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Deformation microstructure of orthorhombic-α\" martensite in a Ti-7.5Mo (wt.%) alloy was investigated by tracking a local area of microstructure using scanning electron microscopy, electron back-scattered diffraction, and transmission electron microscopy. The as-quenched α\" plates contain {111} α\" -type I transformation twins generated to accommodate transformation strain from bcc-β to orthorhombic-α\" martensite. Tensile deformation up to strain level of 5% induces {112} α\" -type I deformation twins. The activation of {112} α\" -type I deformation twinning mode is reported for the first time in α\" martensite in β-Ti alloys. {112} α\" -type I twinning mode was analyzed by the crystallographic twinning theory by Bilby and Crocker and the most possible mechanism of atomic displacements (shears and shuffles) controlling the newly reported {112} α\" -type I twinning were proposed.

Twinning is a fundamental mechanism behind the simultaneous increase of strength and ductility in medium- and high-entropy alloys, but its operation is not yet well understood, which limits their exploitation. Since many high-entropy alloys showing outstanding mechanical properties are actually thermodynamically unstable at ambient and cryogenic conditions, the observed twinning challenges the existing phenomenological and theoretical plasticity models. Here, we adopt a transparent approach based on effective energy barriers in combination with first-principle calculations to shed light on the origin of twinning in high-entropy alloys. We demonstrate that twinning can be the primary deformation mode in metastable face-centered cubic alloys with a fraction that surpasses the previously established upper limit. The present advance in plasticity of metals opens opportunities for tailoring the mechanical response in engineering materials by optimizing metastable twinning in high-entropy alloys. Twinning has been experimentally seen in high-entropy alloys, but understanding how it operates remains a challenge. Here, the authors show that twinning can be a primary deformation mechanism in three well-known medium- and high-entropy alloys that have unstable face-centered cubic lattices.

In materials science, dislocations are irregularities within the crystal structure or atomic scale of engineering materials, such as metals, semi-conductors, polymers, and composites.Discussing this specific aspect of materials science and engineering, Introduction to Dislocations is a key resource for students.

Metastable β-type Ti alloys that undergo stress-induced martensitic transformation and/or deformation twinning mechanisms have the potential to simultaneously enhance strength and ductility through the transformation-induced plasticity effect (TRIP) and twinning-induced plasticity (TWIP) effect. These TRIP/TWIP Ti alloys represent a new generation of strain hardenable Ti alloys, holding great promise for structural applications. Nonetheless, the relatively low yield strength is the main factor limiting the practical applications of TRIP/TWIP Ti alloys. The intricate interplay among chemical compositions, deformation mechanisms, and mechanical properties in TRIP/TWIP Ti alloys poses a challenge for the development of new TRIP/TWIP Ti alloys. This review delves into the understanding of deformation mechanisms and strain hardening behavior of TRIP/TWIP Ti alloys and summarizes the role of β phase stability, α″ martensite, α′ martensite, and ω phase on the TRIP/TWIP effects. This is followed by the introduction of compositional design strategies that empower the precise design of new TRIP/TWIP Ti alloys through multi-element alloying. Then, the recent development of TRIP/TWIP Ti alloys and the strengthening strategies to enhance their yield strength while preserving high-strain hardening capability are summarized. Finally, future prospects and suggestions for the continued design and development of high-performance TRIP/TWIP Ti alloys are highlighted.

Using molecular dynamics simulations, we study the roles of geometry, boundary conditions, and nanotwinned structure on the mechanical response of Cu [Formula omitted] cylindrical nanopillars under tensile loading. Specifically, we investigate the stress-strain responses, deformation mechanisms, and defect evolution in nanopillars of varying height-to-diameter ( [Formula omitted]) ratios, capped with rigid layers to resemble hard coatings, and with microstructures consisting of columnar grains with and without nanoscale coherent twin boundaries (CTBs). Our results indicate that the disk-shaped nanopillars (DPs) with low [Formula omitted] ratios exhibit high yield strength, significant triaxial tension stress, and pronounced plastic deformation. This deformation is accompanied by high defect density near the Cu/rigid layer interfaces, driven by dislocation pile up from multiple activated slip systems. Conversely, the deformed rod-shaped nanopillars of large ratios exhibit localized plastic deformation characterized by necking phenomena. Our results reveal the dominant role of Shockley type dislocations in plastic deformation, particularly in DPs, which display higher dislocation densities due to reduced dislocation annihilation events at free surfaces and pile up at interfaces. Notably, deformed DPs exhibit a unique vacancy-induced nanovoid nucleation mechanism at interfaces, resulting from the coalescence of vacancies generated during shearing of jogs. Additionally, the results demonstrate that dislocations glide between CTBs forming wide stacking faults, or traverse CTBs in a zigzag pattern as perfect dislocations, confirming a recently hypothesized cross-slip-like transmission in a recent experimental observation. Our simulations indicate that nanometer-spaced CTBs in Cu [Formula omitted] nanopillars act as weak barriers to dislocation motion during tensile loading, leading to only a marginal enhancement of mechanical properties.

In situ femtosecond X-ray diffraction measurements reveal that the dominant mechanism of shock-wave-driven deformation in tantalum changes from twinning to dislocation slip as pressure increases. Deformation caught in the act The effect of shock waves travelling through materials has relevance for various areas of study in geology and materials science. Experiments that probe how materials deform on exposure to shock waves are usually carried out in retrospect of the shock event. This paper reports in situ X-ray diffraction studies of the plastic deformation of textured polycrystalline tantalum on exposure to shock compression with shock pressures ranging from 10 gigapascals to around 300 gigapascals (at which the metal melts). Twinning and slip deformations produce distinct changes to the texture of the tantalum sample and these changes could be observed in the diffraction data. In this way, the researchers observed that the dominant deformation mechanism transitioned from minimal twinning to twinning-dominated to slip-dominated as the shock pressure increased above 150 gigapascals. This dynamic material behaviour would be challenging to observe in experiments carried out after the shock event. Pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites 1 , 2 , 3 , the formation of interstellar dust clouds 4 , ballistic penetrators 5 , spacecraft shielding 6 and ductility in high-performance ceramics 7 . At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation is challenging. Experiments that characterized lattice defects 8 , 9 , 10 , 11 have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing 12 and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials 13 , but have only recently been applied to plasticity during shock compression 14 , 15 , 16 , 17 and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ , lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations 18 , 19 , 20 and experiments 8 , 9 , 10 , 11 , 12 have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks 21 , we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. The techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.

Tensile-compression fatigue deformation tests were conducted on AZ31 magnesium alloy at room temperature. Electron backscatter diffraction (EBSD) scanning electron microscopy was used to scan the microstructure near the fatigue fracture surface. It was found that lamellar 10-11-10-12 secondary twins (STs) appeared inside primary 10-11 contraction twins (CTs), with a morphology similar to the previously discovered 10-12-10-12 STs. However, through detailed misorientation calibration, it was determined that this type of secondary twin is 10-11-10-12 ST. Through calculation and analysis, it was found that the matrix was under compressive stress in the normal direction (ND) during fatigue deformation, which was beneficial for the activation of primary 10-11 CTs. The local strain accommodation was evaluated based on the geometric compatibility parameter (m’) combined with the Schmid factor (SF) of the slip system, leading us to propose and discuss the possible formation mechanism of this secondary twin. The analysis results indicate that when the local strain caused by basal slip at the twin boundaries cannot be well transmitted, 10-11-10-12 STs are activated to coordinate the strain, and different loading directions lead to different formation mechanisms. Moreover, from the microstructure characterization near the entire fracture surface, we surmise that the presence of such secondary twins is not common.

The effect of plastic deformation induced by wire drawing on thermal properties in twinning-induced plasticity (TWIP) steel has been investigated. The investigation on the relationship between thermal conductivity (k) and the microstructure in the drawn TWIP steel wire was systematically performed to accurately understand the behavior of the k of a metal during wire drawing. The yield and tensile strengths linearly increased with drawing strain owing to the deformation twins and dislocations that were generated during wire drawing. However, the total elongation sharply decreased with drawing strain. The linear thermal expansion coefficient of the TWIP steel exhibited a similar value regardless of drawing strain. The density decreased linearly with temperature, and it was independent of the drawing strain. k increased initially and then decreased after reaching its maximum value with increasing drawing strains. At a nominal drawing strain of 0.26, k increased compared with the state of hot rolling because the increase in k due to grain elongation was greater than the decrease in k due to dislocations generated during wire drawing. However, as the amount of drawing step increased further, the influence of dislocations on k increased more than that of grain elongation, causing k to decrease.

Developing highly efficient semiconductor metal oxide (SMOX) sensors capable of accurate and fast responses to environmental humidity is still a challenging task. In addition to a not so pronounced sensitivity to relative humidity change, most of the SMOXs cannot meet the criteria of real-time humidity sensing due to their long response/recovery time. The way to tackle this problem is to control adsorption/desorption processes, i.e., water-vapor molecular dynamics, over the sensor’s active layer through the powder and pore morphology design. With this in mind, a KIT-5-mediated synthesis was used to achieve mesoporous tin (IV) oxide replica (SnO[sub.2]-R) with controlled pore size and ordering through template inversion and compared with a sol-gel synthesized powder (SnO[sub.2]-SG). Unlike SnO[sub.2]-SG, SnO[sub.2]-R possessed a high specific surface area and quite an open pore structure, similar to the KIT-5, as observed by TEM, BET and SWAXS analyses. According to TEM, SnO[sub.2]-R consisted of fine-grained globular particles and some percent of exaggerated, grown twinned crystals. The distinctive morphology of the SnO[sub.2]-R-based sensor, with its specific pore structure and an increased number of oxygen-related defects associated with the powder preparation process and detected at the sensor surface by XPS analysis, contributed to excellent humidity sensing performances at room temperature, comprised of a low hysteresis error (3.7%), sensitivity of 406.8 kΩ/RH% and swift response/recovery speed (4 s/6 s).