Analysis on phase selection and microstructure evolution in directionally solidified Zn-Al-Mg-Ce alloy

In the process of hot-dip Zn-Al-Mg alloy coating,the plating solution dissipates heat in the direction perpendicular to the steel plate,which is considered to be a process of directional solidification.To understand the relationship between microstructure and cooling rate of Zn-Al-Mg alloys,both the phase constitution and microstructure characteristic length scales of Zn-9.5Al-3Mg-0.01Ce(wt.%)alloy were investigated by the directional solidification experiments at different growth velocities(V=40,80,160,250μm·s^(-1)).The experimental results show that the microstructure of directionally solidified Zn-9.5Al-3Mg-0.01Ce alloy is composed of primary Al dendrites and(Zn-Al-Mg2Zn11)ternary eutectics at the growth velocities ranging from 40 to 250μm·s^(-1).The primary Al dendrites are aligned regularly along the growth direction,accompanied with obvious secondary dendrites.The relationship between the microstructure length scale and the thermal parameters of solidification is obtained:λ1=374.66V-0.383,andλ2=167.5V-0.563(λ1is the primary dendrite arm spacing,andλ2 is the secondary dendrit arm spacing).In addition,through the interface response function(IRF)and the nucleation and constitutional undercooling(NCU),the phase selection of Zn-9.5Al-3Mg-0.01Ce is obtained:(Zn+Al+Mg2Zn11)ternary eutectics in the Zn-9.5Al-3Mg-0.01Ce alloy will be replaced by ternary eutectics(Zn+Al+MgZn2)when the growth rate is lower than 7.53μm·s^(-1).

Effect of silicon on phase selection of ternary compounds during solidification of ZA84 magnesium alloy

Effect of silicon on the phase selection between τ phase（Mg32（Al,Zn）49） and φ phase（Al2Mg5Zn2） in ZA84（Mg-8Zn-4Al-0.3Mn） magnesium alloy produced by steel mold cast was studied using X-ray diffractometer,scanning electron microscope and differential scanning calorimeter.The results show that with increasing Si addition in ZA84 alloy,the liquidus temperatures of the alloys and the solidification temperature ranges decrease.The ternary compound in ZA84 alloy is mainly τ phase and a little φ phase.When adding Si to ZA84 alloy,the preferential precipitation sequence of the ternary compounds changes,φ phase preferentially forms,whereas τ phase is suppressed.The solidification kinetics study of phase selection indicates that there is a critical degree of undercooling of the melt.If the undercooling exceeds the critical degree,τ phase preferentially forms while φ phase is suppressed;otherwise,φ phase preferentially forms while τ phase is suppressed.

Effect of External Electric Field on Phase Selection and Stability of Amorphous(Nd_(0.1)Fe_(0.9))_3B Alloy

The effect of an external electric field on the crystallization behavior of amorphous (Nd0.1Fe0.9)(3) B alloy was investigated. The crystallization product of Nd2Fe23B3 phase was obtained for this amorphous alloy annealed at 923 K for 300 s in the presence of an external electric field of 300 kV .m(-1) (50 Hz); while the crystallization products are Nd1.1Fe4B4, alpha-Fe, and Fe3B phases under the same annealing condition except for free-electric field. On the other hand, the samples were annealed at 1023 K, which is higher than the decomposition temperature of metastable Nd2Fe23B3 phase, for 600 s. In the case of the presence of an external electric field, the metastable Nd2Fe23 B-3 phase, as a main phase, is still stayed in the sample. This fact suggests that the external electric field enhances the stabilization of the metastable Nd2Fe23B3 phase. The effect of the external electric field on the phase selection and stabilization was explained in terms of the specific conductance difference between the crystallization products.

Phase selection and solidification path transition of Ti-48Al-xNb alloys with different cooling rates

Ti-48Al-xNb alloys were solidified by containerless electromagnetic levitation with quenching system of the conical copper mold.The influence of cooling rates on phase selection of T1-48Al-xNb alloys was investigated.In near-equilibrium solidification condition,the dendrite βphase is observed as the leading phase.No other metastable phase(e.g.,α phase) is observed.In contrast,in rapid solidification condition,the metastable α phase is observed in as-quenched Ti-48Al-2Nb alloy.Furthermore,the metastable α phase is replaced by the primary β phase with Nb addition increasing.For Ti-48Al-(x=4,6,8)Nb alloys,increasing cooling rate results in a solidification path transition.The peritectic reaction(L+β→α) is therefore significantly suppressed.The relationships between primary dendrite arm spacing(λ_(1)) and cooling rate(τ) can be described.

Tungsten-containing high-entropy alloys: a focused review of manufacturing routes, phase selection, mechanical properties, and irradiation resistance properties

Alloying is one of the most effective means to confer superior properties to metal materials.For far too long,conventional W-based alloys were generally improved by the addition of minor elements.The exploitation of conventional W-based alloy is restricted to the corner of multielement phase diagrams with tiny compositional space.High-entropy alloys(HEAs)are a novel kind of alloys consisting of multi-principal alloying elements(usually more than 4)and have attracted increasing attention,since they were first reported in 2004.The emergence of HEAs filled the gap of the unexplored central region of multielement phase diagrams.Among them,tungsten-containing HEAs(TCHEAs)exhibit excellent mechanical properties,especially at extraordinarily elevated temperatures.Moreover,recent studies showed that TCHEAs had outstanding irradiation resistance properties.TCHEAs might serve as a promising candidate for plasma-facing materials in the fusion reactor.Many characteristics of TCHEAs are different from other HEAs due to the addition of tungsten with ultrahigh-melting temperature.Here,this paper aimed to introduce the manufacturing routes of TCHEAs;review the phase selection,mechanical properties,and irradiation resistance properties of TCHEAs;and propose the future prospects of TCHEAs.

Phase Selection and Microhardness of Directionally Solidified AlCoCrFeNi_(2.1) Eutectic High-Entropy Alloy

In the present work,the solidification behaviors and microhardness of directionally solidified AlCoCrFeNi_(2.1) eutectic highentropy alloy(EHEA)obtained at different growth velocities are investigated.The microstructure of the as-cast AlCoCrFeNi_(2.1) EHEA is composed of bulky dendrites(NiAl phase)and lamellar eutectic structures,indicating that the actual composition of the alloy slightly deviates from the eutectic point.However,it is interesting to observe that the full lamellar structure of this alloy is obtained through directional solidification.In order to explain this phenomenon,the maximum interface temperature criterion and the interface response function(IRF)theory are applied to calculate the velocity range of the transition from the primary phase to the eutectic,which is 1.2–2×10^(4)μm/s.Furthermore,microhardness is one of the important parameters to measure the mechanical properties of materials.Therefore,the microhardness test is performed,and the test result indicates that the microhardness(HV)increased with increasing growth velocity(V)or decreased with increasing lamellar spacing(λ).The dependences ofλand HV on V are determined by using a linear regression analysis.The relationships between theλ,V and HV are given as:λ=11.62V^(-0.48),HV=305.5V 0.02 and HV=328.1λ^(0.04),respectively.The microhardness of the AlCoCrFeNi_(2.1) EHEA increases from 312.38 HV to 329.54 HV with the increase in growth velocity(5–200μm/s).Thus,directional solidification is an effective method to improve the mechanical properties of alloys.

Phase selection and microstructure evolution within eutectic Ti-Si alloy solidified at containerless state

Phase selection and microstructure evolution of the undercooled eutectic Ti-Si alloy were systematically investigated by the electromagnetic levitation method, and the maximum undercooling achieved was 318 K(0.2 TE). The migration of the liquidsolid interface was in-situ detected by a high-speed camera system. When the undercooling is smaller than 140 K, the liquid-solid interface is smooth. Once the undercooling arrives at 230 K, the liquid-solid interface is irregular, which reflects the growth transition from the solute control to the combined controls of solute and thermal. The eutectic growth velocity increases as an exponential function of undercooling. The electromagnetic stirring effect makes it difficult to increase undercooling, but plays an important role in accelerating the eutectic reaction velocity at low and moderate undercoolings. Primary dendritic β-Ti phase appears in the solidified alloy from 63 to 176 K undercoolings, and the microstructure is completely composed of eutectic once the undercoolings increase up to 230 K. When the undercoolings exceed 273 K, the microstructure consists of uniformly distributed irregular eutectic. For the drop tube experiments, the microstructures composed of a large amount of dendritic α-Ti phase and eutectic phase are found in a wide range of diameters from 69 to 725 μm. As the decrease of diameter, the solubility of Si in the dendritic α-Ti phase dramatically increases from 6.80% to 10.73%, and the ratio of the area occupied by the dendritic α-Ti on a cross-section of solidified alloy obviously increases from 23.52% to 41.02%, which result from the combined effects of high undercooling and large cooling rate.

NUCLEATION BEHAVIOR OF Al_8Fe_4Nd PHASE IN RAPIDLY SOLIDIFIED Al-Fe-V-Si-Nd ALLOY

The microstructure of Al-Fe-V-Si-Nd alloy prepared by rapid solidification (RS) processing was studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). The phase selection of the alloy during solidification and the nucleation behavior of Al8Fe4Nd phase were analyzed within the framework of time-dependent nucleation theory. The incubation time for Al8Fe4Nd phase was found shorter and the nucleation rate higher than those of α-Al. The results indicate the nucleation of Al8Fe4Nd phase is heterogeneous and the dispersoids of Al8Fe4Nd form as primary particles from the liquid, which is consistent with experimental observation.

The Networked Manufacturing Resources Optimizing Configuration System and Its Partners Selection Method

The three levels optimizing strategy is put forward for the networked manufacturing resources optimizing configuration, namely, the optimizing of a logical manufacturing process, the optimizing of simulation-based integration of process planning and scheduling, and the optimizing of networked production scheduling. Then, the web services-based architecture of networked manufacturing resources optimizing configuration is brought forward. Finally, the key algorithm of the networked manufacturing resources optimizing configuration is discussed, namely, the two phases manufacturing partners selection method, which including the group technology-based manufacturing resources pre-configuration and the genetic algorithm-based executable manufacturing process optimizing.

Study on the instantaneous protection reliability of low voltage circuit breakers

This paper outlines the significance of enhancing the instantaneous protection reliability of low voltage circuit breakers and describes their main failure modes. The instantaneous failure mechanism of low voltage circuit breakers was analyzed so that measures to improve instantaneous protection reliability can be determined. Furthermore, the theory of the instantaneous characteristics calibration device for low voltage circuit breakers and the method of eliminating the non-periodic component of test current are given in detail. Finally, the test results are presented.

Phase and Microstructure Selection During Directional Solidification of Peritectic Alloy Under Convection Condition

A phase and microstructure selection map used for peritectic alloy directionally solidified under convection condition was presented,which is based on the nucleation,constitutional undercooling criterion（NCU criterion）,and the highest interface temperature criterion.This selection map shows the relationships between the phase/microstructure,the G/V ratio（G is the temperature gradient,V is the growth velocity）,and the alloy composition under different convection intensities and nucleation undercoolings.Comparing with the results from directional solidification experiments of Sn–Cd peritectic alloys,this selection map was generally in agreement with the experimental results.

Computer-assisted optimization for the selection of mobile phase in semi-preparative HPLC

A computer-assisted method is presented for optimization for the selection of mobile phase composition in semi-preparative HPLC.The optimization for the expected separation is based on a polynomial estimation from five preliminary runs.Statistical scanning technique was used for optimization.Double criteria simulation system (DCSS) is established for chromatographic perfor- mance measurement in this method.The validity of the optimization strategy is confirmed by applying it to a technical Cypermethrin separation.Excellent agreement is obtained between the predicted and experimental results.

Differential Power Based Selective Phase Tripping for Fault-resilient Microgrid

Modern fault-resilient microgrids(MGs)require the operation of healthy phases during unbalanced short-circuits to improve the system reliability.This study proposes a differential power based selective phase tripping scheme for MGs consisting of synchronous and inverter-interfaced distributed generators(DGs).First,the differential power is computed using the line-end superimposed voltage and current signals.Subsequently,to make the scheme threshold-free,a power coefficient index is derived and used for identifying faulted phases in an MG.The protection scheme is tested on a standard MG operating in either grid-connected or islanding mode,which is simulated using PSCAD/EMTDC.The efficacy of the scheme is also assessed on the OPAL-RT manufactured real-time digital simulation(RTDS)platform.Further,the performance of the proposed protection scheme is compared with a few existing methods.The results show that the selective tripping of faulted phases in MGs can be achieved quickly and securely using the proposed scheme.

Adaptive IF selection and IQ mismatch compensation in a low-IF GSM receiver

This paper presents an algorithm that can adaptively select the intermediate frequency（IF） and compensate the IQ mismatch according to the power ratio of the adjacent channel interference to the desired signal in a low-IF GSM receiver.The IF can be adaptively selected between 100 and 130 kHz.Test result shows an improvement of phase error from 6.78°to 3.23°.Also a least mean squares（LMS） based IQ mismatch compensation algorithm is applied to improve image rejection ratio（IRR） for the desired signal along with strong adjacent channel interference.The IRR is improved from 29.1 to 44.3 dB in measurement.The design is verified in a low-IF GSM receiver fabricated in SMIC 0.13μm RF CMOS process with a working voltage of 1.2 V.

Pore scale numerical investigation of counter-current spontaneous imbibition in multi-scaled pore networks

The multi-scaled pore networks of shale or tight reservoirs are considerably different from the conventional sandstone reservoirs.After hydraulic fracturing treatment,the spontaneous imbibition process plays an important role in the productivity of the horizontal wells.Applying the color-gradient model of Lattice Boltzmann Method(LBM)accelerated with parallel computing,we studied the countercurrent spontaneous imbibition process in two kinds of pore structures with different interlacing distributions of large and small pores.The effect of geometry configuration of pore arrays with different pore-scale and the capillary number Ca on the mechanism of counter-current spontaneous imbibition as well as the corresponding oil recovery factor are studied.We found that the wetting phase tends to invade the small pore array under small Ca in both types of geometry configurations of different pore arrays of four pore arrays zones.The wetting phase also tends to invade the pore array near the inlet for injecting the wetting phase no matter if it is a large pore array or small pore array except for the situation when the Ca is large to a certain value.In this situation,the small pore arrays show resistance to the wetting phase,so the wetting phase doesn't invade the small pore near the inlet,but invades the large pore preferentially.Both the geometry configurations of different pore arrays and Ca have a significant effect on the oil recovery factor.This work will help to solve the doubt about the selectivity of the multi-scaled pores of the wetting phase and the role of pores with different sizes in imbibition and oil draining in countercurrent spontaneous imbibition processes.

Uniformly Dispersed Carbide Reinforcements in the Medium-Entropy High-Speed Steel Coatings by Wide-Band Laser Cladding

A medium-entropy high-speed steel(ME-HSS)coating with the 76 at.%of Fe and multiple alloying elements was prepared by the wide-band laser cladding.Compared with the commercial W6 Mo5 Cr4 V2(M2)HSS coating which contains a large number of network lamellar M2 C-type carbides along the grain boundaries,the presented ME-HSS coating has a high quantity of fi ner and more uniformly dispersed M C-type carbides;on the other hand,the coating has less retained austenite and much lower brittleness as well as similar secondary hardening eff ect and tempering hardness.

Enhancing mechanical properties and corrosion resistance of nickel-aluminum bronze via hot rolling process

The mechanical properties and corrosion behavior of as-cast, as-annealed and hot-rolled nickelaluminum bronze(NAB) alloy(Cu-9 Al-10 Ni-4 Fe-1.2 Mn, all in wt.%) in 3.5 wt.% Na Cl solution were investigated. The results show that annealing introduces a large number of k phases to precipitate in the k phase. However, after further hot rolling, the original continuous k phases are spheroidized and dispersed, increasing the strength, hardness, and elongation of the alloy. In addition to the enhanced mechanical properties, the corrosion resistance of the NAB samples is also improved significantly by hot rolling, as revealed by the mass loss measurements, electrochemical impedance spectroscopy(EIS), and cross-sectional corrosion morphology. Selective phase corrosion occurs by the preferential corrosion of the k phase, which acts as an anode to the k phases, and the uncorroded k phases are retained in the corrosion product film. The interfaces between the k phases and the surrounding corrosion products become discontinuous caused by the spheroidization of k phases, reducing the corrosion of the substrate by the corrosive medium via the channels. As a result, the corrosion rate and the maximum local corrosion depth of the hot-rolled NAB sample are greatly reduced.

Hierarchically Porous Carbon Membranes Derived from PAN and Their Selective Adsorption of Organic Dyes

Porous carbon membranes were favorably fabricated through the pyrolysis of polyacrylonitrile（PAN） precursors, which were prepared with a template-free technique-thermally induced phase separation. These carbon membranes possess hierarchical pores, including cellular macropores across the whole membranes and much small pores in the matrix as well as on the pore walls. Nitrogen adsorption indicates micropores（1.47 and 1.84 nm） and mesopores（2.21 nm） exist inside the carbon membranes, resulting in their specific surface area as large as 1062 m2/g. The carbon membranes were used to adsorb organic dyes（methyl orange, Congo red, and rhodamine B） from aqueous solutions based on their advantages of hierarchical pore structures and large specific surface area. It is particularly noteworthy that the membranes present a selective adsorption towards methyl orange, whose molecular size（1.2 nm） is smaller than those of Congo red（2.3 nm） and rhodamine B（1.8 nm）. This attractive result can be attributed to the steric structure matching between the molecular size and the pore size, rather than electrostatic attraction. Furthermore, the used carbon membranes can be easily regenerated by hydrochloric acid, and their recovery adsorption ratio maintains above 90% even in the third cycle. This work may provide a new route for carbon-based adsorbents with hierarchical pores via a template-free approach, which could be promisingly applied to selectively remove dye contaminants in aqueous effluents.