Magnesium addition in copper‐chromium alloys: The refinement of aging precipitates and improvement on mechanical properties

Herein, we demonstrate the synthesis of copper‐chromium and copper‐ chromium‐magnesium alloys by melting and casting process and explore the effect of the magnesium addition on mechanical and electrical properties of the alloys. This article focuses on the variation of the precipitation sequence and the decrease of strengthening phase sizes induced by the addition of trace magnesium element. The results show that magnesium element has little effect on the hardness of copper‐chromium alloy, but it significantly improves the hardness of the aging alloy and maintains high conductivity. The addition of magnesium element inhibits the growth and structural transformation of the precipitated phase. The refinement impact of magnesium addition on precipitated phase and change in alloy precipitation sequence may be the main reasons for the high hardness of copper‐chromium‐ magnesium alloy. In addition, the magnesium addition shows a significant refinement effect on small size precipitation phase, but it does not present the same refinement effect on large size precipitation phase. This attributes to the presence of a semi‐coherent interface between the matrix and the large size of precipitates, which provides the dislocation‐based diffusion channels for high‐rate chromium diffusion and promotes the precipitate growth.     

Influence of Aging Treatment on the Mechanical and Electrical Properties of Cu-0.5%Be Alloy

The influence of aging treatment on the microstructure,mechanical properties and electrical conductivity of Cu-0.5 wt pct Be alloy for connector material applications was investigated.The properties of mechanical strength and electrical conductivity increase with increasing aging temperature and time.Microstructure of the aged Cu-Be alloy revealed that grain size and fraction of low angle and high angle grain boundary were not greatly changed;however,transmission electron microscopy （TEM） analysis exhibited that beryllides precipitation （CoBe and NiBe） with a size of 50 nm were distributed in grains.It was,therefore concluded that these beryllide precipitates improved the mechanical strength and also it was favor in improvement of electrical conductivity.     

Influence of heat treatment and aging on microstructure and mechanical properties of Mg‐1.8Zn‐0.7Si‐0.4Ca alloy

In order to optimize the aging treatment of Mg‐1.8Zn‐0.7Si‐0.4Ca alloy, different times and temperatures of solid solution and age hardening were applied to the alloy specimens. Microstructures and mechanical properties of the specimens were investigated using the optical microscopy, field emission scanning electron microscopy equipped with an energy dispersive x‐ray spectrometer, x‐ray diffraction, hardness, and shear punch tests. The lowest hardness and strength were achieved by solution treating of the alloy at 500 °C for 8 h, presenting the optimal condition for solution treatment of the alloy. The microstructural examinations revealed three different precipitates consisting of CaMgSi, Ca₂Mg₆Zn₃, and Mg₂Si in the solid solution specimens. It was found that the highest peak hardness and strength are obtained by aging the alloy at 150 °C for 16 h. This condition was confirmed by differential scanning calorimetry (DSC) tests performed on the solid solution and aged specimens.     

Effect of thermomechanical treatment on spray formed Cu – Ni – Si alloy

Abstract

The heat treatment response of a spray formed Cu – 2.4Ni – 0.6Si (wt-%) alloy has been investigated. The spray formed alloy was given various thermomechanical treatments prior to isothermal aging. These treatments included solutionising and/or cold rolling with different reductions in original thickness. The variation in hardness and electrical conductivity of the alloys was measured as a function of the aging time. The results indicated the highest peak hardness value of ~250 kg mm^-2 for the alloy aged after solution treatment and cold rolling to 40% reduction in thickness, compared with the maximum hardness of 220 kg mm^-2 for specimens aged directly in the as spray formed condition. However, the electrical conductivity after aging was observed to be a maximum of 65%IACS (International Annealed Copper Standard) in specimens cold rolled to 80% reduction in thickness before aging. The aging response was observed to accelerate with the degree of cold working. Optical, scanning electron and transmission electron microscopy were used for microstructural characterisation of the materials. Precipitation of the second phase was observed to dominate in deformation bands. The alloy showed evidence of discontinuous precipitation, particularly when the alloys were cold rolled before aging. The onset of discontinuous precipitation led to a drastic deterioration in hardness of the alloys. The precipitation behaviour of the alloy is discussed in the light of microstructural characteristics associated with various processing conditions of the alloy.     

Investigation of structural,electrical and tribological properties of duplex surface treated and aged Cu−Cr−Zr alloy

In this study, Cu−Cr−Zr alloy specimens were first subjected to aging heat treatment at 500 °C for two different durations (2 hours and 4 hours). Three different coating processes (silver, silver/copper duplex, and copper/silver duplex) were applied to the aged specimens using the physical vapor deposition method. Tensile test, microhardness measurement, wear test, electrical conductivity measurement and structural analysis (x-ray diffraction and scanning electron microscope) were applied to the specimens. After the aging processes, the highest hardness and strength values of the Cu−Cr−Zr alloy were obtained in the specimens that were aged at 500 °C for 4 hours. When the wear resistance and electrical conductivity of the coated specimens were examined, it was determined that the specimens with duplex surface treatment performed better.     

Ultrathin 2D Mesoporous TiO2/rGO Heterostructure for High‐Performance Lithium Storage

Lithium‐ion batteries (LIBs) have been widely applied and studied as an effective energy supplement for a variety of electronic devices. Titanium dioxide (TiO₂), with a high theoretical capacity (335 mAh g^?1) and low volume expansion ratio upon lithiation, has been considered as one of the most promising anode materials for LIBs. However, the application of TiO₂ is hindered by its low electrical conductivity and slow ionic diffusion rate. Herein, a 2D ultrathin mesoporous TiO₂/reduced graphene (rGO) heterostructure is fabricated via a layer‐by‐layer assembly process. The synergistic effect of ultrathin mesoporous TiO₂ and the rGO nanosheets significantly enhances the ionic diffusion and electron conductivity of the composite. The introduced 2D mesoporous heterostructure delivers a significantly improved capacity of 350 mAh g^?1 at a current density of 200 mA g^?1 and excellent cycling stability, with a capacity of 245 mAh g^?1 maintained over 1000 cycles at a high current density of 1 A g^?1. The in situ transmission electron microscopy analysis indicates that the volume of the as‐prepared 2D heterostructures changes slightly upon the insertion and extraction of Li⁺, thus contributing to the enhanced long‐cycle performance.     

热处理对Al-Cu合金电导率的影响

通过电导率测量、硬度分析和金相组织观察,研究了不同热处理工艺对Al-4.0%Cu(质量分数,下同)合金电导率的影响,分析了析出相、合金硬度和电导率之间的关系。实验结果表明,Al-4.0%Cu合金的电导率主要受基体中Cu固溶度和析出相状态的影响;双级时效处理对电导率和硬度的决定因素主要为二级时效的温度与时间,一级时效后合金的电导率和硬度会随着二级时效发生改变;退火后的Al-4.0%Cu合金于350℃保温24h后,可获得较高的电导率,此时基体中的析出相为细小、弥散的θ相。     

Determination of transport properties in chromium disilicide nanowires via combined thermoelectric and structural characterizations

The Seebeck coefficient, electrical conductivity, and thermal conductivity of individual chromium disilicide nanowires were characterized using a suspended microdevice and correlated with the crystal structure and growth direction obtained by transmission electron microscopy on the same nanowires. The obtained thermoelectric figure of merit of the nanowires was comparable to the bulk values. We show that combined Seebeck coefficient and electrical conductivity measurements provide an effective approach to probing the Fermi Level, carrier concentration and mobility in nanowires.     

聚乙烯醇/[Nbmd]OH碱性复合阴离子膜的制备及性能

以吗啡啉与溴代十二烷为原料,合成新型[Nbmd]OH碱性双核离子液体,并将[Nbmd]OH引入聚乙烯醇(PVA)的铸膜液中,通过浇铸法制备了掺杂碱性离子液体的复合阴离子膜PVA/[Nbmd]OH。采用热重分析及扫描电镜对所制备的复合阴离子膜的热稳定性及形貌进行表征。同时考察了离子液体含量对PVA/[Nbmd]OH复合膜的含水率、溶胀性能、力学性能及电导率的影响。结果表明,离子液体含量的增加可提高PVA/[Nbmd]OH复合膜的含水率、溶胀度、电导率等。其中,当碱性离子液体质量分数为20%时,复合膜的综合性能达到最优,此时,膜的含水率和拉伸强度分别达到161.6%和23 MPa,在70℃时,膜的电导率为2.11×10~(-3)S/cm,表明碱性离子液体的引入,能明显改善膜的导电性能,但是拉伸强度受到了一定的影响。     

时效处理对Al-Zr-Sc(-Er)合金组织和性能的影响EI北大核心CSCD

通过透射电镜(TEM)和扫描透射电镜(STEM)以及硬度、电导率测试等方法系统研究了时效处理对Al-Zr-Sc三元合金以及Al-Zr-Sc-Er四元合金显微组织和性能的影响。结果表明:对于Al-Zr-Sc合金,增加Sc含量,可显著提高合金时效响应速率、峰值硬度和热稳定性;增加Zr含量,显著提高了合金硬度和热稳定性,但会降低电导率。在Al-Zr-Sc合金中添加Er,进一步提高了合金的时效响应速率,促进了Zr,Sc的脱溶析出。Er与Zr,Sc形成具有核-双壳结构的Al 3(Er,Sc,Zr)相,明显改善合金的硬度和电导率。经300℃单级时效,实验合金硬度较高,但电导率相对较低;经400℃单级时效,实验合金时效响应速率加快,电导率明显提高,但硬度显著下降;经300℃/24 h+400℃的双级时效实验合金可获得电导率、强度和热稳定性的良好匹配。     

热变形方式对2D70耐热铝合金组织与性能的影响

分别采用常规变形方式(直接挤压)、强变形方式(3次多方锻造与挤压变形相结合)制备了大规格2D70耐热铝合金棒材,利用金相显微镜、透射电镜、力学性能测试、电导率测试等手段对比分析了两种工艺所获得棒材的变形态、固溶态显微组织特征以及195℃人工时效强化特性差异。结果表明,与传统直接挤压方式相比,采用强变形工艺所获得的基体组织相对均匀,合金中各类第二相破碎严重、分布合理;经强变形破碎的Al2CuMg、Al2Cu等可溶第二相可在固溶处理过程中充分回溶以提高时效强化潜力,同时,Al9FeNi、Al7Cu4Ni等难溶第二相的尺寸、形态与分布通过强变形得以合理调控,使得合金棒材在195℃人工时效的过时效阶段具有更优越的抗过时效能力,合金热稳定性较好。     

Effect of aging parameters on the mechanical properties of naturally aged Al–Mg–Si alloy

Among the extruded products within the Al–Mg–Si system, AA6082 alloy is regarded as high strength alloy which is used for automotive structural applications. Room temperature storage in between the solution heat treatment and the paint bake cycle is unavoidable problem and undergoes natural aging. Hence, natural aging time in the conventional T4 condition must be modified after the solution heat treatment in order to avoid any hardening during storage before forming processes. The present work was investigated to improve paint bake response of extruded 6082 profiles by employing pre‐aging in between the solution heat treatment and the paint bake in order to obtain sufficient strength for the required in‐service dent resistance. Pre‐aging treatment was performed for 5 min at 180 °C, 200 °C and 225 °C to improve bake hardening response of extruded 6082 profiles. Tensile tests and micro hardness measurements are performed to determine the natural aging effect on mechanical properties. In order to understand the precipitation hardening of this aluminum profile with a different natural aging time, differential scanning calorimetry measurements are performed.     

Ageing characteristics of Cu–Cr in-situ composite

The ageing behaviour of a Cu–15 wt% Cr in-situ composite was investigated systematically by means of hardness testing, electrical conductivity measurement, scanning electron microscopy, analytical transmission electron microscopy and high-resolution electron microscopy. The material was found to have a peak hardness after ageing at around 773 K and a peak electrical conductivity at around 873 K. In contrast with the dilute Cu–Cr alloys, Cr-rich clusters were observed at the early aged condition in the Cu matrix, which matches not only the results of mechanical and physical property measurement but also the theoretical prediction. In addition, the precipitates at peak hardened condition in the Cu matrix were determined to be Cr Guinier–Preston zones. Cr ribbon as the in-situ reinforcing element shows no measurable ageing effect due to the high-temperature solution treatment. © 1998 Chapman & Hall     

Morphology and properties of segregated-network chemically converted graphene-poly(vinyl chloride) composite

The poly(vinyl chloride)-chemically converted graphene (PVC-CCG) composite prepared using colloidal blending, filtration and drying, and followed by compression molding at 175 degrees C, exhibited an electrical percolation threshold as low as 0.4 wt% and an electrical conductivity as high as 46.5 S/m corresponding to 4.0 wt% of CCG. The high electrical conductivity of the PVC-CCG composite was the result of minimizing the amount of surfactant using various methods. For example, the PVC latex was prepared using miniemulsion polymerization, and the CCG was synthesized via hydrazine reduction of graphene oxide at ambient temperature in order to diminish the irreversible agglomeration of CCG sheets during reduction. The morphology of the PVC-CCG composite, characterized using scanning electron microscopy in charge contrast mode, revealed that the CCG sheets created a segregated network in the PVC matrix.     

Mussel‐Inspired Defect Engineering of Graphene Liquid Crystalline Fibers for Synergistic Enhancement of Mechanical Strength and Electrical Conductivity

Inspired by mussel adhesive polydopamine (PDA), effective reinforcement of graphene‐based liquid crystalline fibers to attain high mechanical and electrical properties simultaneously is presented. The two‐step defect engineering, relying on bioinspired surface polymerization and subsequent solution infiltration of PDA, addresses the intrinsic limitation of graphene fibers arising from the folding and wrinkling of graphene layers during the fiber‐spinning process. For a clear understanding of the mechanism of PDA‐induced defect engineering, interfacial adhesion between graphene oxide sheets is straightforwardly analyzed by the atomic force microscopy pull‐off test. Subsequently, PDA could be converted into an N‐doped graphitic layer within the fiber structure by a mild thermal treatment such that mechanically strong fibers could be obtained without sacrificing electrical conductivity. Bioinspired graphene‐based fiber holds great promise for a wide range of applications, including flexible electronics, multifunctional textiles, and wearable sensors.     

Effect of increased manganese addition and mould type on the slurry erosion characteristics of Cr-Mn iron systems

The wear resistance of high chromium iron is well recorded. However, the same is not the case as regards the use of manganese at higher percentages in high chromium irons and its influence on wear behaviour. Hence, this work highlights the slurry wear characteristics of chromium (□ 16–19%) iron following the introduction of manganese at two levels i.e. 5 and 10%. It is known that the wear properties are dictated by the microstructural features. To alter the structure, the cooling rate of casting has been varied by adopting two different types of moulds (i.e. sand and metal) and subsequently subjecting to thermal treatment. The as-cast and heat treated samples are examined for microstructure and then evaluated for hardness and slurry erosion properties. As the manganese content is increased from 5 to 10%, the hardness showed a decrease in value both in the as-cast and heat treated conditions. The slurry erosion loss, expectedly, showed an increase irrespective of the sample condition (i.e. mould type/heat treatment adopted). The findings are corroborated with the microstructural features obtained through optical and scanning electron microscopy.     

Microstructure and Properties of Cu-Cr-Zr Alloy after Rapidly Solidified Aging and Solid Solution Aging

The structure and properties of Cu-Cr-Zr alloy were studied after rapidly solidified aging and solid solution aging. At the early stage of aging (500℃for 15 min), the hardness and the conductivity of the alloy rapidly solidified are 143 HV and 72% IACS, respectively. Under the same aging condition, the hardness and electrical conductivity of the alloy solid solution treated can reach 86 HV and 47% IACS, respectively. The microstructure was analyzed, and the grain size after rapid solidification is much smaller than that after solid solution treatment. By rapidly solidified aging the fine precipitates distribute inside the grains and along the grain boundary, while by solid solution aging there are large Cr particles along the grain boundary.     

Tuning the Doping Type and Level of Graphene with Different Gold Configurations

Au nanoparticles and films are deposited onto clean graphene surfaces to study the doping effect of different Au configurations. Micro‐Raman spectra show that both the doping type and level of graphene can be tuned by fine control of the Au deposition. The morphological structures of Au on graphene are imaged by transmission electron microscopy, which indicate a size‐dependent electrical characteristic: isolated Au nanoparticles produce n‐type doping of graphene, while continuous Au films produce p‐type doping. Accordingly, graphene field‐effect transistors are fabricated, with the in situ measurements suggesting the tunable conductivity type and level by contacting with different Au configurations. For interpreting the experimental observations, the first‐principles approach is used to simulate the interaction within graphene–Au systems. The results suggest that, different doping properties of Au–graphene systems are induced by the chemical interactions between graphene and the different Au configurations (isolated nanoparticle and continuous film).     

Nanocomposites based on MWCNT and styrene–butadiene–styrene block copolymers: Effect of the preparation method on dispersion and polymer–filler interactions

Composites of Kraton-D® 1102 BT (a styrene–butadiene–styrene block copolymer) and multi-walled carbon nanotubes (MWCNTs) were prepared by melt mixing. The composites were characterized by electrical conductivity measurements (Coleman’s method), mechanical properties (DMA and stress–strain tests), thermal stability (thermogravimetry) and morphology of dispersion (SEM). Finally, the resulting composites were compared with those made by the solution casting method. The results showed a strong influence of the preparation methodology on the final properties of the composites due to changes in morphology. Composites prepared by casting showed a higher electrical conductivity than extruded ones; the composites with 6 wt.% of MWCNT prepared by extrusion presented conductivity of the same order of magnitude as the composite with 1 wt.% of MWCNT prepared by casting – 10⁻³ to 10⁻⁴ S cm⁻¹. However, the extruded samples presented better mechanical properties than the casting ones.     

Effect of fluctuation and modification on microstructure and impact toughness of 20 wt.% Cr hypereutectic white cast iron. Einfluss durch Partikelzugaben und Modifikationen auf die Mikrostruktur und die Kerbschlagzähigkeit von übereutektischem weißen Gusseisen mit 20 Gew.‐% Cr

In the present study, Fe‐Cr‐C hypereutectic high chromium white cast iron were prepared from industry‐grade materials and subjected to the treatment of modification using Fe‐Si‐RE alloy, aluminum and a self‐made intermediate alloy, fluctuation (ferroalloy powder), and the combination of the fluctuation and the modification respectively. The structures of the treated alloy were investigated by means of the optical microscopy (OM). The impact toughness of the specimens was also examined. The fractographs of the samples were examined by scanning electron microscopy (SEM). The results showed that, with the addition of fluctuation or modifying agents, the primary carbides were refined and the impact toughness of the alloys was improved, especially with the combination of them.