cBN-Fe磁性磨粒的制备工艺及性能

针对现有烧结法制备的磁性磨粒中研磨相材料硬度较低，对硬度高、导磁性差的钛合金等工件的研磨效果差，且硬度最高的金刚石材料无法作为研磨相用烧结法来制备磁性磨粒的问题，以Fe粉为基体，cBN粉末为研磨相，烧结制备cBN-Fe磁性磨粒；以Ti-6A1-4V(TC4)板为研磨对象，用控制变量法探究烧结法制备的cBN-Fe磁性磨粒中烧结时间、升温速度、原料配比对其研磨性能的影响，确定其最佳的制备工艺参数；并以45^#钢和202不锈钢为研磨工件，比较cBN-Fe与烧结法制备的Al2O3-Fe、Si C-Fe 3种磁性磨粒研磨前后工件的表面粗糙度、表面形貌，探究不同磁性磨粒的研磨性能和使用寿命。结果表明：当Fe粉与cBN粉的质量比为3∶1，烧结温度为1 150℃，烧结时间为6 h，保温时间为2 h，升温速度为3.19℃/min时，制备的cBN-Fe磁性磨粒研磨性能最佳，优于烧结法制备的Al₂O₃-Fe、Si C-Fe磁性磨粒的，且其使用寿命分别是Al₂O₃-Fe磁性磨粒和Si C-Fe磁性磨粒的...     

烧结法制备铁基立方氮化硼磁性磨粒及其磨削性能研究

目的 解决现有烧结法制备磁性磨粒工艺中存在的研磨相单一、研磨相材料硬度相对较低,以及对于高硬度难加工材质的研磨效率低、质量差等问题,采用立方氮化硼粉末作为研磨相烧结制备一种新型磁性磨粒。方法 采用烧结法制备铁基立方氮化硼磁性磨粒,探究原料的粒径比、烧结温度对磁性磨粒磨削性能的影响,以TC4钛合金板和Si3N4陶瓷板为试验对象,通过表面粗糙度测量仪和3D超景深显微镜对比加工前后工件的表面质量,采用扫描电镜观察加工后磁性磨粒的表面形貌,以此作为磁性磨粒的研磨性能和使用寿命的评价指标,并采用面扫描能谱分析仪观察磁性磨粒中研磨相的分布情况。结果 采用烧结法,以铁粉为基体,以立方氮化硼粉末为研磨相材料,制备磁性磨粒。最终确定压制力为90 kN,基体与研磨相的粒径比为3∶1,烧结温度为1 180 ℃,在此条件下制备的磁性磨粒具有良好的磨削性能,相较于烧结法制备的Al2O3/Fe、SiC/Fe磁性磨粒具有更强的磨削性能,可实现Si3N4陶瓷板表面的光整加工,在研磨39 min后可将其表面粗糙度由1.382 μm降至0.117 μm。结论 采用烧结法制备的铁基立方氮化硼磁性磨粒能够解决硬脆材料的表面质量问题,可以作为性能优异的磨削介质参与研磨,满足磁粒研磨光整加工技术的需求。     

磁性磨料的制备技术

磁性磨料是磁性研磨加工的磨具,在分析磁性磨料组成的基础上,介绍了几种磁性磨料的制备技术,重点介绍了粘结法和烧结法制备磁性磨料技术,最后给出了一些有实用价值的工艺参数.     

基于离散元法的磁性磨粒干压成型工艺参数优化

为探究磁性磨粒坯体压制阶段的各工艺参数对其成型质量的影响,优化磁性磨粒的烧结法制备参数,制备出质量优良的磁性磨粒,以铁基氧化铝磁性磨粒为研究对象,建立磁性磨粒干压成型的离散元模型。通过改变压制力、压制方式、摩擦系数、模具高径比等工艺参数,探究其对磁性磨粒坯体成型质量的影响,并实现压制过程中工艺参数的优化。结果表明：压制力越大,坯体孔隙率越小,但压制力过大,坯体外表面产生裂痕,影响坯体表面形貌的完整性,故宜选择75～125 MPa的压制力;双向压制得到的坯体密度更均匀、力学性能更好;模具的高径比越大,坯体的孔隙率相对较大,坯体的轴向应力相对较小;磨料颗粒间摩擦系数及侧壁与磨料颗粒之间的摩擦系数越小,坯体的孔隙率越小、致密度越好,坯体的均匀性也越好。在磁性磨粒混合阶段加入适量润滑液,可适当减小磨料颗粒间及颗粒与模具侧壁间的摩擦系数,进而提高磨粒坯体质量。     

烧结温度对陶瓷刚玉磨料性能的影响

本实验以氧化钙和二氧化硅为烧结添加剂,利用无压烧结工艺制备了陶瓷刚玉磨料,并借助扫描电子显微镜和单颗粒磨料强度测定仪等测试设备,研究了烧结温度对陶瓷刚玉磨料显微结构和力学性能的影响.实验结果表明:对于含CaO/SiO2添加剂的陶瓷刚玉磨料,随着烧结温度的升高,晶粒尺寸逐渐增大,晶粒形状也由各向异性生长逐步向等轴状发育;同时,磨料的单颗粒抗压强度也随着烧结温度的升高先升高后降低,并在1450 ℃时强度达到最大.     

曲面磁性研磨加工的表面粗糙度特性研究

针对大型模具曲面精整加工问题,探讨采用磁性研磨加工模具曲面的工艺.根据磁性研磨加工原理,基于数控铣床研制了磁性研磨实验装置,对曲面的磁性研磨加工进行了实验研究.采用工具旋转的磁性研磨加工方式,磁性磨料受到磁场约束力和离心力的作用,成为影响加工过程正反两方面的因素.经过对磁性研磨加工过程中加工区域的磁感应强度、加工间隙、磁极工具转速及加工次数等参数对曲面工件表面粗糙度影响规律的研究,得到了曲面磁性研磨加工过程优化参数.     

各种树脂砂轮的弯曲蠕变

本文探讨关于锆刚玉、高纯度烧结刚玉系砂轮等现代代表性的荒磨砂轮(树脂砂轮)四点支撑的静态弯曲及弯曲蠕变特性。特别就磨料、粒度、硬度等的影响进行了研究。试验采用厚5mm、宽10mm、长100mm的板状试样。蠕变试验温度为常温～300℃。静态弯曲试验结果表明,25%及40%锆刚玉系和高纯度烧结刚玉系砂轮的弹性模量显著地高于棕刚玉、白刚玉系砂轮。粒度越细、硬度越高,砂轮弹性模量、弯曲强度越高。另外,蠕变变形在200℃～300℃之间急剧增大,并且SR砂轮(高纯度烧结刚玉)难以蠕变。其次是AZ77砂轮(40%锆刚玉)。相反,棕刚玉、白刚玉砂轮易产生蠕变。另外硬度越高蠕变越小,而粒度影响略小     

CBN磁性磨料磁力研磨TC4钛合金工艺参数优化

为提高磁力研磨TC4钛合金的研磨效果,采用了一种新型CBN磁性磨料,通过正交试验法对磁力研磨TC4钛合金试验中各工艺参数进行优化,并通过试验评价新型CBN磁性磨料的结合强度和研磨能力。结果表明:优化工艺参数为:进给速度1mm/min、主轴转速1500r/min、加工间隙1mm和磨料填充量2.5g。在采用CBN磁性磨料和最优工艺参数组合下,钛合金工件经过30min研磨表面粗糙度从0.330μm下降到0.098μm,表面质量明显提高。研磨60min后磁性磨料未出现磨料脱落和破碎现象,磨料结合十分牢固。     

微波烧结硬质合金工艺的升温速度分析

研究WC-11.5Co硬质合金的微波烧结工艺以及升温速度对合金致密度、显微组织、硬度(HRA)的影响.结果表明,微波烧结能够快速制备高致密度、高硬度的硬质合金;在10.4～61.9 ℃/min范围内,升温速度对合金组织和性能未产生明显影响,硬度(HRA)在88.5～89.5之间,高于常规烧结的87.6和牌号为YG11C产品的硬度指标.     

基于响应面法的镍钛合金血管支架管材内壁磁粒研磨工艺参数研究

目的 研究磁粒研磨工艺参数对超细长镍钛合金血管支架管材内壁表面粗糙度的影响.方法 搭建镍钛合金血管支架管材内壁磁粒研磨加工实验设备,使用自由降落气固两相流双级雾化快凝磁性磨料制备方法,制备了铁基金刚石磁性磨料,对内径为1.0 mm、外径为1.2 mm、长度为1800～2000 mm的镍钛合金血管支架管材内壁进行磁粒光整加工.以表面粗糙度为评价指标,设计4因素3水平的响应曲面实验,探究管材旋转速度、磁极进给速度、磨料填充量和磨料粒径对表面粗糙度的影响规律及其相互作用关系,并建立4个工艺参数关于表面粗糙度模型的回归模型.使用Design-Expect 12软件对工艺参数进行优化,得到最优工艺参数组合,并加以试验验证回归模型的准确性.结果 根据响应面分析结果,管材旋转速度与磁极进给速度、管材旋转速度与磨料填充量以及管材旋转速度与磨料粒径,对表面粗糙度的交互影响作用显著.以表面粗糙度为评价指标,各工艺参数对表面粗糙度的影响因素大小排序为:管材旋转速度>磁极进给速度>磨料填充量>磨料粒径.以表面粗糙度值最小为目标,得到工艺参数组合为:管材旋转速度100 r/min,磁极进给速度5 mm/min,磨料填充量0.1 g,磨料粒径100.00μm.预测表面粗糙度Ra为0.101μm,试验实际表面粗糙度Ra为0.112μm,实际值与预测值的误差为10.9％.结论 使用磁粒研磨法对镍钛合金血管支架管材内壁进行光整加工,解决了超细、超长的镍钛合金血管支架管材内壁的光整加工问题.响应曲面法可对镍钛合金血管支架管材内壁磁粒研磨工艺参数进行优化,建立的表面粗糙度模型具有良好的预测能力,对实际工程应用具有指导意义.     

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。