纳米晶YG10复合粉末的烧结及显微结构

利用EDS和SEM等研究了机械合金化法制备的纳米晶YG10硬质合金复合粉末的烧结行为,对其致密化规律及显微结构等作了考察。结果表明：纳米晶YG10粉末烧结致密化快,在1375℃时烧结30min,合金相对密度为99．86％,收缩率为27．2％,合金最大硬度可达91．8HRA;烧结合金中WC晶粒细小,呈杆状特征,其径向尺寸约为100～150nm,长度超过1μm,且WC杆状晶粒随机排列,无固定取向。     

钨铜合金粉热等静压致密化过程的有限元模拟

利用DEFORM-2D有限元软件对钨铜混合粉在包套密封条件下的热等静压工艺过程进行了有限元模拟,分析了坯料在该过程的致密化规律;运用交叉试验法制定出保温温度、保压压力和保温保压时间的正交优化方案,绘制出相对密度在温度和压力平面内的等高线云图,进而提出最优的参数方案;根据模拟结果进行了热等静压试验。结果表明:坯料的致密化过程是先边缘后中心;模拟得到最优的热等静压参数方案为950℃/110MPa/2h,在此方案下,坯料整体的相对密度可达到96%以上;在最佳方案下,相对密度的模拟和试验结果的最大误差为1.27%,平均误差约为0.2%。     

22MnB5热变形行为研究及本构方程建立

以22MnB5为实验材料,在500~950℃范围内和应变速率为0.01s-1、0.1s-1、1s-1的实验条件下,采用热模拟机Gleeble-1500对硼钢进行热拉伸实验,研究了不同变形条件下硼钢的热流变行为;对拉断后的试样断面进行组织分析,阐述了不同变形条件下硼钢的组织对热流变行为变化的影响。研究表明：硼钢的热变形行为属于典型的动态回复型,其流动应力随着温度的升高而减小,随着应变速率的增大而增大,且温度对流动应力的影响更显著;在500℃、应变速率0.01s-1的条件下,硼钢高温下的热力学行为与上述规律有所差别,其流变应力高于高应变速率下的流变应力。最后根据高温拉伸实验所得数据,构建了22MnB5热变形的本构方程,以此来描述硼钢高温下的热流变行为。     

一种新型铝锰合金的热压缩流变行为及热加工图

采用Gleeble-3500型热模拟试验机对一种新型铝锰合金进行了应变速率为0.01~10s-1、变形温度为350~550℃的等温热压缩试验,研究了它的热压缩流变行为;基于动态材料模型获得了该合金的热加工图,并研究了其显微组织与变形温度、应变速率之间的关系。结果表明:试验合金的热压缩流变行为可用双曲正弦模型来描述,其激活能为194.757kJ·mol-1;结合热加工图和显微组织得到的试验合金适宜的加工温度和应变速率分别为500~550℃和0.1s-1;在高Z条件下的亚晶为拉长的变形组织,在低Z条件下则形成了低位错密度的完整亚晶结构。     

2618耐热铝合金的热压缩流变应力行为

用Gleeble-1500热模拟机，对高铁、镍含量的2618耐热铝合金的热压缩流变应力行为进行了研究。结果表明：在所给定的热变形条件下，2618合金热压缩变形存在较明显的稳态流变应力特征；在高应变速率(ε=ls^-1)、变形温度为400℃、变形量为60％时，流变应力出现了明显的峰值应力；流变应力越大，2618合金中粗大Al9FeNi相的破碎效果越好。     

用应力松驰法研究微合金钢碳氮化物的应变诱导析出行为

应用应力松驰法在Gleeble2000热力模拟机上研究了新型非调质油井管用钢33Mn2V在600-950℃内含钒碳氮化物的应变诱导析出行为。结果表明：该钢PTT曲线具有双“C”型特征，碳氮化物析出孕育期最短的温度分别约为850℃和600℃；析出相形貌主要为方形和圆角方形，其中方形颗粒是均热过程中未溶解的TiN，圆角方形颗粒是由钒、碳、氯原子以TiN为基底外延生长析出形成的TixV1-xCyN1-y。     

粉末冶金Ti-22Al-25Nb合金的放电等离子烧结工艺数值模拟与实验研究

选用Ti-22Al-25Nb预合金粉末为实验初始原料,采用放电等离子烧结工艺（SPS）制备组织致密的粉末冶金Ti-22Al-25Nb合金。采用MSC.Marc有限元软件对SPS过程中粉末的致密化过程进行了数值模拟,分析了烧结温度、保温时间和烧结压力对粉末致密化过程的影响,揭示了粉末相对密度随烧结温度、保温时间和烧结压力的变化规律。根据模拟结果,在950~1 200 ℃温度区间、50 MPa烧结压力和10~20 min保温时间的条件下,完成系列SPS烧结实验,制备获得Ti-22Al-25Nb合金。系统分析了50 MPa/10 min烧结条件下温度对Ti-22Al-25Nb合金的相对密度、显微组织和力学性能的影响,揭示了烧结合金的断裂机制。实验结果表明烧结合金在950 ℃/50 MPa/10 min条件下具有最优的综合力学性能,延伸率和屈服强度分别达到8.14%和691.04 MPa。     

烧结温度对ZnO压敏陶瓷电性能的影响

为了获得高电位梯度氧化锌压敏电阻片,采用了传统陶瓷烧结工艺制备ZnO压敏电阻,研究不同烧结温度(1135~1155℃)对ZnO压敏电阻器电性能的影响。实验结果表明,随着烧结温度的增加,ZnO压敏陶瓷的晶粒尺寸增大,电位梯度降低且致密度提高。烧结温度为1135℃时,压敏电阻的电位梯度高达329V/mm,漏电流为8μA,致密度为96.4%。当烧结温度为1140℃时,压敏电阻的电位梯度为301V/mm,漏电流为4μA,致密度为96.6%。通过比较烧结温度为1135℃和1140℃的实验结果,发现烧结温度为1140℃时,ZnO压敏陶瓷的综合电性能达到最佳。     

粉末冶金Ti-22Al-25Nb合金的真空热压烧结工艺

以气雾化法获得的Ti-22Al-25Nb（at.%）预合金粉末为初始原料,采用真空热压烧结工艺方法制备组织致密、成分均匀的粉末冶金Ti-22Al-25Nb合金。应用有限元软件MSC.Marc对Ti-22Al-25Nb（at.%）预合金粉末的致密化过程进行数值模拟,分析了温度和压力对Ti-22Al-25Nb粉末致密化过程的影响,揭示了粉末相对密度随温度和压力变化的规律,得到优化的烧结工艺参数,以指导热压实验烧结。通过热压烧结实验制备了组织致密、成分均匀的Ti-22Al-25Nb合金,发现1 050 ℃/35 MPa/1 h条件下烧结的合金具有最优的室温和650 ℃高温综合力学性能。     

GH4169合金高温变形过程本构方程

使用MMS-300热模拟实验机对GH4169合金在变形温度950℃,980℃,1000℃,1020℃,1040℃,1060℃,1100℃及变形速率0.01mm/s,0.1mm/s,1mm/s,10mm/s条件下进行压缩实验。其中,压下率为50%。在热压缩变形过程中,当温度升高或变形速率减小时,流变应力降低。根据不同的热变形参数对流变应力的影响,利用线性回归的方法分析了Arrhenius形式的本构方程,并求出激活能Q=505.649kJ/mol。最终,建立描述GH4169合金热变形规律的本构方程并分析其预测精度。结果表明:在不同热变形参数下,其流变应力的预测值与实验值的符合程度良好,平均相对误差为5.13%,线性相关度为0.977。     

Microscopic approach of powder compaction using finite element method

An approach for simulating microscopic densification behaviour of powder particles in compaction using a finite element method is proposed. In this method, the contacts between powder particles during the compaction are detected, and plastic deformation of the particles is calculated by the finite element method for a porous metal. The finite element mesh is generated by connecting the centres of the particles in contact. It is assumed that the finite elements are porous metals having an average relative density calculated from the volumes of the powder and pore inside the element. The elements are classified into the triangular and quadrilateral ones used in the conventional finite element methods and a linear one for the simple compression. The accuracy of the stiffness for plastic deformation of the particles is improved by applying the finite element method. The calculated plastic deformation of powder particles in plane-strain compaction is compared with that for a model experiment using aluminium rods.     

粉末流动温压过程中粉末堆积数值模拟与优化

基于离散元法,综合考虑重力、接触力、阻尼、摩擦、范德华力等多种作用力的影响,建立了粉末流动温压过程中粉末堆积的数学模型,对相同材料不同粒径的二元颗粒粉末和相同粒径不同材料的二元粉末颗粒的混粉过程进行了研究。通过实验研究和数值模拟的结合,得到了一个不同数量比的二元堆积的密度规律:在大小粒子直径比为10,当小粒子是大粒子数量的300倍时,获得的最大堆积密度为0.824。通过实验验证了相同粒径不同密度的二元粉末颗粒的填充模拟过程,得到了一致的实验结果。研究结果有效地验证了离散元数学模型的正确性及相关数值模拟的实用性。     

Effect of friction between powder and a mandrel on densification of iron powder during cold isostatic pressing

The effects of friction between the powder and the mandrel on densification behavior of metal powder were investigated under cold isostatic pressing. The friction coefficients between the powder and the mandrels with different surface roughness were determined from the relationship between the compaction pressure and the ejection pressure of the mandrel from powder compacts. The elastoplastic constitutive equations based on the yield function of Shima and Oyane were implemented into a finite element program (ABAQUS) to simulate compaction responses of metal powders during cold isostatic pressing. Finite element results were compared with experimental data for pure iron powder under cold isostatic pressing.     

纳米AlN含量对石墨/铜-0.6%铬复合材料性能的影响

首先采用合金化法制备了铜-铬基体合金粉,然后向其中加入质量分数为10%的石墨粉和不同含量的纳米AlN粉,制备了不同含量纳米AlN颗粒增强的石墨/铜-0.6%铬复合材料,研究了纳米AlN含量对复合材料密度、电阻率、硬度、抗弯强度及磨擦磨损性能的影响。结果表明:随着纳米AlN含量的增加,复合材料的抗弯强度及硬度逐渐增加,密度和导电性逐渐降低,磨损量逐渐减少,摩擦因数变化不大;当纳米AlN质量分数为0.5%时,可在保证不过多降低导电性的前提下,有效提高复合材料的抗弯强度和耐磨性。     

Near-net-shape forming of 316L stainless steel powder under hot isostatic pressing

Near-net-shape forming of 316L stainless steel powder is investigated under hot isostatic pressing (HIPing). A stainless steel powder compact and an insert were encapsulated by a stainless steel container and hot isostatically pressed to produce an axisymmetric near-net-shape part. To simulate densification and deformation of a powder compact in the container during HIPing, the constitutive model of Abouaf et al., and that of McMeeking and co-workers were implemented into a finite element analysis. The thickness effect of the container on densification was also studied for the axisymmetric part during HIPing. Densification of a three-dimensional asymmetric part during HIPing was also investigated by comparing finite element calculations with experimental data by Eisen et al.     

Densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing

Densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing was investigated. Hot isostatic pressing was carried out for a bundle of copper-coated tungsten fibers in copper powder. Due to tungsten-fibers and copper coating layers, the densification rate of a tungsten-fiber-reinforced copper powder compact was slower than that of pure copper powder. The constitutive equations by McMeeking and co-workers and by Abouaf and co-workers were implemented into a finite element program (ABAQUS) to analyze densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing. Finite element calculations were compared with experimental results for the variation of relative density with time for copper powder compacts during hot isostatic pressing. Density distributions in copper powder compacts were also investigated by comparing experimental results with finite element calculations.     

温压致密化机理及其在温压粉末设计中的应用

温压是以较低的成本制造高性能铁基粉末冶金零部件的新型成形技术。试验结果表明，颗粒重排是温压过程的主导致密化机理，而为颗粒重排提供协调性的塑性变形是另一重要的致密化机理，同时还分析了影响这两个致密化机理的主要因素。在此基础上，提出了温压粉末原料的设计原则，并成功地开发了高性能、低成本、合金钢粉末三大体系的温压粉末原料。     

Numerical simulation and experimental investigation on densification,shape deformation,and stress distribution of Ti6Al4V compacts during hot isostatic pressing

Hot isostatic pressing of metal powders involves a complex thermal and mechanical coupling process. A constitutive model based on Perzyna’s elastic-viscoplasticity equation was proposed, and a Lagrangian finite element method was applied to analyze the large deformation, nonlinear friction, powder flow, and densification behavior during hot isostatic pressing. The mechanical behavior of the powders was analyzed in terms of stress distribution. For comparison to the simulation results, the density, shape deformation, and residual stress of the specimens were evaluated using Archimedes’ principle, 3D measuring technology, and Empyrean X-ray diffractometer.     

考虑摩擦因数与滑动速度相关时的轮轨滚动接触有限元分析

使用与滑动速度相关的摩擦因数替代库伦摩擦定律中的常系数,结合mixed Lagrangian/Eulerian方法建立轮轨滚动接触有限元模型,分析牵引力主导的蠕滑工况下的干燥状态的轮轨滚动接触特性。通过与摩擦因数取值为常数的轮轨滚动接触分析结果对比发现:与滑动速度相关的摩擦因数对轮轨滚动接触最大接触应力和接触斑面积影响不大,均在1%以内;但是对轮轨接触斑内最大Mises应力、最大纵向切应力、最大横向切应力和最大等效塑性应变影响较大,特别是对最大纵向切应力影响幅度近20%;更需要引起注意的是对轮轨滚动接触摩擦力矢量分布和切向塑性应变分布影响明显,这对轮轨滚动接触疲劳损伤分析非常重要。     

Mathematical modeling of sintering during powder forming processes

This paper describes a study of densification induced by local capillary forces during compaction of powder based materials. A coupled sinter-compaction model with an internal state parameter was proposed. An internal state parameter was assumed as the sintering stresses on contact areas between powder particles. The mechanical model describing the plastic deformation during the P/M forging of a preform is based on the plasticity theory of porous metals. The numerical investigation of P/M forming processes is based on the rigid-plastic finite element model. A finite element program taking into account the sintering effect during P/M forming is created. A numerical example is considered.