激光熔覆工艺参数对TiC_p/Al表层复合材料的影响

研究了激光功率、扫描速度对原位合成TiCp/Al表层复合材料与基底的界面结合和熔覆层组织均匀性的影响。通过调整工艺参数 ,获得了有良好冶金结合的界面和TiC颗粒分布均匀的熔覆组织。结果表明 :在激光功率一定时 ,过低的扫描速度将使激光束前端一定距离内的基底材料在表面熔化前被加热时间太长 ,以致表面氧化 ;而过高的扫描速度会使靠近界面处的粉料中合成反应不能充分完成而残留一些粉末 ;这两种情况都影响了熔覆层和基底的结合。随着激光输入比能的降低 ,熔覆组织的均匀性降低 ,这是由于合成反应未充分完成所致。当激光功率为 2 2 0 0～ 2 5 0 0W ,扫描速度为 7～ 10mm/s时 ,在ZL10 4合金表面可获得组织均匀、界面结合良好的TiCp/Al复合材料熔覆层。     

氩弧熔敷原位合成TiCp/Al基复合涂层组织及性能分析

利用氩弧熔敷技术,在ZL104合金表面原位合成了TiCp/Al复合材料涂层,利用x射线衍射、扫描电子显微镜及显微硬度计,研究了熔敷层的显微组织及性能.结果表明,(Ti+C)含量在30%以下时,复合材料涂层组织由TiC颗粒和块状的Al3Ti组成;当(Ti+C)含量在30%以上时,氩弧熔敷过程中可以充分反应合成TiC颗粒;...     

激光熔覆工艺参数对TiCp／Al表层复合材料的影响

研究了激光功率,扫描速度对原位合成TiCp/Al表层复合材料与基底的界面结合和熔覆层组织均匀性的影响。通过调整工艺参数,获得了有良好冶金结合的界面和TiC颗粒分布均匀的熔覆组织,结果表明,在激光功率一定时,过低的扫描速度将使激光束前端一定距离内的基底材料在表面熔化前被加热时间太长,以致表面氧化,而过高的扫描速度会使靠近界面处的粉料中合成反应不能充分完成而残留一些粉末;这两种情况都影响了熔覆层和基底的结合。随着激光输入比能的降低,熔覆组织的均匀性降低,这是由于合成反应未充分完成所致。当激光功率为2200－2500W,扫描速度为7－10mm/s时,在ZL104合金表面可获得组织均匀,界面结合良好的TiCp/Al复合材料熔覆层。     

反应合成TiC_p/LY12复合材料的显微组织及界面结构

通过扫描电镜 (SEM )和透射电镜 (TEM) ,研究了TiCp/LY12复合材料的显微组织及反应合成TiC颗粒与Al基体的界面结构。发现反应合成的TiCp 为面心立方 ,其形状细小圆整 ,多为近球形体。TiCp 与Al基体的晶体学关系为 :(2 —2 —0 ) Al∥ (0 2 —2 —) TiC及 [0 1—1—]Al∥ [0 11]TiC。力学性能测试结果表明 :反应合成TiCp/LY12复合材料的抗拉强度和屈服强度分别比基体LY12铝合金提高了 30 %和 47% ;而延伸率仍能达到 4.3% ,表现出良好的综合力学性能     

反应合成TiCp/LY12复合材料的显微组织及界面结构

通过扫描电镜(SEM)和透射电镜(TEM),研究了TiCp/LY12复合材料的显微组织及反应合成TiC颗粒与Al基体的界面结构.发现反应合成的TiCp为面心立方,其形状细小圆整,多为近球形体.TiCp与Al基体的晶体学关系为(2-2-0)Al∥(02-2-)TiC及[01-1-]Al∥[011]TiC.力学性能测试结果表明反应合成TiCp/LY12复合材料的抗拉强度和屈服强度分别比基体LY12铝合金提高了30%和47%;而延伸率仍能达到4.3%,表现出良好的综合力学性能.     

激光熔覆原位合成TiC/Al复合材料的化学反应机制

通过突然停止激光发射的实验方法，研究了经高能球磨活化的Al、Ti和C粉末在激光熔覆条件下TiC合成反应的过程及规律。结果表明：激光辐射的前沿区的组织可以被分为未反应原始粉末区、合成反应过渡组织区及TiC／Al复合材料区。依据组织及结构的分析，活化粉末在激光条件下的合成反应过程及机制得以揭示：原始粉末首先在过渡区发生了3Al Ti→Al3Ti反应，所有的Ti都参与了这一反应，形成了块状的Al3Ti／Al组织，所有的C元素都包裹在了这种块状的组织中；随后发生了Al3Ti C→TiC 3Al反应而形成TiCp／Al复合材料。     

激光熔覆合成TiCp／Al过程反应热焓的确定和计算

为深入研究激光熔覆反应合成TiCp／Al复合材料过程，数值计算该过程的温度场和流场时需将所发生的化学反应热纳入计算。因此本文采用在试样扫描过程中突然停止激光发射的办法，得到反应过程中不同阶段所形成的组织，进而判断出各阶段所发生的反应；利用差热分析法(DTA)和热力学计算法确定反应热焓值。研究表明：激光熔覆条件下Al-Ti-C粉料层中合成反应的过程为：先发生3Al Ti→Al3Ti反应，再发生Al3Ti C→TiC Al反应。3Al Ti→Al3Ti的反应热为146．63kJ／mol，Al3Ti C→TiC Al的反应热为38．60kJ／mol。该反应热焓值可用于温度场和流场的数值模拟计算。     

激光熔覆原位合成TiCp／Al复合材料中TiC体积分数的定量测定

激光熔覆原位合成TiCp/Al表层复合材料中生成的TiC颗粒尺寸很小（400－800nm),这给TiC体积分数的定量测定带来了困难。文章分别使用了两种方法对TiC的体积分数进行测定：（1）使用XRD与SEM能谱成成分析相结合的方法,在合成反应充分完成的前提下。通过计算求得TiC的体积分数;（2）使用计算机图象处理的方法,将表面未腐蚀试样的SEM图片先用Office软件处理成黑白对比强烈的图片,再在Photoshop下通过对不同灰度像素比例的测定而求得TiC体积分数。实验结果表明,用以上两种方法求取TiC的体积百分数是可靠的,其中第二种方法更易于操作。     

铸造Al-4.5%Cu合金熔体中TiCp的合成反应研究

通过预制块在铸造Al-4.5%Cu合金熔体中的自蔓延反应,制备了TiCp/Al-4.5%Cu原位复合材料,分析了TiC形成的热力学及其原位生成过程。试验结果表明,TiCp/Al-4.5%Cu原位复合材料的拉伸性能比基体合金有大幅度地提高;原位反应生成的TiC颗粒呈小圆片状,平均直径0.15μm,与基体结合良好,无界面有害相。提出了一种新的TiC颗粒合成机制:Al依次与Ti、C发生反应生成Al3Ti和Al4C3,同时放出大量的热引发了TiC的生成;Al3Ti和Al4C3作为中间反应产物,由于热力学上的不稳定,最终被TiC取代。     

TiCp/Al基复合材料中TiC颗粒的合成反应研究

应用自蔓延高温合成 铸造法制备出了TiCp／Al基复合材料；TiC颗粒直接在铝熔体中反应生成，合成的TiC颗粒细小(0．5—2μm)、分布均匀、与基体结合良好。工艺较为简单，反应时间短，碳化钛粒子的损失少，制备的复合材料成分均匀、结构致密；热力学及动力学分析表明TiC的合成分三阶段完成：燃烧前反应、燃烧合成反应、燃绕后反应，其中自蔓延燃烧合成反应是生成TiC的主导反应。     

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.     

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.     

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.