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Anthraquinone (AQ) and its derivatives have been attracting more attention as promising electrode materials for lithium storage because of their high specific capacity, structural diversity, and environmental friendliness. The dissolution and poor electrical conductivity of AQ, however, limit its practical application. Here, a novel metal-organic coordination polymer with a one-dimensional (1D) chain ([C

Defects, such as stacking faults (SF) and twins, play a crucial role in stabilizing the order phase and improving the mechanical properties for engineering alloys. The formation mechanism of the γ twins from α2-platelets within β0 areas was analyzed at atomic-scale by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HADDF-STEM). The growth faults (ABA B ˙ CBC) were formed in α2-platelets, yielding a local D019→L10 (α2 → γ) phase transformation. During the annealing process, the growth faults can be rearranged into γ (ABCABC) and γT (ACBACB) platelets via the slipping of Shockley partial dislocations 1 / 3 [ 1 ¯ 01 0] and 1 / 3 [ 10 1 ¯ 0], respectively. The γ and γT can merge into γ twins by accident during growing. The interface steps between α2 and γ platelets implied that this transformation is a diffusion-controlled defect migration process. The present work provides profound insight towards the formation mechanism of γ twins, contributing to microstructure controlling and performance improving for TiAl alloys.

The role of elemental partitioning between β and ω phase in embrittling an originally ductile ω-containing Ti–12Mo (wt.%) model alloy was studied using transmission electron microscopy and atom probe tomography. It is revealed that the embrittlement of this alloy already occurs after aging at 400 °C for as short as 10 min, when the size, inter-particle spacing and volume fraction of the ω particles remain almost unchanged. The origin of the aging-induced embrittlement is attributed to the significant rejection of Mo (>5 at.%) from the ω particles during aging, which leads to remarkable increase in the shear modulus (>30 GPa) of the ω particles, promoting intense plastic flow localization and facilitating crack nucleation prior to macroscopic yielding.

The summary was based on a journal article about a case study that was implemented in a high school at PUNIV-Cazenga for eight weeks to test the effectiveness of Task-based Language Teaching (TBLT) in oral speed and fluency. The research showed that the approach could develop the students’ speaking abilities not only in the speed of their speech but also in the aspect of grammatical accuracy.

We study the effects of transformation-induced plasticity (TRIP) on the micrometer-scale deformation of single crystalline pillars. Plastic deformation mechanisms (i) mediated by pure dislocation glide and (ii) strain-induced epsilon-martensite transformation are separated using compositionally complex model alloys. The results show that transformation-induced plasticity does not strengthen the single crystalline material at the micron-scale when loaded in uniaxial compression as compared to pure dislocation-mediated plasticity. The dynamically introduced phase boundaries effectively hinder the activation and propagation of secondary slip systems, resulting in no increase in local stress due to unobstructed slip on the primary slip system parallel to the phase boundary.

In this paper, a new coordinated deformation mode of ‘pull apart’ has been evidenced by analyzing a series of microscopic deformation steps of Ti48Zr20Nb12Cu5Be15 metallic glass composite after tensile fracture. Different from the two previously found deformation modes of ‘tensile’ and ‘shear’, this mode is characterized by the irregular but completely fitted deformation steps between the two dendritic fragments which are separated by the tortuous matrix. This model describes the coordinated deformation behavior of dendrites and matrix in the microscopic plastic flow process and can be used to interpret the good balance of strength and ductility of metallic glass composites.

The structure and chemistry of the orthorhombic O′ phase after quenching of a Ti-23 at.%Nb-2 at.%O was measured using aberration-corrected transmission electron microscopy and atom probe tomography. The nanosized O′ phase, formed in the vicinity of ω, is enriched with oxygen and slightly depleted in Nb. Upon annealing, ω dissolves and the O′ phase develops in β up to 350 °C, above which temperature it transforms to colonies of fine α phase. Another needle-like form of α with lower Nb content is thought to nucleate from Nb-lean regions related to spinodal decomposition of β.

We studied the role of VC precipitation in improving the shape memory effect (SME) of the as-solution treated Fe–Mn–Si-based shape memory alloys by examining the microstructures developed during aging and deformation using transmission electron microscopy and electron channeling contrast imaging. Our results suggest that VC particles are not the only product of aging. Upon aging at 650 °C, the precipitation of VC particles is accompanied by the formation of profuse dislocations (2.26 ± 0.098 × 1013 m−2). In this case, the SME is not improved compared to the as-solution treated reference state. Upon aging at high temperatures (700–900 °C), a number of stacking faults are formed accompanying the VC precipitation and the SME is significantly improved, where the recovery ratios reach almost twice that of the as-solution treated state (

We have investigated the twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) as well as the influence of ω phase on these two phenomena in a metastable β-type Ti–25Nb–0.7Ta–2Zr (at.%) alloy. We set off with two starting states: one is ω-free and the other one contains a high number density (3.20 ± 0.78 × 1024 m−3) of nanometer-sized (∼1.23 nm) ω particles. Deformation experiments demonstrate that the plastic deformation of the ω-free alloy is mediated by stress-induced β → α" martensitic transformation, {332} twinning and dislocation slip, where the former two induce joint TRIP and TWIP effects and the latter one carries the majority of the plastic strain. In the ω-enriched alloy, the ω particles fully suppress the TWIP and TRIP effects and promote localization of dislocation plasticity into specific ω-devoid channels. Atom probe tomography analysis reveals that the elemental partitioning between β and ω results in only subtle enrichment of solutes in the β matrix, which cannot sufficiently stabilize the matrix to prevent martensitic transformation and twinning. A new mechanism based on the shear modulus difference between β and ω is proposed to explain the suppression of TRIP and TWIP effects by ω particles.

Here we present a microstructure design approach which leads to partial recrystallization and nano-precipitation within the same single-step heat treatment. This produces a dual-constituent microstructure in Ti-Nb based gum metal, which consists of nano-ω-particle-rich ultrafine recrystallized grain chains embedded in ω-lean subgrain-containing recovered zones. This partially recrystallized microstructure exhibits an improved strength-ductility combination that surpasses the inverse strength-ductility relationship exhibited by materials with similar composition. The strengthening effects due to precipitates and grain refinement were studied by nanoindentation. The deformation mechanisms of the partially recrystallized material were investigated by in-situ scanning electron microscope tensile tests, micro-strain mapping and post-mortem microstructure characterization. The improved mechanical properties are attributed to the high yield strength of the recrystallized grains and the sequential activation of dislocation slip and dislocation channeling.

The most efficient way to tune microstructures and mechanical properties of metallic alloys lies in designing and using athermal phase transformations. Examples are shape memory alloys and high strength steels, which together stand for 1,500 million tons annual production. In these materials, martensite formation and mechanical twinning are tuned via composition adjustment for realizing complex microstructures and beneficial mechanical properties. Here we report a new phase transformation that has the potential to widen the application window of Ti alloys, the most important structural material in aerospace design, by nanostructuring them via complexion-mediated transformation. This is a reversible martensitic transformation mechanism that leads to a final nanolaminate structure of α″ (orthorhombic) martensite bounded with planar complexions of athermal ω (a–ω, hexagonal). Both phases are crystallographically related to the parent β (BCC) matrix. As expected from a planar complexion, the a–ω is stable only at the hetero-interface., European Commission. Framework Programme for Research and Innovation (FP7/2007–2013))/ERC Grant agreement 290998 'SmartMet’), Innovative Research Team in University (IRT13034), National Basic Research Program of China (973 Program) (2014CB644003), China. Ministry of Science and Technology. National Key Research and Development Program (2016YFB0701302), National Natural Science Foundation of China (51501145), National Natural Science Foundation of China (51320105014), National Natural Science Foundation of China (51621063)

{332} twinning, an unusual twinning mode in other body-centered cubic (bcc) metals and alloys, has been demonstrated to be a fundamental deformation mode in bcc metastable β titanium alloys. Recent studies suggest that this twinning mode plays an important role in enhancing the work hardening and thus improving the mechanical properties. Here, we studied the mechanism of this twinning mode in a metastable β Ti 36Nb 2Ta 3Zr (wt.%) alloy. Tensile tests were performed to induce the formation of {332} twins. By using electron backscatter diffraction, transmission electron microscopy and in situ scanning electron microscopy, the surface-to-bulk microstructures and the initiation and propagation of {332} twins were investigated. In addition to the previously reported high densities of straight dislocations within the twin, we have observed that an α″ martensite band is present near the surface adjacent to the twin. During annealing at 900 °C, the α″ martensite band transforms into the adjacent twin rather than into the matrix, indicating that {332} twin nucleates within α″ martensite. Further evidence for this is the constitution of the twin in the initial stage of its formation, where the first portion formed consists of α″ martensite. During propagation, the twins propagating to the opposite directions can merge together when their lateral boundaries impinge on each other. Based on the experimental observations, an α″-assisted twinning mechanism is proposed and the origin of the dislocations within {332} twin is discussed accordingly.

Gum metal, a class of multifunctional β titanium alloys, has attracted much attention in the past decade due to its initially-proposed dislocation–free deformation mechanism based on giant faults, i.e., macroscopic planar defects carrying significant plastic strain. Special deformation features were observed in these alloys, such as plastic flow localization, pronounced surface steps, low work hardening, and large elongation. These were all proposed to arise from the special giant fault mechanism activated in the β-Ti matrix, while the initial presence or mechanically-induced formation of other phases was debated in several follow-up studies. Here, we set off with Ti–Nb-based gum metal samples with confirmed presence of large amounts of nanometer-sized hexagonal ω particles. Deformation experiments demonstrate all the features observed in the original reports, mentioned above. However, careful characterization reveals that the deformation bands (similar to giant faults) where plastic flow localized are “dislocation channels” that are depleted of ω phase. These channels are proposed to form by a {1 1 2}〈1 1 1〉 dislocation dissociation mechanism, promoting reverse transformation of the ω phase into the β phase. The deformation induced ω–β transformation and the associated dislocation channeling process can explain the presence of the aforementioned special deformation features in the current gum metal.

Cold-worked alloys exhibit high strength, but suffer from limited ductility. In contrast, Ti-based gum metal was reported to exhibit high strength combined with good ductility upon severe pre-straining. Motivated by this anomaly, we systematically studied the evolution of gum metal microstructure during severe cold working (swaging and rolling) and the resulting deformation and damage micro-mechanical mechanisms during follow-up tensile deformation. To this end, various experimental in situ and post-mortem methodologies are employed, including scanning electron microscopy imaging, high-resolution electron backscatter diffraction mapping and transmission electron microscopy. These observations reveal that intense grain refinement takes place through dislocation plasticity-dominated deformation banding upon cold working. The observed enhancement in crack blunting and failure resistance which prolongs the post-necking ductility of gum metal during follow-up tensile straining can be attributed to the deformation-induced development of local heterogeneities in texture and grain size.

Ti–Nb-based alloys are essential materials for biomedical implant and aerospace applications. They reveal complex phase transformation behavior. Here, a {2 1 1} β 〈1 1 1〉 β twinning induced β (body-centered cubic phase) to ω (hexagonal phase) transition in Ti–Nb-based alloys is demonstrated by transmission electron microscopy and analyzed employing ab initio calculations and the linear elastic inclusion theory. Our theoretical results reveal a distinct energy barrier for the β to ω transition, where the contribution from lattice rearrangement, rather than the elastic contribution associated with lattice parameter mismatch, plays the major role. It is shown that this energy barrier can be overcome by {2 1 1} β 〈1 1 1〉 β shear, explaining why {2 1 1} β 〈1 1 1〉 β twinning or, alternatively, the β to α″ (orthorhombic phase) transition promotes local formation of the ω phase.

Transmission Electron Microscope (TEM) and Electron Backscattered Diffraction (EBSD) are employed to explore the influence of deformation conditions on microstructure and the deformation mechanism of a new near β titanium alloy Ti-7333 after hot compression tests which at temperatures ranging from 770 to 970 °C and strain rates ranging from 0.001 to 10 s −1 . The results showed that the effect of deformation parameters on microstructure evolution is significantly. Both increasing the temperature and decreasing the strain rate seem to promote the dynamic recrystallization process. The mechanism is dominated by dynamic recovery, globularization and dynamic recrystallization. The globularization trend of α phase is more remarkable deformed at higher temperature and lower strain rate. And reverse, the lower temperature and higher strain rate are more favorable to α phase refinement. The fraction of low-angle grain boundaries in the deformation microstructure decreases with the increasing of temperature and decreasing of strain rate. It illustrates the low-angle grain boundaries would turn to high-angle grain boundaries during deformation. The expression of the size of recrystallized grains D r and parameter Z is obtained by regression analysis as ln D r =8.79964−0.33663ln Z . All the deformed samples present strong 〈001〉 and weak 〈111〉 fiber texture. With the increasing of temperature and decreasing of strain rate, the 〈001〉 texture strengthens gradually and 〈111〉 texture weakens gradually until extinction.

The hot deformation behavior of Ti-7333 titanium alloy in the temperature range of 770–970 °C and strain rate range of 10−3-10 s−1 has been investigated by hot compressive testing on the Gleeble-3800 thermal and mechanical simulator. The results show that the maximum stress decreases with decreasing strain rate and increasing temperature. The flow curves characteristic under different deformation parameters show obvious different. And discontinuous yielding occurs to the alloy at a higher strain rate for all the experimental temperatures. The flow behaviors are described by the hyperbolic sine constitutive equation and the hot deformation activation energies in (α + β) and β region are calculated as 333.74 kJ/mol and 213.83 kJ/mol, respectively. By comparing with similar alloys such as Ti-5553 and Ti-1023, the new near β titanium alloy Ti-7333 exhibits weaker deformation resistance. Based on the dynamic materials model, the processing map is generated, which shows that there are three domains of peak efficiency. The highest peak efficiency of power dissipation of 65% occurs at about 855 °C/0.001 s−1. Dynamic recovery and dynamic recrystallization occur during hot compression deformation and the degree of dynamic recrystallization is dependent sensitively on deformation temperature and strain rate. In the instability regimes, the material exhibits flow instabilities manifested in the form of flow localizations.

Dilatometry method was used to study the ω phase transformation kinetics of a near-β titanium alloy Ti–7Mo–3Cr–3Nb–3Al during continuous heating. The local activation energy as a function of transformed volume fraction f ω was determined by Kissinger–Akahira–Sunose (KAS) method, which increases with the transformation proceeding and the average value is about 85.06 kJ/mol. The nucleation and growth mechanism of the ω phase was investigated by the non-isothermal local Avrami exponent n, which appears a significant change with the transformed volume fraction, indicating that the transformation mechanism varies at different stages. The local Avrami exponent lies between 0.5 and 2 in a wide transformed volume fraction range of 0.05–0.9, indicating that the dominating mechanism of ω phase transformation in Ti-7333 titanium alloy is the three-dimensional growth with a near-zero nucleation rate.

Recent studies suggest that the ratio of the shear modulus (G) to the bulk modulus (B) and the Poisson’s ratio (ν) are good indicators of ductility. Using the method of supercell and the first-principles pseudopotential plane-wave method, the G/B and ν of the β-type Ti-Mo binary alloys with Mo molar fraction (x Mo) ranging from 6.25% to 37.5% are calculated. The results show that the ductility of β-type Ti-Mo binary alloys first increases with increasing x Mo and reaches the maximum when x Mo is about 25%, and then reduces with more increasing x Mo. The charge density difference calculations suggest that the x Mo dependence of the ductility can be ascribed to the change of bonding characteristics between Ti and Mo atoms in the [111] direction.

A new metastable β type titanium alloy called TB-13 with the combination of excellent strength and ductility was developed successfully. In order to develop a perspective on this new alloy, the influence of several commonly used heat treatments on the microstructure and properties was studied. In solution-treated and quenched samples, a low-temperature aging at 480 °C results in the precipitation of finer α phase. The precipitation of coarser α phase plate at higher aging temperature (560 °C) leads to the increase of tensile ductility but reduction of strength. During low-temperature aging at 300 °C, quite homogeneous distribution of fine isothermal ω phase particles was found. The isothermal α phase provides nucleation sites for α phase during two-step aging process and makes α phase extremely fine and disperse uniformly in β matrix. Thus, TB-13 alloy is strengthened and its mechanical properties are improved.

The ω phase transformation kinetics of TB-13 titanium alloy has been analyzed by non-isothermal dilatometry. The average value of local activation energy determined is about 91.7 kJ/mol. The nucleation and growth mechanism of the ω phase has been investigated by the non-isothermal local Avrami exponent. Both the local Avrami exponent and the local activation energy during the ω phase transformation process change significantly with the transformed volume fraction, indicating that the ω phase transformation mechanism in this alloy varies at different stages. The local Avrami exponent lies between 1 and 2 in a wide transformed volume fraction range of 0.17–0.95, indicating that the dominating mechanism of ω phase transformation in TB-13 titanium alloy is the three-dimensional growth with a near-zero nucleation rate.

The ω phase is an important metastable phase in metastable s titanium alloys due to its significant influence on the phase transition sequence, microstructure evolution and mechanical properties of the alloys. In the present work, a quantitative phase-field model has been developed to describe the microstructural evolution during the athermal β to ω phase transition based on exact solution of coherent elastic energy and couplings to Ti-Mo metastable thermodynamical database. While reflecting the essential physics of {111}β collapse mechanism that leads to displacive transition, the modeling appropriately described the morphology, orientation and growth process of the athermal ω phase upon different quenching temperatures and Mo contents, which agree remarkably well with available experimental data. Present approach also nicely predicts a selective variant growth which observed in the experiments.

In near β titanium alloys, the precipitation morphology, size and spatial arrangement are strongly correlated to the precipitation behavior occurring during aging treatment. In this work, a newly near β titanium alloy Ti-7333 was subjected to solution and ageing treatment. And the evolution of α phase was analyzed by microstructure observation and quantitative statistics. The results indicated that The needle-like secondary α precipitate morphology formed after solution treatment above β phase followed with aging treatment. When the aging temperature reduced, the length and width of α phase reduced while the volume fraction increased, otherwise the amount and size of α precipitation increased with the increased of the aging time. The increasing in the volume fraction of α phase resulted in the strengthening of the micro-hardness of the alloy. The slower aging respond of α precipitate was observed in Ti-7333 alloy, which resulted from the more slow-diffusing element Mo in Ti-7333 alloy. The more slow-diffusing element Mo in Ti-7333 alloy also resulted in the precipitation of linear liked dot α phase after short time aging.

The high temperature discontinuous yielding behavior of Ti-7333 (Ti-7Mo-3Nb-3Cr-3Al), a new near β titanium alloy, has been examined between 770 and 845 °C over strain rates from 10−3 s−1 to 1 s−1. The results show that the discontinuous yielding of the alloy occurs when its strain rate is above 10−2 s−1 at all the experimental temperatures. The magnitude of the discontinuous yield drop for Ti-7333 alloy increases with decreasing of strain rate at a fixed temperature, and decreases with decreasing of temperature at a fixed strain rate. The magnitude is more sensitive to the strain rate than the temperature in this investigation. The discontinuous yield phenomena observed is associated with the mobile dislocation generated in grain boundaries during plastic deformation spreading to the grain interior with increasing of strain. The grain boundaries act as the sources of mobile dislocation generation. Further analysis suggests that the discontinuous yield drop is related to unlocking of dislocation sources through a localized dislocation climb, a boundary migration and/or a solute rearrangement.