纯铜微镦粗过程尺寸效应的试验研究

在微塑性成形试验机上对纯铜圆柱试样进行恒定速度的微镦粗试验。通过热处理和精细线切割技术,设计不同的试样尺寸和晶粒尺寸。分别研究晶粒尺寸和试样尺寸对微塑性成形的影响。研究发现:试样流动应力随着试样尺寸的减小而减小,其减小趋势与表面晶粒体积分数存在线性关系;当试样尺寸较大时,晶粒尺寸对试样流动应力的影响并不明显,而随着试样尺寸的减小,大尺寸晶粒试样的流动应力要明显低于小晶粒尺寸的试样;当试样尺寸较小时,试样在微镦粗过程中表现出明显的不均匀性。通过表面层理论和细晶强化对有试样尺寸和晶粒尺寸变化引起的尺寸效应现象进行解释,同时,引入尺度参数量化由试样尺寸引起的尺寸效应现象,从而对当应变一定时流动应力随着表面层晶粒体积分数φ呈现近似线性变化的原因进行解释。     

100Cr6轴承钢镦粗过程的微观组织模拟研究

为获得合理的100Cr6轴承钢镦粗工艺和优良的成形质量,通过simufact.forming软件对100Cr6轴承钢的镦粗过程进行数值模拟,得到坯料镦粗过程的等效应变、等效应力及温度分布等场量信息,并研究了坯料温度、上模速度、模具温度、摩擦因数等不同工艺参数对其镦粗成形的动态再结晶及晶粒尺寸等微观组织的影响。结果表明:坯料变形大的心部区域晶粒尺寸最小,坯料周边自由变形表层区域晶粒尺寸次之,与上下模具接触的坯料难变形表层区域晶粒尺寸最大;在其他条件相同的情况下,升高坯料温度,坯料平均晶粒尺寸减小,动态再结晶体积分数增大;提高上模速度,坯料平均晶粒尺寸增大,动态再结晶体积分数减小;增大摩擦因数,坯料平均晶粒尺寸减小,动态再结晶体积分数增大;升高模具温度,坯料平均晶粒尺寸减小,动态再结晶体积分数减小。     

纯钛微镦粗过程的试验研究

在微成形试验机上利用自制的模具对纯钛圆柱试样进行微镦粗试验,研究试样尺寸、应变速率对微塑性成形流变应力的影响。研究表明:相同温度和压下速度下,随着试样尺寸的降低,流变应力呈明显的减小趋势,这种现象可以用表面层模型进行解释;流动应力随着应变速率的提高有增大的趋势,这是由于应变速率的提高导致位错与晶格缺陷等的相互作用来不及发生,致使材料的流变应力增大。     

剧烈塑性变形制备高强度高导电纯铜的研究

研究了纯铜多道次反复镦压剧烈塑性变形后的组织、力学性能及导电性能。结果表明,通过反复镦压能在保持试样原始形状和尺寸的情况下在材料内部累积很大的应变,实现材料组织的超细化,退火纯铜经B路线15道次反复镦压变形后,晶粒细化至亚微米级。随镦压次数的增加,纯铜的硬度和抗拉强度明显提高,抗拉强度达到459.1MPa,伸长率明显下降,但仍在20%以上。纯铜的导电率随镦压次数的增加而下降,但15道次镦压后仍然保持在91.7%IACS,说明反复镦压剧烈塑性变形工艺可以制备出具有高强度和良好导电性的块体纯铜材料。     

晶粒取向对微细加工磨削力作用机理及试验研究

微磨削加工中切削深度尺度一般小于被加工材料晶粒大小平均尺度,磨削刃作用在晶粒内部,工件材料表现为各向异性,因此,材料晶粒取向对磨削力作用较传统磨削更加显著,微磨削力的产生机理也会发生变化.为了探究晶粒取向对微细加工磨削力的作用机理,提出泰勒因子模型,量化晶粒取向对流动应力的影响,完善材料的流动应力本构模型.通过研究剪切面晶粒取向与滑移面之间的夹角以及剪切方向与滑移方向之间的夹角关系,确定激活滑移系的数量及类别,从而得到泰勒因子值.基于考虑泰勒因子模型的流动应力本构模型及平行剪切带理论,分析晶粒取向对切屑成形力作用机理并构建解析模型.通过磨棒形貌试验测量数据提取及拟合,提出新的磨棒静态磨粒密度的计算方法,进而构建动态磨粒密度模型.基于单颗磨粒磨削力模型以及磨棒动态磨粒密度模型,构建微细加工磨削力的预测模型.本模型综合考虑微磨削过程中力-热耦合效果、材料微观结构、磨棒形貌以及微磨削加工工艺,并通过微磨削试验对磨削力模型进行了验证.     

气门变体积镦粗工艺分析

针对电镦成形,提出一种变体积镦粗算法,通过有限元程序对电镦成形工艺进行理论分析,并对比分析不同工艺参数对成形的影响,为后续成形工艺的控制提供理论依据.     

加载方式对Cu棒晶粒细化的影响

为研究加载方式对材料晶粒细化的影响,采用试验的方法,从宏观和微观角度分析准静态和磁脉冲加载对纯铜棒镦粗变形规律和晶粒变形的影响。结果表明,加载方式对晶粒细化有重要影响,随着加载速率增加,试样晶粒平均尺寸愈小,细化效果愈明显。在磁脉冲加载条件下,随着放电电压增加,试样变形量增加,晶粒细化效果越显著。在相同变形量时,高电压下晶粒平均尺寸较低电压小,高电压比低电压具有更好的晶粒细化效果。     

气门变体积镦粗的工艺分析

针对电镦成形，提出了一种变体积镦粗算法，通过有限元程序对电镦成形工艺进行理论分析，并针对不同工艺参数对成形的影响做了对比分析，为后续成形工艺的控制提供理论依据。     

法兰轴零件的冷挤镦成形工艺及模具设计

结合冷挤镦工艺的成形特点,对法兰轴零件进行冷挤镦工艺分析,计算毛坯尺寸及冷挤压镦力,并根据DEFORM软件模拟计算对法兰轴成形工艺进行优化。成形模具分为两步正挤压、一步反挤压与镦粗复合,凹模均采用三层预应力组合形式的凹模,凸模尾部锥面即可保证凹凸模的精准对中,又可保证成形零件的表面及内部质量。     

基于DEFORM-3D的微型螺钉冷成形过程有限元分析

典型的螺钉头部成形过程包括镦粗(预成形)和冲槽(最终成形)两个工步,是个比较复杂成形过程.特别是冲槽阶段,镦粗和反挤压同时进行的,情况更为复杂.利用非线形有限元分析软件DF,FOKM-3D对微型螺钉冷塑性成形过程进行仿真,可以获得成形过程中的应变、应力、材料流动情况,同时还可以对成形过程中的缺陷如折叠、裂纹,进行预测,从而为工艺的设计和改进提供信息.     

洁净度和显微组织对管线钢性能的影响

研究了洁净度和组织均匀性对四种管线钢板坯性能的影响。发现洁净度对钢材冲击韧度的影响要高于对强度的影响，提高洁净度可以大幅度提高钢材的冲击韧度。通过测量四种材料晶粒内部和晶界附近的纳米显微硬度，总体来看，晶界附近的硬度通常比晶粒内部高；而这种差别越小，所对应材料的冲击性能越好。     

激光烧蚀金刚石磨粒及其变质层与微裂纹分析

采用声光调Q Nd:YAG脉冲激光烧蚀金刚石磨粒,研究激光参数对磨粒变质层及微裂纹的影响。首先建立传热学数学模型,进行模拟计算,然后通过烧蚀试验和实际检测进行验证,分析其原因,总结出脉冲激光的重复频率是影响变质层和表面微裂纹的主要因素。     

长期服役后乙烯裂解炉管KHR 45A高温氧化现象研究

针对某公司服役30000 h后的乙烯裂解炉管KHR 45A高温氧化现象进行了试验研究。通过光学显微镜和扫描电镜分析了KHR 45A炉管内、外壁附近显微组织变化情况。结果表明:内、外壁附近均有氧化物、剥蚀区和碳化物区三个区域;内、外表层均有连续的Cr2O3层,亚表层SiO2呈树枝状沿晶界向炉管内部扩展,内、外壁附近剥蚀区分别约180μm和280μm;炉管材料内外壁氧化现象与Petkovic-Luton和Ramanarayan模型基本吻合,其内、外壁附近显微组织变化与该模型第Ⅲ阶段一致。     

Low angle boundary migration of shot‐peened pure nickel investigated by electron channeling contrast imaging and electron backscatter diffraction

Study on recrystallization of deformed metal is important for practical industrial applications. Most of studies about recrystallization behavior focused on the migration of the high‐angle grain boundaries, resulting in lack of information of the kinetics of the low angle grain boundary migration. In this study, we focused on the migration of the low angle grain boundaries during recrystallization process. Pure nickel deformed by shot peening which induced plastic deformation at the surface was investigated. The surface of the specimen was prepared by mechanical polishing using diamond slurry and colloidal silica down to 0.02 μm. Sequential heat treatment under a moderate annealing temperature facilitates to observe the migration of low angle grain boundaries. The threshold energy for low angle boundary migration during recrystallization as a function of misorientation angle was evaluated using scanning electron microscopy techniques. A combination of electron channeling contrast imaging and electron backscatter diffraction was used to measure the average dislocation density and a quantitative estimation of the stored energy near the boundary. It was observed that the migration of the low angle grain boundaries during recrystallization was strongly affected by both the stored energy of the deformed matrix and the misorientation angle of the boundary. Through the combination of electron channeling contrast imaging and electron backscatter diffraction, the threshold stored energy for the migration of the low angle grain boundaries was estimated as a function of the boundary misorientation.     

Localization of plastic deformation along grain boundaries in a hardening material

The deformation characteristics of ductile polycrystalline materials at elevated temperatures were studied numerically by considering a square segment of material subjected to different stress modes. The initial polycrystalline microstructure was generated numerically. The micromechanical modeling of the deformation was performed using the material point method. The constitutive behavior was taken to be isotropic, elastic–plastic with linear hardening. To effectively simulate the deformation at high homologous temperatures, the grain boundary region was assumed to be a layer of finite thickness, bearing a lower yield strength than the interior of the grain. Complex deformation patterns were observed. The deformation is dominated by the formation of zones of concentrated instantaneous deformation along grain boundaries. These zones form paths that vary with time, and depend on the microstructure and macroscopic loading mode. The macroscopic stress, as well as the microscopic stresses at various locations within the grain boundary and grain interior, were seen to correlate with the instantaneous deformation pattern throughout the deformation history. For the sample analyzed, with a relatively small macroscopic strain of 0.01, the grain boundary region experienced plastic strains as large as 0.20, a result which provided a strong indication that failure will initiate in the grain boundaries. Implications of this modeling study to actual creep deformation and failure are discussed.     

Electron microscopy study of different stages of oxidation of Ti-47Al-2Nb-2Cr-0.15B and Ti-45Al-15Nb at 900°C

The initial stage of oxidation of Ti-47Al-2Nb-2Cr-0.15B and Ti-45Al-15Nb alloys was studied. Studies reveal that the X and NbCr₂ phases will form in advance in the transition layer of the 2Nb2Cr alloy compared with the 15Nb alloy. The adherence between the nitride layer and underling layer is good. However, an obvious boundary exists between the mixed layer and the inner layer. The recrystallizing of the base alloy leads to an increase of the volume fraction of grain boundaries that can increase the oxidation rate at the initial oxidation stage. An Nb-based compound forms in the transition layer, which can prevent the formation of X phase.     

软性磨粒流磨粒入射壁面过程及其加工特性研究

针对利用两相流模型无法计算高浓度固—液两相流固相颗粒撞击壁面时颗粒速度的问题,提出一种边界层内颗粒运动轨迹计算模型,基于Mixture两相流模型和Realizable k-ε湍流模型仿真计算结果,通过分析提取颗粒入射前速度、计算边界层厚度、建立边界层内速度场和颗粒运动分析可以得到颗粒撞击壁面时的速度和入射角度。分析加工表面动压力分布和磨粒体积分数分布,结合两种结构约束流道验证仿真结果与加工效果的对应关系。通过对试验结果的分析,为约束模块的设计提供依据。研究结果表明:磨粒入射速度、磨粒体积分数和加工表面所受动压力大小直接影响工件加工效果,并与材料去除量成正相关关系;在本次试验中选择的工艺参数导致加工材料去除量小,适合初始粗糙度低的工件表面加工,对于此次试验的初始粗糙度应在0.2μm以下;约束模块的设计除了要考虑磨粒流流场特性之外,还要对加工表面的原始加工痕迹作详细了解,为约束模块的设计及加工工艺参数提供参考。     

ZrO2-6mol%Y2O3陶瓷中四方ZrO2的析出过程及对力学性能的影响

本文深入研究了ZrO 2-6mol%Y 2O 3陶瓷中四方氧化锆（t-ZrO 2）的析出过程,发现在立方氧化锆（c-ZrO 2）基体上析出t-ZrO 2首先是在试样表面的晶界处进行的,其次在其内部晶界、缺陷处成核,最后才在晶内析出,且粒子大小按此顺序排列。T-ZrO 2不仅可以沿[110]c方向析出,而且在某些特定环境下也可沿[100]c方向析出,晶界上析出的大t-ZrO 2在冷却过程中转变为单斜氧化锆（m-ZrO 2）,对材料的力学性能极为不利,只有在晶内析出的弥散分布的t-ZrO 2才有强韧化作用。     

Quantum-chemical investigation of the effect of grain-boundary segregation on wear resistance of steel

Quantum-chemical calculations of polyatomic clusters modeling the grain boundaries in the surface layer of steel are presented. Along with iron atoms, the clusters contain atoms of doping and impurity elements yielded to the boundary due to grain-boundary segregation. The effect of the chemical composition of segregants on the bond strength between the grains and, ultimately, on the wear resistance of steel is investigated. It is shown that the bond strength of segregated atoms with iron atoms in the surface layer of a metal is a substantial factor affecting the wear resistance.     

利用ANSYS的模具线切割加工表面变质层分析

分析了线切割(WEDM)加工表面变质层的影响因素,根据DK7732机床在模具加工中的应用,用有限元软件AN-SYS对线切割加工过程进行温度分布计算,在采用与真实加工相类似的边界条件下,模拟电参数(脉冲宽度)的变化对线切割加工工件表面变质层的影响,得出在实验条件下,按DK7732机床各档脉冲宽度加工时变质层的分布数据,以及其高温层和低温层区域相对较宽、中温区域很窄的结论,有利于后续的工艺探究。同时提出了减少变质层的相应措施。