熔渗法制备CrW/Cu复合材料的组织与性能研究

采用熔渗法制备了CrW/Cu复合材料,即首先把铬粉和钨粉的混合粉末烧结成骨架,然后把铜液渗入CrW骨架的孔隙中制备CrW/Cu复合材料;研究了气氛、熔渗温度、溶渗时间对CrW/Cu复合材料的显微组织和性能的影响.研究结果表明:真空环境下溶渗法制备的CrW/Cu复合材料组织最致密;当熔渗温度大于1 350℃时,尽管没有达到铬的熔点温度,但W-Cr骨架中的Cr颗粒开始逐步消失,随着熔渗温度的提高或熔渗时间的延长,Cu取代其位置;Cr通过Cu合金液迁移到W骨架的孔隙中,与W形成Cr-W固溶体;材料组织的变化导致材料的硬度明显升高,导电率明显降低.     

TC6钛合金加热和冷却过程中的相转变研究

熔渗技术是制备CuW合金的有效方法,有效控制铜液熔渗过程对获得组织性能优异的CuW合金非常有意义.针对铜液在结构形貌复杂的骨架孔隙中的熔渗过程进行模拟和分析.讨论了二维微观模型下孔隙的形态参数:形状因子、曲折度、孔喉比对铜液充型过程的影响;预测了CuW合金熔渗过程中熔渗速度和界面前沿压力随时间的变化.结果表明:孔隙的均匀性越差,曲折度和孔喉比越大,熔渗时的速率变化越明显;熔渗前沿压力突变也越大.     

制备工艺对铁基粉末冶金气门座圈致密性和性能的影响

采用烧结、熔渗、热处理制备了高性能铁基粉末冶金气门座圈。研究不同工艺对气门座圈的孔隙变化、致密性、显微组织和力学性能的影响,确定气门座圈致密性的最佳工艺条件。结果表明：采用熔渗或提高烧结温度,可使孔隙的形状趋于球化,大大减少孔隙的数量和大小,明显提高气门座圈的致密性。获得气门座圈理想致密性的最佳工艺条件：均匀压入14%~15%（质量分数）的熔渗薄铜片,在1150 ℃下熔渗烧结2 h,然后进行620 ℃高温回火;回火后可得到大量综合性能良好的回火索氏体,明显提高了气门座圈的综合性能     

等离子熔覆CoCrFeNiMo高熵合金相结构及显微组织研究

目的 在普通低碳钢表面制备含难熔金属Mo的CoCrFeNiMo高熵合金熔覆层,研究熔覆层的组织结构及性能。方法 将Co、Cr、Fe、Ni、Mo金属单质粉末按等摩尔比进行配制并混合均匀,利用等离子熔覆法在Q235钢表面制备CoCrFeNiMo高熵合金熔覆层,采用X射线荧光光谱仪(XRF)、X射线衍射仪(XRD)、金相显微镜(OM)、扫描电子显微镜(SEM)、显微硬度计对熔覆层的合金成分、相结构、显微组织和硬度进行研究。结果 在等离子熔覆过程中存在元素烧损现象,熔覆层的实际成分为Co1.17Cr0.92Ni1.06Fe0.92Mo0.92(摩尔分数);熔覆层与基材形成了良好的冶金结合,熔覆层主要由FCC相组成,同时夹杂少量富Mo、Cr的σ相;熔覆层显微组织为树枝晶,枝晶内为固溶多种元素的FCC相,枝晶间是由FCC相和富Mo、Cr的σ相组成的共晶组织。高熵合金物相形成规律较为复杂,其相结构不能仅由热力学参数来预判,仍需要实验结果的验证。由于Mo元素的固溶强化及σ相的沉淀强化,使得熔覆层的硬度明显提高,表面硬度约为485HV。结论 利用等离子熔覆法,在Q235钢表面成功制备了含难熔金属Mo的CoCrFeNiMo高熵合金熔覆层,显著提高了CoCrFeNi高熵合金的硬度。     

高速钢氧氮共渗与渗氮后氧化的组织与性能比较

采用金相分析、显微硬度测试和防锈性湿热试验等方法对比研究了W6Mo5Cr4V2高速钢经氧氮共渗和渗氮后氧化处理的组织与性能.结果表明,W6Mo5Cr4V2高速钢经氧氮共渗和渗氮后氧化处理都可获得具有化合物层和扩散层的渗层组织;氧氮共渗层的硬度明显高于普通气体渗氮,而渗氮后氧化的渗层硬度与普通气体渗氮相差不大;在选择合适通空气量和后氧化温度的条件下,氧氮共渗和渗氮后氧化处理都可获得优于普通气体渗氮的防锈性能,其中以30%(vol.)空气量氧氮共渗试样表面的防锈性能最好,其次是渗氮 350 ℃后氧化处理的试样.     

团聚对熔渗Mo-Cu合金显微组织的影响

采用光学显微镜(OM)观察熔渗Mo-Cu合金的显微组织及微观形貌;采用扫描电镜(SEM)结合背散射电子成像(BSE)对合金的熔渗行为进行分析。研究了团聚体对熔渗Mo-Cu合金显微组织的影响。结果表明,粉体团聚会导致Mo骨架开裂及不均匀性,影响液态Cu在不同区域的熔渗情况及分布。液态Cu在凝固过程中体积收缩,从毛细管中倒流聚集,使Mo-Cu合金的致密度下降。     

淬火温度对25Cr2Ni3Mo垫片组织和性能的影响

本文研究了淬火温度对25Cr2Ni3Mo钢垫片显微组织和力学性能的影响。测试了不同淬火温度下25Cr2Ni3Mo钢垫片试样的常温拉伸性能和-115℃低温冲击吸收能量值;应用金相显微镜、扫描电子显微镜等进行了金相显微组织和扫描电镜高倍组织的观测、冲击断口形貌分析。依据测试和分析结果确定了25Cr2Ni3Mo钢的最佳淬火温度范围,满足25Cr2Ni3Mo钢垫片的高力学性能要求。     

高强匹配Gr91/12Cr1MoV异种钢焊接接头组织及性能

研究了高匹配条件下Gr91/12Cr1MoV异种耐热钢焊接接头各区的显微组织及冲击性能。结果表明:采用高匹配填充材料和焊条电弧焊方法,可获得性能良好、组织稳定的焊接接头;焊缝区的显微组织为回火板条马氏体,与Gr91母材正火+回火态的显微组织类似,但晶粒相对粗大,Gr91侧HAZ的组织主要为回火索氏体组织,而12Cr1MoV侧HAZ的组织主要为铁素体和索氏体;接头具有高的冲击韧性。     

高铬镍基合金熔敷金属的组织和性能

采用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等分析手段研究了一种高铬镍基合金焊丝熔敷金属的显微组织和力学性能。结果表明:试验用焊丝熔敷金属显微组织具有明显的柱状枝晶形态;在凝固过程中,除Cr元素外,Fe,Nb,Mo,Si等主要添加元素均表现出明显的偏析行为;γ基体上的析出物主要是TiC和γ/Laves共晶组织,其中TiC呈块状,分布较为均匀,而γ/Laves共晶组织呈层片状,主要分布于枝晶间区域。熔敷金属的强度较高,其冲击断口形貌为典型的韧窝状,在韧窝附近的γ/Laves共晶组织对熔敷金属的塑性和韧性有不良影响。     

激光功率对高速激光熔覆Ni/316L层组织与力学性能的影响

为研究高速激光熔覆Ni/316L层组织与力学性能随激光功率的演变规律,分别采用1.1、1.3 和1.5 kW激光功率在Q235钢表面熔覆Ni/316L层。采用扫描电镜(SEM)、能谱仪(EDS)、显微硬度计、冲击试验机及Knoop压痕法研究了熔覆层的显微组织、显微硬度、冲击性能与弹性模量。结果表明,激光功率为1.1 kW时熔覆层内部晶粒生长取向存在垂直于界面生长和与界面成一定角度交叉生长两种模式,并含有少量孔隙等缺陷,熔覆层/基体界面元素成断崖式分布,二者互扩散程度较低。随着激光功率升高,熔覆层晶粒转变为以垂直于界面生长为主,且涂层内部致密性高,缺陷较少,熔覆层/基体界面元素互扩散程度提升。激光功率对熔覆层硬度、冲击性能都存在显著影响,但是对弹性模量的影响较低。不同激光功率下,熔覆层最大硬度均出现在距界面100 μm左右的区域;功率从1.1 kW提升至1.5 kW时熔覆层熔合区最大硬度提高约50%;功率为1.5 kW时,试样的冲击性能较基体提高约20%。     

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).     

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.     

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.     

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。