DZ125高温合金定向凝固微观组织的CA法模拟

采用伪二元相图法对DZ125多元合金进行了简化,并用二维Cellular Automaton(CA)法模拟了合金定向凝固微观组织.通过采用不均匀连续形核模型,在考虑到枝晶生长动力学的基础上,模拟了不同抽拉速度下合金定向凝固组织形貌,枝晶界面形态以及一次枝晶间距的变化,说明树枝晶竞争生长中存在"分枝"与"淹没"的机制;并且随凝固速率的增加,合金凝固组织从分枝较少的胞状树枝晶向分枝发达的树枝晶转变.模拟的一次枝晶间距从凝固速率为50 μm/s时的132 μm减少到凝固速率为500 μm/s时的69 μm.模拟结果与实验结果吻合较好.     

试样尺寸对定向凝固Al-4%Cu合金固/液界面特征的影响

采用定向凝固方法研究不同试样尺寸对Al-4%Cu合金凝固固/液界面特征的影响.结果表明:当凝固速率v=1 μm/s时,小尺寸试样的平界面更加平直;当v=5 μm/s时,随着试样尺寸的增大,界面形态分别为浅胞-深胞一初始枝晶,同时,试样边缘的组织比中心的组织更不稳定;在相同凝固速率下,小尺寸试样的温度梯度较大,促使界面稳定性提高;试样尺寸的增大引起径向温差增大,促进溶质流动,使试样边缘产生溶质富集,从而使平界面弯曲;由于试样中心排出的溶质大部分流向界面前沿糊状区的液相中,而枝晶糊状区的液相比胞晶的多,因而形成的枝晶界面弯曲程度比胞晶的小.     

Pb-Bi包晶合金定向凝固微观组织演化

对Pb-(26,28,30,34)Bi(质量分数,%,下同)包晶合金进行平界面生长的低速定向凝固到枝晶状生长的高速定向凝固实验,研究了Pb-Bi包晶合金的微观组织形成及其演化。实验结果表明,在温度梯度G=30K/mm条件下,当凝固速度V=0.25μm/s时,初生α相和包晶β相均以平界面生长,凝固组织的演化过程为:单相初生α相→两相竞争组织→β单相。V=0.5μm/s时,定向凝固组织的演化过程为:单相初生α相→胞状α相+胞间包晶β相→α+β两相竞争组织→β单相。在G=20K/mm条件下,当凝固速度V=1μm/s时,初生α相以胞状领先生长,包晶β相则在胞状α间形核生长,并包裹住α胞。当凝固速度增加至V≥2μm/s时,初生α相由胞状转变为枝晶状,包晶β相则在枝晶间包围α枝晶。     

Nb-Ti-Si基超高温合金的组织演化分析

研究了不同凝固速率下Nb-Ti-Si基新型超高温合金的组织演变。结果表明,Nb-Ti-Si基超高温合金由NbSS、α(Nb,X)5Si3和γ(Nb,X)5Si3组成。共晶胞的等效直径和共晶组织的层片间距随着凝固速率的增大而减小。定向凝固试样进入稳态区后的固/液界面演化过程为胞枝状→树枝状→胞枝状。     

铌硅化物基超高温合金整体定向凝固组织和固/液界面形态演化

采用有坩埚整体定向凝固技术研究了铌硅化物基超高温合金在不同过热温度下的定向凝固组织和固/液界面形态演化.研究结果表明:在抽拉速率均为15μm/s的条件下,当过热温度为1950℃时,定向凝固组织由初生铌基固溶体(Nb_(ss))枝晶和耦合生长的花瓣状(Nb_(ss)+γ-(Nb,X)_5si_3)共晶组成;当过热温度为2000和2050℃时,凝固组织为耦合良好的花瓣状共晶;但随着过热温度进一步提高到2100和2150℃,凝固组织演变为粗大树枝状Nb_(ss)和细小共晶.随着过热温度的提高,固/液界面形态出现树枝状界面→胞状界面→树枝状界面的形貌变化.     

抽拉速率对Ti-47Al-3Nb-0.3Si定向凝固组织的影响

采用电阻加热定向凝固炉对Ti-47Al-3Nb-0.3Si合金在抽拉速率为5、15、50、100 μm/s下进行定向凝固试验,并观察和分析不同抽拉速率下的固液界面形貌、过渡区和定向生长区凝固组织.结果表明,抽拉速率为5 μm/s时,固/液界面以胞状界面向前推进,抽拉速率在15～100 μm/s时,固/液界面以树枝状向前推进,且随着抽拉速率的增大,一次枝晶间距减小.当抽拉速率为5～50 μm/s时,片层组织与生长方向夹角为45°,当抽拉速率增加到100μm/s时,片层组织与生长方向基本垂直.利用扫描电镜背散射观察定向生长区形貌发现,抽拉速率等于或大于15 μm/s时,在柱状晶内部或晶界处形成胞状Al偏析,且出现共晶γ相及Ti5(Si,Al)3相.     

生长速度对Ti-45%Al包晶合金定向凝固组织的影响

通过电磁感应加热和液态金属冷却相结合的实验方法制备了Ti-45%Al(at%)包晶合金的定向凝固试样,并观察在不同生长速度下的微观组织和界面形态。结果发现,抽拉速度为10μm/s时,界面以胞晶形式生长,最终组织的α2 γ片层与生长方向垂直;抽拉速度为50μm/s时,观察到明显的枝晶生长界面,α2 γ片层与生长方向成45°夹角。低速下的胞状间距明显大于高速下的枝晶间距,说明快速凝固有利于减小枝晶间距。     

Al-1.5%Cu合金定向凝固界面形态演化（英文）

采用定向凝固方法研究Al-1.5%Cu合金枝晶-胞晶转变界面形态演化。结果表明,与以往的演化规律不同,凝固组织演化是逐步进行的,在抽拉速率为30~1500?m/s的范围内,凝固组织呈现多样化。枝晶-胞晶转变规律如下:枝晶→条带胞状枝晶→细长型胞晶和枝晶的混合组织→细长型胞晶占主导的胞枝混合组织。根据这种现象,进一步从理论方面研究枝晶-胞晶转变。枝晶尖端形状是枝晶-胞晶转变的重要参数,由于枝晶-胞晶转变偏离平衡凝固,因此,在计算过程中考虑非平衡凝固,得到枝晶-胞晶转变发生在尖端半径最小处。     

界面追踪法研究界面能各向异性对定向凝固枝晶生长的影响

运用基于界面追踪法的数值自洽模型研究了界面能各向异性对定向凝固枝晶生长的影响.模拟结果表明,对于给定的凝固条件,对应不同的一次间距Peclect数范围,存在2个不同的界面形态解区间,其中较小的间距Peclect数解区间对应的界面形态类似胞状晶,较大的间距Peclect数解区间对应的界面形态类似枝状晶,界面能各向异性的增大有利于枝晶解区间的扩大.同时,枝晶生长的尖端临界稳定性参数σ^*与界面能各向异性参数E₄存在幂指数关系,并基于Fisher枝晶扩散解,得到包含界面能各向异性参数的枝晶尖端半径表达式:R_IMS=2.5646[（?）]^0.5E₄^-0.1905,ΔT₀=mC₀（k₀-1）/k₀;界面能各向异性增大,枝晶生长界面前沿过冷度减小.枝晶生长稳态一次间距的选择主要取决于枝晶间溶质扩散场的相互作用,而由于界面能各向异性在枝晶尖端作用的局域化,使得界面能各向异性对定向凝固稳态一次枝晶间距影响较小.     

一种镍基单晶高温合金的高温度梯度定向凝固组织及枝晶偏析

采用双区加热和液态金属冷却法 (LMC) 相结合, 对一种含4%Re (质量分数) 的镍基单晶高温合金进行了高温度梯度定向凝固. 结果表明: 与传统的“ 高速凝固法 (HRS) ” (温度梯度G=20-40 K/cm, 抽拉速率V=50-100 μm/s, 一次枝晶间距 λ₁=200-400 μm)相比, 该技术可以显著提高凝固界面前沿的温度梯度 (G=238 K/cm) 和抽拉速率 (V=500 μm/s). 随着抽拉速率的提高, 凝固界面形态呈现出平面、胞状、粗大枝晶和细枝晶形态, 一次枝晶间距不断减小, 通过固态相变析出的γ' 强化相也被显著细化, 当G=238 K/cm, V=500 μm/s时, λ₁和枝晶干γ' 相平均尺寸分别减小到61.3和0.04 μm. 电子探针测定表明, 随着抽拉速率的提高, 枝晶偏析呈现先增大后减小的趋势. 这是高温度梯度条件下, 固相反扩散作用强烈影响元素在枝晶中分布的结果.     

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.