Phase field simulation for non-isothermal solidification of multicomponent alloys coupled with thermodynamics database

In order to quantitively model the real solidification process of industrial multicomponent alloys, a non-isothermal phase field model was studied for multicomponent alloy fully coupled with thermodynamic and diffusion mobility database, which can accurately predict the phase equilibrium, solute diffusion coefficients, specific heat capacity and latent heat release in the whole system. The results show that these parameters are not constants and their values depend on local concentration and temperature. Quantitative simulation of solidification in multicomponent alloys is almost impossible without such parameters available. In this model, the interfacial region is assumed to be a mixture of solid and liquid with the same chemical potentials, but with different composition. The anti-trapping current is also considered in the model. And this model was successfully applied to industrial A1-Cu-Mg alloy for the free equiaxed dendrite solidification process.

Microstructural characterization and oxidation resistance of multicomponent equiatomic CoCrCuFeNi–TiO high-entropy alloy

CoCrCuFeNi–TiO was prepared by arc melting of the pure elements and Ti_2CO powder under an Ar atmosphere. Both CoCrCuFe Ni and CoCrCuFeNi–TiO alloys are composed of a face-centered cubic(fcc) solid solution, whereas the alloys of CoCrCuFeNi–TiO are basically composed of an fcc solid solution and TiO crystals. The microstructures of CoCrCuFeNi–TiO are identified as dendrite and interdendrite structures such as CoCrCuFeNi. The morphology of TiO is identified as an equiaxed crystal with a small amount of added Ti_2CO. By increasing the amount of Ti_2CO added, the TiO content was dramatically increased and part of the equiaxed crystals changed to a dendrite structure. A test of the oxidation resistance demonstrates that the oxidation resistance of CoCrCuFeNi–TiO is better than that of CoCrCu Fe Ni. However, as the TiO content increases further, a corresponding decrease is observed in the oxidation resistance.

Quantitative multi-phase-field modeling of non-isothermal solidification in hexagonal multicomponent alloys

A quantitative multi-phase-field model for non-isothermal and polycrystalline solidification was developed and applied to dilute multicomponent alloys with hexagonal close-packed structures.The effects of Lewis coefficient and undercooling on dendrite growth were investigated systematically.Results show that large Lewis coefficients facilitate the release of the latent heat,which can accelerate the dendrite growth while suppress the dendrite tip radius.The greater the initial undercooling,the stronger the driving force for dendrite growth,the faster the growth rate of dendrites,the higher the solid fraction,and the more serious the solute microsegregation.The simulated dendrite growth dynamics are consistent with predictions from the phenomenological theory but significantly deviate from the classical JMAK theory which neglects the soft collision effect and mutual blocking among dendrites.Finally,taking the Mg-6Gd-2Zn(wt.%)alloy as an example,the simulated dendrite morphology shows good agreement with experimental results.

Tarnish Testing of Copper-Based Alloys Coated with SiO_2-Like Films by PECVD

The tarnishing test in the presence of hydrogen sulfide（H2S） vapors has been used to investigate the tarnish resistance capability of copper-based alloys coated with Si02-like films by means of plasma-enhanced chemical vapor deposition（PECVD） fed with a tetraethoxysilane/oxygen mixture.The chemical and morphological properties of the films have been characterized by using infrared absorption spectroscopy（IR） and scanning electron microscopy（SEM）with energy disperse spectroscopy（EDS）.The corrosion products of the samples after the tarnishing test have been identified by X-ray diffraction analysis（XRD）.It has been found that SiO2-like films formed via PECVD with a high O2 flow rate could protect copper-based alloys from H2S vapor tarnishing.The alloys coated at the O2 flow rate of 20 sccm remain uncorroded after 54days of H2S vapor tarnish testing.The corrosion products for the alloys deposited at a low O2flow rate after 54 days of tarnish testing are mainly composed of brochantite.

MICROALLOYING EFFECT OF BORON ON COPPER-BASE ALLOYS

The microstructure and properties of boron-modified copper-base alloys were investigated by tension,corrosion,corrosive wear and erosion tests.The results show that by adding boron in copper-base alloys,the strength and hardness of alloys increase,the plasticity decreases somewhat;the corrosion,corrosive wear and erosion resistance of boron-modified copper-base alloys improve obviously.The microalloying mechanism of boron in copper-base alloys was found.

Solute Redistribution Model for Multicomponent AHoys during Rapid Solidification

1.IntroductionThe solute redistribution models for binary alloys during the rapid solidification havebeen extensively studied in recent years[1-10],but up to now the solute redistribution modelfor multicomponent alloys has not been reported.In this paper the solute redistribution mod-el for the multicomponent alloys based on the Aziz model is established theoretically.

COLOR CHARACTERISTICS OF BINARY COPPER-BASE ALLOYS

The effect of Al, Zn, Sn, Mn, Si and Ni on the color characteristics of binary copper-base alloys has been researched systematically and quantitatively. The results show that all alloying elements decrease the red content of an alloy at different levels but have different effects on the yellow color. Al and Zn enhance the yellow content of an alloy, whereas Sn, Mn, Si and Ni decrease the yellow content. When the alloys with different karat gold colors are imitated, Al and Zn are the most important color mixing elements and Sn, Mn, Si and Ni can be used as auxiliary.

Solid solution evolution during mechanical alloying in Cu–Nb–Al compounds

This work concerns the structural evolution of Cu70Nb20Al10(at%) alloy processed by mechanical alloying using a planetary ball mill in air atmosphere for different times(4 to 200 h). The morphological, structural, microstructural, and thermal behaviors of the alloy were investigated by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and differential scanning calorimetry. X-ray diffraction patterns were examined using the Rietveld refinement technique with the help of the MAUD software. A disordered FCC-Cu(Nb,Al) solid solution was formed after 8 h of milling. The crystallite size, microstrain, and lattice parameter were determined by the Rietveld method. With increasing milling time, the crystallite size of the final product-ternary-phase FCC-Cu(Nb,Al)-is refined to the nanometer scale, reaching 12 nm after 200 h. This crystallographic structure combines good mechanical strength and good ductility. An increase in microstrain and partial oxidation were also observed with increasing milling time.

Facile preparation and magnetic study of amorphous Tm-Fe-Co-Ni-Mn multicomponent alloy nanofilm

A facile and efficient synthesis route for the preparation of Tm-Fe-Co-Ni-Mn multicomponent alloy films was reported.Here the films with nanostructures were successfully synthesized by electrodeposition at room temperature.By changing the electrodeposition parameters,such as the deposition potential,deposition time,and the substrates,the styles of the nanostructures and surface morphologies of the deposits could be well controlled.The energy dispersive spectrometer （EDS） indicated that the five elements were co-deposited.The result of XRD suggested that the film was amorphous.The as-deposited alloys showed soft magnetic and superparamagnetic behavior,and the magnetic particles were frozen step by step in the freezing process.

Microstructure and mechanical behavior of laser aided additive manufactured low carbon interstitial Fe_(49.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)multicomponent alloy

Laser aided additive manufacturing(LAAM)was used to fabricate bulk Fe_(49.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)interstitial multicomponent alloy using pre-alloyed powder.The room temperature yield strength(σ_y),ultimate tensile strength(σ_(UTS))and elongation(ε_(UTS))were 645 MPa,917 MPa and 27.0%respectively.The asbuilt sample consisted of equiaxed and dendritic cellular structures formed by elemental segregation.These cellular structures together with oxide particle inclusions were deemed to strengthen the material.The other contributing components include dislocation strengthening,friction stress and grain boundary strengthening.The highε_(UTS)was attributed to dislocation motion and activation of both twinning and transformation-induced plasticity(TWIP and TRIP).Tensile tests performed at-40℃and-130℃demonstrated superior tensile strength of 1041 MPa and 1267 MPa respectively.However,almost no twinning was observed in the fractured sample tested at-40℃and-130℃.Instead,higher fraction of strain-induced hexagonal close-packed(HCP)εphase transformation of 21.2%were observed for fractured sample tested at-40℃,compared with 6.3%in fractured room temperature sample.

Morphological evolution model for unidirectional solidification of multicomponent alloys

Based on the nonlinear interaction of the different species and the calculation of phase diagram,a self-consistent model is developed to describe the interface morphology evolution during unidirectional solidification of multicomponent alloys.This model takes full account of the mutually coupled effect of temperature field,solute field,interface energy and interface attachment kinetics.In comparison with linearization analysis of multicomponent,it not only extends the convergent range of the analysis,but also greatly improves the applicability.

Accelerating matrix/boundary precipitations to explore high-strength and high-ductile Co_(34)Cr_(32)Ni_(27)Al_(3.5)Ti_(3.5) multicomponent alloys through hot extrusion and annealing

Annealing-regulated precipitation strengthening combined with cold-working is one of the most efficient strategies for resolving the conflict between strength and ductility in metals and alloys.However,precipitation control and grain refinement are mutually contradictory due to the excellent phase stability of multicomponent alloys.This work utilizes the high-temperature extrusion and annealing to optimize the microstructures and mechanical properties of the Co_(34)Cr_(32)Ni_(27)Al_(3.5)Ti_(3.5) multicomponent alloy.Hot extrusion effectively reduces grain sizes and simultaneously accelerates the precipitation of coherent L12 nanoparticles inside the face-centered cubic(FCC)matrix and grain boundary precipitations(i.e.,submicron Cr-rich particles and L12-Ni 3(Ti,Al)precipitates),resulting in strongly reciprocal interaction between dislocation slip and hierarchical-scale precipitates.Subsequent annealing regulates grain sizes,dislocations,twins,and precipitates,further allowing to tailor mechanical properties.The high yield strength is attributed to the coupled precipitation strengthening effects from nanoscale coherent L12 particles inside grains and submicron grain boundary precipitates under the support of pre-existing dislocations.The excellent ductility results from the synergistic activation of dislocations,stacking faults,and twins during plastic deformation.The present study provides a promising approach for regulat-ing microstructures,especially defects,and enhancing the mechanical properties of multicomponent alloys.

Novel heating-and deformation-induced phase transitions and mechanical properties for multicomponent Zr_(50)M_(50),Zr_(50)(M,Ag)_(50)and Zr_(50)(M,Pd)_(50)(M=Fe,Co,Ni,Cu)amorphous alloys

Multicomponent alloys of Zr_(50)M_(50),Zr_(50)(M,Ag)_(50)and Zr_(50)(M,Pd)_(50)(M=Fe,Co,Ni,Cu)can be melt-spun to obtain amorphous ribbons.The maximum thickness for fully amorphous ribbons varies with composition in the range 34-53μm.In contrast,fully amorphous ribbons are not obtainable for binary Zr_(50)Ni_(50)or ternary Zr_(50)(Ni,Cu)_(50)alloys.Heating-induced crystallization occurs through:two stages of amorphous[am]→[~(am')+B2]→[B2+B33]for Zr_(50)M_(50);and[am]→[am'+B2]→[B2+AgZr]for Zr_(50)(M,Ag)_(50);and a single stage of[am]→[B2]for Zr_(50)(M,Pd)_(50),while no B2 phase is formed for the binary and ternary Zr_(50)Q_(50)(Q=Ni or/and Cu)alloys.As-spun amorphous ribbons have good bending plasticity.Remarkably,Zr_(50)M_(50)ribbons in tension show 0.22-0.28%plastic elongation and work-hardening(the yield stress is~820 MPa,the fracture stress is~1200 MPa).When cold-rolled at room temperature to 30%reduction in thickness,Zr_(50)M_(50)ribbons show 10%increase in hardness,while retaining good bending plasticity.Cold-rolling induces precipitation of spheroidal B2 and irregular B33 particles,while deformation in tension induces B2,B33 and also plate-like monoclinic precipitates.The B2 and B33 particles form by polymorphic transformation,and include a high density of internal defects.This novel deformationinduced precipitation has not been recognized for any Zr_(50)Q_(50)binary or ternary alloys.The new multicomponent systems are encouraging for future progress as structural amorphous alloys.

Nano-amorphous–crystalline dual-phase design of Al_(80)Li_(5)Mg_(5)Zn_(5)Cu_(5)multicomponent alloy

The design of metallic materials with high strength,high ductility,and high thermal stability has always been a long-sought goal for the materials science community.However,the trade-off between strength and ductility remains a challenge.Here,we proposed a new strategy to design and fabricate bulk amorphous-crystalline dual-phase superior alloys out of the Al_(80)Li_(5)Mg_(5)Zn_(5)Cu_(5)multicomponent alloy.The nano-amorphous phase revealed unexpected thermal stability during fabrication and mechanical testing above the crystallization temperature.The true fracture strength of the Al_(80)Li_(5)Mg_(5)Zn_(5)Cu_(5)nano-amorphous-crystal dual-phase multicomponent alloy was increased from 528 to 657 MPa,and the true strain was increased from 18%to 48%.In addition,the alloy yielded a strength 1.5 times higher than that of the commonly used high-strength aluminum alloys at 250℃.This strategy provided a new approach and concept for the design of high-performance alloys to ensure strength-plasticity balance.

Interstitial concentration effects on incipient plasticity and dislocation behaviors of face-centered cubic FeNiCr multicomponent alloys based on nanoindentation

Interstitial atoms that commonly occupy the octahedral or tetrahedral interstices of face-centered cubic(FCC)lattice,can significantly affect the dislocation behaviors on deformation.Recently,interstitial doping has been applied to tune the mechanical properties of the emerging multicomponent,often termed high-entropy alloys(HEAs)or medium-entropy alloys(MEAs).However,the fundamental mechanisms of the dislocation nucleation and the onset of plasticity of interstitial multicomponent alloys governed by the concentration of interstitial atoms are still unclear.Therefore,in the present work,an instrumented nanoindentation was employed to investigate the interstitial concentration effects of carbon atoms on single FCC-phase equiatomic FeNiCr MEAs during loading.The results show that the pop-in events that denote the onset of incipient plasticity are triggered by the sudden heterogeneous dislocation nucleation via the primary atoms-vacancy exchange with the instant stress field,regardless of the interstitial concentration.Moreover,the measured activation volumes for dislocation nucleation of the FeNiCr MEAs are determined to be increased with the interstitial concentration,which definitely suggests the participation of interstitial atoms in the nucleation process.Besides,it is also found that the average value measured in statistics of the maximum shear stress corresponding to the first pop-in is enhanced with the interstitial concentration.Such scenario can be attributed to the improved local change transfer and lattice cohesion caused by the interstitial atoms with higher concentrations.Furthermore,the significant drag effect of interstitial carbon atoms hinders the mobile dislocations before exhaustion,which severely suppresses the subsequent occurrence of pop-in events in the carbon-doped specimens.The work gives a microscale view of interstitial effects on the mechanical properties of multicomponent alloys,which can further help to develop new interstitial strengthening strategies for structural materials with remarkable performance.

A universal strategy for fast,scalable,and aqueous synthesis of multicomponent palladium alloy ultrathin nanowires

Noble metal alloy nanowires(NWs)with ultrathin diameters(2–3 nm)and precisely controllable elemental compositions have attracted dramatically growing attention for(electro)catalysis.Despites numerous achievements in past two decades,noble metal alloy NWs are mostly synthesized with the traditional oil-phase methods that suffer from some undesirable drawbacks.Here,we report a general strategy for fast,scalable,and aqueous synthesis of multicomponent Pd-based alloy ultrathin NWs with an average diameter of 2.6 nm,ranging from bimetallic PdM(PdFe,PdCo,PdNi,PdCu,PdZn,PdRu,PdRh,PdAg,PdCd,PdIr,PdPt,PdAu)and binary PdS/PdP NWs,to trimetallic PdM1M2 NWs(PdAuCu,PdCoNi,PdCuZn,PdCuNi,PdAgCu,PdAuCu,PdRuAg,PdAuRu,and PdPtAu),and to tetrametallic PdM1M2M3 NWs(PdAuAgCu,PdCoCuNi,PdAuCuNi,PdPtAuCu,and PdIrPtAu).The key to the success of this aqueous synthesis is the utilization of N2H4 as the extremely strong reducing agent that directs the synchronous reduction and anisotropic nucleation growth of multicomponent Pd alloy NWs along nanoconfined columnar phase assembled with amphiphilic dioctadecyldimethylammonium chloride.As-resultant Pd-based alloy ultrathin NWs exhibit multiple structural and compositional synergies,which remarkably optimize the removal of poisoning ethoxy intermediates and thus improve electrocatalytic performance towards ethanol oxidation reaction(EOR).Among them,tetrametallic PdAuCuNi alloy ultrathin NWs hold a high EOR activity of 5.14 A mg-1 Pd and a low activation energy of 13.1 kJ mol^-1,both of which are much better than its counterpart catalysts alloyed with less elements.This work represents an important advance in precise aqueous synthesis of multicomponent noble metal alloy ultrathin NWs as the high-performance electrocatalysts for various targeted applications.

基于微观偏析统一模型及Thermo-Calc的三元合金凝固路径耦合计算

将合金凝固微观偏析统一模型推广到三元合金凝固微观偏析的预测,并提出了能够计算三元匀晶与共晶合金凝固路径的数值计算方法.实现了在源代码层次上与热力学计算软件Thermo-Calc及其数据库的耦合,以获取多元合金凝固路径计算所需的凝固热力学数据.通过Fe-40V-40Cr,Al-4.5Cu 1.0Si.Al 10Cu 2.5Mg和Al-1.49Si-0.64Mg(质量分数,%)等多元/多相合金在不同冷速下凝固路径的实例计算,以及与相应的凝固组织定量金相实验结果对比,验证了本文多元/多相凝固模型和算法的正确性.

相场法模拟潜热的释放对多元合金凝固过程的影响

利用由二元合金相场模型扩展获得的多元合金相场模型,以Fe-C-P合金为例,对等温和非等温条件下的凝固过程进行对比分析.结果表明,在同等凝固时间下,非等温时的固相率、尖端生长速度、溶质偏析比小于等温情况时;在溶质富集区,等温情况下比非等温情况下表现出较明显的溶质梯度;在枝晶生长过程中,固液界面处的温度较高,最高温度值先迅速增加,后呈波动性的缓慢增加.

多元合金等温凝固相场法模拟

利用由二元合金相场模型扩展获得的多元合金相场模型,以Fe-C-P合金为例,研究界面厚度对枝晶生长的影响.结果表明,随着界面厚度的减小,枝晶生长速度增大,界面推进速度提高,主枝晶臂变细,二次枝晶臂越发达,固液界面溶质扩散层的厚度减小,界面前沿溶质分配系数增大,而界面前沿溶质偏析程度也相应增大;相反,随着界面厚度的增加枝晶尖端生长速度逐渐减小,并呈收敛的趋势.