Formation and evolution characteristics of bcc phase during isothermal relaxation processes of supercooled liquid and amorphous metal Pb

The formation and evolution characteristics of bcc phase during the isothermal relaxation processes for supercooled-liquid and amorphous Pb were investigated by molecular dynamics simulation and cluster-type index method （CTIM）. It is found that during the relaxation process, the formation and evolution of bcc phase are closely dependent on the initial temperature and structure. During the simulation time scale, when the initial temperature is in the range of supercooled liquid region, the bcc phase can be formed and kept a long time; while it is in the range of glassy region, the bcc phase can be formed at first and then partially transformed into hcp phase; when it decreases to the lower one, the hcp and fcc phases can be directly transformed from the glassy structure without undergoing the metastable bcc phase. The Ostwald＇s ＂step rule＂ is impactful during the isothermal relaxation process of the supercooled and glassy Pb, and the metastable bcc phase plays an important role in the precursor of crystallization.

Synthesis of indirect work exchange networks considering both isothermal and adiabatic process together with exergy analysis

In this paper, an efficient methodology for synthesizing the indirect work exchange networks(WEN) considering isothermal process and adiabatic process respectively based on transshipment model is first proposed. In contrast with superstructure method, the transshipment model is easier to obtain the minimum utility consumption taken as the objective function and more convenient for us to attain the optimal network configuration for further minimizing the number of units. Different from division of temperature intervals in heat exchange networks,different pressure intervals are gained according to the maximum compression/expansion ratio in consideration of operating principles of indirect work exchangers and the characteristics of no pressure constraints for stream matches. The presented approach for WEN synthesis is a linear programming model applied to the isothermal process, but for indirect work exchange networks with adiabatic process, a nonlinear programming model needs establishing. Additionally, temperatures should be regarded as decision variables limited to the range between inlet and outlet temperatures in each sub-network. The constructed transshipment model can be solved first to get the minimum utility consumption and further to determine the minimum number of units by merging the adjacent pressure intervals on the basis of the proposed merging methods, which is proved to be effective through exergy analysis at the level of units structures. Finally, two cases are calculated to confirm it is dramatically feasible and effective that the optimal WEN configuration can be gained by the proposed method.

Influence of isothermal bainitic processing on the mechanical properties and microstructure characterization of TRIP steel

The mechanical properties of transformation induced plasticity （TRIP） steel are strongly affected by the conditions of iso-thermal bainitic processing. The multiphase microstructure of TRIP steel under different conditions of isothermal bainitic processing was investigated using OM,SEM,XRD and TEM. The volume fraction of retained austenite and the carbon content in austenite were determined quantitatively using X-ray diffraction patterns. The relationship between mechanical properties and isothermal bainitic processing parameters was investigated. The stability of retained austenite was analyzed by the volume fraction of retained austenite and the carbon content in retained austenite. The experimental results show that the multiphase microstructure consists of ferrite,bainite and metastable retained austenite.To obtain good mechanical properties,the optimal conditions of isothermal bainitic temperature and holding time are 410-430°C and 180-240 s,respectively. After isothermal bainitic processing under the optimal conditions,the corresponding volume fraction of retained austenite is 5vol%-15vol%,which can provide enough retained austenite and plastic stability for austenite with high carbon content.

Analysis of isothermal forging process and mechanical properties of complex aluminum forging for aviation

Large complex 7A85 aluminum wing-body joint was forged employing isothermal forging process and its mechanical properties were studied.The tensile strength after forging is up to 587.5 MPa in longitudinal direction,15% higher than that using free forging.Moreover,the tensile strength of the forging is almost the same in three directions.Isothermal forging also performs well on overall fracture toughness,with a maximum value of 39.8 MPa·m1/2,and that of short transverse direction all reaches 36 MPa·m1/2 and above,with a maximum relative error of only 3.6%.The results indicate that the isothermal forging leads to better performance as well as higher uniformity in mechanical properties.

Study on the Isothermal Evaporation Process at 5℃ with the Brine of Laguocuo Salt Lake

1 Introduction Tibet has nurmerous salt lakes.Laguocuo is one of the salt lakes,which is located to the sorthern of Ali Plateau,31°59′02″N-32°04′08″N,84°02′03″E-84°12′03″E.Its lake water is rich in potassium,magnesium,lithium,boron,rubidium,cesium and other resources.The study of

Stiffness Characteristics of a Basic Nonlinear Air Spring Model

This study predicts the characteristics of a compressible polytropic air spring model. A second-order nonlinear autonomous air spring model is presented. The proposed model is based on the assumption that polytropic processes occur. Isothermal and isentropic compression and expansion of the air within the spring chambers are the two scenarios that are taken into consideration. In these situations, the air inside the spring chambers compresses and expands, resulting in nonlinear spring restoring forces. The MATLAB/Simulink software environment is used to build a numerical simulation model for the dynamic behavior of the air spring. To quantify the values of the stiffnesses of the proposed models, a numerical solution is run over time for various values of the design parameters. The isentropic process case has a higher dynamic air spring stiffness than the isothermal process case, according to the results. The size of the air spring chamber and the area of the air spring piston influence the air spring stiffness in both situations. It is demonstrated that the stiffness of the air spring increases linearly with increasing piston area and decreases nonlinearly with increasing air chamber length. As long as the ratio of the vibration’s amplitude to the air spring’s chamber length is small, there is good agreement in both scenarios between the linearized model and the full nonlinear model. This implies that linear modeling is a reasonable approximation of the complete nonlinear model in this particular scenario.

Optimizing temperature coefficient of Sm_(2)Co_(17)-type magnets through adjusting the isothermal aging process

The high-temperature magnetic perfo rmance and micro structure of Sm_(1-x)Gd_(x)(Co_(bal)Fe_(0.09)Cu_(0.09)Zr_(0.025))_(7.2)(x=0.3,0.5) magnets were investigated.With the isothermal aging time decreasing from 11 to 3 h,the temperature coefficient of intrinsic coercivity in the temperature range of 25-500℃,β_(25-500℃),was optimized from -0,167%/℃ to-0.112%/℃ for x=0.3 magnets.The noticeable enhancement(~33%) of temperature stability is correlated with the increased content of 1:5H cell boundary phase and its relatively high Curie temperature as well.However,for the x=0.5 magnet,it is found that the presence of Sm_(5)Co_(19) phases and wider nanotwin variants hinder the formation of 1:5H cell boundary phase.The insufficient 1:5H is not beneficial to the proper redistribution of Cu in cell boundary,making the x=0.5 magnet difficult to achieve higher temperature stability.Consequently,the approach of adjusting the isothermal aging process can offer guidance for attaining superior magnetic performance in the temperature range from 25 to 500℃ for Gd-substituted Sm_(2)Co_(17)-type magnets.

Spheroidization behavior of dendritic b.c.c. phase in Zr-based β-phase composite

The spheroidization behavior of the dendritic b.c.c, phase dispersed in a bulk metallic glass （BMG） matrix was investigated through applying semi-solid isothermal processing and a subsequent rapid quenching procedure to a Zr-basedβ-phase composite. The Zr-based composite with the composition of Z%62Ti138NbsoCuegNi5.6Be125 was prefabricated by a water-cooled copper mold-casting method and characterized by X-ray diffraction （XRD） and scanning electron microscope （SEM）. The results show that the composite consists of a glassy matrix and uniformly distributed fine dendrites of theβ-Zr solid solution with the body-centered-cubic （b.c.c.） structure. Based on the differential scanning calorimeter （DSC） examination results, and in view of the b.c.c.β-Zr to h.c.p, α-Zr phase transition temperature, a semi-solid holding temperature of 900 ℃ was determined. After reheating the prefabricated composite to the semi-solid temperature, followed by an isothermal holding process at this temperature for 5 min, and then quenching the semi-solid mixture into iced-water; the two-phase microstructure composed of a BMG matrix and uniformly dispersed spherical b.c.c.β-Zr particles with a high degree of sphericity was achieved. The present spheroidization transition is a thermodynamically autonomic behavior, and essentially a diffusion process controlled by kinetic factors; and the formation of the BMG matrix should be attributed to the rapid quenching of the semi-solid mixture as well as the large glass-forming ability of the remaining melt in the semi-solid mixture.

Isothermal transformation and precipitation behaviors of titanium microalloyed steels

The microstructure transformation and precipitation behavior of nano-carbides in Ti microalloyed steel during isothermal process were studied by a compression test on a Gleeble 3800 thermomechanical simulator and analyzed by optical microscopy,transmission electron microscopy and other methods.The results show thatγ→αphase transformation and TiC precipitation take place in Ti microalloyed steel during the isothermal process,and time–temperature–transformation curve and precipitation–time–temperature(PTT)curve are all of“C”-type.During the isothermal process,the interphase precipitation of TiC mostly occurs at the period of the phase transformation,and the random precipitation of TiC mostly occurs on the ferrite after the phase transformation.The increment in yield strength at the initial stage of isothermal transformation mainly comes from phase transformation strengthening.With the increase in isothermal time,the precipitation hardening effect becomes more important for nucleation and growth of titanium carbides and eventually reaches the maximum value at the precipitation finished point of the PTT curve.