熔模精密铸造无切削阀板

以硅溶胶为粘结剂精密铸造3Cr13阀板,不进行切削加工,要求阀板和密封面无任何铸造缺陷,不得用焊补修磨方法修复密封面。在试制生产过程中曾出现尺寸超差、凹角金属豆、表面麻坑等缺陷。通过采取严格控制蜡模工艺参数,控制车间环境温度,脱蜡前型壳低温处理、型壳焙烧温度和浇注温度,使铸件尺寸稳定在了公差范围内。沾浆时第一遍浆吹气,第二遍浆预润湿消除了金属豆缺陷。浇注后点燃木屑盖铁皮桶,消除铸件表面麻坑缺陷。     

熔模精密铸造Cr20搅拌杆的工艺要点

以水玻璃为粘结剂的精密铸造Cr20搅拌杆,加工余量仅为2mm。在生产过程中发现高铬铸铁搅拌杆盲孔尺寸超差、型壳浇注时开裂、铸字处存在金属豆、铸件夹砂等铸造缺陷。通过采取蜡模校正工艺控制盲孔尺寸,增加型壳层数及采用铁丝绑扎防止型壳开裂,铸字处用毛刷涂刷预防金属豆,改变模组间距和型壳干燥时间减少铸件夹砂缺陷。     

熔模精铸麻点和麻坑缺陷的工艺改善实践

熔模精铸中麻点及麻坑是常见并较难解决的铸造缺陷,尝试面层采用专用刚玉砂制壳耐火材料,浇注后扣箱,浆料中加石墨,浇注后型壳局部风冷,浇注后型壳局部水冷,设置工艺钉等工艺措施,持续改善工艺条件,寻找到了克服叶片铸件上的麻点、麻坑、龟裂的有效方法.     

薄壁调节片熔模铸造缺陷的控制

某航空发动机用调节片采用熔模精密铸造方法生产。调节片轮廓尺寸200 mm×170 mm,铸件平均厚度1.0 mm。调节片在铸造过程中极易产生铸造裂纹和疏松缺陷,冶金质量控制难度极大。针对以上问题并结合计算机模拟结果,对铸件浇注系统、型壳的焙烧温度、铸件的浇注温度进行改进,最终有效控制了铸造缺陷,提高了产品合格率。     

K432A机匣部件精铸工艺研究

机匣是在研某型号航空发动机上的核心部件,采用铸造高温合金K423A无余量整体精密铸造而成。该部件由内环、外环和空心叶片三部分组成,壁厚相差悬殊,铸造凝固过程极易产生疏松、裂纹等缺陷,铸造难度很大。为确保精铸件的尺寸精度、缩短研制周期,采用了快速成型技术制造熔模,熔模经表面处理后具有良好的表面质量和尺寸精度,表面粗糙度可达Ra6.3μm,尺寸精度可控制在0.5mm以内。设计了联合注入式浇注系统,采用较高的浇注温度和型壳温度,浇注出的铸件冶金质量优良,很好地满足了设计和使用的要求。     

熔模精密铸造冷型浇注研究

本文对熔模精密铸造的冷型浇注进行试验研究。试验表明:熔模精密铸造型壳采用冷型浇注,可防止碳钢及低合金钢铸件的表面的氧化脱碳,有利于提高铸件的表面硬度;并可防止或减轻铸件表面的化学粘砂缺陷。试验中对型壳层在浇注后的温度分布进行了测定,对冷型壳的升温及应力变化规律,以及对型壳强度的影响进行了分析;并探讨了铸钢件表面化学粘砂机理。     

基于ProCAST的叶轮熔模铸造凝固过程数值模拟

运用ProCAST铸造模拟软件对某型叶轮铸造工艺过程进行了数值模拟,分析了在温度场下型壳初始温度对铸件缺陷的影响和在应力场下浇注温度、浇注速度对铸件有效应力的影响,并进行了相关的实验验证.结果表明:当型壳预热温度达到400℃时,可以消除叶轮内部的缩孔、缩松缺陷;适当地增加浇注温度,可以降低铸件的有效应力,得到质量良好的铸件.     

影响熔模铸件尺寸精度和表面粗糙度的因素分析

分析了蜡模工作室温度、壳型材料、涂料和金属的浇注温度等对熔模铸件完整性的影响,研究了壳型材料的膨胀特性,涂料的粘度、耐火粉料的粒度和搅拌时间与表面粗糙度的关系,探讨了控制高精度铸造叶片尺寸和表面粗糙度的方法.     

大尺寸钛合金阀体石墨型铸造工艺研究

针对某大尺寸钛合金阀体铸件，对其结构进行分析后，设计了不同的浇注工艺，采用Pro-cast软件对该钛合金阀体铸件在不同浇注工艺下进行了石墨型铸造计算模拟。结果发现，不同的浇注系统会影响铸件内缺陷分布情况，且铸型预热温度的改变也会使铸件内缺陷体积发生变化。浇注工艺优化后，实际生产验证显示阀体铸件成形完整、无明显表面缺陷；X光检测结果显示铸件内部缺陷分布与模拟结果基本吻合。     

熔模铸造400系列不锈钢铸件表面麻点缺陷探索

400系列不锈钢材质在熔模铸造生产中易发生氧化,导致铸件产生麻点及麻坑缺陷。在制壳过程中加一层石墨砂,使浇注后钢液与型壳接触面形成还原性气氛,可防止麻点麻坑的产生,保证成品率,提高生产效率。     

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.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.