原位TiB2/Fe3Al基纳米复合材料的合成及其晶粒生长动力学(Ⅱ)——热处理过程中机械合金化Fe-Al-Ti-B四元粉体的结构演变与晶粒生长动力学

研究了机械合金化合成的Fe-Al-Ti-B四元粉体在800-1100℃等温热处理过程中的结构演变及晶粒生长动力学,讨论了晶粒生长机制。研究表明,采用机械合金化加后续热处理工艺可以合成原位TiB2/Fe3Al基纳米复合材料粉体。球磨80h的Fe-Al-Ti-B四元粉体在热处理过程中Fe(Al,Ti,B)分解形成纳米晶DO3-Fe3Al及TiB2两个组成相。随热处理温度的升高,Fe3Al晶粒生长由主要受晶界扩散控制过渡到主要受晶格扩散控制。在热处理过程中,Fe3Al晶粒生长的动力学方程为:K=1.5×10-5exp(-578.7×103/RT),晶粒生长受到明显的抑制,原位TiB2/Fe3Al基纳米复合材料粉体的热稳定性高。     

机械合金化过程中Fe50Al50二元系的结构演变

利用高能球磨和后续热处理技术制备纳米晶Fe50Al50(摩尔分数,%)合金粉体.采用X射线衍射、透射电镜和扫描电镜对元素混合粉在机械合金化过程中的结构演变及热处理对合金化粉体结构的影响等进行分析,讨论其机械合金化合成机制.结果表明:球磨过程中Al向Fe中扩散,形成Fe(Al)固溶体.机械合金化合成Fe(Al)遵循连续扩散混合机制;球磨30 h后,粉体主要由纳米晶Fe(Al)构成,晶粒尺寸5.65 nm;热处理导致Fe(Al)纳米晶粉体有序度提高,转变为有序的B2型FeAl金属间化合物,粉体的晶粒尺寸增大,但仍在纳米尺度范围.     

机械合金化及热处理过程中Ti50C50二元系统的结构演变

使用X射线衍射仪（XRD）、透射电子显微镜（TEM）研究了Ti50C50元素混合粉在机械合金化过程中的结构演变以及热处理对粉体结构的影响,讨论了TiC机械合金化合成机制。研究结果表明,机械合金化合成TiC遵循逐渐扩散反应机制,反应首先形成纳米晶Ti（C）粉体,球磨10h析出TiC,随着球磨过程的进行,TiC的量逐渐增多,品格常数增加,晶粒尺寸降低。球磨80h后,粉体主要由纳米晶TiC构成,晶粒尺寸6nm,但仍有少量的Ti（C）剩余。热处理促进残余的Ti（C）转变成TiC,同时导致TiC粉体晶粒生长,晶粒尺寸增大,晶格畸变程度降低,有序度提高。     

机械合金化过程中Fe50Als50二元系的结构演变

利用高能球磨和后续热处理技术制备纳米晶Fe5A150（摩尔分数，％）合金粉体。采用X射线衍射、透射电镜和扫描电镜对元素混合粉在机械合金化过程中的结构演变及热处理对合金化粉体结构的影响等进行分析，讨论其机械合金化合成机制。结果表明：球磨过程中Al向Fe中扩散，形成Fe（A1）固溶体。机械合金化合成Fe（Al）遵循连续扩散混合机制；球磨30h后，粉体主要由纳米晶Fe（A1）构成，晶粒尺寸5．65nm；热处理导致Fe（A1）纳米晶粉体有序度提高，转变为有序的B2型FeAl金属间化合物，粉体的晶粒尺寸增大，但仍在纳米尺度范围。     

双步球磨法制备纳米晶结构TiAl基合金粉末的研究

以元素粉末为起始粉末,采用双步球磨法(球磨+热处理+球磨)制备TiAl基纳米晶多相结构粉末(粉末成分为Ti-47Al(at%)、Ti-45Al-2Cr-2Nb-1B-0.5Ta(at%)).采用xRD、SEM、EDs、DTA、粒度分布仪对两种粉末颗粒在球磨和热处理过程中的特性进行了表征和分析.结果表明,采用双步球磨法制备的多相结构纳米晶粉末杂质含量低,粒度分布均匀,合金元素弥散分布.一步球磨6 h获得Ti/Al均匀复合结构及实现Ti(Al)部分固溶;700℃,2 h热处理获得Ti3Al、Ti、Al3Ti、TiAl相,Al相已经消失;二步球磨实现晶粒尺寸、颗粒尺寸进一步细化.     

Effect of Process Conditions on the Synthesis of TiB2/TiC Nanocomposite Powders by Mechanical Alloying

采用机械合金化的方法利用工业纯Ti粉和B4C粉末合成了TiB2/TiC 纳米复合粉末。结果表明,球磨过程中保护气氛的纯度对合金化过程有着非常重要的影响。在纯氩气保护的情况下球磨5 h,Ti和B4C粉末发生了固相反应,形成了复合TiB2/TiC相,随着球磨时间增加,合成的TiC相的晶粒尺寸减小至10 nm,而TiB2晶粒尺寸略大;如果球磨过程中混入空气,合金化产物中将会出现大量的TiN和TiO     

球磨工艺对原位合成纳米级TiB的影响（英文）

球磨工艺对球磨粉末及其烧结组织的微观结构和形态都有重要的影响。本实验采用低能和高能球磨2种方式对Ti-7Al-0.2B(质量分数,%)合金粉末进行球磨,研究球磨过程中粉末组织和形态的变化,并将球磨后的粉末进行热压烧结,研究不同球磨方式对烧结组织中原位合成TiB增强相形态的影响。研究结果表明:低能球磨过程中,粉末颗粒间有机械合金化发生,其烧结组织中生成的TiB为细长态,在基体中分布均匀,没有联结的粗晶或成簇生长现象。对于高能球磨,粉末颗粒细化效果明显,颗粒平均尺寸降至1μm,球磨过程中除了机械合金化还形成了Ti(Al)过饱和固溶体,并在球磨后期形成了非晶结构。经高能球磨的粉末烧结后,组织中生成了均匀分布的纳米级TiB晶须。     

原位TiB2/Fe3Al基纳米复合材料的合成及其晶粒生长动力学(Ⅰ)--Fe-Al-Ti-B四元粉体的机械合金化

研究了机械合金化过程中Fe-Al-Ti-B四元粉体的结构演变,讨论了其合金化机制.研究表明,Fe-Al-Ti-B四元粉体的机械合金化通过Al、Ti、B原子向Fe晶格中扩散形成Fe（Al,Ti,B）过饱和固溶体.在机械合金化的早期（＜10h）,形成包覆结构的复合颗粒,合金化尚未进行.在机械合金化的中期（10-60h）,首先形成具有几个同心圆环结构的复合颗粒,然后环状结构消失,同时Fe（Al,Ti,B）晶格常数迅速增加,但成分均匀化过程缓慢.在机械合金化的后期（60-80h）,主要发生复合颗粒内部的成分均匀化过程,球磨80h后,复合颗粒内部各组元的成分已经非常均匀.Fe（Al,Ti,B）晶粒细小（6.8nm）,晶格畸变严重,具有近似非晶态的结构.由于Ti、B元素的添加,Fe-Al-Ti-B四元粉体晶粒细化速率更快,但合金化速率明显降低.     

机械合金化合成Invar合金纳米晶粉体

采用商用FeNi30及FeNi50合金粉为原料通过机械合金化(MA)合成纳米晶Invar合金(FeNi36)粉体,研究了不同球磨时间的Invar合金粉体的物相组成、显微组织结构与形貌特征,探讨其合金化机制。结果表明:球磨初期(5~10 h),微锻造和冷焊过程使合金粉体呈扁平形复合层状结构,同时FeNi50中的Ni原子逐渐向FeNi30中扩散,发生成分均匀化;球磨40 h后,已形成了成分均匀的α'-Fe(Ni)固溶体,其平均晶粒尺寸约为12 nm。此时,机械合金化合成的Invar合金粉体呈球形,表面光滑,继续球磨,大颗粒粉体表面出现裂纹,并碎裂,导致粉体细化。     

球磨工艺对原位合成纳米级TiB的影响

球磨工艺对球磨粉末及其烧结组织的微观结构和形态都有重要的影响。本实验采用低能和高能球磨两种方式对Ti-Al-0.2B wt.%合金粉末进行球磨,研究球磨过程中粉末组织和形态的变化,并将球磨后的粉末进行热压烧结,研究不同球磨方式对烧结组织中原位合成TiB增强相形态的影响。研究结果表明：低能球磨过程中粉末颗粒间有机械合金化发生,其烧结组织中生成的TiB为细长态,在基体中分布均匀,没有联结的粗晶或成簇生长现象。对于高能球磨,粉末颗粒细化效果明显,颗粒平均尺寸降至1 μm,球磨过程中除了机械合金化还形成了Ti(Al)过饱和固溶体,并在球磨后期形成了非晶结构。经高能球磨的粉末烧结后,组织中生成了均匀分布的纳米级TiB晶须。     

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.     

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.