P和稀土复合变质的Mg_2Si/Al半固态组织与性能

在原位Mg2Si/Al复合材料中,通过P和混合稀土复合变质及改变半固态等温热处理的保温温度和保温时间,研究了复合变质及等温热处理对合金组织与力学性能的影响。结果表明,P和混合稀土联合变质后初生Mg2Si的形貌由粗大的十字状结构转变为不规则的多边形,均匀分布在铝基体上。初生相颗粒尺寸由未变质前的83μm减小到约17μm;经过570℃×90min半固态等温热处理后,初生Mg2Si相和α-Al相均转变为近球形,初生Mg2Si相形状因子约为0.96,平均等积圆直径约为16μm,此时材料的硬度(HB)达到最大值,为106。     

Zr元素对过共晶Al-6.2Fe合金组织与高温力学性能的影响

研究了Zr元素对过共晶Al-6.2Fe合金组织和高温力学性能的影响。结果表明,Zr元素对过共晶Al-6.2Fe合金中的初生Al3Fe相具有良好的变质作用。随着Zr元素添加量的增加,初生Al3Fe相的平均颗粒尺寸由176μm逐渐减小到28μm,其形貌也由粗大的针片状逐渐转变为细小的短棒状和颗粒状。随着Zr元素添加量的增加,合金的高温力学性能逐渐提高。当添加0.4%的Zr元素时,合金300℃的高温抗拉强度和伸长率分别为147 MPa和1.85%,较未变质合金性能明显提高。     

热处理对Fe-5Cr-1.4B合金组织和性能的影响

研究了不同热处理工艺对Fe-Cr-B合金显微组织和性能的影响.试验结果表明:Fe-Cr-B合金的凝固组织主要由Fe2B、M7(C,B)3(M=Fe,Cr)、α-Fe及γ-Fe组成,共晶组织呈网状分布.经过淬火处理后,呈网状结构的硼化物发生断裂,基体转变为马氏体,并伴有二次碳硼化物M23(C,B)6析出.当淬火加热温度超过1 050℃,二次碳硼化物析出相的数量减少,宏观硬度和显微硬度随温度的升高而增加,在1 050℃时,达到最大值,超过1 050℃时,硬度略有下降.经过回火处理后,马氏体发生回火软化,基体中继续析出细小二次碳硼化物,硬度相对淬火态下略有下降,并随着回火温度的升高,下降趋势增加,在500℃回火时冲击韧度达到最高值,为7.35 J/cm2.     

Fe含量对金属型铸造Al-Fe合金组织形态的影响

研究了不同Fe含量的Al-Fe合金在金属型铸造条件下的组织形态.在金属型铸造条件下,亚共晶Al-Fe组织由发达α-Al枝晶与枝晶间隙链接呈网状的细小共晶Al3Fe相所组成;共晶Al-Fe合金组织为弯曲针棒状共晶Al3Fe相和共晶α-Al相共生生长组织;过共晶Al-Fe合金随着Fe含量增加初生Al3Fe相的形态由针棒状向针片状再向长针状转变,初生相周围共晶Al3Fe相依附在初生相表面生长而形成离异共晶组织.并对不同含Fe量时合金的凝固过程进行了分析探讨.     

变质和细化工艺对原位Mg_2Si/Al复合材料组织与性能的影响

在原位Mg2Si/Al复合材料中,通过添加稀土Ho、P、混合稀土、Ca对Mg2Si相进行变质(细化)处理,观察变质(细化)前后材料的组织与力学性能变化,确定合适的变质(细化)剂。结果表明:经不同变质剂变质处理后,材料中初生Mg2Si相尺寸都有所减小,变质效果依次为:稀土Ho变质P和混合稀土复合变质P或混合稀土单一变质Ca细化。经稀土Ho变质处理后,初生Mg2Si相转变为不规则的块状或长棒状,共晶Mg2Si变成纤维状,聚集在初生Mg2Si相周围,初生Mg2Si相尺寸达到16μm左右;经稀土Ho处理后,该合金的力学性能有所提升,抗拉强度提升至180 MPa以上,硬度提升至84HB以上。     

Ti对Fe-B-C-Ti系堆焊层组织及耐磨性的影响

采用CO_2气体保护实心焊丝堆焊与喷射送粉的方法在Q235钢表面制备了具有一定耐磨性且无缺陷的韧化Fe-B-C-Ti堆焊涂层,通过金相组织观察,XRD, SEM,硬度测试和磨损试验研究了Ti含量对高碳高硼铁基合金堆焊层的组织及耐磨性的影响。结果表明:Ti元素可抑制过共晶高碳高硼堆焊合金组织中Fe_2B相的形态,能细化初生硼化物和共晶硼化物晶粒,使组织分布均匀,提高堆焊层的韧性。堆焊层以Fe_2B初生相和Fe_2B+(α-Fe)共晶组织为主,同时含有少量的Fe_3(B,C),此组织硬度在HRC63以上,有利于提高堆焊层耐磨性。随着Ti含量的增加,析出相尺寸减小、数量增多、且分布均匀,添加Ti元素可有效提高堆焊层的综合性能。     

脉冲电流对过共晶Fe-C-B合金初生相的影响

研究了脉冲电流对过共晶Fe-C-B合金凝固组织初生相的影响。结果表明,脉冲电流影响过共晶Fe-C-B合金中初生硼化物的形核过程,提高硼化物晶核的形成温度,使过共晶Fe-C-B合金中的初生硼化物提前形核,细化初生硼化物,但不能明显增加硼化物晶核数。在相同的热历程下,脉冲电流不改变试样凝固组织物相组成。     

钛和冷速对过共晶Fe-4.5B-1.0C合金组织细化的影响

借助扫描电镜和透射电镜,研究了钛和冷速对过共晶Fe-4.5B-1.0C合金显微组织的影响.该合金加入钛后,可与钢液中的碳在高温下生成大量的TiC.TiC对初生硼化物和共晶硼化物均有细化作用:一部分作为初生硼化物异质形核核心使其细化,另一部分在基体中嵌入初生硼化物阻碍其生长;嵌入初生硼化物的TiC改变了共晶硼化物依附初生硼化物的特点,使共晶硼化物分布细小均匀.初生硼化物对冷速敏感,髓冷速加快,组织细化显著.     

Ni元素和变质剂对亚共晶铝铁合金组织的影响

采用水冷快速冷却铜模制备含铁0.30％～1.55％(质量分数)的亚共晶铝铁合金,用光学显微镜、TEM和EDX分析方法研究了Fe、Ni元素和变质剂对合金组织的影响.结果表明:随着Fe、Ni含量的增加,合金晶界处共晶化合物增多,二次枝晶增多并相互连接成网状,晶界处颗粒状A19FeNi相呈层状分布.当Fe、Ni含量分别增加到1.55％、1.5％时,组织呈层状分布,并含有粗大针状和长针片状初生相.变质剂A1-Ti-B和稀土元素Ce均可显著细化粗大的含铁初生相,消除枝晶组织,但A1-Ti-B对α-Al相晶粒细化效果不明显,而稀土Ce能显著细化α-Al相与共晶组织.     

元素B对DZ417G合金组织性能的影响

为研究合金化元素B对DZ417G合金力学性能及微观组织的影响,制备了不同B含量的合金,并进行力学性能测试和微观组织形貌观察。结果表明:随着B含量增加,DZ417G合金900℃的抗拉强度和屈服强度均有所降低,塑性先降低后升高。980℃、216 MPa条件下,合金的持久寿命随B含量的提高而降低,760℃、725 MPa条件下,随B含量的提高合金的持久寿命变化不大。随合金中B含量的提高,合金中晶界区域析出碳硼化物数量增加,当合金中的B含量达到0.02%时,在共晶相周边可以观察到珠状硼化物共晶组织。经热处理后合金中γ′相由细小γ′相和粗大的γ′相组成。     

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。