动态载荷下胞状铝合金的压缩行为

用分段式Hopkison压杆研究了胞状铝合金及胞状纯铝在高应变速率(600～1800s-1)下的压缩行为.试验表明,胞状纯铝的平台应力随应变速率的增大缓慢增加,而胞状铝合金的平台应力对应变速率不敏感,后者在上述应变速率条件下,可以不考虑应变速率的变化,可以静态压缩σ-ε数据作为应用参考.     

应变速率对闭孔泡沫铝力学性能和能量吸收性能的影响

采用分离式霍普金森压杆 (SHPB)技术 ,研究了应变速率 (1× 10 - 3s- 1 ～ 2 5 0 0s- 1 )对泡沫铝力学性能和能量吸收性能的影响。结果表明 :泡沫铝有较高的应变速率敏感性 ,随应变速率的增加 ,泡沫铝的屈服强度和吸能能力增加 ,泡沫铝的应变速率敏感性随应变、应变速率变化幅度的增加而增加。     

时效处理对泡沫铝动态力学性能和能量吸收性能的影响

采用分离式霍普金森压杆 (SHPB)技术 ,研究了时效处理对泡沫铝在高应变速率 (15 0 0s-1～ 2 6 0 0s-1)条件下力学性能的影响 ,并与准静态条件下 (1× 10 -3 s-1)的力学性能进行了对比。结果表明 :时效处理可提高泡沫铝材料的屈服强度 ,但远没有块体材料那么显著 ;时效处理对泡沫铝平台区长短几乎没有影响 ;时效处理可提高泡沫铝材料的能量吸收能力 ,这在泡沫铝用作冲击保护材料时 ,显得尤其重要。     

基于Johnson-Cook模型的TC16钛合金动态本构关系

利用Instron液压实验机和分离式Hopkinson压杆动态加载实验,在温度为298～773K、应变率为0．001～15550／s范围内得到TC16钛合金的准静态拉伸及动态压缩条件下的真应力-真应变曲线,并基于Johnson-Cook模型对其进行拟合分析。提出拟合Johnson-Cook方程的简便方法：即引入材料应力-应变曲线发展趋势项,避免对材料绝热温升的估算。结果表明：真应力随应变速率的增加而增加,随温度的增加而降低;当应变速率为10^5／s及温度高于673K时,材料此时的真应力低于准静态下的真应力;获得TC16动态本构关系,能较好地预测TC16钛合金的流变应力。     

应变速率对含稀土TRIP/TWIP钢变形行为的影响

分析了含RE的TRIP/TWIP钢的变形行为。结果表明:在动态条件下,屈服强度随应变速率的增加呈缓慢上升的态势,但当应变速率达到1×10~3s~(-1)时,屈服强度显著增加;抗拉强度随应变速率的增加而下降,应变速率达到1×10~3s~(-1)时,抗拉强度增加;应变速率愈快,屈服强度与抗拉强度的差值愈小;伸长率则随应变速率的增加在低应变速率下变化不明显,当达到1×10~3s~(-1)时,下降较明显。在1×10~3s~(-1)下的应变速率,屈服强度和n值高于静态下的屈服强度和n值,这说明高速应变下的抗载能力和拉延性更强。     

偻体发泡法泡沫铝制备工艺及性能的研究

本文研究一种新的泡沫铝制备方法－粉体发泡法。其工艺原理为：混合铝粉与一种发泡剂粉末（TiH2)，在一定温度下轴向压缩得到具有气密结构的预制品，加热预吕使发泡剂分解释放出气体迫使预制品膨胀得到泡沫铝。混合、压制和发泡是粉体发泡法的三个重要环节。本论文详细研究了各个工艺过程，确定了其在试验条件下的最佳工艺参数。混合速率250r/min，混合时间大于6h可以保证得到混合均匀的粉末混合物。压力130－150MPa，压制混合400℃－450℃时可以得到具有气密结构的预制品。同时调整发泡工艺中的参数发泡剂用量（1％左右）、发泡温度（600℃－7200℃），发泡时间（3－15min)可以得到不同孔结构的泡沫铝。泡沫铝的吸能能力和其压缩性能紧密相连。在其压缩应力应变曲线上有很长的一段平台区，显示出较大的吸能能力。其吸能能力受孔隙率的影响，随孔隙率呈非单调变化，在某一孔隙率下具有最大的吸能能力。吸能效率随应变的增加先增大后减小，在应变0．1－0．3之间存在一个峰值。泡沫铝的吸能能力和其压缩性能紧密相连。在其压缩应力应变曲线上有很长的一段平台区，显示出较大的吸能能力。其吸能能力受孔隙率的影响，随孔隙率呈非单调变化，在某一孔隙率下具有最大的吸能能力。吸能效率随应变的增加先增大后减小，在应变0．1－0．3之间存在一个峰值。研究了闭孔泡沫铝的导热性能，结果表明泡沫铝的导热性能低于实体铝，其导热性能不仅与孔隙率有很大的关系，而且其它孔结构及其宏观结构的影响也是不容忽视的。     

不同温度下闭孔泡沫铝压缩性能研究

为了探讨不同温度下闭孔泡沫铝压缩性能,将不同孔隙率泡沫铝在-30℃到800℃的温度范围内进行处理,对处理后的试件进行静态压缩试验,分析加温温度对闭孔泡沫铝的力学性能影响。通过试验表明,不同温度处理的泡沫铝的压缩应力应变曲线与常温条件下相同,具有明显的线弹性阶段、屈服平台阶段和强化阶段;当温度低于600℃时,泡沫铝性能变化很小;当温度高于600℃时,泡沫铝表现出明显的温度软化效应,屈服强度和弹性模量明显降低。高温处理后泡沫铝的应力应变公式中引入温度软化项,并应用该公式对不同温度处理后泡沫铝的实验数据进行拟合,拟合效果很好。     

多孔CoCrNi中熵合金的制备和吸能特性分析

本文采用粉末烧结-溶解法成功制备了孔隙率为63%~78%,孔径1.3~2.2mm的多孔CoCrNi中熵合金,借助SEM和XRD对试样的孔形貌和物相组成进行分析,并对试样进行轴向准静态压缩实验研究。结果表明：多孔CoCrNi中熵合金的弹性模量和屈服平台应力均随孔隙率、孔径的增大而减小;相对孔隙率而言,孔径对力学性能的影响程度较低;不同孔隙率的多孔CoCrNi中熵合金其致密应变下单位体积的能量吸收值为34.8~14.3MJ/m₃^,约为泡沫铝的3.8倍,且5种孔隙率的理想吸能效率(I)都接近0.8,说明该多孔CoCrNi中熵合金有潜力成为一种理想的吸能材料。     

应变率和相对密度对泡沫SiCp/ZL104压缩性能的影响

对采用熔体发泡法制备的泡沫5%(体积分数,下同)SiCp/ZL104复合材料进行了准静态和动态压缩性能的测试和分析.结果表明:无论是动态下压缩还是准静态下压缩,泡沫5%SiCp/ZL104复合材料的应力-应变曲线都呈现出典型的3个阶段:线弹性段、平台段和致密段;屈服应力对应变率很敏感,使得应变率增加时,屈服应力增加,且有应变硬化现象发生;随着相对密度的增大,泡沫5%SiCp/ZL104复合材料的动态屈服应力和流动应力与准静态载荷相比显著增加.     

热轧TB2钛合金织构多晶板动态压缩性能的各向异性

利用Instron 电子拉伸机和分离式霍普金生压杠(SHPB)实验装置, 研究了准静态和动态压缩条件下热轧TB2钛合金织构多晶板的力学性能。对TB2钛合金板材的轧向、横向以及轧制平面内与轧向成45°等3个方向进行了压缩实验, 得到了不同应变速率下的应力-应变曲线。结果表明：热轧TB2钛合金板材不同方向上的流变应力均随应变速率的增加而增加, 表现出明显的应变速率强化效应。准静态和动态力学性能均表现出各向异性, 且准静态和动态压缩行为规律不一致。考虑准静态和动态变形时可能的塑性变形机制, 基于微观晶体塑性变形理论, 定性讨论了热轧织构多晶TB2钛合金板屈服强度的各向异性     

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.