Effect of Co on Solidification Characteristics and Microstructural Transformation of Non-equilibrium Solidified Cu-Ni Alloys

Non-equilibrium solidification structures of Cu55Ni45 and Cu55Ni43Co2 alloys were prepared by the molten glass purification cycle superheating method.The variation of the recalescence phenomenon with the degree of undercooling in the rapid solidification process was investigated using an infrared thermometer.The addition of the Co element affected the evolution of the recalescence phenomenon in Cu-Ni alloys.The images of the solid-liquid interface migration during the rapid solidification of supercooled melts were captured by using a high-speed camera.The solidification rate of Cu-Ni alloys,with the addition of Co elements,was explored.Finally,the grain refinement structure with low supercooling was characterised using electron backscatter diffraction(EBSD).The effect of Co on the microstructural evolution during nonequilibrium solidification of Cu-Ni alloys under conditions of small supercooling is investigated by comparing the microstructures of Cu55Ni45 and Cu55Ni43Co2 alloys.The experimental results show that the addition of a small amount of Co weakens the recalescence behaviour of the Cu55Ni45 alloy and significantly reduces the thermal strain in the rapid solidification phase.In the rapid solidification phase,the thermal strain is greatly reduced,and there is a significant increase in the characteristic undercooling degree.Furthermore,the addition of Co and the reduction of Cu not only result in a lower solidification rate of the alloy,but also contribute to the homogenisation of the grain size.

Preparation of Laser Cladding Coating Undercooling Cu-based Alloy and Co on Non-equilibrium Solidification Structure

The effect of the gradient content of Co element on the solidification process of Cu-based alloy under deep under cooling conditions was explored.The non-equilibrium solidification structure of the under cooled alloy samples were analyzed.It is found that the rapidly solidified alloy has undergone twice grain refinement during the undercooling process.Characterization and significance of the maximum undercooling refinement structure of Cu60Ni35Co5 at T=253 K were analyzed.High-density defects were observed,such as dislocations,stacking faults networks,and twinning structures.The standard FCC diffraction pattern represents that it is still a single-phase structure.Based on the metallographic diagram,EBSD and TEM data analysis,it is illustrated that the occurrence of grain refinement under high undercooling is due to stress induced recrystallization.In addition,the laser cladding technology is used to coat Co-based alloy(Stellite12) coating on 304 stainless steel substrate;the microstructure of the coating cross-section was analyzed.It was found that the microstructure of the cross-section is presented as columnar crystals,planar crystals,and disordered growth direction,so that the coating has better hardness and wear resistance.By electrochemical corrosion of the substrate and coating,it can be seen that the Co and Cr elements present in the coating are more likely to form a dense passivation film,which improved the corrosion resistance of the coating.

An analytical transient coal permeability model:Sorption non-equilibrium index-based swelling switch

Long-term permeability experiments have indicated that sorption-induced swelling can switch from internal to bulk depending on the evolutive sorption status.However,this sorption swelling switch mechanism has not been considered in current analytical permeability models.This study introduces a normalized sorption non-equilibrium index(SNEI)to characterize the sorption status,quantify the dynamical variations of matrix swelling accumulation and internal swelling partition,and formulate the sorption swelling switch model.The incorporation of this index into the extended total effective stress concept leads to an analytical transient coal permeability model.Model results show that the sorption swelling switch itself results in the permeability switch under stress-constrained conditions,while the confined bulk swelling suppresses the permeability recovery to the continuous reduction under displacement-constrained conditions.Model verifications show that current experimental observations correspond to the early stages of the transient process,and they could be extended to the whole process with these models.This study demonstrates the importance of the sorption swelling switch in determining permeability evolution using simple boundary conditions.It provides new insights into experimentally revealing the sorption swelling switch in the future,and underscores the requirement of a rigorous model for complex coupled processes in large-scale coal seams.

Capturing the non-equilibrium state in light–matter–free-electron interactions through ultrafast transmission electron microscopy

Ultrafast transmission electron microscope(UTEM) with the multimodality of time-resolved diffraction, imaging,and spectroscopy provides a unique platform to reveal the fundamental features associated with the interaction between free electrons and matter. In this review, we summarize the principles, instrumentation, and recent developments of the UTEM and its applications in capturing dynamic processes and non-equilibrium transient states. The combination of the transmission electron microscope with a femtosecond laser via the pump–probe method guarantees the high spatiotemporal resolution, allowing the investigation of the transient process in real, reciprocal and energy spaces. Ultrafast structural dynamics can be studied by diffraction and imaging methods, revealing the coherent acoustic phonon generation and photoinduced phase transition process. In the energy dimension, time-resolved electron energy-loss spectroscopy enables the examination of the intrinsic electronic dynamics of materials, while the photon-induced near-field electron microscopy extends the application of the UTEM to the imaging of optical near fields with high real-space resolution. It is noted that light–free-electron interactions have the ability to shape electron wave packets in both longitudinal and transverse directions, showing the potential application in the generation of attosecond electron pulses and vortex electron beams.

A new formula of recovery factor for non-equilibrium transport of graded suspended sediment in the Middle Yangtze River

Suspended sediment concentrations in the Middle Yangtze River(MYR)reduced greatly after the Three Gorges Project operation,causing the composition of bed material to coarsen continuously.However,little is known about the non-equilibrium transport of graded suspended sediment owing to different bed material compositions(BMCs)along the MYR,and it is necessary to determine the magnitude of recovery factor.Using the Markov stochastic process in conjunction with the hiding-exposure effect of non-uniform bed-material,a new formula is proposed for calculating the recovery factor including the effect of different BMCs,and it is incorporated into the non-equilibrium transport equation to simulate the recovery processes of suspended load in both sand-gravel bed and sand bed reaches of the MYR.The results show that:(i)the recovery rate of graded sediment concentrations at Zhicheng was slower than that at Shashi during the period 2003-2007;(ii)the mean recovery factors of the coarse,medium,and fine sediment fractions in the ZhichengShashi reach were 0.152,0.0012,and 0.0005,respectively,and the coarse sediment recovered up to the maximum sediment concentration of 0.138 kg/m3over a distance of 15 km;and(iii)the results of the new formula that can consider the effect of bed material composition are in general agreement with the field observations,and the spatial and temporal delay effects are inversely related to particle size and BMC.Consequently,the BMC effect on the nonequilibrium sediment transport in different reaches of the MYR needs to be considered for higher simulation accuracy.

Permeability evolution and gas flow in wet coal under non-equilibrium state:Considering both water swelling and process-based gas swelling

Accurate knowledge of gas flow within the reservoir and related controlling factors will be important for enhancing the production of coal bed methane.At present,most studies focused on the permeability evolution of dry coal under gas adsorption equilibrium,gas flow and gas diffusion within wet coal under the generally non-equilibrium state are often ignored in the process of gas recovery.In this study,an improved apparent permeability model is proposed which accommodates the water and gas adsorption,stress dependence,water film thickness and gas flow regimes.In the process of modeling,the water adsorption is only affected by water content while the gas adsorption is time and water content dependent;based on poroelastic mechanics,the effective fracture aperture and effective pore radius are derived;and then the variation in water film thickness for different pore types under the effect of water content,stress and adsorption swelling are modeled;the flow regimes are considered based on Beskok’s model.Further,after validation with experimental data,the proposed model was applied to numerical simulations to investigate the evolution of permeability-related factors under the effect of different water contents.The gas flow in wet coal under the non-equilibrium state is explicitly revealed.

Critical anomaly and finite size scaling of the self-diffusion coefficient for Lennard Jones fluids by non-equilibrium molecular dynamic simulation

We use non-equilibrium molecular dynamics simulations to calculate the self-diffusion coefficient, D, of a Lennard Jones fluid over a wide density and temperature range. The change in self-diffusion coefficient with temperature decreases by increasing density. For density ρ＊ = ρσ3 = 0.84 we observe a peak at the value of the self-diffusion coefficient and the critical temperature T＊ = kT/ε = 1.25. The value of the self-diffusion coefficient strongly depends on system size. The data of the self-diffusion coefficient are fitted to a simple analytic relation based on hydrodynamic arguments. This correction scales as N-α, where α is an adjustable parameter and N is the number of particles. It is observed that the values of a 〈 1 provide quite a good correction to the simulation data. The system size dependence is very strong for lower densities, but it is not as strong for higher densities. The self-diffusion coefficient calculated with non-equilibrium molecular dynamic simulations at different temperatures and densities is in good agreement with other calculations fronl the literature.

Interplay between Micro-Anisotropy and Macro-Isotropy on Evolution of Non-Equilibrium Morphology

Non-equilibrium morphology has received much attention from both scientific and engineering points of view for its intricate pattern selection mechanisms and useful industrial application. Most study of non-equilibrium is about the metal, alloy and other simple system. The complex silicate system is rarely involved. However, silicate is very important in geosciences and ceramic industry. In this paper, two kinds of non-equilibrium crystal morphologies of silicate: dendrite of diopside and spherulite of plagioclase, were introduced. Combining with the other kinds of non-equilibrium morphologies, the characteristics of micro-macro and anisotropy-isotropy of the non-equilibrium morphologies were discussed. Dendrite of diopside is micro- and macro-anisotropic, spherulite of plagioclase is micro-anisotropic, but macro-isotropic, fractal of NH4Cl is also micro-anisotropic, but macro-isotropic, dense-branching morphology (DBM) formed in non-crystalline system is micro-and macro-isotropic. Based on the micro-macro interplay on the pattern formation, it is proposed that the interplay between micro-anisotropy of crystal structure vs macro-isotropy of undercooling in crystal growth system will control the morphological evolution. The nucleation rate related to the anisotropy for the morphological evolution was also discussed. The fact that diopside develops dendrite and plagioclase develop spherulite in our experiment is due to their structural anisotropy difference.

Non-equilibrium between ions and electrons inside hot spots from National Ignition Facility experiments

The non-equilibrium between ions and electrons in the hot spot can relax the ignition conditions in inertial confinement fusion[Fan et al.,Phys.Plasmas 23,010703(2016)],and obvious ion-electron non-equilibrium could be observed by our simulations of high-foot implosions when the ion-electron relaxation is enlarged by a factor of 2.On the other hand,in many shots of high-foot implosions on the National Ignition Facility,the observed X-ray enhancement factors due to ablator mixing into the hot spot are less than unity assuming electrons and ions have the same temperature[Meezan et al.,Phys.Plasmas 22,062703(2015)],which is not self-consistent because it can lead to negative ablator mixing into the hot spot.Actually,this non-consistency implies ion-electron non-equilibrium within the hot spot.From our study,we can infer that ion-electron non-equilibrium exists in high-foot implosions and the ion temperature could be~9%larger than the equilibrium temperature in some NIF shots.

Catalytic Effect of Activated Carbon and Activated Carbon Fiber in Non-Equilibrium Plasma-Based Water Treatment

Catalysis and regeneration efficiency of granular activated carbon （GAC） and activated carbon fiber （ACF） were investigated in a non-equilibrium plasma water treatment reactor with a combination of pulsed streamer discharge and GAC or ACF. The experimental results show that the degradation efficiency of methyl orange （MO） by the combined treatment can increase 22% （for GAC） and 24% （for ACF） respectively compared to pulsed discharge treatment alone, indicating that the combined treatment has a synergetic effect. The MO degradation efficiency by the combined treatment with pulsed discharge and saturated GAC or ACF can increase 12% and 17% respectively compared to pulsed discharge treatment alone. Both GAC and ACF show catalysis and the catalysis of ACF is prominent. Meanwhile, the regeneration of GAC and ACF are realized in this process. When H202 is introduced into the system, the utilization efficiency of ozone and ultraviolet light is improved and the regeneration efficiency of GAC and ACF is also increased.

Effect of La_2O_3/γAl_2O_3 Catalyst on the Activation of CH_4 and CO_2 to C_02 Hydrocarbons under Non-equilibrium Plasma

In the reaction of methane and carbon dioxide to C2 hydrocarbons under non-equilibrium plasma, methane conversion was decreased, but selectivity of C2 hydrocarbons was increased when using La2O3/?Al2O3 as catalyst. So the yield of C2 hydrocarbons was higher than using plasma alone. The synergism of La2O3/?Al2O3 and plasma gave methane conversion of 24.9% and C2 yield of 18.1%. The distribution of C2 hydrocarbons changed when Pd- La2O3/?Al2O3 was used as catalyst, the major C2 product was ethylene.

NON-EQUILIBRIUM SOLUTE SEGREGATION TO AUSTENITIC GRAIN BOUNDARY IN FERRUM-NICKLE ALLOY

The development of non-equilibrium segregation of boron at grain boundaries in Fe-4 0%Ni alloy during continuous cooling process was experimentally observed with boron Particle Tracking Autoradiography (PTA) and Transmission Electron Microscopy (TEM,). The samples with 10ppm boron were cooled at 2℃/s to 1040, 980, 920, 860, 780 and 640℃ respectively after pre-heat treatment of 1150℃ for 15mm with a Gleeble-1500 heat simulating machine, then water quenched to room temperature. The width of segregation layer and boron depletion zone, rich factor and other parameters were measured by a special image analysis system. The experimental results of PTA show that the grain boundary segregation of boron during cooling process is a dynamic process and the development of the non-equilibrium segregation experiences three stages: first increases rapidly from 1150 to 1040℃, then gently from 1040 to 860℃, and rapidly again from 860℃ to 640℃. The width of boron depletion zone increases from about 11μm at 1040℃ to 26μm at 640℃. TEM observation shows that boron precipitates exist at grain boundaries when the samples are cooled to below 860℃. The experimental phenomena are briefly discussed.

Experimental Study of a Minitype Atmospheric Non-equilibrium Plasma Source

A mini-type of plasma source was studied experimentally. The results showed that the plasma density, which was generated by an atmospheric non-equilibrium plasma source, rises with the increase in driving electric-field and the momentum of gas particles. For a driving electricfield of 56 kV/cm and a gas particles＇ momentum of 10^9 × 10^-22 g·m/s, the ion density can exceed 10^10/cm^3 while the effective volume of the plasma source is only 2.5 cm^2. This study may help develop a method to generate a minitype plasma source with low energy consumption but high ion concentration. This source can be used in chemical industry, environmental engineering and military applications.

Discussion on the Non-Equilibrium Phase of the Gliding Arc Plasma Driven by the Transverse Magnetic Field

a gliding arc driven by the transverse magnetic field was ignited between the electrodes with a complicated shape at atmospheric pressure and a non-equilibrium plasma was gencrated. Under our experimental conditions, a phenomenon was clearly observed where the arc power decreased with the increase in arc voltage. As the arc voltage was higher than 3.375 kV, the are power acquired from the power supply decreased, and the arc plasma began to switch to a non-equilibrium phase. The existence of the non-equilibrium arc plasma was very short, about 10 ms in one gliding arc discharge cycle.

Non-equilibrium ignition criterion for magnetized deuterium–tritium fuel

In this paper, non-equilibrium ignition conditions for magnetized cylindrical deuterium–tritium plasma in the presence of an axial magnetic field have been investigated. It is expected that temperature imbalance between ions and electrons as well as the axial magnetic field will relax the threshold of ignition conditions.Therefore, ignition conditions for this model are derived numerically involving the energy balance equation at the stagnation point. It has been derived using parametric space including electron and ion temperature(T_e, T_i), areal density(q R), and seed magnetic field-dependent free parameters of B/q, mB, and BR. For B/ρ < 10~6 G cm^3 g^(-1),mB < 4 × 10~4 G cm g^(-1), and BR <3 × 10~5 G cm, the minimum fuel areal density exceeds between ρR >0.002 g cm^(-2), ρR> 0.25 g cm^(-2), and ρR > 0.02 g cm^(-2),respectively. The practical equilibrium conditions also addressed which is in good agreement with the corresponding one-temperature magnetized mode proposed in previous studies. Moreover, it has been shown that the typical criterion of BR ≥(6.13–4.64) × 10~5 G cm would be expectable. It is also confirmed that the minimum product of areal density times fuel temperature in equilibrium model is located in the range of T = 6–8 keV for all these free parameters, depending on the magnitude of the magnetic field. This is the entry point for the non-equilibrium model consistent with equilibrium model.

Non-equilibrium turbulent phenomena in the ?ow over a backward-facing ramp

Non-equilibrium turbulence phenomena have raised great interests in recent years. Significant efforts have been devoted to non-equilibrium turbulence properties in canonical flows, e.g., grid turbulence, turbulent wakes, and homogeneous isotropic turbulence(HIT). The non-equilibrium turbulence in non-canonical flows, however, has rarely been studied due to the complexity of the flows. In the present contribution, a directnumerical simulation(DNS) database of a turbulent flow is analyzed over a backwardfacing ramp, the flow near the boundary is demonstrated, and the non-equilibrium turbulent properties of the flow in the wake of the ramp are presented by using the characteristic parameters such as the dissipation coefficient C and the skewness of longitudinal velocity gradient Sk, but with opposite underlying turbulent energy transfer properties. The equation of Lagrangian velocity gradient correlation is examined, and the results show that non-equilibrium turbulence is the result of phase de-coherence phenomena, which is not taken into account in the modeling of non-equilibrium turbulence. These findings are expected to inspire deeper investigation of different non-equilibrium turbulence phenomena in different flow conditions and the improvement of turbulence modeling.

Partial Remelting of Thixotropic Magnesium-Rare Earth Alloy from Near Non-Equilibrium-Liquidus Casting

After the investigation on partial remelting of thixotropic magnesium serial alloys （ZK60） by near non-equilibrium liquidus casting （NNLC）, the primary solid grains of ZK60-2Ca alloy spheroidized notably during partial remelting processing, however, coarsening and polygonization as occurred holding time prolonged. The refining and globularity of the thixotropic alloys are promoted after further alloyed by Y, RE, Nd and/or Ag, and the results vary with those addition. The remelting structure of ZK60-2Ca-1Y alloy is finer than its base alloy. And the effect of RE, especially Ag, on the refinement of microstrueture is notable, but Nd does nothing on it. There is little impact of remelting temperature fluctuation on partial remelted microstrueture as holding time in general. On the contrary, it is more sensitive at longer holding time. The quality thixotropic silver-contained alloy can be achieved by remelted partially at 600℃ for 10 min.

A Mixed-control Mechanism Model of Proeutectoid Ferrite Growth under Non-equilibrium Interface Condition in Fe-C Alloys

By combining the α/γ interface migration and the carbon diffusion at the interface in Fe-C alloys, a mathematical model is constructed to describe the mixed-control mechanism for proeutectoid ferrite formation from austenite. In this model, the α/γ interface is treated as non-equilibrium interface, i.e., the carbon concentration of austenite at γ/α interface is obtained through theoretical calculation, instead of that assumed as the local equilibrium concentration. For isothermal precipitation of ferrite in Fe-C alloys, the calculated results show that the rate of interface migration decreases monotonically during the whole process, while the rate of carbon diffusion from γ/α interface into austenite increases to a peak value and then decreases. The process of ferrite growth may be considered as composed of three stages: the period of rapid growth, slow growth and finishing stage. The results also show that the carbon concentration of austenite at γ/α interface could not reach the thermodynamic equilibrium value even at the last stage of ferrite growth.

Stress Field of Non-equilibrium Grain Boundaries in Nano-crystalline Metals

Introducing the stress distribution near grain boundaries to improve the dislocation pileup model for the Hall-Petch (H-P) relation, the continuous distribution of dislocations in the pileup could be solved by means of Tschebysheff polynomials for the Hubert transformation. An analytical formula of the stress intensity factor for the dislocation pileup is obtained. The reverse H-P relation may be explained by the modified dislocation-pileup-model.

Numerical Analysis of MHD Accelerator with Non-Equilibrium Air Plasma

Magnetohydrodynamic （MHD） accelerator is proposed as a next generation propulsion system. It can be used to increase the performance of a propulsion system. The objective of this study is to investigate the performance of MHD accelerator using non-equilibrium air plasma as working gas. In this study, the fundamental performance of MHD accelerator such as flow performance and electrical performance is evaluated at different levels of applied magnetic field using I-D numerical simulation. The numerical simulation is developed based on a set of differential equations with MHD approximation. To solve this set of differential equations the MacCormack scheme is used. A specified channel designed and developed at NASA Marshall Space Flight Centre is used in the numerical simulation. The composition of the simulated air plasma consists of seven species, namely, N2, N, O2, O, NO, NO＋, and e-. The performance of the non-equilibrium MHD accelerator is also compared with the equilibrium MHD accelerator.