Csf/Si3N4复合材料的力学性能和微波介电性能研究

采用热压烧结的方法,以α-Si3N4粉和短切碳纤维为主要原料,以Y2O3和La2O3为烧结添加剂,制备Csf/SiN4复合材料,研究了其力学性能和微波介电性能.结果表明,该Csf/Si3N4复合材料的抗弯强度随纤维含量的增加呈现下降的趋势,是由于碳纤维氧化所产生的缺陷所致;当纤维含量较低时,断裂韧性随纤维含量增大而增大,由于纤维氧化产生的缺陷阻止了裂纹进一步的扩展或使裂纹发生了偏转.当纤维含量超过1%(质量分数)后,随着纤维含量的增大,氮化硅显微结构发生变化,氮化硅陶瓷本身断裂韧性减小,使Csf/Si3N4复合材料断裂韧性逐步降低.当碳纤维含量在0～1%(质量分数)时,随着碳纤维含量的增加,介电常数ε',ε"和介电损耗tanδ均随着纤维含量的增加而增大,而且所制得的复合材料表现出较强的频散效应;当纤维含量继续增加时,在相同的频率下,介电常数下降,材料的频散效应逐渐消失.     

热压烧结氮化硅陶瓷的力学性能研究

采用Y2O3-La2O3和LiF-MgO-SiO2 2组烧结助剂，通过短切碳纤维增韧的方法，热压烧结制备了氮化硅陶瓷，并对所得氮化硅陶瓷的相组成、微观结构和力学性能进行了分析和讨论。结果表明：长柱状β-Si3N4晶粒有利于提高材料的力学性能；加入纤维不仅不能使材料的抗弯强度提高，反而有所下降，其原因是在高温制备过程中，碳纤维与氧发生反应，在氮化硅陶瓷中产生的缺陷所致。但是加入碳纤维能够提高氮化硅陶瓷的断裂韧性，其原因是碳纤维与氧反应形成的缺陷，侄裂纹在断裂过程发生了偏转。     

碳纤维复合吸波材料的频散特性影响规律研究

目的归纳总结碳纤维长度和含量对碳纤维复合吸波材料(CFCAM)频散特性的影响规律。方法以水性聚氨酯(PR)为基体树脂,碳纤维(CF)为填料,制备了不同长度和含量的CFCAM,采用扫描电镜和X射线衍射仪对CF改性前后的微观形貌和物质结构进行表征,用矢量网络分析仪测试CFCAM介电常数(ε),归纳总结出CF长度、含量对CFCAM的频散特性的影响规律。结果随着CF长度的增大,CFCAM的ε先增大后减小,当CF长度为3 mm时,CFCAM不仅具有较好的频散特性,实部(ε′)和虚部(ε′′)都较大;随着CF含量增大,CFCAM的?增大,当CF质量分数为0.9%时,ε′达到18左右,ε′′达到9左右,预示着该含量下CFCAM有较大的储存能量的能力,并且对电磁波有较强的电损耗能力。结论 3 mm碳纤维在质量分数为0.9%时具有较好的频散特性,适宜用来制备吸波性能强、频带宽的雷达吸波涂层材料。     

自蔓延高温合成Cf／TiC-TiB2复合材料的力学性能研究

为提高TiC—TiB2复合材料的强度和韧性以拓宽其应用，用自蔓延高温合成结合准热等静压（SHS／PHIP）的方法制备了碳纤维质量分数分别为0％，1％，3％，5％，7％的Cr／TiC—TiB2复合材料。通过实验测定，随碳纤维含量的增加，Cf／TiC—TiB2复合材料的弯曲强度和断裂韧性都呈现先增加后降低的趋势。当碳纤维含量达到3％时，强度和韧性分别为406．12MPa和6．26MPa．m^1/2，均高于纯TiC-TiB2陶瓷。纤维的断裂、桥连和裂纹的偏转是复合材料的主要增韧机制。     

Al对ZrO_2增韧Si_3N_4烧结体的相变及性能的影响

在高温 (140 0℃ )、超高压 (4.2GPa)条件下制备了Al ZrO2 (Y2 O3 ) Si3 N4 烧结体。采用XRD分析及力学强度测试等方法 ,研究了Al对ZrO2 相变能力及ZrO2 增韧烧结体作用的影响。结果表明 :在烧结体中加入 2 %Al,利用Al与N反应生成AlN可阻止Zr O N化合物生成 ,避免ZrO2 在Si3 N4 基体中被N稳定生成不可相变t′ ZrO2 ,提高ZrO2 的t→m相变能力 ,使ZrO2 起到增韧氮化硅烧结体的作用 ;当Y2 O3 含量为 2 %～ 2 .5 % (摩尔分数 )时 ,烧结体抗压强度及断裂韧性均较高 ,ZrO2 相变增韧作用最大。     

陶瓷基复合材料的微观结构和力学性能(英文)

采用添加剂热压烧结制备了短纤维增韧氮化硅基复合材料,并对材料的力学性能和微观结构进行了分析和讨论.结果表明:Y_2O_3-La_2O_3添加剂促进了α-Si_3N_4→β-Si_3N_4的相转变,这个体系经过1800 ℃的热压烧结后,其中的碳纤维产生退化.而经过1600 ℃热压烧结的含LiF-MgO-SiO_2添加剂的体系中,纤维保持完好,晶粒没有发生相转变.两个体系的复合材料的断裂韧性值均高于氮化硅基体的值,其提高幅度均接近20%,这归因于纤维拉拔、裂纹偏转和界面松解机制.     

粉料表面氧含量对GPS烧结氮化硅陶瓷显微结构的影响

通过研究GPS烧结氮化硅陶瓷的室温和高温抗弯强度、晶界相含量和成分以及晶界析晶相随氮化硅粉料表面氧含量的变化规律，发现当粉料表面氧含量低于1．35mg／m^2时，氮化硅陶瓷在室温下的抗弯强度基本保持不变。试样在1200℃时的抗弯强度明显低于室温强度，且随着粉料表面氧含量的增加有一最高值。由于烧结助剂引入的O和Si在烧结过程中的还原气氛下发生反应而损失，烧结体中晶界相的实际含量显著低于粉料中烧结助剂的加入量。随粉料表面氧含量的增加，氮化硅陶瓷烧结体中的二次析晶相α-Y2Si2O7和β-Y2Si2O7消失，只有β-Si3N4晶相和晶界玻璃相存在。     

自蔓延高温合成Cf/TiC-TiB2复合材料的力学性能研究

为提高TiC-TiB2复合材料的强度和韧性以拓宽其应用,用自蔓延高温合成结合准热等静压(SHS/PHIP)的方法制备了碳纤维质量分数分别为0%,1%,3%,5%,7%的Cf/TiC-TiB2复合材料.通过实验测定,随碳纤维含量的增加,Cf/TiC-TiB2复合材料的弯曲强度和断裂韧性都呈现先增加后降低的趋势.当碳纤维含量达到3%时,强度和韧性分别为406.12 MPa和6.26 MPa.m1/2,均高于纯TiC-TiB2陶瓷.纤维的断裂、桥连和裂纹的偏转是复合材料的主要增韧机制.     

氧化铝基复合陶瓷物理和力学性能的研究

采用热压烧结致密化工艺,在1550,1600,1650℃3个不同的烧结温度下,烧结制备了Si3N4含量从O．25w％到6w％的A1203／Si,N。纳米复相陶瓷。对所制备的试样进行了密度、硬度、断裂韧性的测试。实验结果表明,所有试样达到了较高的致密度,且致密度随烧结温度的升高而增加。硬度在Si3N。含量为0．75w％和3w％时达到峰值。韧性在Si3N4含量3w％达到峰值。材料的性能较纯A120,陶瓷有较大幅度提高。     

成孔剂和硅粉粒度对反应烧结氮化硅性能的影响

以硅粉为原料，通过添加不同含量的成孔剂，反应烧结制备出具有不同气孔率的低密度多孔氮化硅陶瓷，研究了成孔剂含量和硅粉粒度对反应烧结氮化硅性能的影响。结果表明，随着成孔剂含量的增加，试样气孔率变大，强度随之减小，烧结后试样中的α-Si3N4相增多，介电常数实部和介电损耗降低，最低介电常数实部可达到2．4左右；不同粒度硅粉中添加30％（质量分数，下同）成孔剂的坯体烧结，在气孔率保持不变的条件下，初始硅粉粒度越小，烧结后试样强度越大，介电常数实部和介电损耗明显减小。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。