Probing the peripheral self-generated magnetic field distribution in laser-plasma magnetic reconnection with Martin-Puplett interferometer polarimeter

Magnetic reconnection of the self-generated magnetic fields in laser-plasma interaction is an important laboratory method for modeling high-energy density astronomical and astrophysical phenomena.We use the Martin-Puplett interferometer(MPI)polarimeter to probe the peripheral magnetic fields generated in the common magnetic reconnection configuration,two separated coplanar plane targets,in laser-target interaction.We introduce a new method that can obtain polarization information from the interference pattern instead of the sinusoidal function fitting of the intensity.A bidirectional magnetic field is observed from the side view,which is consistent with the magneto-hydro-dynamical(MHD)simulation results of self-generated magnetic field reconnection.We find that the cancellation of reverse magnetic fields after averaging and integration along the observing direction could reduce the magnetic field strength by one to two orders of magnitude.It indicates that imaging resolution can significantly affect the accuracy of measured magnetic field strength.

Ultrafast two-dimensional x-ray imager with temporal fiducial pulses for laser-produced plasmas

It is challenging to make an ultrafast diagnosis of the temporal evolution of small and short-lived plasma in two dimensions. To overcome this difficulty, we have developed a well-timed diagnostic utilizing an x-ray streak camera equipped with a row of multi-pinhole arrays. By processing multiple sets of one-dimensional streaked image data acquired from various pinholes, we are capable of reconstructing high-resolution two-dimensional images with a temporal resolution of 38 ps and a spatial resolution of 18 μm. The temporal fiducial pulses accessed from external sources can advance the precise timing and accurately determine the arrival time of the laser. Moreover, it can correct the nonlinear sweeping speed of the streak camera. The effectiveness of this diagnostic has been successfully verified at the Shenguang-II laser facility,providing an indispensable tool for observing complex physical phenomena, such as the implosion process of laser-fusion experiments.

Hot deformation behavior of Super304H austenitic heat resistant steel

Super304H 奥氏体的热的热压缩测试抵抗的钢用一个 Gleeble 3500 热机械的模拟器在第 800-1200a 0.005-5 s ^-1 被执行，并且它的变丑行为是 Super304H 钢的流动压力与紧张率的减少和变丑温度的增加减少的 analyzed.The 结果表演；钢的热变丑激活精力是在山峰压力和变丑温度和紧张率之间的热变丑方程和关系是的 485 kJ/mol.The 弄软的 obtained.The 由变丑加热引起了当变丑温度和紧张率更高时，不能被忽视。

Characterization and numerical simulation of nucleation-growth-coarsening kinetics of precipitates in G115 martensitic heat resistance steel during long-term aging

The service performance of heat resistance steels is largely determined by the precipitation kinetics.The nucleation-growth-coarsening behaviors of precipitates in G115 martensitic heat resistance steel during long-term aging at 650℃ have been systemically investigated.The microstructural characteristics,precipitate morphology and alloying element distribution were studied by scanning electron microscopy,transmission electron microscopy and scanning transmission electron microscopy.The lognormal distribution fitting combined with the multiple regression analysis was adopted to evaluate the precipitate size distributions.Laves phase has longer incubation time,and its coarsening rate is almost one order of magnitude higher in comparison with that of M_(23)C_(6) carbide.Furthermore,the nucleation rate,number density,average radius,and volume fraction of two precipitates are simulated based on the classical nucleation theory and the modified Langer-Schwartz model.The precipitation behavior of Laves phase can be well explained with the Fe-W system as the interfacial energy takes 0.10 J/m^(2).In contrast,the simulation results of M_(23)C_(6) carbide in the Fe-Cr-C system are significantly overestimated,which results from the inhibitory effect of boron on coarsening.

Effect of removing Al and Ti elements on peak flow stress of nickel-based heat-resistant alloy 617

The hot deformation behavior and the microstructure characteristics of alloy 617 and alloy C-HRA-2 were compared and analyzed.The removal of Al and Ti elements has a significant change in the hot deformation of the alloy,and there are two opposite effects on the flow stress before and after recrystallization.The results show that the removal of Al and Ti elements increases the flow stress of the alloy under high temperature or low strain rate deformation conditions.This is mainly due to the increase in the stacking fault energy of the alloy so that the alloy contains a higher twin boundary fraction after dynamic recrystallization(DRX).However,before DRX occurs,that is,at low temperature and high strain rate,the flow stress of this alloy is relatively reduced.This is due to the reduction in Peierls-Nabarro stress,making the alloy more prone to dislocation slip.

Hot Deformation Behavior of SA508GR.4N Steel for Nuclear Reactor Pressure Vessels

A hot compression experiment （1073 1473 K, strain rates of 0. 001-10 s -1 ） of SAS08GR. 4N low alloy steel was performed using a Gleeble-3800 thermal-mechanical simulator, and the hot deformation behavior of the steel was investigated by analyzing both the true stress true strain curves and its microstructures. The thermal de formation equation and hot deformation activation energy （Q） of SA508GR. 4N steel were obtained by regression with a classic hyperbolic sine function. The hot processing map of SAS08GR. 4N steel was also established. An empirical equation for the stress peak was described for practical applications. The SA508GR. 4N steel showed a critical Zener-Hollomon parameter （lnZc） for dynamic recrystallization （DRX） of 37.44, below which full DRX may occur. The sensitivity of the SA508GR. 4N steel increased linearly with test temperature, such that higher temperatures led to enhanced workability.

Heat Treatment of a Candidate Material for 700 ℃ A-USC Power Plants

The preliminary chemical composition optimization and heat treatment parameters of Inconel 740H were investigated systematically. Six heats of experimental alloys （designated as heat 401 to heat 406） with varied chemi- cal compositions were subjected to standard heat treatment at four different solution temperatures. Due to its superi- or combination of strength, ductility, and toughness together with its minor mechanical property changes at different solution temperatures, heat 405 was chosen as an optimized one to conduct further heat treatment investigations. The evolution of grain size with solution temperature for heat 405 was studied and the optimal solution temperature was determined. After solution treatment at the optimal temperature, four different cooling rates were applied to investi- gate the effect of cooling rate on the size distribution modal and mean radius of the γ′ precipitates. No bi-modal size distribution of γ′ precipitates was found for all cooling rates and water cooling was recommended for Inconel 740H. In addition, the effect of pre-aging at 800 ℃ for 16 h on the microstrueture of Inconel 740H aged for a long time was studied. It is found that pre-aging at 800 ℃ would result in bi-modal size distribution of γ′ precipitates after long time aging at 750 ℃ compared with mono modal size distribution in samples without pre-aging, which might be caused by the difference in initial size distribution modal before Ostwald ripening of γ′ precipitates in samples with and without pre-aging at 800 ℃.

Microstructure Evolution and Mechanical Properties of HR3C Steel during Long-term Aging at High Temperature

Microstructure evolution and the changes in mechanical properties of HR3 Csteel during long-term aging at650,700 and 750℃ were investigated.The precipitated phases of the aging steel included M23C6 carbides,Z-phase and a trace amount of Nb（C,N）.The M23C6 carbides were distributed mainly at the grain boundary,while Z-phase was mainly inside the grains.Amounts of both M23C6 carbides and Z-phase during the aging process increased with increasing aging period and temperature.Coarsening of M23C6 carbides was influenced significantly by aging time and temperature,while the size of the Z-phase was relatively less affected by the aging time and temperature,which had a steady strengthening effect.Coarsening of the M23C6 carbides was the main reason for the decline in high temperature yield strength during long-term aging at 750℃.The M23C6 carbides were linked into a continuous chain along the grain boundary which accounted for the decrease of toughness during aging.

Hot Deformation Behavior of F6NM Stainless Steel

The hot deformation behavior of F6NM stainless steel was investigated by hot compression test in a Gleeble-1500D thermal-mechanical simulator. The flow strain-stress curves were obtained and the corresponding metallographic observation of this steel under different deformation conditions was also carried out. This steel exhibi- ted dynamic recrystallization （DRX） in the temperature range of 1 273- 1473 K and the strain rate range of 0.01- 0.1 s^-1. The activation energy for hot deformation was determined to be 457.91 kJ/mol, and the hot deformation equations were also established. The flow instability zone was determined and could be divided into two regions. The first one was located in the temperature range of 1 173- 1 348 K and the strain rate range of 0. 056-10 s^-1 , while the second one is in the temperature range of 1398-1448 K and the strain rate range of 1.25-10 s^-1. In the end, the optimum conditions for hot working were provided.

Constitutive modeling and critical strain of dynamic recrystallization in SA508Gr.4N steel for advanced pressure vessel materials

Using a Gleeble-1500D thermal-mechanical simulator,the hot-deformation behavior and critical strain in the dynamic recrystallization of SA508Gr.4N steel were investigated by compression tests from 1050 to 1250℃ with strain rates from 0.001 to 0.1 s^-1.Stress-strain curves were fitted by a nonlinear fitting method.Based on these tests,the flow stress constitutive equations of the work-hardening dynamical recovery period and dynamical recrystallization period Were established for SA508Gr.4N steel.The stress-strain curves of SA508Gr.4N steel predicted by the established models are in a good agreement with the experimental ones.Curves of ln θ -ε and --(a)(lnθ)/(a)ε-ε (where θ is the work-hardening rate and ε is true strain)were plotted from experimental data.A critical strain (εc)and a peak strain (εp)of dynamic recrystallization were obtained and exhibited a linear relationship,i.e.,εc =0.386εp.The predicted model of εc could be described by the equation of εc=1.604×10^-3Z^0.127.

Effect of Mn content on microstructure, tensile and impact properties of SA508Gr.4N steel for reactor pressure vessel

The effect of manganese(Mn)on the microstructure,tensile and impact properties of SA508Gr.4N steel has been experimentally investigated.The influence of Mn content on the substructure of SA508Gr.4N steel was investigated using the scanning electron microscope,electron back-scattered diffractometer and transmission electron microscope.It was found that the increased Mn content had a beneficial effect on both strength and toughness.Examination of microstructure revealed smaller size of block and larger number of high-angle grain boundaries with higher Mn content.The change of the ultimate tensile strength and toughness with increasing Mn content was attributed to the increased hardenability,the number of high-angle grain boundaries and the crack propagation path by the block refining.

Effects of long term aging on microstructure and properties of a tungsten bearing heat resistant alloy

The effects of long-term aging at 700 and 750℃ on microstructure and mechanical properties of a new developed tungsten bearing heat-resistant alloy used for advanced ultra-supercritical power plant was investigated both experimentally and thermodynamically.Experimental results showed that the mechanical properties maintained excellent stability after long-term aging at 700℃ for 10,000h,while the impact absorbing energy decreased sharply after 1000-h aging and then kept constant till 10,000h.The main precipitates after long-term aging at 700 and 750℃ were M23C6,MC and homogeneous γ′-phases.The mass fraction of M23C6 carbides increased with increasing aging time,and M23C6 carbides precipitated in shape of chains and lamellas on grain boundaries.The slight decrease in MC carbides during aging may be due to degradation reaction.The weight fraction of γ′-phase increased with the aging time,and then changed little after 5000h;γ′-phase exhibited excellent microstructure stability and low coarsening rate during long-term aging at 700℃.However,the coarsening rate of γ′-phase was much higher at 750℃.

Laves Phase in 22Cr-27Ni-2Ti-Al Austenitic Valve Steel

The Thermo Calc software was employed to calculate the equilibrium phase of 22Cr-27Ni-2Ti-Al austenitic valve steel, and the Laves phase in this steel was investigated after solid solution and aging by means of scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and X- ray diffraction （XRD）. Results show that the microstructure of the experimental steel consists of γ, γ′, Laves and NbC. I.aves phases mainly precipitate on grain boundaries, with granular and fibrous morphologies. The size of the granular Laves phase is about 50-600 nm, and the fihrous Laves phase is composed of short strip Laves phases which are 300-600 nm in length and 50 150 nm in width. These two morphologies of Laves phase coarsen with increasing aging temperature, and this steel possesses the highest strength and hardness at aging temperature of 760 ℃.

Static recrystallization behavior of SA508Gr.4N reactor pressure vessel steel during hot compressive deformation

The two-pass isothermal hot compression method was used to study the effect of different thermal deformation conditions on static recrystallization behavior in Ni-Cr-Mo series SA508Gr.4N low alloy steel with interval holding time ranging from 1 to 300 s,temperature ranging from 950 to 1150℃,strain rate ranging from 0.01 to 1 s^(-1),true strains ranging from 0.1 to 0.2,and initial austenite grain size ranging from 175 to 552μm.It can be concluded that the static recrystallization volume fraction gradually increases with the increase in the deformation temperature,strain rate,strain and pass interval,and the decrease in the initial grain size,which is mainly due to the increase in the deformation energy storage and dislocations.Moreover,strain-induced grain boundary migration is the nucleation mechanism for static recrystallization of SA508Gr.4N low alloy steel.Based on the stress-strain curve,the predicted value obtained from the established static recrystallization kinetics model is in good consistence with the experimental value,and the static recrystallization thermal activation energy of SA508Gr.4N steel was calculated as 264,225.99 J/mol.

Microstructural evolution and mechanical properties of a new Ni-based heat-resistant alloy during aging at 750℃

Microstructural evolution and mechanical properties of a new candidate Ni-based heat-resistant alloy for advanced ultra-supercritical （A-USC） steam turbine rotors were investigated during aging at 750℃ up to 10000 h. The evolutions of γ＇ particles inside austenitic grain and M_23 C_6 carbides along grain boundaries were characterized according to their morphologies, distributions, and growth kinetics. Mean radius of the γ＇ spherical particles grew from 20.3 to 90.0 nm after aging for 10000 h, and;the corresponding coarse- ning behavior was conformed to the law of Lifschitz-Slyosovd-Wagner （LSW）. The weight fraction of γ＇ particles slightly increased from 10.0 to 12.0 wt. % after aging of long duration at 750 ℃.The Cr-rich M_23C_6 carbides discontinuously precipitated along grain boundaries, while other detrimental phases were not formed during the aging treatment, and hence the strength of grain boundary was enhanced by these discontinuously distributed carbides. The critical size of γ＇ had a direct influence on the maximum hardness of this alloy. Moreover, this alloy presented a good impact toughness for the safety after long time aging at high temperature.

Effect of annealing and cooling rate on toughness of G115 heat-resistant steels

The effects of annealing before normalizing and different cooling ways, i.e., air cooling, quenching, and water mist cooling after normalizing on the toughness of G115 steels were investigated. The impact tests showed that the annealed samples had better toughness compared to the unannealed samples for three cooling ways. Microstructure observations revealed that the annealed samples had a more uniform grain distribution, smaller size and area fraction of M_(23)C_(6) particles along the grain boundaries, and lower dislocation density than those in the unannealed samples, which performed together for good toughness. Among three cooling ways, air cooling gave the best toughness due to the smallest occupancy of M23C6 particles in the grain boundaries. Thus, the combination of annealing conducted before normalizing and air cooling selected after normalizing can improve the toughness a lot of G115 steels.

Thermal deformation behavior and microstructure evolution of modified IN617 alloy with different initial states

The thermal deformation behaviors of the as-cast and wrought modified IN617 nickel-based heat-resistant alloys at different temperatures(1000–1180℃)and strain rates(0.01–1 s^(−1))were studied.The constitutive equation was established to describe the relationship of the flow stress,temperature,and strain rate during thermal deformation.The effect of the thermal deformation conditions on the microstructure evolution of alloys was studied using electron backscatter diffraction.The results revealed that the thermal deformation activation energy of the as-cast alloy was greater than that of the wrought alloy.The dynamic recrystallization(DRX)process is slow at intermediate strain rate(0.1 s^(−1))due to the comprehensive influence of various factors,such as the critical strain of DRX nucleation and stored energy.The DRX volume fraction increases with the improvement of deformation temperature.The varied dynamic softening mechanisms induce the different thermal deformation behaviors of as-cast and wrought alloys.The dynamic recovery,discontinuous dynamic recrystallization(DDRX)and nucleation at slip zone caused by strain incompatibility in grains were observed during thermal deformation of as-cast alloys.In the process of thermal deformation of wrought alloys,DDRX was the primary dynamic crystallization mechanism.The continuous dynamic recrystallization was an auxiliary nucleation mechanism.

Microstructure and impact toughness of 16MND5 reactor pressure vessel steel manufactured by electrical additive manufacturing

Electrical additive manufacturing can improve manufacturing efficiency and reduce the cost of 16MND5 reactor pres-sure vessel steel. Impact tests were conducted to compare the impact toughness of 16MND5 steels manufactured by the electrical additive manufacturing and conventional forging, respectively. It is found that the impact toughness of electrical additive manufacturing specimen was slightly higher than that of conventional forging specimen. The characterizations of microstructure show that there were large ferrites and carbides in electrical additive manufacturing specimen. The fracture mechanisms of electrical additive manufacturing specimen were that microvoids or microcracks were prone to nucleate at the large ferrite/bainite interface and large carbide/bainitic ferrite interface, where the stress concentration was high. In addi-tion, the block size and high-angle grain boundaries played a vital role in hindering crack propagation of electrical additive manufacturing specimen, helping to improve the impact energy and leading to a low ductile–brittle transition temperature. The results suggest that the electrical additive manufacturing technology was an effective method to enhance the impact toughness of 16MND5 steel.

Metadynamic recrystallization behaviors of SA508Gr.4N reactor pressure vessel steel during hot compressive deformation

The metadynamic recrystallization(MDRX)model is established,and the coefficients determined by multiple linear regression analysis are used to describe the microstructure evolution of SA508Gr.4N steel.The effects of compression temperature of 950–1150℃,strain rate of 0.001–0.1 s^(-1),pre-strain of 0.3–0.6,initial austenite grain size(IAGS)of 136–552 lm,and interval time of 1–300 s on the MDRX kinetics and microstructure evolution were analyzed,using twopass compression test method on Gleeble thermo-mechanical simulator.The results show that MDRX kinetics and austenite grain size are strongly dependent on compression temperature and strain rate,MDRX volume fraction increases with increasing compression temperature and strain rate,and the grain size decreases with increasing strain rate and decreasing compression temperature,while less affected by the pre-strain and IAGS.Meanwhile,the values predicted using MDRX model and the ones calculated from experiment are compared,and the results show that the proposed model can give a reasonable estimate of MDRX behavior for SA508Gr.4N steel.

Hot deformation behavior of a heat-resistant alloy without γ′-phase

The hot compression behavior of the nickel-based heat-resistant alloy C-HRA-2®was investigated by a Gleeble-1500 thermo-mechanical simulator with the deformation temperature range of 950-1150℃and the strain rate of 0.001-10 s^−1.The constitutive equation of the alloy was established by using a hyperbolic sine function,and the peak stress followed a power law relationship with the Zener-Hollomon parameter(Z).The activation energy was about 446 kJ mol^−1 for the whole hot deformation domain in this alloy.The optimum hot deformation condition was obtained in the temperature range of 1050-1150℃and the strain rate range of 0.005-0.1 s^−1.Unsafe domains during the hot deformation would occur in the strain rate range of 0.1-10 s^−1 with inhomogeneous microstructure and high-density twins in the alloy.The dominant nucleation mechanism of dynamic recrystallization(DRX)was continuous dynamic recrystallization with sub-grain rotation at high strain rate,while DRX at low strain rate was discontinuous dynamic recrystallization with original grain boundaries bulging.