水溶性型芯在60万瓩汽轮机组铸钢汽封体上的应用

本文介绍的以无机水溶性化合物为粘结剂的水溶性型芯,湿压强度为0．022MPa(φ50×50mm试样测得),常温干抗压强度达12．5MPa、抗弯达3．25MPa,高温强度(600~1200℃)1．5MPa以上,型芯发气量为13ml/g,透气性在65以上,具有良好的水溶性。用这种型芯在1620℃浇注的ZG15Cr1Mo汽封体,当铸件冷却至100℃时放入水中,型芯在40分钟内脱除完毕,气路内腔光洁。     

树脂砂型低压铸造紫铜结晶器工艺研究

研究了紫铜结晶器砂型低压铸造工艺,重点从砂芯设计、紫铜熔炼等方面进行了探讨。采用酚醛树脂为粘结剂的型砂,砂芯含水量为8%,湿态透气性>70Pa,湿压强度为0.02~0.03MPa,干拉强度为0.1~0.2MPa,型芯烘干,最高炉温为180~200℃;采用中频感应电炉熔炼,Cu温在1200~1220℃,可脱氧浇注。磷铜脱氧加入量<0.05%,并采用真空除气。     

氧化铝陶瓷型芯凝胶成型因素研究

溶胶-凝胶成型是制备成分均匀、结构复杂陶瓷型芯最理想的成型工艺。以降低浆料粘度和提高固相含量为研究方向,从不同固相含量、颗粒度、添加剂对型芯性能的影响进行分析,以及研究pH值对浆料流动性的影响,并制备出固相含量为58%、动力粘度为0.46MPa.s的氧化铝陶瓷浆料,其成型后坯体湿强度可达约34MPa,完全满足后续加工要求。     

单晶叶片用硅基陶瓷型芯制备与性能研究

以石英玻璃粉为基体材料制备了单晶叶片用硅基陶瓷型芯,研究了陶瓷型芯的抗弯强度、热变形、收缩率,采用扫描电镜对试样微观结构进行了表征。结果表明:经1190℃焙烧,型芯的烧成收缩率为0.59%,高温强度可达29.07 MPa,热变形量为0.10 mm。     

烧结陶瓷铸造砂混制粘土砂的性能及特点

对烧结陶瓷铸造砂和石英砂混制粘土砂时的表现行为进行了试验研究,发现由烧结陶瓷铸造砂和石英砂混制粘土砂的湿压强度随膨润土加入量的增加而提高。在膨润土加入量一定的情况下,型砂的湿压强度和透气性随型砂中水分含量的增加而提高,待达到最大值后,水分继续增加,型砂的湿压强度和透气性降低。在相同膨润土加入量的情况下,由70/140烧结陶瓷铸造砂混制无煤粉和含煤粉粘土砂及由50/100烧结陶瓷铸造砂混制无煤粉粘土砂的湿压强度低于相同条件下由石英砂混制相应粘土砂的湿压强度,由50/100烧结陶瓷铸造砂混制含煤粉粘土砂的湿压强度等于或略低于由石英砂在相同条件下混制含煤粉粘土砂的湿压强度。在相同工艺条件下,由烧结陶瓷铸造砂混制粘土砂的透气性高于由石英砂混制粘土砂的透气性。     

硅树脂粘结球形SiO_2陶瓷型芯的制备及性能研究

以球形SiO_2颗粒为基体、硅树脂为粘结剂,通过干压法制备多孔SiO_2陶瓷型芯,研究了硅树脂添加量和烧结温度对陶瓷型芯性能的影响。研究结果表明:硅树脂作为粘结剂通过交联、裂解从而实现对球形SiO_2颗粒的包覆和粘结,明显改善了球形SiO_2颗粒的烧结性能。在1 350℃烧结温度下,随着硅树脂含量增大,型芯样品的失重率不断增大,收缩率反而不断减小;在硅树脂含量为20%时,收缩率仅为0.42%,能较好地保证型芯的尺寸精度;硅树脂含量为10%时,在1 300℃烧结2 h,陶瓷型芯室温抗弯强度为11.8 MPa、线性收缩率为0.49%、显气孔率为30.9%,综合性能最佳。     

Al_2O_3纤维含量对硅基陶芯性能的影响及增强机制

为提高硅基陶瓷型芯性能,将不同含量的Al_2O_3纤维添加至型芯浆料中,采用热压注法造芯,研究不同Al_2O_3纤维添加量下型芯抗弯强度及气孔率的变化,并观察试样断面微观形貌。结果表明,添加Al_2O_3纤维对陶瓷型芯抗弯强度和气孔率影响显著,纤维含量为1%,型芯抗弯强度达到最大值,为20.48MPa;纤维含量为0.75%,型芯气孔率达到最大值为36.16%;纤维添加量超过1%,纤维分散性较差,纤维桥联作用发挥不明显,增强效果削弱。Al_2O_3纤维增强陶瓷型芯包括两种机制:桥联增强和拔出增强。     

聚乙烯醇纤维增强水溶性型芯的制备与性能

以云母粉、NaHCO₃为填料,聚乙二醇为黏结剂,聚乙烯醇（polyvinyl alcohol, PVA）纤维为增强材料,利用热压注法制备了水溶性型芯,研究了PVA纤维含量对水溶性型芯性能的影响。结果表明：随着PVA纤维含量的增加,水溶性型芯的抗弯强度和水溶速率都呈先增大后减小的趋势;当PVA纤维质量分数为1.0%时,型芯的抗弯强度最高,为17.01 MPa;当PVA纤维质量分数为0.5%时,型芯的水溶速率最大,为1.52×10^-3 g/s。同时,随着纤维含量的增加,型芯的抗吸湿性提高。此外,采用扫描电子显微镜分析了型芯断口的微观形貌,并探究了PVA纤维增强水溶性型芯性能的作用机制。     

有机硅树脂粘结Al_2O_3粉制备陶瓷型芯

以球形Al_2O_3颗粒为基体、液态有机硅树脂为粘结剂,通过干压法制备Al_2O_3陶瓷型芯,考察有机硅树脂加入量对焙烧后陶瓷型芯微观组织形貌、物相组成、显气孔率、线性收缩率、体积密度以及抗弯强度的影响。结果表明,1 500℃烧结温度下,有机硅树脂浓度为0.5wt%时,其均匀分布在球形Al_2O_3颗粒周围,此时陶瓷型芯显气孔率为39%、体积密度2.4 g/cm~3、线性收缩率0.7%及抗弯强度35.9 MPa,在硅树脂考察范围内抗弯强度达最高。     

氧化锆纤维对氧化硅陶瓷型芯性能的影响

为提高硅基陶瓷型芯的综合性能,将不同含量的氧化锆短纤维添加至以锆英粉为矿化剂的型芯基体粉料中,通过热压注法制备氧化硅陶瓷型芯,研究型芯收缩率、显气孔率和力学性能的变化,并观察试样断面微观形貌。结果表明,当氧化锆纤维掺入量从0增加到5%,陶瓷型芯试样的室温和1 550℃高温抗弯强度先上升后下降;当氧化锆纤维掺入量为1%时,室温和1 550℃高温抗弯强度最好,分别为18.64 MPa和28.06 MPa,与未纤维强化的陶瓷型芯试样对比,分别提升15.84%和13.46%;氧化锆纤维掺入量为1%的陶瓷型芯试样的收缩率为0.89%,显气孔率为30.4%,高温变形量为0.71mm。分析认为,氧化锆纤维掺入量较高导致纤维的完整性被破坏且出现团聚现象、对基体起割裂作用是陶瓷型芯试样综合性能变差的主要原因。     

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。