渗硼层脆性判据K的物理本质

从实验和理论上对显微硬度压痕结合声发射测量渗硼层脆性的合理性及及其脆性判据Ｋ的物理意义进行了讨论，Ｋ值可以反映渗硼层显微压痕裂纹长度随负荷增加的变化率，因而可以表征渗硼层的脆性。根据断裂力学可以导出Ｋ与ＧＩＣ之间存在如下关系：Ｋ＝β（ＧＩ－ＧＩＣ）。Ｋ值间接反映了渗硼层的断裂韧性，可以作为定量评价渗硼层本质脆性的力学参量。     

沿渗硼层不同深度的脆性行为研究

研究了沿渗硼层不同深度扩展的脆性裂纹,发现渗硼层的脆性裂纹扩展具有一定的方向性,且在渗硼外层及过渡区部位易形成并扩展裂纹,脆性较大。用显微硬度压痕结合声发射测量渗硼层各部位En－P直线的斜率K值时发现,沿渗硼层不同深度的K值分布呈“浴盆”状。     

渗硼工艺研究与应用现状及发展

渗硼能够显著提高金属表面的性能，目前的研究方向主要是降低渗硼温度。多元复合渗硼改善渗层显微组织、显微硬度、脆性和耐磨性，以及渗硼共晶化使渗层与基体呈冶金结合，从而改善以往的渗硼层脆性大、容易剥落等问题。     

4Cr13不锈钢渗硼工艺及渗层组织和性能的研究

采用正交试验方法优化4Cr13钢渗硼的渗硼剂和工艺参数，获得了良好的效果。优化后渗硼层组织致密，表面稍有疏松，硼化物显微硬度压痕完整，降低了渗层脆性；硼化物层主要由FezB、(Fe，Cr)2B相和少量的FeB相组成，过渡区形成Fe3(C，B)、Fe4N相及Cr的碳化物，不存在软带现象，有效地强化了对硼化物层的支撑作用．有利于硼化物层与基体的结合；渗硼样的耐磨性明显高于直接淬火样。     

电镀镍及扩散预处理提高渗硼层韧性

渗硼层高温硬度高,抗氧化性能好,但脆性大,提高渗硼层韧性是扩展实际工程应用的关键。文中在45CrNiMoV钢基体上采用电镀镍+高温扩散预处理,在表层形成γ-(Fe,Ni)层后,再用固体渗硼法制备出含镍渗硼层,并与直接渗硼层进行对比。用扫描电镜(SEM)、X射线衍射(XRD)和显微压痕法对镀镍渗硼层的截面形貌,组织结构及硬度分布和断裂韧性进行了研究。结果表明:电镀镍+扩散预处理能显著提高渗硼层的断裂韧性,淬火+低温回火热处理几乎不影响镀镍渗硼层断裂韧性,而对直接渗硼层则有显著降低。镀镍渗硼层中的γ-(Fe,Ni)相能有效缓解冲击载荷,提高渗层断裂韧性。     

碳氮共渗预处理对渗硼层组织性能的影响

研究了碳氮共渗对16Mn钢渗硼层组织结构和性能的影响。结果表明，碳氮共渗预处理使渗硼层的组织、显微硬度分布、脆性、耐磨性比单一渗硼层有明显的改善。碳氮共渗预处理可以得到具有较强支撑作用的过渡层，从而使耐磨性提高。通过复合渗处理的灰砂砖模板，其使用寿命可提高2～3倍。     

表面渗硼层改性的研究

为改善渗硼层脆性,本文以光镜、电镜、显微硬度及断口形貌等分析手段对5CrNiMo钢的渗硼层进行激光改性的研究。着重阐明表面渗硼层激光改性处理前后渗层组织结构的变化与改善渗层脆性之间的内在联系。从而可望探索到在保持高的表面硬化作用的同时,降低渗硼层脆性的一种途径。     

稀土对45钢渗硼层组织和性能的影响

研究了稀土对45钢渗硼层组织和性能影响，并对影响机理进行了初步探讨。结果表明，稀土一硼共渗层的组织、显微硬度、脆性、耐磨性比单一渗硼层明显改善，尤其是耐磨性显著提高，稀土元素(La)在渗层中呈不均匀状态。     

YG8硬质合金渗硼层组织和性能的分析

用Ｘ射线衍射、电子探针、透射电镜和光学金相方法，研究了钨钴类硬质合金渗硼层的硬化机理。结果表明：ａ）钨钴类硬质合金渗硼导致显微组织发生变化，碳化钨颗粒的间距增大，棱角变圆，相对量减少。ｂ）ＹＧ８渗硼层中发现了钴的硼化物和钨的硼化物。前者的硬度为１４００－２０００ＨＶ，后者的硬度为２０００－３１００ＨＶ。Ｃ）电子探针分析表明：渗硼过程中在硼的扩散层内元素重新布，钴向内迁移，钨和碳向外扩散。ｄ）ＹＧ８     

Q235钢电镀镍渗硼层组织及抗高温氧化性能北大核心CSCD

对Q235钢电镀镍层进行渗硼处理,研究其渗层组织特性及抗高温氧化性能。用扫描电子显微镜（SEM）对镀镍渗硼层横断面进行了显微组织观察,用X射线能谱仪（EDS）分析了渗层不同部位的元素分布。结果表明,渗硼层为Fe2B,Ni4B3和Ni31Si12相,渗层厚度为33~254μm,并随着渗硼温度和渗硼时间的增加而增加。用显微硬度计测试渗层的硬度分布,复合层（硼化物和硅化物层）的硬度值约为1753 HV,硼化物层的硬度值为1645~2003 HV,基体硬度为173 HV。镀镍层与镀镍渗硼层经700℃氧化40 h的高温氧化动力学曲线显示镀镍渗硼层的抗高温氧化性能优于镀镍层,Ni3Si,B2O3和Si O2产物起到提高其抗高温氧化性能的作用。     

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.     

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。     

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).     

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.     

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.