奥氏体模型钢等温过程中的晶粒长大行为

奥氏体的层错能在较宽的温度范围内与Fe-40Ni合金的层错能相近。含Ni的含量达到40%(质量分数,%)时,Fe-Ni合金的面心立方结构可以保持到室温而不发生相变。运用光学显微镜、透射电子显微镜(TEM)对Fe-40Ni-Ti合金在不同温度等温过程中的晶粒长大行为进行了研究,结果表明:等温150 min,从880℃到1160℃合金晶粒长大缓慢;1220℃左右时,晶粒的长大倾向可以明显观察到;当温度达到1300℃后,等温30 min晶粒迅速长大并粗化。通过透射电镜观察发现,凝固过程中形成的TiN颗粒和应变诱导析出相快速回溶到合金基体中,导致晶界迁移容易进行。利用Fe-40Ni-Ti合金奥氏体模型钢能够模拟高温时奥氏体晶粒的长大行为。     

Fe-40Ni-Ti合金中晶界高温迁移特征

利用金相观察、定量统计及透射电子显微镜分析,研究了含Ti和无Ti的Fe-40Ni合金在高温等温过程中的晶界迁移行为。结果表明:Fe-40Ni-Ti合金原始试样中存在两种析出,分别是凝固过程中形成的尺寸较大的Ti N颗粒及锻压过程中形成的应变诱导析出相,尺寸为10 nm左右。在1100℃等温30 min后,没有发现应变诱导析出相存在。直接观察结果则显示粗大的Ti N颗粒对晶界迁移有明显的阻碍作用,以类似于位错绕过析出颗粒的Orowan机制绕过Ti N颗粒,其主要原因可能是高温时晶界自由能明显各向同性,只有直接面对析出相的局部晶界受到析出相的阻碍,能够发生大曲率弯曲,晶界表现出较强的"柔性",此时析出粒子必然无法对其运动产生强烈的阻碍作用。     

Fe-40Ni-Ti合金等温松弛过程中的微结构演化

利用热模拟技术、金相观察及透射电子显微技术,对Fe-40Ni-Ti奥氏体模型合金850℃变形后等温松弛过程中的应力松弛曲线、微观组织及亚结构演化进行了分析。结果表明:试验合金的应力在松弛过程中各个阶段均高于无Ti的模型合金。松弛200 s时,观察到有再结晶发生;松弛1000 s时晶界周边出现大量的再结晶小颗粒。同时,松弛过程中位错由混乱的状态向多边形结构改变,松弛1000 s时出现完整的位错胞,未溶解的Ti N析出质点在一定程度上阻碍了再结晶的发生。     

超低碳微合金钢中碳氮化物的溶解行为

利用萃取复型,结合TEM和EDX技术,研究了超低碳Nb-Ti微合金钢中析出相粒子在1300℃保温后的回溶行为.结果表明,基体中存在两类析出相:一类为凝固过程中形成的比较粗大的析出相,另一类为应变诱导下产生的析出相,尺寸比较细小.凝固过程中形成的析出相中富Ti,应变诱导下的细小析出相富Nb.在1300℃回溶时应变诱导析出相不稳定,2h后基本不存在,而凝固过程中形成的析出相在回溶48 h后,还存在含Nb的(Nb,Ti)(C,N)复合相.在钢中含Ti的情况下,Nb碳氮化物的稳定性大幅提高.     

应变诱导析出对7050合金连续热变形组织的影响

利用Gleeble 1500热模拟试验机、光学显微镜(OM)、X射线衍射仪(XRD)、透射电镜(TEM)和背散射衍射(EBSD),研究变形工艺对7050铝合金析出相颗粒的影响,以及应变诱导析出颗粒对连续热变形组织的影响。结果表明:变形可使析出相颗粒发生球化,低应变速率促使析出相颗粒细化和再析出,高应变速率则促使析出相颗粒回溶和粗化;在连续热变形过程中,应变诱导析出的细小球形颗粒仍大量弥散分布在合金中,尺寸略有长大,并且析出相颗粒钉扎位错和晶界,晶内取向差变大。变形条带晶粒被细化,合金基体中形成大量多边形亚结构,这可能对铝合金强度和断裂韧性的提高产生积极作用。     

EB-PVD制备NiCrCoAl薄板800℃热处理微观组织研究

对采用电子束物理气相沉积（EB-PVD）技术制备Ni基高温合金薄板800℃真空保温过程中微观组织结构与硬度进行了研究。结果表明：制备态NiCrCoAl合金组织为γ-Ni固溶体，组织均匀细化、无沉淀析出相、无位错，存在孪晶，晶粒中出现大量应变条纹：在热处理态800℃，5×10^-3Pa真空保温过程中，合金组织相结构未发生变化，合金的平面和截面组织呈现层片状结构，存在大量亚结构缺陷——孪晶、少量位错，在800℃保温16h，有少量碳化物沉淀析出物；随着合金保温时间的延长，应变条纹随之消除，沿（220）晶面的晶粒择优取向迅速长大。同时，显微硬度随之降低。     

INTERACTION BETWEEN THE DISLOCATIONS AND STRAIN--INDUCED PRECIPITATES DURING STRESS RELAXATION AFTER DEFOR-MATION OF Fe--Ni--Nb--Ti--C ALLOY

对Fe--Ni--Nb--Ti--C合金在850℃变形后的等温弛豫过程中位错组态的演变以及应变诱导析出过程进行了TEM观察分析. 样品的应力弛豫曲线可以明显地区分为三个阶段, 分别对应应变诱导析出的孕育、形核长大和粗化过程. 变形过程中产生的高密度、相互缠结的位错在等温弛豫过程中密度降低, 并逐渐形成胞状结构. 应变诱导析出在离散位错与胞界的位错网络上均能形核, 但离散位错上颗粒析出密度更大. 析出对位错产生的钉扎作用减缓了位错组态演变的进程. 一旦析出颗粒发生粗化, 则其钉扎作用减弱, 而位错则以绕过机制摆脱析出颗粒的钉扎.     

Fe-Ni-Nb-Ti-C合金变形后等温弛豫过程中位错与析出的相互作用

对Fe-Ni-Nb-Ti-C合金在850℃变形后的等温弛豫过程中位错组态的演变以及应变诱导析出过程进行了TEM观察分析．样品的应力弛豫曲线可以明显地区分为三个阶段，分别对应应变诱导析出的孕育、形核长大和粗化过程．变形过程中产生的高密度、相互缠结的位错在等温弛豫过程中密度降低，并逐渐形成胞状结构．应变诱导析出在离散位错与胞界的位错网络上均能形核，但离散位错上颗粒析出密度更大．析出对位错产生的钉扎作用减缓了位错组态演变的进程．一旦析出颗粒发生粗化，则其钉扎作用减弱，而位错则以绕过机制摆脱析出颗粒的钉扎．     

6082铝合金的淬火特性及微观组织研究

采用末端淬火和中断淬火方式,结合透射电镜(TEM),研究了6082铝合金的淬火特性及微观组织变化特征。结果表明：在末端淬火试验条件下,6082铝合金的淬透深度为15-20 mm;淬火敏感区间的平均冷却速率达20 ℃/s时,合金时效后形成细小弥散的β″相,无沉淀析出带(PFZ)窄小。在中断淬火的高温保温过程中,几乎没有β平衡相的析出,时效后获得了较高的硬度;在中温保温过程中,β平衡相因消耗周围的溶质原子而快速形成并长大,导致时效后合金性能大幅度下降;低温保温过程中,β平衡相形成缓慢,随时间增加,析出数量增多并长大,影响后续时效强化效果。合金在慢冷和保温过程中,析出的β平衡相大多是以富铁相颗粒作为不均匀形核的核心,这是造成合金淬火敏感性高的原因之一。     

形变热处理对Al-Si-Mg铸造合金组织与性能的影响

通过Brinell硬度和拉伸测试以及OM,SEM和TEM的组织观察,研究了形变热处理对Al-12.0%Si-0.2%Mg合金组织与力学性能的影响.结果表明,通过形变热处理可以显著提高试验合金的硬度、强度及伸长率.该合金经500 ℃热挤压、(535±5)℃固溶、160 ℃时效12 h处理后Brinell硬度可达85.7 HBS,抗拉强度为256.3 MPa,伸长率为15.0%.热挤压过程加速共晶Si相发生碎断与球化,细小的Si颗粒分布均匀,结合强化相在时效过程中弥散析出,导致形变热处理条件下合金的强度及伸长率同时提高.SEM和TEM观察显示,合金在热挤压过程中发生了基体Al的再结晶及Si和Mg2Si相的析出.     

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.     

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.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.