Flow softening and dynamic recrystallization behavior of a Mg-Gd-Y-Nd-Zr alloy under elevated temperature compressions

Flow softening behavior of a homogenized Mg-7Gd-4Y-1Nd-0.5Zr alloy under compression to a final strain of∼1.8 at elevated temperatures of 450∼550℃ and a constant strain rate of 2s^(−1) has been investigated by optical microscopy,scanning electron microscopy,electron back-scattered diffraction and transmission electron microscopy.The results show that true stress first rises to the peak point and then drops to the bottom value and increases again with further increasing strain at each temperature.Twinning dynamic recrystallization(DRX)and continuous DRX contribute to the formation of new fine grains at temperatures 450∼475℃ when the restoration is caused by both DRX and texture change due to extension twinning,resulting in the larger softening degrees compared with the softening effects owing to continuous DRX and discontinuous DRX at 500∼550℃ when twinning activation is suppressed.500℃ is the transition temperature denoting a significant decline in the contribution of twinning and TDRX to the strain with increasing temperature.The cuboid-shape phase exists in both homogenized and compressed samples,while the compositions are varied.

Transient stimulated Raman scattering spectroscopy and imaging

Stimulated Raman scattering(SRS)has been developed as an essential quantitative contrast for chemical imaging in recent years.However,while spectral lines near the natural linewidth limit can be routinely achieved by state-of-the-art spontaneous Raman microscopes,spectral broadening is inevitable for current mainstream SRS imaging methods.This is because those SRS signals are all measured in the frequency domain.There is a compromise between sensitivity and spectral resolution:as the nonlinear process benefits from pulsed excitations,the fundamental time-energy uncertainty limits the spectral resolution.Besides,the spectral range and acquisition speed are mutually restricted.Here we report transient stimulated Raman scattering(T-SRS),an alternative time-domain strategy that bypasses all these fundamental conjugations.T-SRS is achieved by quantum coherence manipulation:we encode the vibrational oscillations in the stimulated Raman loss(SRL)signal by femtosecond pulse-pair sequence excited vibrational wave packet interference.The Raman spectrum was then achieved by Fourier transform of the time-domain SRL signal.Since all Raman modes are impulsively and simultaneously excited,T-SRS features the natural-linewidth-limit spectral line shapes,laser-bandwidth-determined spectral range,and improved sensitivity.With~150-fs laser pulses,we boost the sensitivity of typical Raman modes to the sub-mM level.With all-plane-mirror high-speed time-delay scanning,we further demonstrated hyperspectral SRS imaging of live-cell metabolism and high-density multiplexed imaging with the natural-linewidth-limit spectral resolution.T-SRS shall find valuable applications for advanced Raman imaging.

Super-resolution vibrational microscopy by stimulated Raman excited fluorescence

Inspired by the revolutionary impact of super-resolution fluorescence microscopy,super-resolution Raman imaging has been long pursued because of its much higher chemical specificity than the fluorescence counterpart.However,vibrational contrasts are intrinsically less sensitive compared with fluorescence,resulting in only mild resolution enhancement beyond the diffraction limit even with strong laser excitation power.As such,it is still a great challenge to achieve biocompatible super-resolution vibrational imaging in the optical far-field.In 2019 Stimulated Raman Excited Fluorescence(SREF)was discovered as an ultrasensitive vibrational spectroscopy that combines the high chemical specificity of Raman scattering and the superb sensitivity of fluorescence detection.Herein we developed a novel super-resolution vibrational imaging method by harnessing SREF as the contrast mechanism.We first identified the undesired role of anti-Stokes fluorescence background in preventing direct adoption of super-resolution fluorescence technique.We then devised a frequency-modulation(FM)strategy to remove the broadband backgrounds and achieved high-contrast SREF imaging.Assisted by newly synthesized SREF dyes,we realized multicolor FM-SREF imaging with nanometer spectral resolution.Finally,by integrating stimulated emission depletion(STED)with background-free FM-SREF,we accomplished high-contrast super-resolution vibrational imaging with STED-FM-SREF whose spatial resolution is only determined by the signal-to-noise ratio.In our proof-of-principle demonstration,more than two times of resolution improvement is achieved in biological systems with moderate laser excitation power,which shall be further refined with optimized instrumentation and imaging probes.With its super resolution,high sensitivity,vibrational contrast,and mild laser excitation power,STED-FM-SREF microscopy is envisioned to aid a wide variety of applications.

Enhanced Mechanical Properties of AA5083 Matrix Composite via Introducing Al_(0.5)CoCrFeNi Particles and Cryorolling

High-entropy alloy particles(HEAPs)can markedly enhance the mechanical properties of metal matrix composites(MMCs).In this study,AA5083/Al_(0.5) CoCrFeNi HEAPs MMCs with diff erent HEAPs contents(0,1,and 3 wt%)were prepared via a stir-casting,and then these MMCs sheets were hot rolled(573 K)and cryorolled(77 K),respectively.The mechanical properties of the MMCs sheets were measured by tensile testing and microhardness test.Additionally,their microstructures were analyzed by scanning electron microscopy and transmission electron microscopy.Results revealed that the ultimate tensile strength(UTS)of the as-cast AA5083/Al_(0.5) CoC rF eN i HEAPs MMCs were improved from 203 to 257 MPa by adding 3 wt%HEAPs.And the mechanical properties of the MMCs sheets were improved after cryorolling.After cryorolling with 50%rolling reduction ratio,the MMCs with 1 wt%HEAPs had an UTS of 382 MPa,which was 1.9 times that of the MMCs before rolling.Finally,the strengthening mechanisms of HEAPs and cryorolling on the AA5083/HEAPs MMCs were discussed.

Resonance-assisted light–control–light characteristics of SnS_2 on a microfiber knot resonator with fast response

An all-optical light–control–light functionality with the structure of a microfiber knot resonator (MKR) coated with tin disulfide (SnS_2) nanosheets is experimentally demonstrated. The evanescent light in the MKR [with a resonance Q of ～59,000 and an extinction ratio (ER) of ～26 dB] is exploited to enhance light–matter interaction by coating a two-dimensional material SnS_2 nanosheet onto it. Thanks to the enhanced light–matter interaction and the strong absorption property of SnS_2, the transmitted optical power can be tuned quasi-linearly with an external violet pump light power, where a transmitted optical power variation rate ΔT with respect to the violet light power of ～0.22 dB∕mW is obtained. In addition, the MKR structure possessing multiple resonances enables a direct experimental demonstration of the relationship between resonance properties (such as Q and ER), and the obtained ΔT variation rate with respect to the violet light power. It verifies experimentally that a higher resonance Q and a larger ER can lead to a higher ΔT variation rate. In terms of the operating speed, this device runs as fast as ～3.2 ms. This kind of all-optical light–control–light functional structure may find applications in future all-optical circuitry, handheld fiber sensors, etc.