compression experiments were conducted on sandstone-like materials with prefabricated fissures. The high-speed camera and DIC (digital image correlation) method were employed to analyze the strain distribution and the crack evolution of the specimen. The results demonstrated that the presence of fissures reduces the stress for crack initiation, with intact specimens producing new cracks from about 75% of peak strength and fissured specimens producing new cracks from 50% to 60% of peak strength. The fissure reduced the strength and elastic modulus of the specimen while increasing the strain. The fissure inclination of 45° exhibited the most significant changes compared to the intact specimen. The peak strength and elastic modulus decreased by 54.52% and 35.95%, respectively, and the strain increased by 151.42%. The intact specimen and specimen with 90° inclination are mainly distributed with the shear crack, tensile crack, and far-field crack, which are mainly tensile–tension damage; specimens with 0~75° inclination are mainly distributed with the wing crack, anti-wing crack, oblique secondary crack, and coplanar secondary crack, which are mainly shear slip damage. The direction of the extension of cracks is related to the fissure inclination. For specimens with 0° inclination, the new cracks mainly propagate in the direction perpendicular to the fissure; for specimens with 30° and 45° inclinations, the new cracks mainly propagate in the direction parallel and perpendicular to the fissure; for specimens with 60° and 75° inclinations, the new cracks propagate in the direction parallel to the fissure; and for specimens with 90° inclination, the new cracks propagate in the direction parallel to the fissure. Full article

The photon storage time in a superconducting coplanar waveguide (CPW) resonator is contingent on the loaded quality factor, primarily dictated by the input and output capacitance of the resonator. The phase-slip based superconducting quantum interference device (PS-SQUID) comprises two phase-slip (PS) junctions connected in series with a superconducting island in between. The PS-SQUID can manifest nonlinear capacitance behavior, with the capacitance finetuned by the gate voltage to minimize the impact of magnetic field noise as much as possible. By substituting the coupling capacitance of the CPW resonator with the PS-SQUID, the loaded quality factor of the resonator can be changed by three orders, thus, we get a microwave photon switch in superconducting quantum computation architectures. Furthermore, by regulating the loaded quality factors, the coupling strength between the CPW and superconducting quantum circuits can be controlled, enabling the ability to manipulate stationary qubits and flying qubits. Full article

This work presents an overview of the mechanical response and microstructure evolution of specifically oriented pure magnesium single crystals under plane strain compression at room temperature. Crystals of ‘hard’ orientations compressed along the c-axis exhibited limited room temperature ductility, although pyramidal ⟨c + a⟩ slip was readily activated, fracturing along crystallographic $\left\{11\overline{2}4\right\}$ planes as a result of highly localized shear. Profuse $\left\{10\overline{1}2\right\}$ extension twinning was the primary mode of incipient deformation in the case of orientations favorably aligned for c-axis extension. In both cases of compression along ⟨$11\overline{2}0$⟩ and ⟨$10\overline{1}0$⟩ directions, $\left\{10\overline{1}2\right\}$ extension twins completely converted the starting orientations into twin orientations; the subsequent deformation behavior of the differently oriented crystals, however, was remarkably different. The formation of $\left\{10\overline{1}2\right\}$ extension twins could not be prevented by the channel-die constraints when c-axis extension was confined. The presence of high angle grain boundaries and, in particular, $\left\{10\overline{1}2\right\}$ twin boundaries was found to be a prerequisite for the activation of $\left\{10\overline{1}1\right\}$ contraction twinning by providing nucleation sites for the latter. Prismatic slip was not found to operate at room temperature in the case of starting orientations most favorably aligned for prismatic slip; instead, cooperative $\left\{10\overline{1}2\right\}$ extension and $\left\{10\overline{1}1\right\}$ contraction twinning was activated. A two-stage work hardening behavior was observed in ‘soft’ Mg crystals aligned for single or coplanar basal slip. The higher work hardening in the second stage was attributed to changes in the microstructure rather than the interaction of primary dislocations with forest dislocations. Full article

Numerous studies have demonstrated the widespread presence of chemical short-range order (SRO) in medium and high entropy alloys (M/HEAs). However, the mechanism of their influence on macroscopic mechanical behavior remains to be understood. In this paper, we propose a novel dislocation-based model of crystal plasticity, by considering both the dislocation blocking and coplanar slip induced by SRO. The effect of SRO on the plastic deformation of CoCrNi MEAs was investigated. We found that the yield strength increases monotonically with increasing SRO-induced slip resistance, but the elongation first appeared to increase and then decreased. Further analysis suggested that the plastic elongation is a result of the competition between grain rotation-induced deformation coordination and stress concentration, which depends on the slip resistance of the SRO. Full article

This paper reviewed the research progress of studies on the crystal rotation of single crystals that were deformed by tension and shear and the influences of crystal rotation and dislocation evolution on strain hardening behavior in crystals that were deformed with different initial orientations. The crystal rotation is entirely different depending on whether the single crystal was deformed by tension or shear. A three-stage work hardening behavior, which is not one of the intrinsic properties of materials, is generated when FCC metallic single crystals are deformed by tension along unstable oriFigurFigurentations, but single crystals do not exhibit this three-stage hardening behavior when they are deformed by simple shear at room temperature. Under tension, crystal rotation causes the transition from work hardening stage I to stage II, while the transition from work hardening stage II to III is caused by dislocation evolution. The evolution of the dislocation structure is related to deformation loading and can be classified into three types when a crystal is deformed by tension. Different from tension, shear stress can directly act on one of the 12 slip systems when a crystal is deformed by simple shear. When FCC single crystals are deformed by shear along the (1$\overline{1}$1)[110], (111)[11$\overline{2}]$ and (001)[110] orientations, the single slip system, co-planar slip systems and co-directional slip systems are activated, respectively, and the crystals hardly rotate under the shear conditions. The slip direction of [110] forces the crystal to rotate toward the shear direction under simple shear. The dislocation tangles tend to form the dislocation cells and wall structures when multiple slip systems are activated under simple shear. Full article

The deformation behavior of aluminum single crystals subjected to compression along the [100] and [110] directions is numerically examined in terms of crystal plasticity. A constitutive model taking into account slip geometry in face-centered cubic crystals is developed using experimental data for the single-crystal samples with lateral sides coplanar to certain crystal planes. Two sets of calculations are performed using ABAQUS/Explicit to examine the features of plastic strain evolution in perfectly plastic and strain-hardened crystals. Special attention is given to the discussion of mechanical aspects of crystal fragmentation. Several distinct deformation stages are revealed in the calculations. In the first stage, narrow solitary fronts of plastic deformation are alternately formed near the top or bottom surfaces and then propagate towards opposite ends to save the symmetry of the crystal shape. The strain rate within the fronts is an order of magnitude higher than the average strain rate. The first stage lasts longer in the strain-hardened crystals, eventually giving way to an intermediate stage of multiple slips in different crystal parts. Finally, the crystal shape becomes asymmetrical, but no pronounced macroscopic strain localization has been revealed at any deformation stage. The second stage in perfectly plastic crystals relates to abrupt strain localization within a through-thickness band-shaped region, accompanied by macroscale crystal fragmentation. Stress analysis has shown that pure compression took place only in the first deformation stage. Once the crystal shape has lost its symmetry, the compressive stress in some regions progressively decreases to zero and eventually turns tensile. Full article

A modified Taylor model, hereafter referred to as the MTCS (Mechanical-Twinning-with-Coplanar-Slip)-model, is proposed in the present work to predict weak texture components in the shear bands of brass-type fcc metals with a twin–matrix lamellar (TML) structure. The MTCS-model considers two boundary conditions (i.e., twinning does not occur in previously twinned areas and coplanar slip occurs in the TML region) to simulate the rolling texture of Cu–30%Zn. In the first approximation, texture simulation using the MTCS-model revealed brass-type textures, including Y{1 1 1} <1 1 2> and Z{1 1 1} <1 1 0> components, which correspond to the observed experimental textures. Single orientations of C$\left(1 1 2\right)\left[\overline{1} \overline{1} 1\right]$ and S’$\left(1 2 3\right)\left[\overline{4} \overline{1} 2\right]$ were applied to the MTCS-model to understand the evolution of Y and Z components. For the Y orientation, the C orientation rotates toward T(5 5 2)[1 1 5] by twinning after 30% reduction and then toward Y(1 1 1)[1 1 2] by coplanar slip after over 30% reduction. For the Z orientation, the S’ orientation rotates toward T’$\left(3 2 1\right)\left[2 \overline{1} \overline{4}\right]$ by twinning after 30% reduction and then toward Z$\left(1 1 1\right)\left[1 0 \overline{1}\right]$ by coplanar slip after over 30% reduction. Full article

Dislocation interactions with twin boundary (TB) have been well-established in nanotwinned metals. Penta-twins, as an extreme of crystal twinning, are tacitly assumed to be more effective at blocking dislocation motions than conventional single or coplanar nanotwins. However, the mechanism underlying the interactions between dislocations and penta-twins remains largely unclear. Here, by combining in situ transmission electron microscope (TEM) nanomechanical testing and atomistic simulations, we rationalize the fundamental interactions between dislocations and penta-twins in Au nanocrystals. Our results reveal that the interactions between dislocations and penta-twins show some similar behaviors to the ones in the cases of coplanar nanotwins, including dislocation impedance at TBs, cross-slip into the twinning plane and transmission across the TB. In addition, penta-twins also exhibit some unique behaviors during dislocation interactions, including multiple cross-slip, dislocation-induced core dissociation and climb-induced annihilation/absorption at the penta-twin core. These findings enhance our mechanistic understanding of dislocation behaviors in penta-twins, shedding light on the accessible design of high-performance nanomaterials with multi-twinned nanostructures. Full article

Beam deflection experiments were used to systematically examine size effects on the low cyclic fatigue (LCF) deformation behaviour of micro-sized bending beams of copper (Cu) single crystals oriented for single slip, critical and coplanar double slip. We present cyclic hardening curves and fatigue surface roughness, as well as dislocations structures of the micro-sized beams with sizes between 1 and 15 µm. A clear crystal orientation and size effect on the cyclic hardening curves, surface roughness, and the dislocation microstructures were observed. Based on the experimental results, the fatigue damage in single slip orientations clearly decreased with decreasing the sample size, however, below a critical size regime, the surface damage suddenly increases. Additionally, samples with sizes larger than 5 µm clearly revealed, besides PSBs-like structures, the emergence of kink bands leading to larger surface roughness in comparison to the smaller ones. Fatigue surface damages in microcrystals oriented for critical double slip became more prevalent compared to single slip orientations. Quantitatively, the correlation of the fatigue surface damage was also demonstrated with the formation of PSBs-like structures. Full article

The $[\overline{2}33]$ coplanar double-slip-oriented Cu single crystals were pre-fatigued up to a saturation stage and then uniaxially tensioned or compressed to fracture. The results show that for the specimen pre-fatigued at a plastic strain amplitude γ_pl of 9.2 × 10⁻⁴, which is located within the quasi-plateau of the cyclic stress-strain (CSS) curve, its tensile strength and elongation are coincidently improved, showing an obvious strengthening effect by low-cycle fatigue (LCF) training. However, for the crystal specimens pre-fatigued at a γ_pl lower or higher than the quasi-plateau region, due to a low pre-cyclic hardening or the pre-induction of fatigue damage, no marked strengthening effect by LCF training occurs, and even a weakening effect by LCF damage takes place instead. In contrast, the effect of pre-fatigue deformation on the uniaxial compressive behavior is not so significant, since the compressive deformation is in a stress state more beneficial to the ongoing plastic deformation and it is insensitive to the damage induced by pre-cycling. Based on the observations and comparisons of deformation features and dislocation structures in the uniaxially deformed $[\overline{2}33]$ crystal specimens which have been pre-fatigued at different γ_pl, the micro-mechanisms for the effect of pre-fatigue on the static mechanical behavior are discussed. Full article