Kinds Of Alloys Research Articles

Multi- objective modeling and optimization of dissimilar laser welding by integrating an artificial intelligence predictive model with NSGA-II algorithm

This study presents a pioneering approach in laser welding of two dissimilar materials by integrating an Artificial Intelligence (AI)-based on predictive model with the Non-dominated Sorting Genetic Algorithm II (NSGA-II) for optimizing key performance characteristics of Nickel-based alloy and duplex 2205 stainless steel. Focusing on four primary input variables including laser power, welding speed, focal distance and deviation, the research aims to predict and optimize the responses including temperature field adjacent to the melt pool, penetration depth, and tensile strength of the joint according to the experimental results. The developed AI model first accurately forecasts these characteristics based on the inputs. This predictive accuracy is critical in defining the optimal target values. Considering the multidimensional nature of the problem, where enhancing one characteristic could compromise another, the study employs a Multi-Objective Optimization (MOO) strategy. This is where the innovative integration with NSGA-II becomes pivotal. Renowned for its efficiency in navigating multiple, potentially conflicting objectives, NSGA-II assists in achieving a balanced optimization of all target parameters. This method is adept at considering the complex interdependencies among various characteristics. The novelty of this work lies in its unique combination of AI for prediction and MOO for optimization and it is for the first time that machine learning is applied on this kind of alloys with four features and four targets.

Customized heat treatment process enabled excellent mechanical properties in wire arc additively manufactured Mg-RE-Zn-Zr alloys

Customized heat treatment is essential for enhancing the mechanical properties of additively manufactured metallic materials, especially for alloys with complex phase constituents and heterogenous microstructure. However, the interrelated evolutions of different microstructure features make it difficult to establish optimal heat treatment processes. Herein, we proposed a method for customized heat treatment process exploration and establishment to overcome this challenge for such kind of alloys, and a wire arc additively manufactured (WAAM) Mg-Gd-Y-Zn-Zr alloy with layered heterostructure was used for feasibility verification. Through this method, the optimal microstructures (fine grain, controllable amount of long period stacking ordered (LPSO) structure and nano-scale β′ precipitates) and the corresponding customized heat treatment processes (520 °C/30 min + 200 °C/48 h) were obtained to achieve a good combination of a high strength of 364 MPa and a considerable elongation of 6.2%, which surpassed those of other state-of-the-art WAAM-processed Mg alloys. Furthermore, we evidenced that the favorable effect of the undeformed LPSO structures on the mechanical properties was emphasized only when the nano-scale β′ precipitates were present. It is believed that the findings promote the application of magnesium alloy workpieces and help to establish customized heat treatment processes for additively manufactured materials.

Effect of Al/Ni Ratio on the Microstructure and Properties of Nickel-Aluminum Bronze Alloys.

To study the effect of aluminum and nickel elements on the microstructures and properties of the nickel-aluminum bronze (NAB) alloy, four kinds of alloys with different compositions, ZCuAl7-7-4-2, ZCuAl8-6-4-2, ZCuAl9-5-4-2, and ZCuAl10-4-4-2, are prepared by vacuum-melting technology. The effects of different Al/Ni ratios on the microstructures of NAB are investigated using a metalloscope, scanning electron microscopy, transmission electron microscopy, and XPS analysis. The mechanical property is evaluated with microhardness testing and tensile mechanical testing. The corrosion resistance is evaluated using mass-loss testing, electrochemical testing, and corrosion-product characterization. The results show that with the increase of the Al/Ni ratio, the content of precipitated phases increases, while β' and hard κ, which have a different morphology, appear. As the Al/Ni ratio rises from 1 to 2.5, the hardness increases from 104 HV to 202 HV, and the tensile strength increases by 394 MPa from 356 MPa to 751 MPa, but the elongation decreases substantially from 50.50% to 11.00%. The best corrosion resistance is shown on ZCuAl7-7-4-2, with a corrosion rate of 0.00267 mm/a after 30 d of static immersion corrosion in 3.5 wt.% NaCl solution. Through electrochemical testing and corrosion-product characterization, it is found that ZCuAl7-7-4-2 has the largest polarization resistance Rp, and the selective corrosion of the surface is mild.

Effect of Pd addition in BNi-2 interlayer on microstructure and properties in the TLP joints of FeCoNiTiAl and FGH98 alloys

L12-strengthed High-entropy alloys (HEAs) have attracted much attention in the field of manufacturing components that need to serve in high-temperature environments like aviation engine due to their high strength, toughness, and excellent high-temperature mechanical performance. Moreover, owing to great comprehensive mechanical properties, powder metallurgy (PM) superalloys have been widely applied for fabricating key parts of aircraft engine such as turbine disks. Hence, joining the two kinds of alloys is significant and potential in the engine manufacturing field. The key points to achieve joint with high strength and ductility (even at high temperature) were composition design of interlayer and the optimization of bonding parameters. In this study, Transient liquid phase (TLP) bonding was applied for joining HEA of FeCoNiTiAl and FGH98 superalloy using BNi-2 interlayer with addition of Pd. The experimental results demonstrate there were multiple second phases including γ’, borides (M3B2 and TiB2), etc., precipitated in the TLP joint. Furthermore, with the bonding time increased, accumulation of Al diffused from BMs can lead to a eutectic reaction of L → γ’ + AlPd + Cr5B3 occurred in the centerline of joint, which was harmful to the joint properties. Therefore, after bonding for 30 min at 1150 °C, owing to homogeneous joint microstructure of no defects and little eutectic compounds, the highest shear strength of 934 MPa was achieved.

Effects of the Growth Rate on the High-temperature Tensile Properties and Micro-organization of Directionally Solidified Ti-44Al-9Nb-1Cr-0.2W-0.2Y Alloys

In this experiment, Ti-44Al-9Nb-1Cr-0.2W-0.2Y alloy was prepared by the directional solidification method. The effect of different growth rates on tensile properties and microstructure orientation at high temperature was studied. Three kinds of alloys with different growth rates of 10 μm/s, 15 μm/s and 20 μm/s were prepared. The results show that the tensile properties of the alloy at 800 ℃ decrease with increasing growth rate, and recrystallization occurred at the position of intracrystal fracture in the microstructure. The size of columnar crystals decreases with the increase of the growth rate, increasing the number of grains and decreasing the orientation difference between the growth and axial directions as well as the preferred orientation of lamellar, and the anisotropy of the material, which leads to the obvious decrease of the tensile strength and plasticity. Combined with electron backscattering diffraction test results, the lamellar orientation of the effective parts of the three specimens after high temperature stretching was studied. It was found that the axial preferred orientation of the alloy specimens decreased obviously with the increase of the growth rate, and the orientation became disorderly and the uniformity of lamellar thickness decreased gradually with the increase of the growth rate. In addition, it was found that a new single-phase γ phase is formed in the microstructure after high temperature stretching, and the distribution range increased with the increase of the growth rate, which seriously degraded the axial preferred orientation of the alloy. It can be concluded that the directionally solidified alloy with a growth rate of 10 μm/s has better microstructure orientation and high temperature tensile properties.

Influence of cutting velocity on surface roughness during the ultra-precision cutting of titanium alloys based on a comparison between simulation and experiment.

The Ti-6Al-4V titanium alloy is a kind of light alloy material with high specific strength, corrosion resistance and heat resistance. Because of its excellent performance, it has become an important material in aerospace industry. However, this kind of alloy has very poor machinability, and rapid tool wear is a very serious problem in titanium alloy processing. At present, it is difficult to guarantee the ultra-precision machining quality of titanium alloy materials, which limits its application in high-tech fields. In order to solve this problem, the influence of cutting speed on ultra-precision cutting process of titanium alloy was analyzed comprehensively. and it was found that better surface quality could be obtained at lower cutting speed. In order to study the influence of cutting speed in ultra-precision cutting of titanium alloys, cutting experiments have been carried out. Additionally, a finite element model was established to analyze the ultra-precision cutting process. Also, the constitutive model, damage model, friction model, and heat transfer in the modeling process were discussed. The chip morphology, cutting temperature, cutting force, and surface morphology under different cutting velocities are analyzed by simulation. Then, the simulation results were compared with the experimental results. The findings show that cutting speed has great influence on the ultra-precision turning of the Ti-6Al-4V alloy and the surface roughness obtained by ultra-precision cutting of titanium alloy can be lower than 20 nm at a lower cutting speed.

Tailoring the radiation tolerance of eutectic high-entropy alloy via phase-composition control

Eutectic high-entropy alloys (EHEAs) take advantage of heterogeneous crystal structures, numerous interfaces, and multicomponent composition designs, implying a potential radiation tolerance in the nuclear environment. In this work, we employed the He ion irradiation to study the irradiation behavior of two types EHEAs (Fe42Ni31Al17Cr10, abbreviated as Fe42, and Fe47Ni26Al17Cr10, abbreviated as Fe47) with different phase designs. The results showed that the FCC + B2 constituted Fe42 EHEA and BCC + B2 constituted Fe47 EHEA retained their general phase-composition features up to ∼ 1.2 dpa at 1073 K, while the long-range order of B2 phase was slightly disrupted in both alloys and more severe in the Fe42 EHEA. The quantification on He bubbles formation in different phases further indicated that the ordered B2 phase in Fe47 EHEA has a superior radiation resistance with smaller bubble size and less population. The differences in phase compositions and structures were believed to influence the vacancy-mediated helium diffusion during irradiation, which can account for the He bubble behaviors in the two kinds of alloys. The analysis on the width of bubble denuded zone along the phase boundary further suggested a higher energy barrier for the vacancy migration in the B2 phase, which consistently supported our inference on the underlying mechanism of bubble formation resistance of Fe47 EHEA. We believe that this work will provide a new strategy for designing EHEAs with excellent resistance to irradiation at elevated temperatures.

The Effect of Cu Addition on Corrosion Resistance of Al-Si-Mg-Cr Alloy

Two kinds of alloys with and without the addition of Cu, Al-7%Si-0.3%Mg-0.3%Cr and Al-7%Si-0.3%Mg-0.3%Cr-1.5%Cu, are studied in this work. The addition of Cu can notably improve notably the strength of Al alloy but it reduces its corrosion resistance. In this study, the electrochemical workstation is used to measure the open circuit potential and polarization curve of alloys and immersion corrosion is carried out. SEM and TEM images are taken before and after immersion corrosion to observe the pitting and intergranular corrosion of the alloy. Results show that the addition of Cu accelerates the immersion corrosion rate of Al alloy by 26.8% to 269.2%. This affects the peak ageing and overageing samples the most. The influence is less evident for underaged samples. At the same time, the addition of Cu aggravates the aggregation of pitting corrosion in the primary step of corrosion of Al alloy and the intergranular corrosion around and within the pitting hole. β″-Mg5Si6 precipitates and θ″-Al3Cu precipitates are observed in Al-7%Si-0.3%Mg-0.3%Cr-1.5%Cu alloy. The Cu atoms occupy Si3/Al site of β″ and segregate at the edge of β″. It is believed that the deterioration of corrosion performance essentially is attributed to the Si-enriched particles, Al13Cr4Si4 phase and the Cu-enriched precipitates, β″-Mg5Si6 precipitates and θ″-Al3Cu precipitates.

Development of high strength high plasticity refractory high entropy alloy based on Mo element optimization and advanced forming process

Refractory high entropy alloy is a potential substitute material for high temperature structures because of its excellent mechanical properties of high temperature resistance. In this paper, three kinds of refractory high-entropy alloys, M0, M10 and M20, were designed by adjusting the content of Mo element and formed by Laser powder bed melting(LPBF) technology. The solidification thermodynamics, microstructure and mechanical properties of the three kinds of alloys were analyzed. The effect of Mo content on the microstructure and mechanical properties of the three kinds of alloys was studied. With the increase of Mo element content, the grain size of the alloy becomes smaller and smaller, the yield strength increases greatly, and the plasticity of the alloy decreases continuously. The compressive yield strength of high strength M20 alloy is up to 1285 MPa, the ultimate strength is 2447 MPa, and the elongation is 27%. The high plasticity M0 alloy exhibits compressive superplasticity. The tensile yield strength and ultimate strength of M10 alloy are 1184 MPa and 1403 MPa, and the elongation is 5.1%. In this paper, the matching problem between plasticity and strength of refractory high-entropy alloys at room temperature is solved by combining alloy composition optimization and LPBF forming technology, which lays a foundation for the industrial application of refractory high-entropy alloys.

Conceptual design of solid-type Pb x Li y eutectic alloy breeding blanket for CFETR

As a key component of the Chinese Fusion Engineering and Test Reactor (CFETR), the blanket is responsible for tritium breeding, neutron shielding and energy conversion. Blankets can be classified into solid and liquidaccording to the form of tritium breeder. Among them, the solid blanket utilizes the pebble beds as both the tritium breeder and neutron multiplier, and it has been a popular scheme due to its advantages, such as good material compatibility and non-magnetohydrodynamic effects. However, it usually adopts beryllium or an alloy (i.e. Be and Be12Ti) for multiplying neutrons, causing a very high cost of the solid blanket due to the scarcity of natural resources of beryllium, and this hinders its development. In this paper, a novel solid blanket utilizing a PbLi eutectic alloy was proposed to make up the above deficiency. Pb83Li17 is usually applied in a liquid blanket due to its lowmelting point. However, this kind of alloy can have a higher melting point by adjusting the atomic ratio of Pb/Li, and thus it can be used in the solid blanket both for the tritium breeder and neutron multiplier. Based on the blanket modular design of CFETR, the optimization of the radial layouts, the atomic ratio of Pb/Li and the packed structure of the pebble beds are studied through neutronic and thermal hydraulic analysis. The results indicate that the solid-type Pb x Li y can satisfy the requirement of tritium self-sufficiency, and the global tritium breeding ratio is larger than 1.0. In addition, the cooling system design can retain the maximum temperature of Pb x Li y at a lower level without melting. Overall, this kind of solid-type Pb x Li y blanket is feasible from the perspective of neutronic and thermal hydraulics, and it avoids using beryllium; thus, the cost is highly reduced.

First-principles calculations to investigate strong half-metallic ferromagnetic and thermoelectric sensibility of LiCrX (X = S, Se, and Te) alloys

The electronic, elastic, and thermoelectric behaviors of the half-Heusler LiCrX (X = S, Se, and Te) compounds in the Type I phase are investigated. These three kinds of alloys have minimum energies of type I, rather than types II and III. As a result, Li, Cr, and X (X = S, Se, Te) atoms prefer the positions (0.25, 0.25, 0.25), (0.75, 0.75, 0.75), and (0, 0, 0) respectively. LiCrSe and LiCrTe are true half-metal ferromagnetic compounds with a spin polarization of 100 %, whereas LiCrS is a false half metal alloy. The mBJ-GGA potential technique is also used for calculating electronic, magnetic, and thermoelectric features. The predicted total magnetic moment of LiCrSe and LiCrTe alloys is 5 µB per formula unit, the majority of which is contributed by Cr. So, LiCrSe and LiCrTe alloys could be suitable for spintronic applications. The elastic properties of LiCrS, LiCrSe, and LiCrTe alloys in Type I phase are analysed and obey to the stability criteria, both LiCrS and LiCrSe are anisotropic, while LiCrTe is isotropic. The classical Boltzmann theory has been employed to investigate thermoelectric performance. The ZT of LiCrTe and LiCrSe can be increased to a comparatively high value (ZT = 0.9495 for LiCrSe and ZT = 0.9507 for LiCrTe) by optimizing the carrier concentration to n = 84.6 * 1021 cm−3 for LiCrSe and 67.4 * 1021 cm−3 for LiCrTe, respectively. In addition, decreasing the chemical potential of LiCrSe by 0.013 Ryd and LiCrTe by 0.025 Ryd, respectively, yields the same results for ZT. The ZT value of LiCrS exhibits a considerable value, and at 1000 K, it can be as high as 0.7091.

Newly synthesized NiCoFeCrW High-Entropy Alloys (HEAs): Multiple impacts of B4C additive on structural, mechanical, and nuclear shielding properties

High-Entropy Alloys (HEAs) are regarded as potential structural materials for fusion and next-generation fission reactors, which will be required to fulfil growing nuclear energy demands. In this study, a HEA-composite was synthesized by adding B4C to an HEA containing Ni. The microstructure of the obtained HEA-composite was examined and the changes in its mechanical properties were revealed. Additionally, the nuclear radiation shielding properties of the Ni-containing HEA, and the HEA-composite are investigated using experimental and theoretical methods. Our initial findings showed that with the addition of 2.5% B4C to the alloy, the hardness increased more than two times. The addition of B4C to the HEA matrix resulted in a more than 90% and a nearly twofold increase in compressive strength. The shielding qualities of gamma-ray and neutron radiation were investigated using experimental and theoretical approaches. Our findings demonstrated that increasing the B4C reinforcement considerably enhanced the composite material's neutron attenuation capabilities. On the other hand, no significant change in the gamma-ray shielding characteristics of HEA and HEA-composite samples was observed. The gamma-ray shielding characteristics of HEA and HEA-composite samples were compared to those of other alloy shields and commercial products. Our findings indicate that both HEA and HEA-composite samples exhibit superior gamma-ray shielding characteristics when compared to the control samples. It can be concluded that increasing B4C reinforcement may be a multifunctional tool in terms of improving the mechanical properties as well as neutron attenuation properties for advanced applications in nuclear radiation facilities and next-generation fission reactors. Additionally, due to their promising material features and higher gamma-ray shielding capabilities compared to other kinds of alloys and commercial shields, HEAs may be beneficial materials.

First-Principles Investigations on Structural Stability, Elastic Properties and Electronic Structure of Mg32(Al,Zn)49 Phase and MgZn2 Phase

Al–Mg–Zn alloys reinforced by T–Mg32(Al,Zn)49 phase had higher structure stability and strength than Al–Zn–Mg–(Cu) alloys reinforced by MgZn2 phase, but the reasons for these two kind of alloys was not well-known. To reveal the discrepancy between T phase and MgZn2 phase, the lattice parameters, cohesive energy, and electronic structure as well as the elastic properties were investigated based on density functional theory. Four types of T phase unit cell were employed according to symmetry of space group. The calculated lattice constants well-agreed with experimental data. Compared to MgZn2 phase, T phases obtained lower cohesive energy owing to their partial covalent bond, which may result in a higher structure stability. The elastic modulus E of T phase depended on the occupation of Al atom, and the effect of the occupation of Al atom on the structure and properties of T phase was also discussed.

Remarkable cryogenic strengthening and toughening in nano-coherent CoCrFeNiTi0.2 high-entropy alloys via energetically-tuning polymorphous precipitates

In the present work, three kinds of precipitates with different morphologies, structures, sizes, and volume fractions were obtained via energetically-tuning the microstructures of the nano-precipitated CoCrFeNiTi0.2 high-entropy alloy (HEA). Subjected to the heavy cold rolling immediately after homogeneous precipitation, L12 structured spherical nano-particles with an average size of 16.5 nm rapidly grow into 200 nm-sized spherical ones due to Ostwald ripening. On the other hand, superfluous mechanical energy storage energetically facilitates the phase transformation from spherical L12 to rod-shaped D024 structures for initially formed nano-precipitates. Besides, some other newly formed nano-precipitates with an average size of 6.5 nm are available, originating from heavily plastically deformed-induced nucleated sites. Multi-scale precipitates interact with dislocations in different ways. The strengthening provided by dislocations cutting through smaller nano-particles and bypassing grown ones account for 57.7% and 42.3% of precipitation strengthening, respectively, while rod-shaped precipitates can act as equivalent interfaces to hinder dislocation movement. Their synergistic effect has achieved remarkable strengthening and toughening. Specially, dislocation slips dominate at 298 K, while stacking faults (SFs) assist plastic deformation at 77 K. Compared with 298 K, the yield strength (YS) and ultimate tensile strength (UTS) of the current HEAs at 77 K are increased by 38.9% and 38.2% to 1 GPa and 1.5 GPa, respectively, and the tensile strain is slightly increased to 35% instead of loss, realizing excellent strength and plasticity combination. Theoretically established strengthening models agree well room-temperature and cryogenic yield strengths experimentally. Moreover, the tensile elongation is effectively predicted by the Whitehouse-Clyne model. This strengthening strategy of energetically-tuning polymorphous precipitates provides the basic guidance to develop high-performance nano-precipitated alloys. The current strengthening and plasticity models can be employed to well predict the mechanical properties of such kinds of alloys at cryogenic temperatures.

Effects of trace Mn and B on microstructure and memory properties of additive manufacturing Cu-Al-Fe alloy

In this paper, the Cu-13Al-4Fe alloy was selected as the object, and the powder core wire with the “skin coated powder” damage-resistant structure was selected as the material for additive manufacturing. Three kinds of alloys: Cu-13Al-4Fe, Cu-13Al-4Fe-0.6Mn, and Cu-13Al-4Fe-0.2B were prepared by wire arc additive manufacturing technology. An optical microscope observed the as-deposited and quenched microstructures of the alloys before and after adding trace fourth phase elements. Their shape recovery rates under different pre-strain amounts (4%, 6%, and 8%) were tested by the bending deformation method, and the results were obtained. The mechanism of action of the fourth phase elements is discussed. The results show that the addition of trace amounts of Mn and B not only refines the microstructure of additively manufactured Cu-Al-Fe alloys but also improves the memory properties of Cu-13Al-4Fe alloys. Especially the Cu-13Al-4Fe alloys with trace amounts of B added. the shape recovery rate is 100% under the pre-strain of 4% and 6%, and the shape recovery rate is still 98.39% under the pre-strain of 8%.

Effect of heat treatment on the microstructure and mechanical properties of cryogenic rolling 2195 Al–Cu–Li alloy

Cryogenic deformation had been proved to promote the strength and toughness in several kinds of alloys. The microstructure responses and mechanical properties of cryogenic rolling 2195 Al–Cu–Li alloy after heat treatment were investigated systematically in this study. The annealed 2195 Al–Cu–Li alloy plates were subjected to cryogenic rolling to a reduction of 80% at −190 °C, followed by the solid solution at 540 °C for 2 h and aging treatment at 175 °C for different durations. Both the tensile strength and ductility of heat-treated specimen increased compared with the as-rolled sample, while the yield strength of the cryogenic rolling sample was higher anomaly. In addition, the tensile strength, yield strength, and elongation of the heat-treated samples increased firstly and then decreased with the increase of aging time. The number of T1 phases was initially increased with the aging time extended to 12 h and decreased after the aging duration was increased to 16 h. While the number of θ' gradually decreases with aging time increased. Based on the precipitation kinetics, aging kinetics, and dislocation theory, a physically based model considering the variation of dislocation density and volume fraction of the T1 phase and aging duration was established in this paper, which is in good agreement with the experimental data. Meanwhile, a strong connection between the dislocation density and fraction of the T1 phase and aging duration is established.

Size effect of the width of beta-Li phase on the ductility of magnesium–lithium dual-phase alloys

The size effect on ductility is not sufficiently understood and developed to be calculated by equations like that of the well-known Hall-Petch relationship for the size effect on strength. To improve the understanding of the size effect on ductility, in this work, small amount of rare earth (Sc and Y) elements were submitted to Mg–Li dual-phase alloys, possessing hexagonal-close-packed alpha-magnesium (α-Mg) and body-centra-cubic beta-lithium (β-Li) phases. An abnormally high elongation of 43%, more than two times as those of common magnesium alloys, was acquired in an as-cast Mg–Li dual-phase alloy. The abnormally high ductility possessed by Mg–Li dual-phase alloys in both this work and previous literatures, during tension and compression, was attributed to the size effect of the width of β-Li phase in this kind of alloys. The critical value of this size effect, which is believed to be twice of the interface-affected zone (IAZ), presented to lay in the range of 3–8 μm. Based on this size effect, a duplex Mg–Li alloy, after the working process, is expected to achieve a high elongation via making the width of β-Li phase to satisfy the critical value presented in this work.

A novel ultra-low current and temperature controlled electrochemical method for exposing various kinds of secondary phase precipitates: Application to the sample preparation of zirconium alloys and some other common alloys

Secondary phase particles (SPPs) have attracted extensive attention because of their effects on the properties and performance of alloy materials. In the present study, a novel ultra-low current and temperature controlled electrochemical (ULCT) method, which can expose contained SPPs on the alloy surface, has been proposed for the first time. We demonstrated that the exciting new approach is feasible for the high-quality bulk sample preparation of various common alloys including Zircaloy-4 (Zr-4 alloy), GH99 super alloy and 2A12 aluminium alloy. Results show that this ULCT method is a real universal and promising method for the specific sample preparation, which will make SEM-based techniques become invaluable for routine characterization of SPPs in various kinds of alloys.

Investigation of metastable austenite in Q&P steels and medium Mn steels through deep-cryogenic treatment

Three kinds of alloys were dexterously performed via different heat treatment conditions, i.e., Q&P steel with quenching & partitioning process, 6Mn steel with hot-rolling and 9Mn steel with intercritical annealing. The results show that C and Mn concentrations in metastable austenite (γ) for Q&P, 6MnHR and 9MnIA samples could be viewed as 0.99C-1.5Mn, 0.45C-6Mn and 0.167C-12.5Mn (wt%) under the condition of thermal processes, respectively. The content of γ in three steels changed with different degree by deep-cryogenic treatment (DCT), which primarily attributes to the influence of C and Mn atoms on transformation temperature (MS) and Néel temperature (TN).

Lead isotope and trace element analysis of the Wuzhu coins from Doujiaqiao hoard, Tianjin City, North China

The minting of coins in almost all societies is related to the central authority. The evolution of the central government's control over the coinage power in the Han Dynasty (202 BC-220 AD) of ancient China reflects the rise and decline of the central authority. Unfortunately, there is no historical record referring to the condition of coinage material management in the HD. Thus, in this paper, XRF, metallography, MC-ICP-MS and ICP-AES were used to study the alloy composition, microstructure, lead isotope and trace element characteristics of 11 Wuzhu (五铢) coins of the Eastern Han Dynasty (25-220 AD) from the Doujiaqiao hoard, Tianjin city, North China. The XRF results showed that there were two kinds of alloy in these coins: one group with high lead content more than 7.6 wt.%, while the other with low lead content less than 1.9 wt.%. And all of these samples had tin content less than 2.9 wt.%. The metallography results indicated that all of these samples were cast, while one sample showed annealing signs. According to the lead isotopic ratios, the lead material of the five high-lead coins had two different provenances: the Yangtze and the Southern China geochemical province. In addition, the copper material of the other six low-lead coins may be derived from several different copper mines. Furthermore, the data of trace elements confirmed that the copper source of the EHD coins in the Doujiaqiao hoard came from different mines, which is consistent with the lead isotope analysis results and further indicates that the copper and lead mines for coinage might be exploited by several local authorities in the EHD.