In present work, the abrasive-free jet polishing (AFJP) of bulk single-crystal KDP was first fulfilled, when using a newly-designed low-viscosity microemulsion as the AFJP fluid. The novel AFJP fluid ...shows a typical water-in-oil structure, in which the water cores uniformly distribute in the BmimPF6 IL, with a particle size of about 20-25 nm. What's more, the AFJP fluid is a controllable and selective non-abrasive jet fluid that the shape of the removal function is regular and smooth, presenting a similar Gaussian function, meanwhile, the dispersion coefficient of the removal rate is only 1.9%. Finally, the surface quality of the bulk single-crystal KDP is further improved by AFJP, meanwhile, the subsurface damage is first obviously mitigated.
Extensive grape pomace from red-winemaking may seriously pollute the environment and cause the waste of resources. Cellulose after fermentation in grape pomace is suitable as the source of extract ...outstanding cellulose nanocrystals (CNCs). Herein, CNCs were successfully extracted from grape pomace with an eco-friendly and facile deep eutectic solvent (DES). The green DES with the composition of lactic acid/choline chloride (the molar ratio was 2:1), were used to fabricate CNCs. Importantly, the obtained CNCs as a robust nanocomposite can be successfully utilized to prepare the self-healing nanocomposite hydrogels. After added of Fe(III) and borax, the excellent self-healing performance of the guar gum-based hydrogels were achieved by the reversible noncovalent bonding interaction. Specifically, the hydrogels showed good mechanical properties (the stress was about 0.95 MPa, the strain was about 170%) and self-healing ability (the self-healing efficiency was about 90.0%). These biologically self-healing nanocomposite hydrogels can greatly broaden the recycling and utilization of grape pomace.
The hot working behavior of Mg-Gd-Y-Nb-Zr alloy was investigated using constitutive model and hot processing maps in this work. Isothermal compression tests were conducted with temperature and strain ...rate range of 703-773 K and 0.01-5 s~（-1）, respectively. Improved Arrhenius-type equation incorporated with strain compensations was used to predict flow behavior of the alloy, and the predictability was evaluated using correlation coefficient, root mean square error and absolute relative error. Processing maps were constructed at different strains for Mg-Gd-Y-Nb-Zr alloy based on dynamic materials model.The processing maps are divided into three domains and the corresponding microstructure evolutions are referred to the forming of straight grain boundaries, twinning, dynamic recrystallization and grain growth. Instability occurred mainly at the strain rate range of 0.3s~（-1）-0.5s~（-1）. The optimum processing domain is mainly at the temperature range of 703-765 K with the strain rate range of 0.01-0.1 s~（-1）.
Nowadays, hydrogels as flexible materials have attracted considerable attention in frontier fields such as wearable electronic devices, soft actuators and robotics. However, water-based hydrogels ...inevitably freeze at subzero temperatures and suffer damage from contact with objects, which greatly reduce their service life and practical value. Herein, nanocomposite hydrogels with self-healing performance at subzero temperatures were proposed by introducing binary water-glycerol continuous phase and dual self-healing interactions. The binary solvents were emphasized in preventing the formation of ice crystals, enhancing flexible and self-healing abilities of hydrogels in subzero environment. Linseed oil as healing agent was effectively loaded in Pickering droplets by cellulose nanocrystals. Owing to non-covalent bonding and external healing agent, the obtained hydrogels showed improved mechanical properties and self-healing abilities. Particularly, after incorporating Pickering droplets, the rupture stress of nanocomposite hydrogels was 0.24 MPa, the rupture strain was 1900% and the healing efficiency could be up to 80.1% for 12 h at − 20 °C. Therefore, the obtained hydrogels with frost resistance, stretchability and self-healing properties should have broader potential applications, especially in subzero environment.
In order to improve the detection sensitivity and stability of scanning laser ultrasound techniques, we propose a transmission time delay method, based on the time delay of transmitted longitudinal ...waves, for the evaluation of the size and position of an internal cavity. By studying the interacting process between the longitudinal wave and the internal cavity through theory and finite element method, the relationships among the time delay, cavity radius, and the detection distance were determined. The monotonicity of the relationship indicates that the time delay can be used to inverse the radius and the depth position of the internal cavity. The laser ultrasound experiments were performed on three aluminum samples with different internal cavities through the concentric transmission method. The C-scan results show that compared with using amplitude attenuation to detect the cavity, the time delay of transmitted waves can detect the internal cavities more stably and accurately. The experimental data are close to the theoretical and simulation results, and the inversion of cavity depth was achieved based on the measured parameters (the time delay, cavity radius, frequency, velocity). The results demonstrate that the transmission time delay method has a great application potential in the localization and quantification of the internal defects.
Ni47Ti44Nb9 alloys were successfully fabricated by laser powder bed fusion (LPBF) technique with different laser powers. The phase transformation behavior, tensile properties and shape memory ...response before and after heat treating were also investigated. The Ni47Ti44Nb9 LPBF alloys have good shaping properties, though a few defects were discovered. Phase transformation peaks did not appear in the as-built samples, but were observed in the heat-treated samples. The phase transformation temperatures of the heat-treated samples increase with the increase in laser power. The tension test at room temperature indicates that the LPBF samples exhibit poor tensile ductility, which may be related to the existence of pores and Ti2Ni or Ti4Ni2Ox phase during the LPBF process. However, the LPBF samples after heat treating still possess good shape memory effect (with recovery strain about 7.82–8%) and relatively high reverse transformation temperature (about 36–52.6 °C) when deformed to 8%.
The work presents a full mathematical description of the stress-strain compression curves in a wide range of strain rates and deformation temperatures for Armco-type pure iron. The constructed models ...are based on a dislocation structure evolution equation (in the case of dynamic recovery (DRV)) and Avrami kinetic-based model (in the case of dynamic recrystallization (DRX)). The fractional softening model is modified as: X = ( σ 2 − σ r 2 ) / ( σ d s 2 − σ r 2 ) considering the strain hardening of un-recrystallized regions. The Avrami kinetic equation is modified and used to describe the DRX process considering the strain rate and temperature. The relations between the Avrami constant k ∗ , time exponent n ∗ , strain rate ε ˙ , temperature T and Z parameter are discussed. The yield stress σ y , saturation stress σ r s , steady stress σ d s and critical strain ε c are expressed as the functions of the Z parameter. A constitutive model is constructed based on the strain-hardening model, fractional softening model and modified Avrami kinetic equation. The DRV and DRX characters of Armco-type pure iron are clearly presented in these flow stress curves determined by the model.
In the present work, three NiTiNb alloys with nominal compositions of Ni50–x/2Ti50–x/2Nbx (x = 18, 20 and 22, at.%) were prepared. The microstructure, thermal-induced phase transformation, and phase ...components of NiTiNb hypoeutectic, eutectic, and hypereutectic alloys were investigated by scanning electron microscopy coupled with energy dispersive spectrometer (SEM/EDS), differential scanning calorimetry (DSC), and X-ray diffraction (XRD), respectively. Two peaks occurred in the DSC curves of Ni41Ti41Nb18 solution at 750 and 850 °C. The different microstructures of NiTiNb hypoeutectic, eutectic and hypereutectic alloys, the occurrence of two peaks in the DSC curves, and the characteristic of martensite transformation temperature were analyzed and discussed. The results show that different Nb content leads to different microstructures of Ni50–x/2Ti50–x/2-Nbx alloys. Moreover, the difference of Ni/Ti ratio between the primary NiTi matrix and NiTi in eutectic structure strongly influenced the phase transformation behavior that the DSC curves of Ni41Ti41Nb18 alloy show two peaks. Furthermore, under the same solution treatment, the Ni40Ti40Nb20 alloy has a lower Ms than the other two alloys. The Ms has a tendency to decrease with an increase in solution temperature.
To clarify the origin of the high hardness of the 55NiTi alloy, the relationships between precipitation, martensitic transformation and hardness were investigated in three different highly Ni-rich ...NiTi alloys after different heat treatments. The results showed that, independent of the overall Ni content, the hardness of highly Ni-rich NiTi alloys depended only on the start temperature (Ms) of the B19′ martensitic transformation. The hardness at room temperature increased as the Ms temperature was lowered due to the increasing difficulty of stress-induced B19′ martensitic transformation. The pre-occurrence of an overlapped R-phase transformation lowered the hardness and the effect of a separated R-phase transformation on the hardness was weak. The much higher hardness of the 55NiTi alloy resulted from the difficulty of the stress-induced B19′ martensitic transformation.
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•The hardness of three highly Ni-rich NiTi alloys was investigated.•The hardness was independent of the overall Ni content in NiTi alloys.•The hardness depended on the Ms temperature.•The overlap of two martensitic transformation significantly reduced the hardness.
Grain Boundaries and voids are common defects in nanocrystalline metals, playing pivotal roles in plastic deformation. This study conducted molecular dynamics simulation to explore the incipient ...plasticity of Σ5 STGB bicrystalline Cu with a spherical void, alongside its constituent monocrystals at 10 K. The results reveal homogeneous nucleation of an elliptical 1/6 Shockley partial dislocation loop in the monocrystals. In the void-free Σ5 STGB bicrystal, initial dislocation nucleates homogeneously in grain interior rather than from the Σ5 STGB, forming a Shockley partial dislocation loop. In the monocrystals with a large spherical void, four initial dislocations nucleate from void surface on four slip systems. In the Σ5 STGB bicrystals with a spherical void, when the void diameter is 0.5 nm, the initial dislocation is an arc-shaped Shockley partial dislocation nucleated from the Σ5 STGB. For void diameters larger than 0.5 nm, initial dislocations nucleate from void surface. Through this study, the conditions for the nucleation, number, and morphology of initial dislocations are further understood, facilitating the evaluation of subsequent plastic deformation. This research contributes theoretical underpinnings for improving the mechanical properties and designing high-performance nanocrystalline metals.
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•Initial dislocations nucleation begins with local lattice transition.•Nucleation of a Shockley partial dislocation loop in void free single crystal.•Initial dislocation nucleates in grain interior in the void free Σ5 STGB bicrystal.•Dislocation nucleation transits from GB to void surface at D = 0.5 nm.•4 initial dislocations nucleate from large void surface, while 2 from small void.
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