High temperature oxidation behavior of directionally solidified NiAl-31Cr-2.9Mo-0.1Hf-0.05Ho eutectic alloy

The isothermal oxidation behavior of NiAl-31Cr-2.9Mo-0.1Hf-0.05Ho directional eutectic alloy was investigated with the help of scanning electron microscopy and X-ray diffraction.The results revealed that a continuous Al2O3 scale was formed and owned excellent oxidation resistance in the temperature range of 900-1100°C.When the temperature was up to 1150°C,the continuous Al2O3 oxide film ruptured.Trace rare earth element Ho distributed uniformly in the alloy and relatively high level of Al in Cr（Mo）phase are beneficial to the formation of continuous and compact Al2O3 scale.During the oxidation,a phase transformation fromθ-Al2O3 toα-Al2O3 existed on the surface of oxidation film.It resulted in the abnormal oxidation mass gain happening when the alloy was oxidized at 1000°C or 1050°C.

High Temperature Tensile Property and Fracture Behavior of Directionally Solidified Fe-Al-Ta Eutectic Composites

Fe-Al-Ta eutectic composites with solidification rates of 6,20,30,80 and 200μm/s were obtained by a modified Bridgman directional solidification technique and alloying.Moreover,tensile property and fracture behavior of Fe-Al-Ta eutectic composites were studied at 600℃.The relationship between mechanical property and microstructure at high temperature was studied.Microstructure of Fe-Al-Ta eutectic is composed of Fe_(2)Ta(Al)Laves phase and Fe(Al,Ta)matrix phase.In addition,the tensile strength at high temperatures is higher than that at room temperature.The tensile strength is increased with the increase of solidification rate.Moreover,fracture morphology transforms from cleavage fracture to dimple fracture as the solidification rate is increased at high temperatures.

Electrochemical nucleation and growth of aluminum nanoparticles and leaf-like flat microstructures from reline deep eutectic solvent: Effect of temperature and angular speed of working electrode

The main objective of this work was to use reline deep eutectic solvent,containing Al(III)ions,for the electrochemical study of the nucleation and growth of aluminum onto a glassy carbon electrode at different temperatures and angular speeds(ω)of the working electrode.In order to fulfill this,electrochemical and surface characterization techniques were used.It was found that as temperature increased,the onset of the Al(III)DES reduction occurred at less negative potentials while the current peak of the voltammograms increased.These indicate that Al deposition thermodynamics and kinetics were favored.Practically,no anodic current was detected due to Al passivation by Al(OH)_(3)(s)andγ-Al_(2)O_(3)(s).Atω=0 r/min,the Al deposition chronoamperograms were analyzed by a theoretical model comprising Al 3D diffusion-controlled nucleation and growth and residual water reduction.However,those recorded at different angular speeds were analyzed with a theoretical model where adsorption−desorption and diffusion-controlled nucleation−growth occurred simultaneously.The deposits were characterized by SEM,EDX,XPS and XRD.Atω=0 r/min,formation of well distributed nanoparticles((78.1±9.5)nm)was observed,while atω=900 r/min the deposit was formed by multiple 10μm diameter leaf-like flat microstructures,composed by Al,Al(OH)_(3)(s)andγ-A2O3(s).

HIGH-TEMPERATURE TENSILE FRACTURE BEHAVIOR OF DIRECTIONALLY SOLIDIFIED Ni,Cr,Al-TaC EUTECTIC SUPERALLOY

The high-temperature tensile fracture behavior of the Ni, Cr, Al-TaC eutectic superal-loy directionally solidified under high temperature gradient is investigated. The high-temperature tensile fracture of this in situ composite has ductile character with lots of ductile nests whose diameters decrease with the increasing solidification rates. The maximum σb and δ are respectively 668.5MPa and 19.6%. There is α TaC whisker in the center of each nest, and the deformation of γ' and TaC is uneven. The high-temperature tensile behavior cannot be explained by the rule of mixtures but is decided by the formation of the plastic deformation band. The crack extension model is given.

High-temperature mechanical properties of near-eutectoid steel

The high-temperature mechanical properties of near-eutectoid steel were studied with a Cleeble-1500 simu- lation machine. Zero strength temperature （ZST）, zero ductility temperature （ZDT）, hot ductility curves, and strength curves were measured. Two brittle zones and one plastic zone were found in the temperature range from the melting point to 600℃. Embrittlement in zone I is caused by the existence of liquid film along dendritic interfaces. Ductility loss in zone Ⅲ mainly results from precipitates and inclusions as well as S segregation along grain boundaries. Pearlite transformation also accounts for ductility deterioration in the temperature range of 700-600℃. Moreover, the straightening temperature of the test steel should be higher than 925℃ for avoiding the initiation and propagation of surface cracks in billets.

Preparation of Mg-Yb alloy film by electrolysis in the molten LiCl-KCl-YbCl_3 system at low temperature

The electrochemical behavior of Yb3+ and electrodeposition of Mg-Yb alloy film at solid magnesium cathode in the molten LiCl-KCl-YbCl3(2 wt.%) system at 773 K was investigated.Transient electrochemical techniques,such as cyclic voltammetry,chronopotentiometry and chronoamperometry were used in order to explore the deposition mechanism of Yb.The reduction process of Yb3+ is stepwise reactions which are single-electron and double-electron reversible charge transfer reactions.The speed control step was a diffu...

Extraction of lithium from the simulated pyrometallurgical slag of spent lithium-ion batteries by binary eutectic molten carbonates

The effective and low-temperature extraction of lithium from the pyrometallurgical slag of spent lithium-ion batteries(LIBs)remains a great challenge.Herein,potassium carbonate/sodium carbonate(K_(2)CO_(3)/Na_(2)CO_(3)),which could form a eutectic molten salt system at 720℃,was used as a roasting agent to extract lithium from pyrometallurgical slag.Lithium was successfully extracted from the slag by K_(2)CO_(3)/Na_(2)CO_(3) roasting followed by water leaching.Theoretical calculation results indicate that the lengths of Li-O bonds increase after K^(+)/Na^(+)adsorption,resulting in the easy release of Li^(+)from the LiAlSi_(2)O_(6) lattice after roasting with K_(2)CO_(3)/Na_(2)CO_(3).Thermogravimetry-differential scanning calorimetry results indicate that the eutectic phenomenon of K_(2)CO_(3) and Na_(2)CO_(3) could be observed at 720℃ and that the reaction of the slag and eutectic molten salts occurs at temperatures above 720℃.X-ray diffraction results suggest that Li^(+)in the slag is exchanged by K^(+)in K_(2)CO_(3) with the concurrent formation of KAlSiO_(4),while Na_(2)CO_(3) mainly functions as a fluxing agent.The lithium extraction efficiency can reach 93.87%under the optimal conditions of a roasting temperature of 740℃,roasting time of 30 min,leaching temperature of 50℃,leaching time of 40 min,and water/roasted sample mass ratio of 10:1.This work provides a new system for extracting lithium from the pyrometallurgical slag of spent LIBs.

Overheating temperature of 7B04 high strength aluminum alloy

The microstructure and overheating characteristics of the direct chill semicontinuous casting ingot of 7B04 high strength aluminum alloy,and those after industrial homogenization treatment and multi-stage homogenization treatments,were studied by differential scanning calorimetry(DSC),optical microscopy(OM)and scanning electron microscopy with energy dispersive X-ray spectroscopy(SEM-EDX).The results show that the microstructure of direct chill semicontinuous casting ingot of the 7B04 alloy contains a large number of constituents in the form of dendritic networks that consist of nonequilibrium eutectic and Fe-containing phases.The nonequilibrium eutectic contains Al,Zn,Mg and Cu,and the Fe-containing phases include two kinds of phases,one containing Al,Fe,Mn and Cu,and the other having Al,Fe,Mn,Cr,Si and Cu.The melting point of the nonequilibrium eutectic is 478℃for the casting ingot of the 7B04 alloy which is usually considered as its overheating temperature.During industrial homogenization treatment processing at 470℃,the nonequilibrium eutectic dissolves into the matrix of this alloy partly,and the remainder transforms into Al2CuMg phase that cannot be dissolved into the matrix at that temperature completely.The melting point of the Al2CuMg phase which can dissolve into the matrix completely by slow heating is about 490℃.The overheating temperature of this high strength aluminum alloy can rise to 500?520℃.By means of special multi-stage homogenization,the temperature of the homogenization treatment of the ingot of the 7B04 high strength aluminum alloy can reach 500℃without overheating.

Effect of Rare Earths on Solidification Microstructure and High Temperature Mechanical Property of Sn60-Pb40 Solder alloy

Trace rare earth elements were used in order to strengthen the Sn60 Pb40 solder alloy. The experimental results show that the high temperature tensile strength of near eutectic Sn60 Pb40 solder alloy is increased by about 70% after adding trace rare earth elements. Analysis shows that the high affinity between rare earth element and Sn leads to the variation of contact angle at the three phase junction of S/L interface during eutectic growth and further changes the Pb concentration at the S/L interface needed for coupled eutectic growth. Thus the eutectic microstructure can directly grow upon the primary Pb rich phase and the formation of coarse Sn rich halo is suppressed. Therefore homogeneous metallurgical microstructure can be obtained.

Morphological Variation of Eutectic Carbide in Twin-Roll Casting Strip of W9Cr4Mo2

The netlike eutectic carbide in twin-roll casting strip of W9Cr4V2 was dissolved and broken up gradually with increasing heating temperature during annealing treatment.Almost all eutectic carbides exist in granular form with heating temperature up to 950 ℃.It is considered that the refining of lamellar spacing made it possible for eutectic carbide to be granulated.

Relationship between Primary Crystal Temperature and Carbon Equivalent in Cast Iron

CE （=%C＋（1/3）x（%Si）） does not suit experiment results in many cases. In this work, the effect of alloy elements on primary crystal temperature was measured and the relationship between primary crystal temperature （Tc） and carbon equivalent （CEL） was investigated. The results show that Tc （Celsius degree） = 1650-110 × （%C） -25 × （%Si）＋3 × （%Mn） -35 × （%P） -71 × （%5）-2 × （%Ni） -7 × （%Cr）; CEL=%C ＋ 0.23×（%Si）-0.03× （%Mn）＋0.32×（%P）＋0.64×（%S） ＋0.02×（%Ni）＋0.06×（%Cr）. That is, in hypo eutectic composition, carbon equivalent should be calculated with CEL=%C＋ 0.23×（%Si）, not with CE=%C＋（1/3） x（%Si）.

DESIGN OF A/AD_m-BC_n DIRECTIONAL EUTECTIC COMPOSITES

Design process of A/ADm-BCn type directional eutectic composites was instanced by investigating Al-Mg-Si-Li and Ni-Mo-C-Al systems in this study by thermoanalysis and directional solidification techniques. It was demonstrated that A(D)-BCn eutectic alloys could be obtained more conveniently by using Smith′s thermoanalysis method to trace change of the eutectic Points of A-BCn induced by addition of components D. A/ADm-BCn directional eutectic composites could be produced from directionally solidified A/ADm-BCn alloys after proper heat treatments if components D have higher solid solubility in components A at high temperature and stable of metastable phases ADm could be formed at room temperature.

Application of Deep Eutectic Solvents in the Separation of Rare Earth Elements

Deep eutectic solvent(DES)is usually a mixture prepared by the complexation of hydrogen bond acceptor(HBAs)and hydrogen bond donor(HBDs)at mild performance temperature.Similar to ionic liquid,DES has unique physicochemical properties such as low steam,strong conductivity,stable electrochemical window and strong design ability.Under a relatively mild condition,DES still shows a strong dissolving ability for a variety of insoluble substances.

Deep eutectic solvent-based gel electrolytes for flexible electrochromic devices with excellent high/low temperature durability

With the increasing interest in the application of electrochromism to flexible and wearable electronics in recent years,flexible electrochromic devices(ECDs)that can function at extreme temperatures are required.However,the functionalities of flexible ECDs are severely hampered by the inadequate choice of electrolytes,which might ultimately result in performance fading during low-and high-temperature operations.Here,we develop a deep eutectic solvent(DES)-based gel electrolyte that can maintain its optical,electrical,and mechanical properties over a wide range of temperatures(-40 to 150℃),exhibiting an extremely high visible-range transmittance over 90%,ion conductivity of 0.63 mS cm^(-1),and fracture strain exceeding 2000%.Owing to the excellent processability of the DES-based electrolytes,provided by dynamic interactions such as the lithium and hydrogen bonding between the DES and polymer matrix,a directly written patterning in ECDs is realized for the first time.The fabricated ECDs exhibit an excellent electrochromic behavior superior to the behavior of the ECDs fabricated with traditional gel electrolytes.The introduction of such DES-based electrolytes is expected to pave the way for a widespread application of electrochromic products.

Effects of Strontium,Magnesium Addition,Temperature Gradient,and Growth Velocity on Al-Si Eutectic Growth in a Unidirectionally-solidified Al-13 wt%,Si Alloy

Al-Si eutectic growth mechanism was investigated in a directionally-solidified AI-1 3 wt% Si alloy with different strontium （Sr） and magnesium （Mg） additions, growth velocities and temperature gradients. Macro- and micro- scale metallographic analyses revealed that addition level of Sr and Mg, temperature gradient and growth velocity are important factors affecting stability of solidifying AI-Si eutectic front and the final morphology of eutectic grains in the solidified A1-13 wt% Si alloys. By varying （tailoring） these factors, a variety of eutectic grain structures and morphologies such as planar front, cellular structure, a mix of cellular and columnar, or equiaxed dendrites, can be obtained. Increasing temperature gradient, reducing growth velocity, or decreasing Sr and Mg contents is beneficial to stabilizing planar growth front of eutectic grains, which is qualitatively in accordance with constitutional supercooling criterion for binary eutectic growth. In contrast, adding more Sr and Mg, increasing growth velocity, or decreasing temperature gradient produces large constitutional supercooling, leading to columnar-equiaxed transition （CET） of eutectic structure, which can be interpreted on the basis of Hunt＇s Model. It is also found that both solute concentration and solidification variables have significant impact not only on eutectic growth, but also on gas porosity formation.

Eutectic mixture promoted CO_2 sorption on MgO-TiO_2 composite at elevated temperature

The development of carbon dioxide(CO_2) sorbents that can operate at elevated temperatures is significant for the advancement of pre-combustion capture technologies.Recently, promoter-based systems composed of alkali/alkaline earth metal nitrates and/or carbonates have been considered as next-generation solid sorbents due to their improved CO_2 uptake and kinetics. However, obtaining stable MgO sorbents against temperature swing regeneration still remained challenging. Herein, we report MgO-TiO_2 solid sorbents promoted by eutectic mixture(KNO_3 and LiNO_3) for elevated temperature CO_2 sorption. The developed sorbents show improved CO_2 sorption capacity, which may be attributed to the alternative CO_2 sorption pathway provided by the ionization of highly dispersed MgO in the eutectic mixture. The MgO-TiO_2 framework was also shown to assist in retaining the MgO configuration by constraining its interaction with CO_2. Furthermore, it is demonstrated that constructing composite structures is essential to improve the CO_2 sorption characteristics,mainly recyclability, at elevated temperatures. The developed promoter integrated sorbents showed exceptionally high CO_2 sorption capacity of > 30 wt.% at an elevated temperature(300°C) with pronounced stability under temperature swing operation.

固溶和时效处理对新型低钴高温合金组织和高温力学性能的影响

采用真空感应熔炼方法制备了一种新型低钴高温合金,利用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)和电子万能试验机等研究了固溶处理和高温时效处理对合金组织和高温拉伸性能的影响。结果表明:低钴高温合金铸态组织中包含(γ+γ′)共晶组织、富W/Ta的MC_((1))碳化物和富Ta/Hf的MC_((2))碳化物,以及大小两种尺寸的γ′相,Hf、Ta元素明显偏析于枝晶间。随着固溶温度升高和时间延长,(γ+γ′)共晶组织逐渐回溶、元素偏析消除,小尺寸γ′相的含量升高。固溶过程中MC_((1))碳化物逐渐溶解,边缘转变为富W的M6C型碳化物,MC_((2))中Hf含量升高而Ta含量降低。经1295℃固溶处理6 h及1090℃高温时效8 h后,合金中的共晶组织的体积分数降至1.3%,具有较好的高温拉伸性能。

氮化硅陶瓷低温烧结助剂研究进展

氮化硅陶瓷性能优异,然而由于其共价键较强,自扩散系数小,烧结难度较大。目前高性能氮化硅陶瓷主要通过高温气压烧结法制备,烧结温度在1800℃以上,对设备要求较高,制备成本也较高,限制了氮化硅陶瓷的实际应用。低温烧结作为降低氮化硅生产成本的有效途径之一,受到了业界广泛关注。目前国内外关于氮化硅陶瓷低温烧结的研究主要集中在烧结助剂的选择方面,烧结助剂可以分为两类:使用与SiO_(2)共晶温度较低的烧结助剂和使用多组分烧结助剂。综述了这两类低温烧结助剂的研究进展,并提出了低温烧结助剂选择的合理方案。综合来看,要在低温下制得性能良好的氮化硅陶瓷,需选用与SiO_(2)具有低共晶点的烧结助剂,并配合使用多元组分调控氮化硅陶瓷的微观结构和性能。

Cr8扁钢轧制模拟与工艺优化

共晶碳化物是影响Cr8冷作模具钢服役性能及使用寿命的关键因素。针对Cr8钢连铸坯轧制成扁钢后出现的碳化物不均匀度超过国家标准GB/T 1299—2014(3级)的问题进行分析。采用Deform有限元模拟软件建立Cr8扁钢的轧制模型,对轧制过程中的等效应变、应变速率、温度变化情况进行模拟,并研究了不同温度下保温(时间)Cr8扁钢碳化物的形貌特征,与其连铸坯进行对比。模拟与实验结果表明,轧制过程中,Cr8扁钢中心至1/4厚度区域温度达到1 230℃,使Cr8扁钢的三角晶界区碳化物重新溶解析出,导致碳化物不均匀度的级别超过3级。因此,通过降低加热温度,控制轧制温度低于1 200℃,将厚度24 mm的Cr8扁钢碳化物不均匀度由4级降低至2级,使产品质量显著提高,同时降低了能耗、节约了成本。