钢中贝氏体相变机制的研究

简要地总结了国内近年来在贝氏体相变理论研究方面的主要成果,包括以下方面;(1)发现钢中的贝氏体超精细结构;(2)贝氏体表面浮突完全由贝氏体铁索体长大过程中形变产生,单一超亚单元对应的浮突呈帐篷型;(3)贝氏体铁索体宽面上存在三维巨型台阶,在近N—W关系下相变单元宽面接近(335)f,为扩散型界面;(4)发现钢中贝氏体碳化物在α／γ界面的γ侧形核并向奥氏体内生长;(5)建立了贝氏体激发形核一台阶长大模型,理论计算表明这种机制是合理的,它成功地解释了贝氏体的多层次复杂结构,以及上贝氏体、下贝氏体等不同形态的形成原因等。     

贝氏体和马氏体相变及应用的研究

系统总结了清华大学相变及复相新材料研究组近年来在贝氏体相变领域关键性的最新研究成果，包括三维巨型及纳米台阶存在的客观性和普遍性、台阶阶面的可动性、贝氏体片条的内部超精细结构、贝氏体浮突的特征及本质、贝氏体碳化物的来源及形成模型、马氏体浮突的扫描隧道显微镜（ＳＴＭ）及原子力显微镜（ＡＦＭ）研究；进一步论述贝氏体相变的激发形核－台阶长大（ＳＮＬＧ）机制，并用ＳＮＬＧ机制解释了贝氏体的多层次复杂亚结构；同时，还论述了空冷贝氏体／马氏体复相钢的工业应用。     

Cu—Zn—Al合金贝氏体及马氏体表面浮突的扫描隧道显微镜研究

首次用扫描隧道显微镜（ＳＴＭ）观察了ＣｕＺｎＡｌ合金的贝氏体和马氏体表面浮突，发现贝氏体浮突是由许多亚单元组成的浮突群，单个亚单元浮突呈“Ｖ”型，不同于马氏体相变不变平面应变的“Ｎ”型浮突，从而说明贝氏体不可能切变形成。同时在实验结果的基础上，提出了贝氏体激发形核－台阶生长的形成机制     

贝氏体和马氏体浮突的扫描隧道显微镜研究

本文首次用扫描隧道显微镜（ＳＴＭ）研究了Ｆｅ－Ｃ－Ｃｒ钢中贝氏体和马氏体浮突的形态，利用ＳＴＭ所独具的优异的纵向分辨率，发现贝氏体浮突实际上是贝氏体的亚片条，亚单元及超亚单元造成的表面浮突所组成的浮突群，完全不符合马氏体浮突的不变平面应变特征，说明了贝氏体相变不可能按切变机制进行。     

贝氏体相变的形核与长大——贝氏体相变新机制(一)

研究贝氏体形核长大具有重要理论价值。实验观察了贝氏体的形核,从块状贝氏体形成机理研究起,延伸到各种碳含量钢的贝氏体相变机制,指出在超低碳钢中是γ→BF相变,在其他钢中是贫碳区(γ)→BF相变,本质上相同,仅仅组织形貌不同。奥氏体中存在贫碳区,依靠涨落形成贫碳区,贝氏体铁素体在贫碳区中形核。形核地点优先选择奥氏体晶界,仅下贝氏体可在晶内形核。计算了临界晶核尺寸和形核功。贝氏体形核-长大是界面上原子非协同热激活跃迁过程。超低碳贝氏体可呈块状、条片状,增加碳含量时,则以亚单元方式形成贝氏体铁素体(BF),形貌从块状向条片状演化。     

贝氏体相变简介

钢、有色合金和一些陶瓷材料中都存在贝氏体相变。贝氏体钢正成为有益的工程材料。总结评述切变学派和扩散学派作者们以形貌、动力学或晶体学对贝氏体相变机制所持的论点。钢中贝氏体相变以过饱和铁素体开始形成之说迄未得到支持。一些实验已发现替代（置换）型合金元素在相界面上的偏聚，并以此所呈现的拖曳效应说明相变的不完全现象，切变学者以切变机制来解释这个现象，但此现象不是钢中贝氏体相变的普遍情况。贝氏体形成时呈现帐篷形浮突，不具不变平面应变特征；有时马氏体相变晶体学表象理论能近似地应用于贝氏体相变晶体学，但不能以此来判定其相变机制为扩散或切变。溶质拖曳效应以及高分辨电镜对相界面结构实验、热力学研究、磁场和应力场对贝氏体相变影响以及一些预相变现象都确证贝氏体相变籍扩散机制进行。本文作者定义贝氏体为：在Ms温度以上，经扩散相变的产物，多呈片状，形成时会在自由表面上呈现帐篷形浮突。提出贝氏体相变机制进一步研究和应用的展望。     

锰硅系贝氏体／马氏体复相钢中贝氏体精细结构的研究

利用原子力显微镜（AFM）、扫描隧道显微镜（STM）、透射电子显微镜（TEM）、光学显微镜（OM）等分析手段对锰硅系贝氏体／马氏体复相钢中贝氏体的结构进行了研究。观察到氏碳锰硅钢中的贝氏体组织由亚片条、亚单元组成,利用原子力显微镜（AFM）及透射电子显微镜（TEM）在贝氏体单元中发现有以残余奥氏体膜为分界面的精细结构的存在。观测结果可用贝氏体相变的激发形核－台阶长大机制做合理解释,为锰硅系贝氏体／马氏体复相钢的合金组织设计、组织结构和性能关系的研究提提供了实验依据。     

钢中贝氏体相变研究新进展

最近支持扩散或切变机制的学派都提供了很多实验观察的事实和理论计算的结果。目前对贝氏体相变机制争论的重点在于:碳原子和合金元素原子在贝氏体相变时的行为,贝氏体的形核理论和整体动力学,贝氏体相变造成的表面浮凸及贝氏体相变晶体学等。对最近这些方面的研究成果以及外界条件(应力、磁场)对贝氏体相变的影响总结分析后发现,钢中贝氏体相变机制可能与钢的成分和相变温度相关而非单一的相变机制。日后需对贝氏体相变与钢的成分和温度之间的关系进行深入研究而并不是仅限于论证贝氏体是由单纯的扩散还是切变机制形成。     

贝氏体与马氏体相变及应用的研究

系统总结了清华大学相变及复相新材料研究组近年来在贝氏体相变领域关键性的最新研究成果，包括三维巨型及纳米台阶存在的客观性和普遍性，台阶阶面的可动性，贝氏体条的内部超精细结构，贝氏体浮突的特征及本质，贝氏体碳化物的来源及形成模型，马氏体浮突的扫描隧道显镜及原子力显微镜研究。     

Fe—C—Si—Mn合金中贝氏体表面浮突的精细结构

用扫描隧道显微镜对Ｆｅ－Ｃ－Ｓｉ－Ｍｎ合金中的下贝氏体浮突进行了观察研究。发现用透射显微镜观察到的最小结构单元－－亚单元是由更小的超亚单元组成的。超亚单元的浮突为“帐篷”型,而非不变平观应变型,表明它不是切变形成;超亚单元的浮突高度为６０－１４０ｎｍ,最大形状变型量约为０．２３,贝氏体的多层次结构以及合金元素Ｃ和Ｓｉ对它的影响可用激发形核－台阶生长机制来解释。     

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.