SIMA法预变形工艺参数对100Cr6钢晶粒细化的影响

采用轴向多道次镦粗拔长工艺,研究了SIMA法预变形工艺中的锻造比和镦拔道次对100Cr6钢晶粒细化的影响。试验结果表明:随着锻造比和镦拔道次的增加,晶粒的平均直径逐渐减少,晶粒的细化效果越好,在锻造比为2.00,镦拔道次为3次时,试样心部晶粒的平均直径从274.1μm减小到25.0μm,减小了90.9%,试样边部晶粒的平均直径从293.4μm减小到23.1μm,减小了92.1%。;试样边部晶粒的细化效果优于心部晶粒,镦拔道次对试样晶粒的细化效果强于锻造比。研究结果表明,轴向多道次镦粗拔长预变形工艺对晶粒的细化效果显著,镦拔后可以获得晶粒细小的非枝晶坯料,且工艺简单,操作安全,是优良的预变形晶粒细化工艺。     

TC11钛合金镦粗过程的有限元模拟

在求得钛合金(TC11)的应力应变曲线之后,用有限元法模拟钛合金镦粗过程,得到变形过程温度场、应变场.由于钛合金对温度敏感,因而对温度场特别关注.计算结果表明,在加热温度低时,出现"温度小岛"现象,"小岛"区温度高于周围,坯料内温度最高区是坯料中心.实验证明"温度小岛"存在.     

变形工艺对TC11钛合金超塑性的影响

为了研究TC11(Ti-6.5Al-3.5Mo-1.5Zr-0.3Si)钛合金的超塑性变形行为,采用两种改锻工艺细化坯料原始组织,然后在电子拉伸试验机上分别以恒速、恒应变速率和最大m值法进行拉伸实验.结果表明,TC11钛合金在α+β区通过三维镦拔改锻工艺,可以获得晶粒度为6μm的细晶等轴组织,而在β区拔长改锻的组织为粗大的魏氏组织.在变形温度为900℃的条件下,TC11钛合金通过最大m值超塑变形方式获得了异常高的超塑性,最大伸长率达到2300%;而采用常规的恒应变速率和恒速超塑变形,伸长率分别为1147%和1100%.说明TC11钛合金在α+β区通过三维镦拔改锻细化晶粒后,以最大m值超塑变形是获得较好超塑性的有效方法.     

多向镦拔对医用TC4钛合金组织和力学性能的影响

通过实验对TC4方坯进行多向镦拔,对制备的径锻棒材进行组织和力学性能测试分析。结果表明:多向镦拔能有效细化TC4合金组织晶粒、提高力学性能。随镦拔变形量及次数的增加,α相晶粒逐渐细小、等轴化,2火次75%变形量多向镦拔可获得α相晶粒为5μm;3火次75%变形量多向镦拔变形下,准65mm径锻棒的屈服强度及抗拉强度分别高达940MPa和1015MPa,伸长率为17%。     

航空用超大规格TC18钛合金棒材的制备及组织性能研究

经3次真空自耗电弧熔炼得到规格为φ720 mm的TC18钛合金铸锭,再经80 MN快锻机开坯锻造和多道次镦拔锻造,成功制备了航空用φ500 mm超大规格棒材,并对其组织均匀性及力学性能稳定性进行了评价分析。结果表明：TC18钛合金铸锭头、中、尾不同部位的主元素极差在0.1%以内,成分均匀性良好;TC18钛合金棒材不同部位的低倍组织均匀模糊,高倍组织呈现出典型的双态组织,且组织均匀一致性良好;棒材不同部位的力学性能差异较小,具有良好的性能稳定性。     

基于圆环镦粗法的TC4钛合金热成形摩擦因数测定

为了准确测定玻璃润滑涂层的摩擦因数,通过分析圆环镦粗变形理论,修改传统DEFORM-3D有限元模型并完成TC4钛合金圆环镦粗正交数值模拟,得到3种摩擦因数标定曲线.对比分析了理论解析、传统有限元模型和改进有限元模型数值模拟所得3种摩擦因数标定曲线的差异性和分散度.研究了坯料温度、模具温度、镦粗速度和热传导系数工艺参数对...     

加工工艺对TC4-DT合金组织和性能的影响

研究不同锻造工艺(三火次镦拔、五火次镦拔、五火次镦拔+中间β均匀化处理)对TC4-DT钛合金显微组织和力学性能的影响,对比分析了不同锻造工艺的微观组织和力学性能的关系.结果表明,与常规锻造和常规均匀锻造相比,采用常规均匀锻造+β均匀化处理(C工艺)的组织在普通退火后具有与力学性能的最佳匹配,并且在后续的变形过程中,随着变形量增大,C工艺由于畸变能以及再结晶的作用产生了许多细小的等轴组织,因此采用C工艺具有细化晶粒的作用,对提高合金的整体性能有益.     

连续变断面循环挤压TC4钛合金的变形模拟北大核心CSCD

采用Deform软件模拟TC4钛合金棒材以连续变断面循环挤压细化组织效果较好的一组参数:变形温度800℃,挤压速度2 mm/s,6道次循环变形时的应力场、应变场及温度场。结果表明,随着变形循环道次的增加,应变量随之增加,在圆柱坯料高度方向的中间区域等效应变分布较为均匀;对比同一变形循环的挤压工序与镦粗工序,挤压工序的等效应力稍大;此外,变形试样中心区域的温度较高且为大变形区,其原因是试样外表面与模具之间存在热交换而导致试样表面温度较低。但就整体而言,试样变形量分布还是相对均匀,这与其显微组织及显微硬度沿径向分布较均匀的试验结果一致。     

连续变断面循环挤压TC4钛合金的变形模拟

采用Deform软件模拟TC4钛合金棒材以连续变断面循环挤压细化组织效果较好的一组参数:变形温度800℃,挤压速度2 mm/s,6道次循环变形时的应力场、应变场及温度场。结果表明,随着变形循环道次的增加,应变量随之增加,在圆柱坯料高度方向的中间区域等效应变分布较为均匀;对比同一变形循环的挤压工序与镦粗工序,挤压工序的等效应力稍大;此外,变形试样中心区域的温度较高且为大变形区,其原因是试样外表面与模具之间存在热交换而导致试样表面温度较低。但就整体而言,试样变形量分布还是相对均匀,这与其显微组织及显微硬度沿径向分布较均匀的试验结果一致。     

变形工艺对纯Mo棒组织和横向弯曲性能的影响

通过弯曲性能测量、金相、SEM以及TEM观察对不同工艺锻造的纯Mo棒横向弯曲性能及组织进行了研究.结果表明:纯Mo棒直接拔长时,随着变形量的增加,其横向塑性变化不大,纵向晶粒逐渐被拉长,当变形量达到96%时,出现明显的纤维组织,断口呈冰糖状.若纯Mo棒在1100℃镦粗50%再拔长到φ45mm,这样反复进行三次,随后在此温度下从φ45mm直接拔长到φ18mm,其横向组织与直接拔长后的相比变化不大.纵向晶粒虽有拉长,但较直接拔长的晶粒长宽比要小,且晶粒不规则程度增加,此锻造工艺仍然不能有效改善其横向塑性.若纯Mo棒在1100℃先镦粗50%再拔长到φ45mm,反复进行三次后,再将在此温度下从φ45mm直接拔长到φ18mm的纯Mo棒镦粗50%后,其横向塑性可得到大幅度提高,弯曲变形量5%;金相观察表明,其横向晶粒边界变得不很明晰,扭曲程度加重;而纵向晶粒之间晶界相互穿插程度较为严重;其弯曲断口以穿晶断裂为主,断口上有大量的解理面,具有明显的河流状花样和解理台阶;TEM观察表明,其大部分区域以亚晶组织为主,部分区域存在位错胞组织且缠结有大量位错线.     

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.