几何特征对SiC颗粒增强Al基复合材料力学行为的影响

利用有限元方法建立三维模型分析SiC颗粒在不同形状、不同体积分数和不同尺寸时对Al基复合材料力学行为的影响,并进行拉伸试验研究.结果表明,颗粒形状比颗粒尺寸和颗粒体积分数对材料的应力、应变分布及材料韧性的影响大.颗粒尖角附近有严重的应力集中现象,在外力方向上颗粒端部附近的基体上的应变也有集中现象.随颗粒角度的减小,颗粒的应力很快增大而韧性减小,材料的弹性模量有增大的趋势.随颗粒体积分数的增大,颗粒的应力有减小趋势,材料的弹性模量呈增大趋势.颗粒尺寸较小时(平均尺寸为5 μm),颗粒尺寸对材料的应力及应变的影响小.     

颗粒增强镁基复合材料热残余应力的有限元分析

由于基体与增强相之间热膨胀系数的差异,颗粒增强镁基复合材料在制备和热处理过程中,在颗粒和基体的界面处会产生热残余应力。通过建立了随机颗粒模型,利用有限元模拟分析了复合材料降温过程中颗粒形状、颗粒尺寸和颗粒质量分数对基体热残余应力的影响。结果表明:颗粒形状对基体热残余应力影响较大。颗粒形状越接近球形,基体上等效应力越小;单胞、多胞模型基体上热残余应力随颗粒尺寸的增大而增大,相同尺寸下随颗粒质量分数的增大而增大;对于多胞模型基体,颗粒与基体应力的交错会使热残余应力有所降低。     

颗粒增强镁基复合材料热残余应力及其对宏观力学性能的影响

采用有限元方法对Si CP/AZ91复合材料制备后的热残余应力进行了数值模拟,建立了平面应力多颗粒随机分布的几何模型,研究了颗粒形状对该复合材料热残余应力的影响。通过简化模型,研究了受静态外力载荷时复合材料内部的热残余应力场变化。同时利用Taylor非局部应变梯度塑性理论和有限元法相结合,研究了热残余应力、颗粒形状及颗粒尺寸效应对颗粒增强金属基复合材料拉伸变形行为的影响。同时还说明了热残余应力对基体塑性变形的影响过程。     

SiC颗粒增强铜基复合材料热残余应力的数值模拟

利用有限元方法建立轴对称模型分析了SiC颗粒尺寸、体积分数以及温度对铜基复合材料热残余应力的影响.结果表明,随温度的升高,残余应力很快增大;随SiC颗粒尺寸和体积分数的增大,残余应力均呈增大趋势.基体受残余拉应力,颗粒受残余压应力,在结合界面处存在最大残余拉应力.     

SiC对SiC/6066铝基复合材料挤压过程力学行为的影响

利用有限元方法分析了SiC颗粒在不同形状、体积分数时对Al基复合材料挤压过程力学行为的影响,并对试样进行了拉伸试验。结果表明,随着SiC颗粒角度减小,颗粒的应力很快增大,基体的应变呈增大趋势;随SiC颗粒体积分数的增大,颗粒的应力、基体的应变以及该复合材料的弹性模量及屈服强度呈增大的趋势。     

颗粒增强金属基复合材料近邻颗粒间的应力及应变分布（英文）

采用内聚力模型研究颗粒增强金属基复合材料近邻颗粒间的应力及应变分布。结果表明,复合材料的应变主要集中于基体上,在加载路径上存在一个应变较高的区域,从而促进了颗粒极点附近空洞的形成。基体的应力和应变都随着基体与增强颗粒距离的增大而减小。模拟结果表明,增强颗粒之间的相互影响有一个临界距离,而且这个临界距离会随粒径的增大而增大。此外,加载方向和颗粒的中心线夹角对应力和应变的分布也有一定的影响,当加载方向和颗粒的中心线夹角为0°时,颗粒之间的相互影响最大,其夹角为45°时颗粒之间的相互影响最小。     

TiC颗粒增强钛基复合材料的静动态力学性能

利用伺服式疲劳实验机和杆一杆型冲击拉伸实验机对TiC颗粒增强钛基复合材料TP650和基体钛合金的静动态力学性能进行研究,得到不同应变率下复合材料的应力一应变曲线.结果表明,复合材料和基体材料的屈服应力均随应变率的增加而提高,属于应变率敏感材料;TP650的破坏形式以颗粒附近基体的撕裂以及颗粒与基体合金的脱粘为主,几乎没有发生颗粒破碎现象.假设复合材料的微观结构为非均质单胞在空间的周期性重复排列,利用有限元软件对钛基复合材料的静动态力学性能进行数值模拟研究,计算结果与实验结果吻合良好.进一步通过数值模拟预测了颗粒形状和颗粒体积分数的变化对TiC颗粒增强钛基复合材料静动态力学性能的影响.     

颗粒增强铁基复合材料拉伸应力场数值分析

采用有限元方法分析了颗粒增强铁基复合材料强度和应力与颗粒形状、尺寸以及体积分数的关系。结果表明，颗粒尖锐化会导致颗粒尖端应力集中和基体内的应变集中。同时，颗粒长径比增大，颗粒的应力集中也增大；颗粒尺寸减小和体积分数增加都有助于提高复合材料的强度。     

SiC颗粒对轧辊表面镀层应力影响的有限元分析*

目前针对多颗粒复合镀层有限元模型的建立尚不准确。以轧辊的服役工况为背景,利用Python语言和ABAQUS软件建立试块底面带有SiC颗粒增强Ni基复合镀层的环-块滑动摩擦有限元模型,系统研究SiC颗粒含量和尺寸对涂层表面及涂层-基体界面峰值等效应力的影响规律。结果表明：当SiC颗粒含量为3 vol.%～9 vol.%时,涂层表面和涂层-基体界面峰值应力随颗粒含量的增大而增大,分别增大了78.01%和32.06%;当SiC颗粒含量为9 vol.%～15 vol.%时,随着颗粒含量的增大,涂层表面峰值应力呈下降趋势,降低了13.02%,而涂层-基体界面峰值应力基本保持不变;当SiC颗粒直径为0.8～1μm时,涂层表面及涂层-基体界面峰值应力随颗粒尺寸的减小而增大,分别增大了51.5%和32.6%;当SiC颗粒直径为0.3～0.8μm时,涂层表面及涂层-基体界面峰值应力基本保持不变。综合考虑轧辊表面镀层的性能需求以及实际复合电镀工艺,依据界面应力与镀层结合状态之间的关系,SiC颗粒含量以9 vol.%左右为宜,SiC颗粒直径以0.8μm左右为宜。所建立的多颗粒随机分布涂层基体的有限元模型更接...     

夹杂物尺寸对粉末高温合金低周疲劳寿命影响的机制

为了研究夹杂物尺寸对粉末高温合金低周疲劳寿命的影响,将夹杂分别位于试样中心、表面、亚表面并改变其尺寸,研究同一位置下,不同夹杂物尺寸对应力应变分布的影响,结果表明:当夹杂物界面上不含微孔洞时,夹杂物与基体尺寸比例在实验室尺度（1:25）到工程尺度（1:10 000）范围内,夹杂物尺寸对应力应变影响很小;工程实际中,缺陷往往会与基体形成不完好的连接界面,即初始损伤破坏——微孔洞。缺陷对寿命的影响原因:夹杂物尺寸越大,它与基体的界面就越大,出现不完好连接和缺陷的概率就会增加,容易在界面处产生初始损伤破坏;当夹杂物界面上含有微孔洞时,随着夹杂物尺寸变大,界面正应力明显增大,界面切应力微弱减小,基体最大正应力和最大塑性应变均明显增大。     

粒度大小和颗粒间相互作用对白钨矿浮选的影响(英文)

通过浮选试验和理论计算研究白钨矿粒度分布(粒径小于10μm的微细粒含量)对浮选的影响。结果表明,颗粒粒径对白钨矿浮选回收率以及组合药剂性能都有影响;扩展的DLVO(EDLVO)理论证明白钨矿颗粒之间存在相互吸引力。颗粒之间的相互作用能、流体剪切力大小都与颗粒粒径有关,这是小于10μm粒级白钨矿对粗粒级白钨矿回收率的影响随着粗粒级粒度的改变而发生变化的主要原因。以组合药剂为捕收剂时,白钨矿的最高回收率和组合药剂的最佳配比与颗粒粒度以及药剂性能有关,而组合药剂的最佳添加顺序与颗粒粒度无关,只与药剂性能有关。     

微粉粒度测量中形貌因素的影响

从理论上分析了用电阻法(库尔特)颗粒计数器和激光粒度仪测量相同的非圆球颗粒样品时,测试结果不一致的必然性,并进行了对比实验.实验结果显示:对圆球形颗粒,两者的测试结果一致(在合理的误差范围内);但是对非圆球形颗粒,二者有明显的差异.激光粒度仪测量的结果比电阻法颗粒计数器测量的结果分布宽,所得d50的值大;同时样品的平均圆度越小,则所述的差异越大.实验结果说明:用不同原理的仪器测量磨料微粉的粒度时,必然存在测量上的差异,并且差异的大小随微粉颗粒形状的变化而变化.因此,不同原理仪器之间的测量差异不能用一个固定的数值来修正;另一方面,这种差异可以用来表征颗粒偏离圆形的程度.     

Effect of particle characteristics on deformation of particle reinforced metal matrix composites

The particle characteristics of 15% SiC particles reinforced metal matrix composites (MMC) made by powder metallurgy route were studied by using a statistical method. In the analysis, the approach for estimation of the characteristics of particles was presented. The study was carried out by using the mathematic software MATLAB to calculate the area and perimeter of each particle, in which the image processing technique was employed. Based on the calculations, the sizes and shape factors of each particle were investigated respectively. Additionally, the finite element model (FEM) was established on the basis of the actual microstructure. The contour plots of von Mises effective stress and strain in matrix and particles were presented in calculations for considering the influence of microstructure on the deformation behavior of MMC. Moreover, the contour maps of the maximum stress of particles and the maximum plastic strain of matrix in the vicinity of particles were introduced respectively.     

Thermodynamics of particle coarsening

The coarsening of precipitate particles during the heat treatment of alloys depends both on the diffusivity of the surrounding phase and on the concentration differences given by the Gibbs-Thomson equation, both of which depend on the solution thermodynamics of the surrounding phase. However, it is now known that thermodynamic terms cancel in the theory; therefore coarsening is independent of solution behavior. The equations that confirm this prediction for multicomponent systems are derived and discussed. In addition, it is shown for ternary and higher order systems that a generalized form of the Gibbs-Thomson equation gives a vector that is normal to the matrix-precipitate phase diagram boundary.     

Single particle impact experiments for studying particle induced flow corrosion

An experimental set-up for the investigation of particle induced flow corrosion is described. It allows high speed monitoring of the repassivation current transient resulting from the impingement of a single particle. High purity aluminium microelectrodes with a diameter of 125 μm were used as targets in a neutral acetate buffer. Zirconia spheres of similar diameter were impinged at a flow rate of 7 m s⁻¹. After an activation period of about 6 μs the current reaches a peak current of 10 μA. The current returns to its initial base line within one millisecond. Subsequent ex situ investigation of the samples in a SEM allows linking the detected surface destruction to its current transient. A crater of some 20 μm diameter is observed that shows a nanoscopic substructure resulting from the nanostructure of the particle. Part of the repassivation charge must be determined by an extrapolation of the high field oxide growth. A comparison of the consumed charge to the microscopic observations gives insights into the destruction mechanisms.     

Effect of spray particle trajectory on the measurement signal of particle parameters based on thermal radiation

The influences of the dimensions of optical components and the trajectories of spray particles on the variations of the waveforms of the radiation signals from the spray particles were studied both theoretically and experimentally for correct simultaneous measurement of the particle parameters including particle velocity, surface temperature, size, and spatial distribution. Two types of filtering masks, including single-windowed and dual-windowed, were used as models in the current study. The evolution of the radiation pulse from a moving thermal spray particle was simulated through the change of the projected area of the particle image spot on the filtering mask window. The experimental detection of the thermal radiation pulses was performed for the high velocity oxygen fuel (HVOF) process using an optoelectronic measurement system. The theoretical simulation clearly showed that the characteristic waveforms of the thermal radiation signals from the spray particles are varied with the distance and orientation of the trajectories of thermal spray particles with respect to the ideal image plane of the filtering window plane. The typical variations of the characteristic waveforms obtained theoretically have been observed experimentally with HVOF spraying. The waveforms expected theoretically were correlated well with those observed experimentally. The characteristic waveforms of the radiation signals from the spray particles in a trapezoid shape with a saturated top platform contain the information for spray particle parameters including velocity, surface temperature, size, and spatial distribution. With the dual-windowed filtering mask, the particle velocity can be correctly measured with the bi-peak radiation signal in triangle-like shape, and the surface temperature may be estimated reasonably. However, the particle size cannot be estimated correctly. It was revealed that the characteristics of the waveforms were remarkably influenced by the image spot size. Therefore, the expansion of the image spot based on the relation between the image spot size of an in-flight particle and optical lens parameters obtained optically was discussed. The influence of the image spot size on the waveform characteristics was examined.     

Dispersed hard particle strengthening of metals

A review is presented of the various methods utilized to strengthen metals and alloys for high temperature service by a suitable dispersion of finely divided hard particles. Alloys such as SAP, produced by powder metallurgy, and other sintered aluminum powders, molybdenum containing small quantities of refractory oxides and magnesium containing a dispersed intermetallic, are considered. Internal oxidation and other methods of achieving a hard particle dispersion are discussed. New data on the high temperature strength and stability of the alloy systems Cu-Al₂O₃, Ni-Al₂O₃ and Be-Be₂C are shown. The theoretical aspects of the hardening and strengthening mechanism are presented and consideration is given to the problems associated with the powder metallurgy of the various processes.     

Nomograms for rapid assessment of particle sedimentation behaviour in liquid phase processing of particle reinforced metal composites

Abstract

A procedure is developed for practical assessment of the sedimentation and flotation behaviours of particulate reinforcement in remelting and shape casting of particulate reinforced metal matrix composites. The procedure allows for rapid determination of combinations of particle size and particle volume fraction that yield identical sedimentation behaviours in different composite melts. The application of the procedure is demonstrated using composites of practical importance such as A359/SiC_P, A359/Al₂O₃, A359/Gr_P and C90300/Gr_P composites.