纳米材料和纳米结构生长的原位热动力学研究

首次对目标纳米材料的生长过程进行原位在线监测,同时获取了过程的动力学和热力学信息,由热动力学的理论和方法解析了化学反应、单体的形成、成核生长、纳米结构演变的热力学和热动力学参数;揭示热动力学特征与纳米结构,纳米结构演变的不同阶段热动力学变化与阶段纳米结构,阶段热变速率与阶段纳米结构的特征和规律,初步建立了目标纳米材料生长的特征、规律与热动力学参数之间的关系,为纳米材料的可控生长提供了新的技术方法和理论支撑。     

温度对金刚石刀具影响的理论模型和实验分析

为减小大型金属反射镜在金刚石车削中,刀具的热变形对加工精度的影响,研究了金刚石刀具在温度影响下的热变形规律,结合俄罗斯在热力学方面的研究成果,根据金刚石晶体和刀体的热膨胀系数和导温系数的不同,建立了刀具变形量随温度变化的理论计算模型,并采用高精度的热像仪和电感测微仪记录刀具的温度变化和变形量,发现当温度从23．4℃升高到32．1℃时,刀具变形量达到1．48μm．     

热耗散变形下干气密封系统轴向振动稳定性分析

基于非线性振动理论,建立了气膜-密封环系统轴向振动模型,同时考虑了热耗散有热弹变形对气膜厚度和刚度的影响。在特定的工况下,求解并拟合了非线性气膜的轴向刚度和阻尼,获得了一个非线性受迫振动微分方程。在无外激励情况下,通过求解Floquet指数,讨论了系统分岔的问题,分析了螺旋角对系统稳定性的影响,得到了干气密封系统稳定运行的螺旋角范围,并求得螺旋角为75°54′36″时系统发生Hopf分岔。将数据结果与无热耗散有热弹变形、无变形下的数据进行比较。研究结果表明:考虑热耗散有热弹变形下的系统稳定的螺旋角范围比无热耗散有热弹变形和无变形的螺旋角范围更大。热耗散热弹变形下发生Hopf分岔的分叉点位置相比无热耗散有热弹变形和无变形的分岔点更加突出。这与先前利用龙格-库塔法研究的结果一致,从而验证该方法的正确性。其结果说明,热耗散有热弹变形对干气密封系统的稳定运行有一定的干扰,对工程实际具有一定应用价值。     

块状金属玻璃形成能力的研究与进展

大尺寸块状非晶合金的制备和形成能力的表征是目前非晶态合金研究的热点.介绍了科研人员在Inoue经验理论的指导下发现的判定块状金属玻璃形成能力的方法:①用合金摩尔熔化热判定金属玻璃形成能力;②由液相稳定性和抗晶化能力判定金属玻璃形成能力;③由于物理参数研究金属玻璃形成能力.探讨了热力学、动力学和合金液体微观结构3个因素对金属玻璃形成能力的影响.最后指出,块状金属玻璃形成能力的研究是一个比较复杂的问题,应该在积累更多经验的同时致力于研究出一套严谨的理论.     

热耗散变形下干气密封角向摆动稳定性的研究

干气密封系统角向摆动对密封端面造成磨损和影响密封的稳定性,通过数值求解和试验测试来探究密封角向摆动的稳定性规律。基于非线性振动理论,建立了气膜-密封环系统角向摆动模型,同时考虑热耗散变形对气膜厚度和刚度的影响。将气膜刚度和阻尼表示为含有摆角的多项式变量代入振动方程并设置无外激励,利用Floquet指数对非线性振动微分方程进行求解。在热耗散变形下的螺旋角为75°48'32″和无热耗散变形下的螺旋角为75°42'55″时,密封将会发生Hopf分岔,表明考虑热耗散变形下系统稳定运行时的螺旋角范围更大,热耗散变形对螺旋角和分岔点位置有一定影响。选取75°50'和75°两种螺旋角测试热耗散变形下角向摆动对密封端面和泄漏量的影响,发现考虑热耗散变形下螺旋角75°50'的干气密封端面擦痕严重,泄漏量不断增加,无法稳定,相比较螺旋角75°的泄漏量更大,说明热耗散变形对干气密封角向摆动有一定的影响,为干气密封的动态优化设计提供了理论指导。     

计及金属铰链的环形可展天线热-结构分析

空间热环境对环形可展天线在轨服役稳定性的影响很大，时刻变化着的热环境会造成天线温度的剧烈波动，从而导致天线结构的热变形，使得天线的形面精度恶化，影响天线电信号的传输甚至导致天线失效，因此有必要对天线进行热-结构分析。以环形可展天线为研究对象，考虑天线在轨服务环境中的各类因素（包括空间真空、空间低温、微重力和空间热源等），基于斯忒藩-玻尔兹曼定律和傅里叶热传导理论，利用有限元软件建立计及金属铰链的环形可展天线的热辐射-热传导分析模型，研究了环形可展天线的非均匀温度场；基于弹性热力学理论及有限元理论，建立计及与不计及金属铰链的环形可展天线的热变形分析模型，研究了非均匀温度场对环形可展天线形面精度和张力比的影响规律。研究结果表明：相较于不计及金属铰链的环形可展天线，计及金属铰链的环形可展天线的形面精度和张力比均发生恶化，其中形面精度变化值已达到毫米级。研究结果对同类型环形可展天线的热-结构分析有重要的借鉴意义，可为天线的结构设计提供参考。     

金属/陶瓷界面的第一原理热力学研究

系统地阐述了用于金属/陶瓷界面稳定性研究的第一原理热力学方法.首先介绍了第一原理热力学方法的理论基础,在第一原理计算中引入了化学势的概念,通过连接能把第一原理计算值与热力学参数(活度,气体偏压)连接起来,构成了第一原理热力学计算的基本理论基础.其次给出了第一原理热力学方法用于金属/Al2O3界面研究的具体例子,如Ni/Al2O3的界面结构稳定性与环境变量活度、氧偏压和化学势差之间的定量关系,进一步阐述该方法的有效性.     

基于突变理论的机械产品突破性创新耗散结构模型及其评价

为揭示机械产品突破性创新内在的动态演化机制,提出了一种基于突变理论的机械产品突破性创新耗散结构模型及其评价方法.首先叙述了耗散结构理论与熵变;然后应用发明问题解决理论(TRIZ)中的冲突解决原理分析了机械产品突破性创新尖点突变过程,建立了机械产品突破性创新耗散结构模型,指出了机械产品是在一个非平衡的开放系统中,系统内各技术子系统之间非线性相互作用下,以尖点突变的形式产生的宏观的“巨涨落”,从而形成的一种新的有序的耗散结构;最后基于信息熵理论提出了机械产品突破性创新的评价方法.以中药滴丸机为例,对2种不同状态下的滴丸机进行定量分析,结果较好地验证了该方法的合理性.     

低温变形Nb微合金钢铁素体相变的数学模型

以热力学和动力学理论为基础，研究了Nb微合金钢热变形过程中铁素体相的形核及长大过程，在形核速率计算中引入变形储能、晶界凸阶及微合金元素的作用，建立了低温变形诱导铁素体相变的动力学模型，分析了热变形参数和化学成分对相变分数和晶粒尺寸的影响．变形温度的降低和变形程度的增加，促进了α相变过程，相变体积分数增加，晶粒得到细化．C与Mn含量增加的效果则相反．模型应用于热轧带钢生产过程的模拟，计算结果和实测结果吻合良好．     

船舶搁浅于台型礁石场景下双层底纵桁上纵骨变形机理研究

以典型船舶双层底结构中纵桁上的纵骨为研究对象,运用塑性力学理论和数值仿真手段,讨论了纵桁上骨材在船舶搁浅于台型礁石场景下的变形过程和破坏机理。研究中应用LS_DYNA仿真模拟得到结构变形模态和能量耗散结果,在研究变形模态基础上建立底纵桁骨材塑性变形发展过程的数学模型。运用塑性力学理论求解纵桁上骨材变形吸收的结构变形能和平均变形阻力;同时,应用数值仿真结果进行验证。研究得到的纵桁骨材变形阻力和变形能解析计算公式,对船舶双层底耐撞性结构设计和耐撞性能评估都具有一定的指导意义。     

Process of self-organization in metal

Conclusions 1. As a result of special features of the physical and chemical structure the dissipative structure in the solid forms only in a thin subsurface layer of the metal during friction and represents dynamic nonequilibrium interaction of the diffusion flow of climbing dislocation with counterflows of vacancies. This results in inhalation of the dislocations which formed during deformation of the layer (selective transfer).2. In addition to special conditions (selective dissolution), formation of the dissipative structure in the surface layer is supported by the proximity of the surface creating suitable conditions for saturating the layer with the vacancies and for formation of a dislocation sink. The fact that these conditions do not exist in the volume indicates that the dissipation systems are insufficient for organizing the dissipative structure in the volume of the solid.3. If the phase transition in dislocation movement is not completed by the evolution of the structures as in, for example, the system of boundary friction (close system), the development of dissipative subsystems nevertheless may continue (synergetics of the zero order) together with an increase of the degree of chaos.4. Structural adaptability in the closed system of the solid (synergetics of the zero order), generated from the outside or formed naturally during evolution of the structures, may be used to reduce the entropy rate.A. A. Blagonravov Engineering Institute, Russian Academy of Sciences, Moscow. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 2, pp. 19–27, March–April, 1993.     

搅拌铸造SiCp/2024复合材料热挤压-轧制变形组织及性能

利用搅拌铸造-热挤压-轧制工艺制备SiCp/2024复合材料薄板。通过金相观察(OM)、扫描电镜(SEM)及力学测试等手段研究了该复合材料在铸态、热挤压态及轧制态下的显微组织及力学性能,分析了材料在塑性变形过程中显微组织及力学性能的演变。结果表明,该复合材料铸坯主要由80～100μm的等轴晶组成,粗大的晶界第二相呈非连续状分布,SiC颗粒较均匀地分布于合金基体中;热挤压变形后,晶粒沿挤压方向被拉长,SiC颗粒及破碎的第二相呈流线分布特征;轧制变形后,基体合金组织进一步细化,晶粒尺寸为30～40μm,SiC颗粒破碎明显,颗粒分布趋于均匀,轧制变形对挤压过程中形成的SiC颗粒层带状不均匀组织有显著的改善作用。数学概率统计指出,塑性变形有利于提高颗粒分布的均匀性。力学测试表明,塑性变形后,复合材料的抗拉强度、屈服强度和延伸率显著提高。SiCp/2024铝基复合材料主要的断裂方式为:合金基体的延性断裂、SiC颗粒断裂及SiC/Al界面脱粘。     

Microstructural aspects of titanium metal matrix composites in consolidation processing

Foil–fiber–foil (FFF) method together with vacuum hot pressing (VHP) has been used for the development of titanium metal matrix composites (MMCs). Heterogeneous microstructures prior to and following consolidation have been quantified, and the relations to densification behavior investigated. As shown by the results, dramatic variations of the microstructures including equiaxed α, transformed β and Widmanstätten α are obtained during the process according to the fiber distributions. The dependence of microstructures on the consolidation then has been explained in terms of the change in mechanisms such as grain growth and recrystallization that occur with changing levels of inhomogeneity of deformation.     

Graphitization of Spray-formed Ultrahigh Carbon Steels Containing Si during Hot Rolling

The graphitization behavior of ultrahigh carbon steels containing Si in hot rolling processes was investigated. The graphite stringers went mostly through the small pores and generally paralleled to the rolling direction. The influence of alloy elements on graphitization was estimated based on thermodynamics, which showed that Si content was important for graphitization. Graphite stringers nucleated at small pores and grew with carbon diffusion during hot rolling. Alloy contents, pores and hot deformation at γ+Fe3C phase range were the key factors for the formation of graphite. The probable effect of deformation on graphite formation during hot rolling was discussed in this paper.     

奥氏体不锈钢Cr15Mn9Cu2Ni1N连铸坯壳层的热塑性

为认识连铸坯壳层中热塑性的变化及其原因,从奥氏体不锈钢Cr15Mn9Cu2Ni1N连铸坯壳层不同深度区域及芯部制取小型试样,在热模拟试验机上进行高温拉伸试验.结果表明:变形温度高于1050℃时,表层试样断面收缩率较低,由表及里逐渐增加,在距壳层表面27 mm左右处达到最高;变形温度低于1050℃时,壳层各深度区域断面收...     

Thermodynamic costs of dynamic function in active soft matter

Living matter combines complex structures and dissipative processes to achieve dynamic functions that rely on material organization in space and time. In this Review, we discuss recent progress in creating synthetic material systems capable of four such functions–keeping time, powering motion, building structures, and making copies. Chemical oscillators coordinate the temporal activity of material assemblies; molecular motors and active colloids convert chemical energy into mechanical forces and motions; chemical activation of self-assembling components provides temporal control over dissipative structures; information-rich nanomaterials replicate their structures in exponential fashion. These and other dynamic functions cannot be achieved at thermodynamic equilibrium but instead require flows of energy and matter to create and maintain spatiotemporal order. Such systems are captured within the framework of stochastic thermodynamics, which describes the fluctuating thermodynamic quantities of driven systems. Even far from equilibrium, these quantities obey universal relations, which establish fundamental trade-offs between the rate of energy dissipation and performance metrics such as precision, efficiency, and speed. For each function considered, we present a simple kinetic model that offers general insights that inform the design and creation of dissipative material systems capable of dynamic functions. Overall, we aim to bridge experimental efforts in active soft matter and theoretical advances from stochastic thermodynamics to inform future research on material systems inspired by living matter.     

铁基低镍电热合金的热变形行为

利用热模拟技术对铁基低镍电热合金的热变形行为进行了试验研究。绘制出了该合金的高温变形真应力－真应变曲线，并结合热变形后的显微组织分析了影响合金热变形行为的因素，给出了该合金热变形的回复激活能。     

金属热成形过程的综合数值模拟

金属在热成形过程中的微观组织演变是影响产品力学性能的关键因素,该演变过程取决于温度、应变和应变速率。本文基于有限变形理论和微观组织演变的数学模型,建立了能够模拟变形过程、温度变化过程和微观组织演变过程的有限元法,研制了通用的三维有限元计算软件,并在H型钢三维热轧模拟方面进行了深入开发,给出了原材料为C-Mn钢的H型钢热轧过程综合模拟结果。综合对比了8组不同工艺下的热轧实验结果和计算机模拟结果,二者均吻合良好,表明本文方法能够较好地预报金属热成形过程。     

Strain rate effects in the ultrafine grain and nanocrystalline regimes—influence on some constitutive responses

Mounting evidence is pointing to some emerging novel behaviors of metals with ultrafine-grain (UFG) and/or nanocrystalline (NC) microstructures. One such novel behavior is related to the thermodynamic and kinetic aspects of plastic response in the UFG/NC regime. Two inter-related parameters, viz., the strain rate sensitivity (SRS) and the activation volumes of plastic deformation, are used as fingerprints for the thermodynamics and kinetics of plastic deformation. Changes of these parameters with grain size may indicate transition of plastic deformation mechanisms. Therefore, investigations of these phenomena may bring out new strategies for ingenious design and synthesis of UFG/NC materials with desirable properties. In this article, we present a critical review on the experimental results and theories associated with the SRS of UFG/NC metals with different lattice structures, and the influences on some constitutive responses.     

Amelioration of surface cracking during hot rolling of AISI D2 tool steel

Reported is a relationship between a profile edge cracking during hot rolling of AISI D2 tool steel and material and processing parameters. Several months of observation of industrial hot rolling was done for neural network analysis and complemented with equilibrium thermodynamics calculations and laboratory hot deformation tests. Industrial results, in general, show that for the same chemical composition, hot rolling yield decreases with an increased profile aspect ratio. Cr content is significant for the soaking and strongly correlated with a hot workability at upper and lower limits of the hot working temperature range. Laboratory hot compression tests were employed to determine the optimal soaking temperature and to study hot workability to expand safe hot working temperature window.