Tensile creep behavior of a SiC-fiber/SiC composite at elevated temperatures

The tensile creep behavior of a SiC-fiber-reinforced SiC composite has been investigated in argon at temperatures of 1000–1300°C. The apparent stress exponents for creep of the composite and the apparent activation energies for creep increase with decrease in stress. The threshold stress approach can be used to treat the data. Creep of the CVI–SiC matrix controls the creep of the composite. The relationship between creep rate and the time to rupture can be described by the Monkman–Grant equation which provides a method of life prediction. The Larson–Miller parameter can also be used for creep-life prediction of the composite when the appropriate constant is selected.     

Effects of mechanical milling and arc-melting processes on the electrochemical performance of Si-based composite materials

The Si–Ni composite and Si/Ni alloy composite were prepared by high-energy mechanical milling and arc-melting, respectively, in order to investigate the effects of these processes on the electrochemical performance. The microstructures of Si–Ni composite and Si/Ni alloy composite were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The electrochemical properties have been investigated during 50 cycles for Si–Ni–C composite and Si/Ni alloy–C composite. As a result, both composites demonstrate a higher reversible capacity accompanied with a good cycling stability than the existing Si–C composite. Homogeneously dispersed Ni improved electric conductivity and induced fast charge transport significantly in Si–Ni–C composite whereas the secondary phases (NiSi and NiSi₂) played a role of media to accommodate a large volume change of Si during cycling in Si/Ni alloy–C composite. Consequently, it was identified that electrochemical performances of electrode material are affected by structural factors caused by the different processes.     

重力分离SHS陶瓷内衬复合管界面现象

利用自蔓延高温合成-重力分离法制备了陶瓷内衬20碳钢、Cr25Ni20耐热钢和1Cr18Ni9Ti不锈钢高炉煤粉喷吹复合管。对其界面现象的研究表明,金属/陶瓷间的结合主要表现为机械结合。其中,在不锈钢复合管中除有更强的机械锚固效应外,还兼以由Ti元素扩散而形成的溶解和浸润结合迹象。各复合管经使用后,碳钢、耐热钢复合管界面仍表现为机械结合,而在不锈钢复合管中,钢基中Ti元素和煤粉中C元素在界面区富集,陶瓷/金属间过渡区加宽,且陶瓷一侧组织中出现TiC新相,使其结合方式逐渐向扩散结合过渡,并呈现部分反应结合迹象。      

10CrNi3MoV(L)低合金高强钢自动埋弧焊焊接性能研究

采用等强匹配的 1 0MnNi2MoTi合金焊丝和 70 5 ch熔炼焊剂 ,通过改变焊接线能量及道间温度对不同碳含量连铸 1 0CrNi3MoV低合金高强钢板焊接性进行了研究。结果表明 ,连铸 1 0CrNi3MoV钢板具有较好的接头力学性能和焊接工艺适应性 ,但在较大线能量条件下 (～ 4 0kJ cm) ,接头韧性降低。为保证连铸1 0CrNi3MoV钢接头韧性水平 ,在限制自动埋弧焊线能量的同时 ,还应提高钢板韧性 ,控制钢板碳含量     

碳纤维布增强酚醛/碳化硅烧结合金的研究

为改善碳/碳复合材料的高温抗氧化性能,在碳布/液体酚醛中引入超细碳化硅(α-SiC)粉进行复合,并在高纯氮气保护下高温烧结,初步制成了碳布增强SiC/C共烧结合金材料。热分析表明,该新型材料在900℃高温下的热失重率比常规的碳/碳复合材料降低数十倍,经浸渍处理并高温烧结,烧结合金的密度、力学性能及高温抗氧化性能均有显着提高。本文较系统地考察了原料配比,成型工艺及浸渍处理对烧结合金亚微形态及宏观性能的影响规律。     

泵头体高强钢材料的力学性能

为了进一步研究泵头体高强钢25Cr2Ni4MoV和30CrNi2MoV的力学性能,采用拉伸、冲击和裂纹尖端张开位移(CTOD)试验对其进行测试。结果表明:材料在常温下具有较好的综合力学性能;在静载荷条件下,具有优良的断裂韧度。     

SPS制备TiNi增强镁合金复合材料的微观结构及力学性能

以AZ31镁合金为基体,TiNi形状记忆合金丝为增强体,利用放电等离子烧结法（SPS）制备了TiNi/Mg复合材料,用OM、SEM、EDS对其微观形貌进行表征,并用XRD及DSC研究TiNi丝的相变,同时对该复合材料进行准静态拉伸实验,对其室温及高温力学性能进行研究。结果表明,所制备的TiNi/Mg复合材料中界面处存在Mg、Ti、Ni元素的互扩散现象,并形成宽度约为2 μm的互扩散层;所制备的TiNi/Mg复合材料的高温力学性能高于室温,其中其屈服强度、抗拉强度及弹性模量在100℃时（分别为157 MPa,292 MPa,22 GPa）较室温分别提高了12%、33%和29%,150℃时（分别为143 MPa,251 MPa,20 GPa）较室温分别提高了2%、14%和18%。     

Thermal stability and elevated temperature mechanical properties of electroslag remelted Fe-16wt.%Al-(0.14–0.5)wt.%C intermetallic alloys

Addition of carbon in the range of 0,14–0.5 wt.% to the Fe₃Al-based intermetallic Fe-16wt.%Al (Fe-28at.%Al) alloy results in the formation of a thermally stable dispersion of Fe,AIC carbide phase. The volume fraction of these precipitates increases with increase in carbon content. Processing of these alloys through a combination of air induction melting and electroslag remelting leads to enhanced elevated temperature mechanical properties compared to those reported for the low (< 0.01 wt.%) carbon alloys with similar Al contents. Enhancement of up to 30% in elevated temperature yield strength was observed at the test temperatures (600, 700 and 800°C) used. The improvement in mechanical properties may be attributed to the presence of strengthening Fe₃AlC phase as well as the interstitial carbon present in the alloy matrix. The addition of carbon also leads to improved room temperature mechanical properties in contrast with other alloying additions (such as Mo, Ti and Si) used for enhancing elevated temperature properties of Fe₃Al-based intermetallic alloys. It is suggested that carbon may be an important alloying addition to these alloys.     

Effects of age heat treatment and thermomechanical processing on microstructure and mechanical behavior of LAZ1010 Mg alloy

An Mg–Li–Al–Zn (designated as LAZ1010) alloy containing about 10 wt% of Li has been prepared by melting and solidification in a carbon steel crucible, and extruded at a billet preheating temperature of 200 °C with an extrusion ratio of approximately 29. Effects of age heat treatments and thermomechanical processing on microstructures and mechanical properties were performed in this study. Hardness, optical microscopy, X-ray diffraction studies, and tensile testes were carried out to explore the variations in microstructures and mechanical behaviors during processing. The results showed that LAZ1010 alloy presented age hardening effect at temperatures below 50 °C. Rapid decrease in hardness with aging temperature at intermediate temperatures should be resulted from the transformation of θ phase into the equilibrium phase AlLi. Kocks–Mecking type plots were used to illustrate different stages of work hardening of the cold rolled specimens. The results indicated that cold rolled LAZ1010 alloy showed stage III and stage IV work hardening behaviors.     

In-situ synthesis of TiC/Fe alloy composites with high strength and hardness by reactive sintering

Fe alloy composites reinforced with in-situ titanium carbide(Ti C) particles were fabricated by reactive sintering using different reactant C/Ti ratios of 0.8,0.9,1 and 1.1 to investigate the microstructure and mechanical properties of in-situ Ti C/Fe alloy composites.The microstructure showed that the in-situ synthesized Ti C particles were spherical with a size of 1–3 μm,irrespective of C/Ti ratio.The stoichiometry of in-situ Ti C increased from 0.85 to 0.88 with increasing C/Ti ratio from 0.8 to 0.9,but remained almost unchanged for C/Ti ratios between 0.9 and 1.1 due to the same driving force for carbon diffusion in Ti Cxat the common sintering temperature.The in-situ Ti C/Fe alloy composite with C/Ti = 0.9 showed improved mechanical properties compared with other C/Ti ratios because the presence of excess carbon(C/Ti = 1 and 1.1) resulted in unreacted carbon within the Fe alloy matrix,while insufficient carbon(C/Ti = 0.8)caused the depletion of carbon from the Fe alloy matrix,leading to a significant decrease in hardness.This study presents that the maximized hardness and superior strength of in-situ Ti C/Fe alloy composites can be achieved by microstructure control and stoichiometric analysis of the in-situ synthesized Ti C particles,while maintaining the ductility of the composites,compared to those of the unreinforced Fe alloy.Therefore,we anticipate that the in-situ synthesized Ti C/Fe alloy composites with enhanced mechanical properties have great potential in cutting tool,mold and roller material applications.     

机械合金化合成Fe-Ni-C系非晶态合金

用机械合金化方法合成了Fe—Ni—C系非晶态合金,用X射线衍射仪对球磨不同时间的Fe—Ni—C系混合粉末进行了分析．结果表明：在Fe—Ni合金中加入C可促使其形成非晶;原子分数分别为Fe40Ni40C20、Fe60Ni20C20的混合粉末在一定的机械合金化条件下可获得非晶．     

Oxidation resistance of dense carbon fiber/Si–O–C glass composite fabricated by pre-oxidation and spark plasma sintering

The carbon fiber/Si–O–C glass composite was prepared from the silicone and carbon fiber by pre-oxidation and spark plasma sintering (sintered composite). The mass loss of the sintered composite oxidized at 1200 °C for 90 min was 5%, which was lower than that of same dimension for similar composites, although the mass loss at 600 °C was still high. This indicated its excellent oxidation resistance at elevated temperature. No cracks and pores were found in the sintered composite, indicating that the combination of pre-oxidation and spark plasma sintering was better than the pyrolysis for manufacturing dense composites. Compared with the flexural strength of about 60 MPa for carbonaceous composites, the flexural strength of the sintered composite was obviously improved to 220 MPa. Moreover, microstructures of the specimen before and after sintering as well as after oxidation were investigated.     

34Cr2Ni2Mo 合金结构钢热本构方程研究

目的基于实测的流动应力曲线,构建可用于热成形模拟的34Cr2Ni2Mo合金结构钢高精度本构方程。方法采用热模拟试验测试该材料的流动应力曲线,在动态再结晶的条件下,构建了基于物理机制的热本构方程,通过曲线拟合获得了本构方程参数。结果热模拟试验测试的流动应力曲线具有明显的动态再结晶现象,构建的本构方程包括流动应力、屈服/饱和/临界/稳态应力、发生50%再结晶的时间等内变量计算方程,在参数拟合后对其误差分析表明,本构方程计算的流动应力偏差控制在±15 MPa以内。结论 34Cr2Ni2Mo合金结构钢本构方程能够较为准确的描述该钢在热成形过程的流动应力变化特征,具有较强的数值稳定性和外延拓展性。     

Effect of in situ synthesized TiB whisker on microstructure and mechanical properties of carbon–carbon composite and TiBw/Ti–6Al–4V composite joint

Carbon–carbon composite (C–C composite) and TiB whiskers reinforced Ti–6Al–4V composite (TiB_w/Ti–6Al–4V composite) were brazed by Cu–Ni + TiB₂ composite filler. TiB₂ powders have reacted with Ti which diffused from TiB_w/Ti–6Al–4V composite, leading to formation of TiB whiskers in the brazing layer. The effects of TiB₂ addition, brazing temperature, and holding time on microstructure and shear strength of the brazed joints were investigated. The results indicate that in situ synthesized TiB whiskers uniformly distributed in the joints, which not only provided reinforcing effects, but also lowered residual thermal stress of the joints. As for each brazing temperature or holding time, the joint shear strength brazed with Cu–Ni alloy was lower than that of the joints brazed with Cu–Ni + TiB₂ alloy powder. The maximum shear strengths of the joints brazed with Cu–Ni + TiB₂ alloy powder was 18.5 MPa with the brazing temperature of 1223 K for 10 min, which was 56% higher than that of the joints brazed with Cu–Ni alloy powder.     

预歧化处理的高性能锂离子电池SiO/C负极材料

以SiO和蔗糖为原料,SiO经高温歧化反应处理后,通过机械球磨、喷雾干燥、高温热解工艺制备出具有优异电化学性能的锂离子电池SiO/C负极材料。经XRD、FTIR、XPS、SEM、TEM结构分析表明,歧化反应处理的片状SiO包含非晶态SiO和纳米晶相Si、SiO_2,蔗糖热解形成的无定形碳包覆在细片状SiO的表面,组成球形SiO/C颗粒。电化学测试结果表明,预歧化处理的SiO/C复合材料的首次放电容量为1 314.6mAh/g,首次库伦效率达到71%;100周循环后的放电容量为851.2mAh/g,容量保持率达到78.5%,循环稳定性远高于未经歧化处理的SiO/C复合材料。电化学性能的提高归因于SiO预歧化反应及热解碳包覆。     

Electrochemical properties of the ball-milled LaMg10NiMn alloy with Ni powders

The electrochemical characteristics of the ball-milled LaMg₁₀NiMn alloys with Ni powders were investigated. It was found that the ball-milled LaMg₁₀NiMn + 150 wt.% Ni composite exhibited higher first discharge capacity and better cycle performance. By means of the analysis of electrochemical impedance spectra (EIS), it was shown that the existence of manganese in LaMg₁₀NiMn alloy increased the electrocatalytic activity due to its catalytic effect, and destabilized metal hydrides, and so reduced the hydrogen diffusion resistance. These contributed to the higher discharge capacity of the ball-milled LaMg₁₀NiMn–Ni composite. According to the analytical results of X-ray diffraction (XRD), EIS and steady-state polarization (SSP) experiments, the inhibition of metal corrosion is not the main reason for the better cycle performance. The main reason is that the electrochemical reaction resistance of the ball-milled LaMg₁₀NiMn–Ni composite is always lower than that of the ball-milled LaMg₁₀Ni₂–Ni composite because the former one contains manganese, which is a catalyst for the electrode reaction.     

Amorphization behaviour in mechanically alloyed Ni—Ta powders

Amorphization behaviour of NixTa100–x alloy powders synthesized by mechanical alloying mixtures of pure crystalline Ni and Ta powders with a Spex high energy ball mill was studied. The mechanically alloyed powders were amorphous for the composition range between Ni10Ta90 and Ni80Ta20. This range is larger than amorphous alloys prepared by the rapid-quenching process or by electron-gun deposition technique. A supersaturated nickel solid solution formed for Ni-rich composition. The thermal stability has been investigated by differential thermal analysis. The crystallization temperature of amorphous Ni—Ta powders was proportional to the Ta content, and the activation energy of amorphous Ni—Ta powders exhibited a maximum near the eutectic composition. It is found that the amorphization rate at the early stage of the mechanical alloying process was faster in the intermediate compositions than those at both Ni- and Ta-rich compositions.     

Microstructure evolution in a Ni–Mo–Cr superalloy subjected to simulated heat-affected zone thermal cycle with high peak temperature

A typical Ni–Mo–Cr superalloy with basic composition of Ni–17Mo–7Cr (wt.%) was fabricated and the relationship between the microstructure and mechanical properties while it underwent simulated heat-affected zone thermal cycle (HAZ) treatment was investigated. The results show that the Ni–Mo–Cr alloy was mainly made up of Ni based solid solution and MoC carbides. The critical peak temperature that a unique lamellar-like structure occurred in the alloy was found to be 1300 °C, and they were firstly determined to be Ni matrix and carbides (MoC and chromium carbides) generated through local melting. Due to the formation of unique structure, the alloy exposed to HAZ thermal cycle with a peak temperature of 1300 °C could still maintain excellent high-temperature mechanical performance. The work carried out here will provide valuable guidelines in designing and applying the Ni–Mo–Cr series superalloys.     

Reactive Milling and Mechanical Properties of NiAl Composite with HfC Dispersoids

A NiAl-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni,Al,Hf and C powders.The formation mechanism of NiAl-HfC during milling can be attributed to two chemical reactions:Ni Al→NiAl ΔH;Hf C→HfC ΔH,induced by mechanical collision in a certain period of time,which results in an abrupt exothermic reaction.Hot pressing(HP) and hot isostatic pressing(HIP) have been used to make the NiAl-10HfC compacts near fully dense.Compressive testing from room temperature to 1000℃ indicated that the yield stress of NiAl-10HfC composite is 3-4 times higher than that of cast NiAl and correspond to the MA NiAl-10TiB2 composite.In the meantime,yield strength at high temperature is dependent on strain rate, and deformation is controlled by diffusion mechanism.     

碳纳米管对Fe-P非晶的力学性能和晶化行为影响的研究

采用快速凝固技术制备了碳纳米管／铁碳非晶复合材料,并对其组织、力学性能和热稳定性进行了研究检测结果表明,碳纳米管在非晶基体中的弥散存在,使得非晶抗拉强度提高,晶化激活能增加,晶化特征温度明显提高,加入２Ｗ／％碳纳米管,使铁磷非晶的室温抗拉强度提高了１２０％,晶化激活能增加了约４０％,晶化开始温度提高了约１００Ｋ,此外,在温度高于其晶化温度约２００Ｋ时,碳纳米管和非晶基体界面间发生了固相反应。