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Spin dynamics in antiferromagnets has much shorter timescales than in ferromagnets, offering attractive properties for potential applications in ultrafast devices 1 – 3 . However, spin-current generation via antiferromagnetic resonance and simultaneous electrical detection by the inverse spin Hall effect in heavy metals have not yet been explicitly demonstrated 4 – 6 . Here we report sub-terahertz spin pumping in heterostructures of a uniaxial antiferromagnetic Cr 2 O 3 crystal and a heavy metal (Pt or Ta in its β phase). At 0.240 terahertz, the antiferromagnetic resonance in Cr 2 O 3 occurs at about 2.7 tesla, which excites only right-handed magnons. In the spin-canting state, another resonance occurs at 10.5 tesla from the precession of induced magnetic moments. Both resonances generate pure spin currents in the heterostructures, which are detected by the heavy metal as peaks or dips in the open-circuit voltage. The pure-spin-current nature of the electrically detected signals is unambiguously confirmed by the reversal of the voltage polarity observed under two conditions: when switching the detector metal from Pt to Ta, reversing the sign of the spin Hall angle 7 – 9 , and when flipping the magnetic-field direction, reversing the magnon chirality 4 , 5 . The temperature dependence of the electrical signals at both resonances suggests that the spin current contains both coherent and incoherent magnon contributions, which is further confirmed by measurements of the spin Seebeck effect and is well described by a phenomenological theory. These findings reveal the unique characteristics of magnon excitations in antiferromagnets and their distinctive roles in spin–charge conversion in the high-frequency regime. Pure spin currents are simultaneously generated and detected electrically through sub-terahertz magnons in the antiferromagnetic insulator Cr 2 O 3 , demonstrating the potential of magnon excitations in antiferromagnets for high-frequency spintronic devices.

In this article, we provide a broad and extensive review of beta titanium alloys. Beta titanium alloys are an important class of alloys that have found use in demanding applications such as aircraft structures and engines, and orthopedic and orthodontic implants. Their high strength, good corrosion resistance, excellent biocompatibility, and ease of fabrication provide significant advantages compared to other high performance alloys. The body-centered cubic (bcc) β-phase is metastable at temperatures below the beta transus temperature, providing these alloys with a wide range of microstructures and mechanical properties through processing and heat treatment. One attribute important for biomedical applications is the ability to adjust the modulus of elasticity through alloying and altering phase volume fractions. Furthermore, since these alloys are metastable, they experience stress-induced transformations in response to deformation. The attributes of these alloys make them the subject of many recent studies. In addition, researchers are pursuing development of new metastable and near-beta Ti alloys for advanced applications. In this article, we review several important topics of these alloys including phase stability, development history, thermo-mechanical processing and heat treatment, and stress-induced transformations. In addition, we address recent developments in new alloys, phase stability, superelasticity, and additive manufacturing.

Ti alloys have attracted continuing research attention as promising biomaterials due to their superior corrosion resistance and biocompatibility and excellent mechanical properties. Metastable β-type Ti alloys also provide several unique properties such as low Young’s modulus, shape memory effect, and superelasticity. Such unique properties are predominantly attributed to the phase stability and reversible martensitic transformation. In this study, the effects of the Nb and Zr contents on phase constitution, transformation temperature, deformation behavior, and Young’s modulus were investigated. Ti–Nb and Ti–Nb–Zr alloys over a wide composition range, i.e., Ti–(18–40)Nb, Ti–(15–40)Nb–4Zr, Ti–(16–40)Nb–8Zr, Ti–(15–40)Nb–12Zr, Ti–(12–17)Nb–18Zr, were fabricated and their properties were characterized. The phase boundary between the β phase and the α′′ martensite phase was clarified. The lower limit content of Nb to suppress the martensitic transformation and to obtain a single β phase at room temperature decreased with increasing Zr content. The Ti–25Nb, Ti–22Nb–4Zr, Ti–19Nb–8Zr, Ti–17Nb–12Zr and Ti–14Nb–18Zr alloys exhibit the lowest Young’s modulus among Ti–Nb–Zr alloys with Zr content of 0, 4, 8, 12, and 18 at.%, respectively. Particularly, the Ti–14Nb–18Zr alloy exhibits a very low Young’s modulus less than 40 GPa. Correlation among alloy composition, phase stability, and Young’s modulus was discussed.

Herein, a thin polymeric film prepared by spin coating technique using the blend of poly(vinylidene floride-co-hexafluoropropylene) (PVDF-HFP) and poly(methyl methactrylate) PMMA (1:1 mixing ratio) was introduced and compared with the pure PVDF-HFP. SEM, XRD, FTIR, TGA and DSC characterizations were conducted. Piezoelectric response was measured by hand made setup and the produced signal measured by a digital oscilloscope. Blending with PMMA increased the β-phase content, improved the heat stability. Crystallization point decreased from 140 to 129 °C and glass transition temperature changed from 59 to 94 °C. A uniform porous film structure was obtained with a thickness value of 12 µm. Piezoelectric potential obtained by applying mechanical force was found 4.385 V and 8.101 V for pure PVDF-HFP and the blend film, respectively. 84.7% increase found in the piezoelectric potential could be a promising result for energy harvesting and sensors applications. Graphic abstract

In this paper, we observe for the first time that a metastable beta-Zr in the body-centered cubic (BCC) structure can form via a new phase transformation route. The as-received alpha-Zr in the hexagonal closed-packed (HCP) structure transforms partially to the gamma-Zr in the face-centered cubic (FCC) structure via Shockley partial dislocations during deformation, while the gamma-Zr can continuously transform to the beta-Zr by a uniform shear along the 112 FCC direction on the 111 FCC plane during subsequent hot deformation. The beta phase is in a Pitsch–Schrader relationship ( ( 110 ) BCC | | ( 0001 ) HCP , [ 1 1 ¯ 0 ] BCC | | [ 10 1 ¯ 0 ] HCP ) with the matrix alpha phase and in a Nishiyama–Wassermann relationship ( ( 110 ) BCC | | ( 1 1 ¯ 1 ¯ ) FCC , [ 1 1 ¯ 0 ] BCC | | [ 12 1 ¯ ] FCC ) , with the gamma phase, both of which have not been reported in Zr previously. Combined with corresponding molecular dynamics simulations, the phase transition mechanism and stability of the beta phase are studied. The results show that the beta-Zr phase can be retained in the gamma phase when the cooling is fast enough. Graphic abstract

Metastable phase diagrams of β (BCC)-Ti high-temperature shape memory alloys (HTSMAs) have been investigated extensively, where however β →isothermal ω (iso-ω, hexagonal) transition upon heating has not been accessed. Following α ” (orthorhombic)→ β reverse martensitic transformation on heating, iso-ω precipitation is commonly encountered. These two transitions may overlap within certain composition range, but have not been clearly differentiated. It is of vital importance for the understanding of the subsequent transition behaviors. In this paper, phase transformations upon heating at various heating rates were characterized in quenched Ti-(16–25 at.%)Nb HTSMAs. In contrast to the linear increase in A s (the starting temperature of α ”→β transition) with decreasing Nb-content, ω s (the starting temperature of β→ iso-ω transition) exhibits normal decrease firstly and shows abnormal increase below 20Nb. It is because iso-ω precipitates only in the reversed β phase but not in α” martensite proved by transmission electron microscopy observations. Namely, β →iso-ω transition is postponed to higher temperature due to the suppression of α” martensite below 20Nb. On this basis, the characteristics of both transformations can be determined for Ti-Nb below 20Nb by proper peak deconvolution. New metastable phase diagrams of Ti-Nb are formulated, including both α ”→ β and β →iso-ω transitions upon heating. Moreover, effective activation energies for β →iso-ω transition during isochronal annealing are determined by the Kissinger method. Graphical abstract

Isothermal torsion tests were performed on a Ti–6Al–4V alloy in the two-phase region. The results show that straining leads to an increase in the beta phase fraction, which increases slightly with strain rate. Transformation took place at 880, 940, 960, 980 and 1000 °C. The extent of this type of dynamic transformation (alpha to beta) was increased when the temperature approached the transus temperature. The reverse transformation (beta to alpha) occurred during isothermal holding after torsion and the volume fraction retransformed increased with time. The driving forces promoting dynamic and reverse transformation together with the energy barriers opposing these transformations were derived and compared. The critical stresses required to initiate dynamic transformation are calculated from the flow curves. This analysis confirms that the peak stresses are always higher than the critical stresses at the temperatures employed in the present tests, which makes it possible for the transformation to occur.

Effect of frequency and peak current density of electropulsing on springback behaviors of Ti-6Al-4V titanium alloy was investigated during electrically assisted V-bending tests. The experiments were carried out by controlling variable parameters with a frequency of 0–450 Hz and peak current density of 0–62.5 A/mm 2 . The results show that springback angle and V-bending load value decrease with increasing frequency and peak current density. Springback can almost be eliminated at 450 Hz and 43.1 A/mm 2 . Based on neutral layer offset and microstructure analysis, it demonstrates that the reductions of neutral layer radius, bending moment, and residual stress are responsible for the springback reduction. In addition, the refined β phase particles, dissolution of clustered β phase, the reduction of β particle spacing at outer layer, and enhancement of β particle spacing at inner layer contribute to the balance of tensile and compression residual stress, contributing to springback reduction. Effect of peak current densities on the springback behavior under similar RMS current density was carried out and it was found that athermal effect could promote the dislocation motion and unraveling of dislocation pile-ups, further promoting to the springback reduction.

Titanium alloys display formation of β , α , and ω phases under different processing conditions. Understanding structural transformations involving these phases on a unified basis and identifying a possible path of transformation seem to be interesting from the point of view of studies on phase transformations. An alternative and unified description pertaining to these is being presented here. This is accomplished by making an appeal to four dimensional structural description. It will be shown that such a model requires an angular distortion ( θ ) around the threefold axis. Such a distortion helps one define a scalar order parameter ( η ) with values lying between 0 and 1. The two terminal values recover all the symmetrical characteristics of β phase corresponding to η = 0 and that of ω phase pertaining to η = 1 . α phase formation in this model takes place for θ = cos - 1 ( 1 4 ) and η = 13 16 . It is important to point out here that all structures related to choice of η always preserve a minimal threefold symmetry. This led us to conclude that formation of trigonal phases may be taking place during the paths of transformation. In addition to all these advantages, the model also provides a general possibility of understanding commensurate and incommensurate modulations along threefold axis.

Intergranular corrosion (IGC) of Al-Mg alloys in aqueous solutions is reviewed. Al-Mg alloys containing more than 3 wt% Mg can form β phase (Al3Mg2) that will precipitate via heterogeneous nucleation and growth when exposed to temperatures as low as 50°C for long periods of time, leading to sensitization and susceptibility to intergranular attack. The β-phase precipitates nucleate preferentially on grain boundaries, at second-phase particles, at dislocations, and throughout the bulk matrix. The grain boundary precipitation of β phase is dependent on Mg content, temperature, exposure time, and grain boundary characteristics, and is often practically characterized by degree of sensitization (DoS) defined by ASTM G67, but more scientifically by β-phase grain boundary coverage. IGC initiates readily from surfaces exposed to aqueous electrolytes (i.e., it does not require deep pits as precursor sites) and can penetrate to significant depths. IGC initiation can be explained in terms of an electrochemical framework based on differences between the pitting potentials of the Al-Mg solid solution and the β phase, which exist in a broad range of solutions and pH levels. Surface spreading of β-phase attack is reliant on the lateral spacing and proximity of β-phase particles and governed by DoS, grain size, and electrolyte concentration effects. IGC penetration depends on DoS, but more directly β-phase coverage, grain orientation, temper, and critically on electrochemical potential in NaCl solution. An aggressive fissure chemistry must be maintained to sustain IGC growth; this maintenance depends on the dissolution properties of both α and β phases. Threshold potentials are observed for IGC in NaCl solution. The origins of both the threshold and potential dependency of growth are discussed herein.