TiAl合金细小全层片组织形成机理

根据对细小全层片组织及其高温转变中间组织的金相和电镜观察分析结果,提出了一种新的双相钛铝合金层片组织形成机理,即γ／α层片结构在α单相区温度下沿γ相基体中不同取向（１１１）惯习面成束形成,而后在冷却过程中转变为层片团细小的γ／α２全层片组织。     

影响细长薄壁细晶叶片铸造成形因素研究

通过对某发动机超薄细长细晶铸造低压涡轮工作叶片型壳保温方式、型壳预热温度和浇注温度的调整,研究了铸造工艺参数对合金欠铸、冷隔、晶粒度及疏松缺陷的影响.研究结果表明,采用填砂和保温毡包裹对型壳保温,对叶片的欠铸、冷隔和疏松等缺陷的影响相同.当型壳的预热温度高于1 150℃时,导致细长叶片晶粒粗大;而当型壳预热温度为1 100℃,浇注温度为1 450℃时,容易出现欠铸和冷隔缺陷.当采用1 100℃对型壳预热,1 500℃浇注叶片时,能够有效避免冷隔、欠铸、晶粒粗大等缺陷,通过浇冒系统改进,能够解决薄壁细长叶片疏松问题.     

硬型铸造Ti-Al合金的组织与拉伸性能

试验研究了石墨和铸钢两种硬型铸造Ti-Al合金板片状试样的缺陷、层片间距和室温拉伸性能,并与用陶瓷型壳铸造的Ti-Al合金进行对比.结果表明,采用硬型铸造Ti-Al合金在比较高的冷却速度下凝固的板片状试样无宏观和微观裂纹;与陶瓷型壳铸造的组织相比,硬型铸造Ti-Al合金的板片状试样铸态组织平均层片间距大幅度减小,其中石墨型铸造的减小了近一半;由于硬型铸造Ti-Al合金的板片状试样的层片间距的减小使得其室温拉伸强度有较大幅度的提高,其中石墨型铸造板片试样的层片问距减小了0.35 μm,屈服强度提高了40 MPa.     

薄细长细晶叶片冶金缺陷影响因素研究

通过对薄细长细晶低压涡轮工作叶片浇冒系统、型壳预热温度、型壳保温方式和浇注温度的调整,研究了铸造工艺参数及浇冒系统对铸件浇不足、冷隔、晶粒度及缩松缺陷的影响。结果表明,采用填砂或保温毡包裹进行型壳保温,对叶片晶粒粗大、浇不足、冷隔和缩松等缺陷的影响相同。当型壳预热温度高于1 150℃时,导致细长叶片晶粒粗大;而当型壳预热温度为1 100℃,浇注温度为1 450℃时,容易出现浇不足和冷隔。当型壳预热温度为1 100℃,浇注温度为1 500℃时,能够有效避免冷隔、浇不足、晶粒粗大等缺陷,同时,通过浇冒系统改进,能够解决薄壁细长叶片缩松问题。     

基于ProCAST的TiAl叶片缩孔缩松预测及工艺优化

应用铸造模拟软件ProCAST预测了精密铸造Ti-47Al-2Cr-2Nb合金叶片缩孔、缩松的形成情况,并与试验结果进行对照,吻合良好,表明ProCAST软件对缩孔、缩松的预测准确可靠。鉴于单独靠冒口的补缩作用无法全部消除叶片的缩孔缩松,因此通过模拟方法比较了底部铜板+型壳预热法、型壳纵向外加温度梯度法及型壳整体预热法对TiAl叶片缩孔缩松的消除效果。结果表明,最佳的工艺是模壳整体预热法,当型壳预热温度达到1000℃时,能够完全消除叶片的宏观缩孔缩松缺陷。     

缺口对铸造单一取向层片组织TiAl合金断裂行为的影响

研究了缺口对铸造单一取向层片组织TiAl合金断裂形貌特征和断裂机制的影响。通过对断口进行观察发现,缺口对单一取向的层片组织有较大影响。研究表明,在光滑试样的拉伸过程中,裂纹起源于试样内部,然后迅速扩展至断裂;在缺口试样的拉伸过程中,微裂纹于断口边缘产生,在切应力的作用下扩展、连接形成裂纹稳态扩展区,然后在正应变控制下从裂纹稳态扩展区向裂纹失稳扩展区过渡,同时试样失稳。     

型壳预热及浇注温度对某联体叶片铸造成形性的影响

通过对一种多联体导向叶片型壳保温包覆方式、型壳预热温度和浇注温度的调整,完成了某航空发动机用多联体导向器叶片的精密铸造工艺探索。研究结果表明,当仅包覆型壳外表面时,叶片出现冷隔、浇不足问题。当对横浇道及型壳外表面均包覆保温毡后,铸件的成形性较好,但叶身出现裂纹。通过调整型壳预热温度、浇注温度和降低冷却速度的方法使叶片的合格率稳定在80%左右。采用不同的保温包裹方式铸造的多联体叶片微观组织形貌相同,合金性能均能满足铸件标准要求。     

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 本文通过拉伸试验研究了铸造TiAl合金单一取向层片组织在缺口应力集中系数分别为2、3和4时的缺口敏感性。发现,该合金在沿层片界面方向的应力作用下,对应各Kt水平的缺口试样均具有大于光滑试样的抗拉强度,且其缺口敏感系数相当;并根据该合金具有较好的拉伸塑性和缺口拉伸断口上存在裂纹萌生和稳态扩展区域的特征,分析讨论了其形成缺口强化效应的机制。     

单一取向层片组织TiAl合金缺口敏感性的研究

通过拉伸试验研究了铸造TiAl合金单一取向层片组织在缺口应力集中系数分别为2、3和4时的缺口敏感性。发现该合金在沿层片界面方向的应力作用下,对应各Kt水平的缺口试样均具有大于光滑试样的抗拉强度,且其缺口敏感系数相当;并根据该合金具有较好的拉伸塑性和缺口拉伸断口上存在裂纹萌生和稳态扩展区域的特征,分析讨论了其形成缺口强化效应的机制。     

硬模铸造TiAl合金的凝固组织分析

试验观察分析了两种硬模和陶瓷型壳铸造TiAl合金宏观、微观组织特点。结果表明,硬模铸造板片的表面细晶层的晶粒尺寸成倍减小,柱状晶宽度明显变窄,中心等轴晶体积分数大幅度降低、尺寸减小;硬模铸造板片的表面细小晶粒由取向随机的层片团组成,柱状晶由有取向的层片组成,层片方向垂直于柱状晶生长方向,中心等轴晶由取向随机的层片组织组成,层片间距明显减小。     

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.     

新型的治疗阿尔茨海默氏症药物(1-二甲基磷酰基-2,2,2-三氯)-乙基-1-醇烟酸醋对体外神经细胞的作用

目的: 观察本实验室合成的一种治疗阿尔茨海默氏症(AD)的药物(1-二甲基磷酰基-2, 2, 2 -三氯)-乙基^-1-醇烟酸醋(NMF),对体外培养的皮层神经细胞活性的影响以及对海人藻酸(KA)所致的神经损伤的保护作用。方法: 采用体外培养皮层神经元的方法,解剖分离 15 d胚胎小鼠皮层神经细胞, 接种于 96孔板,48 h 后加药并培养 72 h,以 MIT 法 观察 NMF 对小鼠皮层神经细胞活性的影响;同时将接种于 24 孔板的细胞预先给予 NMF,d 3 时加或不加KA处理后,以台盼蓝染色鉴别并计数死、活细胞,可得出细胞的存活率。结果: NMF 明显促进胎鼠皮层神经元活性,其中 NMF1、0. 1、10nmol·L^-1促进神经元活性增殖率分别高达 34.7%、37.4%、36. 7%, NMF 明显促进正常胎鼠皮层神经元存活卒,与对照组比较,10nmol·L^-1 NMF 对皮层神经元的存活率分别提高 39.3%、73.5%。 NMF能显著 对抗 KA 所致的神经元损伤,与 KA 损伤组相比, NMF0.1、10、10nmol·L^-1对损伤皮层神经元的保护率分别为 77.30%、80.10%、84.15%。结论: NMF 明 显促进胎鼠皮层神经元的洁性、提高正常皮层神经元,的存活卒,并能有效地保护KA所致的神经元损伤,提示 NMF 是一种很有潜力的治疗 AD 的药物。     

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.     

Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study

Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial confi guration. The fi nal shape of the ferrite is closely related to the misfi t between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC) method. The strain energy calculation in the framework of Eshelby's inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.     

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.