冷却速度对快速凝固Ti-48Al-4Cr合金组织转变规律及力学性能

采用单辊旋淬快速凝固设备制备了不同辊速条件下的Ti-48Al-4Cr(原子分数,%)薄带,研究冷却速度对快速凝固Ti-48Al-4Cr合金的组织及力学性能变化规律。结果表明,快速凝固Ti-48Al-4Cr合金凝固在辊速为10和20 m/s时,基体为等轴的γ相,基体中含有少量的B2相、α_2相颗粒和片层组织;辊速进一步增加至30 m/s时,基体转变为α_2相,片层组织消失。快速凝固Ti-48Al-4Cr纳米硬度随着冷却速度的增加而增加,纳米硬度由常规凝固时的5.04±0.09 GPa增加至辊速为30 m/s时的10.48±0.13 GPa。该结果为研究Ti Al合金组织转变,减少Ti Al合金偏析,提高其力学性能提供了基础。     

热处理对快速凝固Ti-48Al-4Cr合金组织影响规律研究

采用单辊旋淬快速凝固设备制备了Ti-48Al-4Cr(at.%)薄带,并在真空封装后进行热处理实验,研究热处理对快速凝固Ti-48Al-4Cr合金的组织演变规律。结果表明,快速凝固Ti-48Al-4Cr合金凝固基体为等轴的γ相,基体中含有少量的B2相、α2相颗粒和片层组织;经723℃保温1h空冷后,亚稳的α2相颗粒失稳,但片层组织仍然比较稳定;热处理温度升高至932℃时,片层组织中的杆状α2相开始按照瑞利分解失稳,分解成大量短杆状或者颗粒状的α2相;在995℃保温1h以后,基体中已较难发现片层组织存在,但存在着排列方向相同的棒状α2相,同时在等轴γ相晶界处发现了数量较多的颗粒状B2相。本论文的研究为进一步研究快速凝固条件下的TiAl金属间化合物的组织与相转变提供了基础,丰富了快速凝固理论。     

热处理对快速凝固Ti-48Al-4Cr合金组织的影响

采用单辊旋淬快速凝固设备制备了Ti-48Al-4Cr(at%)薄带,并在真空封装后进行热处理,研究了热处理对快速凝固Ti-48Al-4Cr合金组织演变的影响。结果表明,快速凝固Ti-48Al-4Cr合金凝固基体为等轴的γ相,基体中含有少量的B2相、α_2相颗粒和片层组织;经723℃保温1 h空冷后,亚稳的α_2相颗粒失稳,但片层组织仍然比较稳定;热处理温度升高至932℃时,片层组织中的杆状α_2相开始按照"瑞利"分解失稳,分解成大量短杆状或者颗粒状的α_2相;在995℃保温1 h以后,基体中已较难发现片层组织存在,但存在着排列方向相同的棒状α_2相,同时在等轴γ相晶界处发现了数量较多的颗粒状B2相。     

冷却速率对含TiB2的TiAl合金凝固组织和力学性能的影响

通过熔模精密铸造制备不同厚度的Ti-48Al-2Cr-2Nb和Ti-48Al-2Cr-2Nb-0.25TiB2合金铸板,研究冷却速率和TiB2添加对合金凝固组织和力学性能的影响.实验结果表明,当凝固速率从37增加至2×102 K/s时,合金的凝固路径并未发生改变.基体合金的晶粒从650细化至300μm,Ti-48Al-...     

快速凝固Ti-48Al合金的组织及纳米硬度(英文)

研究冷却速度对熔体旋转法制备的快速凝固Ti-48%Al合金组织的影响。结果表明:同传统凝固相比,快速凝固明显细化了Ti-48%Al合金的组织,并使合金的成分变得均匀。随着冷却速度的增加,合金的晶粒明显细化。研究薄带厚度、辊速与冷却速度的关系。随着辊速的增加,冷却速度增加,薄带厚度呈减小的趋势。由于细晶强化的作用,快速凝固薄带的纳米硬度随着冷却速度的增加而增加。     

TiAl合金冷却相变研究进展及细晶组织调控

TiAl合金是目前航空航天轻质高温结构的热点材料,其最终显微组织很大程度上决定于其冷却过程。由于TiAl合金相图和相变的复杂性,通过冷却过程控制,获得细晶组织结构成为关注的重要问题。综述了TiAl合金冷却相变的研究成果,并给出了关于Ti-48Al-4Nb-2Cr合金相关的进展:首先介绍了TiAl合金的凝固路径与相变行为,然后分别分析了连续冷却转变(CCT)和等温冷却转变(TTT)行为。进一步建立了Ti-48Al-4Nb-2Cr合金CCT图,并指导获得了一种细晶近片层组织。     

连续冷却条件下Ti-1300合金的组织演变与连续转变图

通过OM、SEM、TEM和EBSD研究了Ti-1300合金在连续冷却条件下组织演变规律和亚稳β相的分解形式,并采用高精度膨胀法建立了合金的连续冷却转变动力曲线。结果表明：当连续冷却速度比较缓慢时,Ti-1300合金发生β → α + β转变,并获得集束状的显微组织;而当冷却速度0.3 °C/s ＜v＜ 1.5 °C/s时,Ti-1300合金发生β → α + β + β_m,并获得细针状的α + β组织和残余的β_m相;当冷却速度大于3 °C/s时,Ti-1300合金基本获得全部β相,所以把3 °C/s认为是合金的临界冷却转变速度。在缓慢冷却过程中,Mo当量梯度是合金中α相生长主要动力。随着冷却速度的增加,Ti-1300合金的显微硬度先增加后降低,在冷却速度为0.3 °C/s时,显微硬度达到最大值。     

Ti/TiAl复合板大压下率热轧复合行为及组织性能研究

采用大压下率包套热轧法成功制备了界面无缺陷的Ti-6Al-4V(质量分数,%)/Ti-43Al-3V-2Cr(原子分数,%)复合板,并对复合板的显微组织和力学性能进行了研究。结果表明,界面区域无明显缺陷,成功避免了Kirkendall现象。复合板界面厚度约为230μm,根据相组成不同,可将界面分为2个区域,其中1区域为近Ti-6Al-4V合金界面处,主要由α/α₂+β/B2组成;界面2区域为近TiAl合金界面处,主要由α/α2+β/B2+γ组成。界面区域组织是由于Ti-6Al-4V合金中Ti元素扩散到TiAl合金层以及TiAl层的Al和Cr元素扩散到Ti-6Al-4V合金层所致。测试了复合板的界面维氏硬度和不同加载方式的三点抗弯强度。结果表明,界面1区域具有最高的显微硬度,横向试件垂直表面加载时复合板表现出最佳的抗弯能力,抗弯强度达到1150.82 MPa。基体和界面区域均为脆性断裂,界面结合处未发生断裂。     

抽拉速率对Ti-48Al-6Nb合金籽晶法定向凝固组织的影响

以Ti-44Al-3Nb-2Si为籽晶,研究了不同抽拉速率对Ti-48Al-6Nb合金籽晶法定向全片层组织的影响。结果表明,6μm/s抽拉速率下,固/液界面为平界面生长,凝固组织中片层方向能够与生长方向保持一致。当抽拉速率增加到15μm/s时,固/液界面以枝晶方式生长,凝固组织中出现非择优<112軈0>取向的α相与择优取向β相共生生长组织。当抽拉速率增加到25μm/s时,α相树枝晶生长将在枝晶间析出β相,破坏定向全片层组织。用Ti-44Al-3Nb-2Si籽晶,低抽拉速率保证高温α相以平界面生长,可以实现Ti-48Al-6Nb合金的引晶。     

快速凝固Al—Ti—Fe系合金的组织演化

采用单辊旋铸技术制备Al-2.5Ti-2.5Fe,Al2.5Ti-2.5Fe-2.5V和Al-2.5Ti-2.5Fe-2.5Cr(at%，下同）合金薄带，利用X射线衍射（XRD）和透射电镜（TEM）分析了这些合金的急冷态和退火态组织。结果表明：快速凝固Al-2.5Ti-2.5Fe合金急冷态组织中存在Al3Ti和Al5Ti2两种初生相，快凝合金经400℃退火10h后，组织中出现了Al13Fe4相，在450℃退火，组织中析出了弥散Al3Ti相；快速凝固Al-2.5Ti-2.5Fe-2.5V合金急冷态组织中存在Al11V相和Al80V20相，400℃退火10h后，初生Al11V相转变为Al80V20相，且固溶在α-Al基体中的Ti,Fe以Al23Ti9相和Al13Fe4相的形式析出；快速凝固Al-2.5Ti-2.5Fe-2.5Cr合金急冷态组织中存在Al3Ti和Al13Cr2两种初生相，快凝合金经300℃退火10h后，组织中析出了Al13Cr2和Al3Ti两种弥散相，400℃退火10h时后组织中出现了Al13Fe4相。     

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.