基于双隐层神经网络的边界膜强度计算模型

本文用双隐层ＢＰ人工神经网络建立了丝杆螺母副表面边界膜温度特性的磨损自补偿数学模型。该模型可用于准确地预测温度对边界膜强度的影响。并采用Ｌ－Ｍ规则进行神经网络学习训练可使网络收敛快，误差小。网络输出结果与实验结果比较有极好的吻合性。该神经网络可为工程设计人员在摩擦学设计时提供有效的计算工具。     

Approximate method for calculations using concentration-dependent diffusion coefficients

Standard methods are available for calculating the results of diffusion processes providing the diffusion coefficient is a constant. In fact, the diffusion coefficient changes radically with composition in most alloy systems and therefore the standard methods are not quantitatively applicable. It is shown that a correction can be made for the variation of the diffusion coefficient with concentration by employing a special coordinate transformation. Illustrative calculations for two types of variation of the diffusion coefficient with concentration show that the accuracy of this approximate method is of the order of 20 pct for large changes in the diffusion coefficient. The relation of the present method to that of Wagner is discussed.     

Kinetics of growth of the diffusion layer in nitriding by the thermogasocyclic method

Metal Science and Heat Treatment - Studies were made of the process of regulating the phase composition and structure of the surface layer of Armco iron when it is nitrided by a new...     

Computer program for equilibrium calculation and diffusion simulation

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Controlling Al/Cu composite diffusion layer during hydrostatic extrusion by using colloidal Ag

In this study, intermetallic compound formation at the interface between aluminum and copper during hydrostatic extrusion was simulated by performing a solid state diffusion bonding experiment with various processing parameters, including bonding temperature and pressure and holding time, and by inserting an Ag colloid layer between the aluminum and copper. Regression equations were developed to predict thickness of diffusion layer and interface hardness.An intermetallic compound formed at the interface between the Al and Cu during diffusion bonding at 420 °C and 240 MPa for 60 min, and it was effectively controlled by inserting an Ag colloid. These experimental data will be useful for setting up processing parameters to prepare Al/Cu matrix composite materials by using hydrostatic extrusion.     

Grain boundary diffusion and segregation of Ni in Cu

Grain boundary (GB) diffusion of ⁶³Ni in polycrystalline Cu was investigated by the radiotracer technique in an extended temperature interval from 476 to 1156 K. The independent measurements in Harrison’s C and B kinetic regimes resulted in direct data of the GB diffusivity D_gb and of the so-called triple product P = s · δ · D_gb (s and δ are the segregation factor and the diffusional GB width, respectively). Arrhenius-type temperature dependencies for both the D_gb and P values were measured, resulting in the pre-exponential factors $D_{\mathrm{gb}}^0=6.93\times {10}^{-7}$ m² s⁻¹ and P₀ = 1.89 × 10⁻¹⁶ m³ s⁻¹ and the activation enthalpies of 90.4 and 73.8 kJ mol⁻¹, respectively. Although Ni is completely soluble in Cu, it reveals a distinct but still moderate ability to segregate copper GBs with a segregation enthalpy of about −17 kJ mol⁻¹.     

VNbMoTaWCo高熵合金氮化物扩散阻挡层的制备及其热稳定性

利用直流磁控溅射镀膜机设置不同氮气流量参数,制备VNbMoTaWCoN_x薄膜,氮气流量为20%时,在洁净的硅基底上沉积厚度约为15 nm的VNbMoTaWCoN₂₀高熵合金氮化物薄膜,并在其上面再溅镀一层厚度约为50 nm的Cu膜,最终形成Cu/VNbMoTaWCoN₂₀/Si 三层复合结构。采用四点探针电阻测试仪(FPP)、X射线衍射仪(XRD)、原子力显微镜(AFM)、场发射扫描电镜(SEM)对三层复合结构500 ℃退火前后的方块电阻、物相结构、粗糙度以及表面形貌进行了分析表征,研究了VNbMoTaWCoN₂₀高熵合金氮化物薄膜作为扩散阻挡层的热稳定性。研究结果表明,当氮气流量占比为20%时,VNbMoTaWCo₂₀高熵合金氮化物薄膜为非晶态,且出现了微量纳米晶;此氮气流量占比下制备的薄膜表面平整光滑、致密度最佳、粗糙度数值最小。Cu/VNbMoTaWCoN₂₀/Si三层复合结构进行500 ℃退火8 h后,Cu膜的方块电阻仍然维持在较低的数值,即0.065 Ω/sq,虽然Cu膜发生团聚,但是并未检测到高阻态Cu-Si化合物。VNbMoTaWCoN₂₀高熵合金氮化物薄膜作为扩散阻挡层在500 ℃温度下退火8 h后,表现出了优异的热稳定性。     

AlCrTaTiZrV高熵合金氮化物扩散阻挡层的制备及其热稳定性

为研究氮气含量的变化对AlCrTaTiZrV高熵合金薄膜性能的影响,检验在最佳氮气含量下厚度为15 nm的(AlCrTaTiZrV)N扩散阻挡层的热稳定性.采用直流磁控溅射设备在N型Si(111)基底上溅射不同氮气含量的高熵合金氮化物;选取最佳氮气含量为制备条件,在硅基底上沉积15 nm厚的AlCrTaTiZrVN10...     

Al/Mg扩散层的形成规律和机理

采用镶嵌式扩散偶,在不同退火热处理条件下,对Al/Mg扩散层进行了研究.利用扫描电子显微镜和电子探针观察和分析了扩散层的形态和结构,从扩散、溶解与结晶角度探讨了扩散层的形成机理.结果表明,当580℃保温60 h退火处理后,在Al/Mg界面处形成厚度约265μm、结构为AL/Mg<,2>Al<,3>/MgAl/Mg<,3...     

Interaction mechanism between void and interface grain boundary in diffusion bonding

Abstract

The interaction process between void and migrating interface grain boundary (IGB) in the bonding interface of 1Cr11Ni2W2MoV steel joints produced by diffusion bonding has been examined, and the corresponding interaction mechanism was analysed. The results showed that there were two cases occurring in void–IGB interaction by comparing the IGB velocity with void velocity: if the IGB velocity exceeded the void velocity, the void would separate from the IGB and be trapped inside the grain; otherwise, the void would attach to and migrate with the IGB. It was also found that the void–IGB interaction was related to the radius of void. The bigger voids easily separated from the migrating IGB, while the smaller voids tended to attach to it. The approximate theoretical values of critical radius of voids for separation/attachment were derived, and they agreed well with the experimental values obtained.     

基于离散单元方法的冷轧轧制力计算

考虑了轧制变形区内带钢变形抗力的变化,根据卡尔曼方程,推导了塑性变形区内轧制力的计算公式,为避免直接积分的复杂性,将塑性变形区进行单元划分,分别求解前滑区和后滑区各单元的平均轧制力,将所有单元轧制力之和+入口弹性压缩区的轧制力+出口弹性恢复区的轧制力,得到了总的轧制力。计算结果表明,单道次计算时间t<30ms,在2000组计算结果中,计算值与实测值之间有93.3%的相对误差保持在±10%范围内,预测精度较高,满足冷轧在线控制的要求。     

Rapid calculation of eddy current field Green's function using the matrix pencil method

The paper presents an efficient method to calculate dyadic Green's function of eddy current field in a conducting plate. The spectral domain integrands in vector potential are approximated by a short series of complex exponential functions, and the generalized Sommerfeld integrals (GSI) in vector potential can be evaluated as a closed-form expression. The poles and residues of integrands are obtained by using the matrix pencil method (MPM). The singular-value decomposition and total least-squares method are used to find the poles and residues accurately. An efficient technique of determining the sampling interval is presented. A closed-form expression of the spatial Green's function is obtained straightforward. The variations of different Green's function components with spatial coordinates are studied. The accuracy and calculation speed of the present method are compared with those of numerical integration. It is shown that this method can give an error of <1% at the distance between field-to-source point less than 5 skin depths, and achieve a computation speed of over 100 times faster than numerical integration.     

不可压缩SPH方法模拟非牛顿流边界设置

基于不可压缩SPH(ISPH)算法,针对螺杆挤出螺槽横截面内非牛顿流的计算,对镜像粒子法和静态粒子法两种边界设置方法进行研究。对比分析计算得到的速度场、粘度场、剪切应变率分布发现,使用静态粒子法计算的边界附近粒子的粘度场分布之所以不会剪切变稀,是因为剪切应变率计算的错误造成;而采用镜像粒子法则不会出现这种问题。该研究为不可压缩SPH方法在聚合物挤出加工模拟中的应用打下基础。     

热等静压扩散焊制备耐磨层的组织与性能

采用热等静压粉-固连接工艺,研究了0Cr18Ni1oTi合金与Stellite6钴基粉末经热等静压扩散连接及热处理后,耐磨层的组织、力学性能及界面区元素扩散情况.结果表明,热等静压制备的耐磨层组织均匀,主要由Co、Cr3C2、Cr23C6和CrSi2等相组成;界面处W、Fe、Co、Ni和Cr等元素相互扩散,扩散区宽度为40 μm,形成了良好的冶金结合,其结合强度约为500 MPa;耐磨层硬度达到55 HRC以上.钴基耐磨层具有良好的耐磨性,热处理后,耐磨层材料的硬度及强度有所提高,XRD分析显示有CoWSi、CrSi2和C06 W6C相析出有利于提高材料的硬度.     

Al/Ti扩散层形成的扩散溶解机制

分别在铝组元熔点之下和之上对Al/Ti镶嵌式扩散偶进行退火热处理,形成固-固和固-液扩散偶.利用光学显微镜、扫描电子显微镜和电子探针显微分析仪观察和分析Al/Ti固-固和固-液扩散层的形态和结构,并对其形成微观机理进行了研究.结果表明,Al/Ti固-固扩散层由一层TiAl₃构成;固-液扩散层由TiAl₃单相层与TiAl₃和Al(Ti)固溶体双相层两层构成,双相层TiAl₃和Al(Ti)固溶体的形态自铝向钛呈现规律性变化.Al/Ti固-固TiAl₃扩散层和固-液TiAl₃单相层的形成都是铝扩散溶解到钛中形成以钛为溶剂的Al-Ti固溶体结晶形成的;而Al/Ti固-液TiAl₃和Al(Ti)固溶体双相层是钛先溶解再扩散到液态铝中形成的Al-Ti液溶体结晶形成的.铝液中Ti原子浓度自铝向钛逐渐升高,导致了双相层TiAl₃和Al(Ti)固溶体形态的规律性变化.