Compression Mechanical Behaviour of 7075 Aluminium Matrix Composite Reinforced with Nano-sized SiC Particles in Semisolid State

The 7075 aluminium matrix composite reinforced with nano-sized Si C particles was fabricated by ultrasonic assisted semisolid stirring method. The compression mechanical behaviour of the fabricated composite in semisolid state was investigated. The results show that the microstructure of the composite before semisolid compression consists of fine and spheroidal solid grains surrounded by liquid phase.Semisolid compression led to a nonuniform plastic deformation of solid grains. A slight plastic deformation occurred in the locations near the free surface due to the dependence of deformation on liquid flow and flow of liquid incorporating solid grains. However, obvious plastic deformation occurred in the central location and location contacting to die due to the contribution of plastic deformation of solid grains.The true stress–strain curve of the sample compressed at 500 °C consists of rapid increase of true stress and steady stage. However, rapid increase of true stress and decrease of true stress and steady stage are involved in the true stress–strain curves of the samples compressed at 550, 560, 570, 580 and 590 °C.The true stress–strain curve at 600 °C is similar to that at 500 °C. Apparent viscosity decreases with an increase of shear rate, indicating a shear thinning occurrence. When soaking time increases from 5 min to 15 min, the peak stress and steady stress decrease significantly. A further increase of the soaking time led to a slight change. Peak stress and steady stress increase with increasing volume fraction of Si C particles. A sudden increase or decrease of compression velocity led to a significant increase or decrease of the steady stress. The destruction of the samples compressed at solid state temperature mainly depends on cracks parallel to compression direction. However, the destruction forms of the samples compressed at semisolid temperatures consist of cracks parallel to compression direction and partial collapse. Increasing soaking time led to an obvious change of the destruction forms. Compression velocity affects slightly the macro appearance of the sample compressed at semisolid temperatures.

A Facile Route for Synthesis of LiFePO_4/C Cathode Material with Nano-sized Primary Particles

A facile and practical route was introduced to prepare LiFePO4/C cathode material with nano-sized primary particles and excellent electrochemical performance. LiH2PO4 was synthesized by using H3PO4 and LiOH as raw materials. Then, as-prepared LiH2PO4, reduced iron powder andα-D-glucose were ball-milled, dried and sin-tered to prepare LiFePO4/C. X-ray diffractometry was used to characterize LiH2PO4, ball-milled product and LiFePO4/C. Differential scanning calorimeter-thermo gravimetric analysis was applied to investigate possible reac-tions in sintering and find suitable temperature for LiFePO4 formation. Scanning electron microscopy was em-ployed for the morphology of LiFePO4/C. As-prepared LiH2PO4 is characterized to be in P21cn（33） space group, which reacts with reduced iron powder to form Li3PO4, Fe3（PO4）2 and H2 in ball-milling and sintering. The appro-priate temperature for LiFePO4/C synthesis is 541.3-976.7 ℃. LiFePO4/C prepared at 700 ℃ presents nano-sized primary particles forming aggregates. Charge-discharge examination indicates that as-prepared LiFePO4/C displays appreciable discharge capacities of 145 and 131 mA·h·g^-1 at 0.1 and 1 C respectively and excellent discharge ca-pacity retention.

Effect of nano-size nickel particles on wear resistance and high temperature oxidation resistance of ultrafine ceramic coating

In order to improve the wear resistance and high temperature oxidation resistance of titanium and titanium alloy, the high temperature ultra fine ceramic coating containing nano-size nickel particles was prepared by flow coat method on the surface of industrially pure titanium TB1-0. The effects of nano-size nickel particles on the wear resistance and high temperature oxidation resistance of coating substrate system were investigated through oxidation kinetics experiment and wear resistance test. The morphologies of the specimens were examined by means of optical microscopy, scanning electron microscopy and X-ray diffraction. The results show that the high temperature ultra fine ceramic coating has notable protection effect on industrially pure titanium TB1-0 from oxidation. The oxidation and wear resistance properties of the coating can be effectively improved by adding nano-size nickel particles. The oxidative mass gain of the specimen decreases from 11.33 mg·cm-2 to 5.25 mg·cm-2 and the friction coefficient decreases from 1.1 to 0.6 by adding nano-size nickel particles, and the coating containing 10% （mass fraction） nano-size nickel shows the optimum properties.

Aging Behavior of High Volume Fraction SiC Particles Reinforced 2024Al Composite

2024 Al matrix composite reinforced by SiC particles with 45% volume fraction and 1 um diameter was successfully fabricated by squeeze-exhaust casting method. The aging behavior of SiCp/2024AI composite at four temperatures was investigated and compared to 2024 alloy. It was found that the addition of high volume fraction SiC particles does not alter the aging sequence, but it significantly accelerates the kinetics of precipitation in the composite matrices. Therefore, the aging peak of the composite appears earlier than that of 2024AI alloy. This is attributed to the decrease in the activation energy for the precipitate formation and the increase in the precipitate growth rate due to the high density dislocations in the composite with high volume fraction particles. The high density dislocations, as preferential nucleation sites for precipitates, bring about the tiny and dense precipitates in the composite.

无压烧结温度对15%SiC/2009Al复合材料微观组织与力学性能的影响

针对传统粉末冶金工艺制备成本高、制备效率低等问题,采用冷等静压结合无压烧结及热挤压工艺制备15%(体积分数,下同)SiC/2009Al复合材料。研究不同烧结温度(600,620,640℃)对15%SiC/2009Al复合材料微观组织及力学性能的影响。结果表明:在600℃下烧结,SiC与基体间的结合差,微观下可观察到较多的大尺寸孔隙,材料的致密度低,力学性能差;在640℃高温下烧结,坯锭产生大量液相,并溢出到坯锭表面,造成心部合金元素下降,此外,640℃会引发强烈的界面反应,生成较多大尺寸脆性相,成为材料断裂过程中的裂纹源,导致材料性能下降;620℃为最佳烧结温度,产生较多的液相能填充坯锭中的部分孔隙,进而提高材料致密度以及界面结合强度,复合材料的强度和塑性均取得最佳值,抗拉强度与屈服强度分别达到505,345 MPa,伸长率达到7.2%。

Incorporation of nano/micron-SiC particles in Ni-based composite coatings towards enhanced mechanical and anti-corrosion properties

Ni-based composite coatings incorporated with nano/micron SiC particles were fabricated via electrochemical co-deposition in Watts bath,followed by the evaluation of their mechanical and anti-corrosion properties.The micrographic observations suggest that the SiC particles with various sizes can be well incorporated to the Ni substrate.X-ray diffraction(XRD)patterns indicate that SiC particles with smaller sizes could weaken the preferential growth of Ni along(200)facet.In addition,it is found that the incorporated SiC particles with medium micron sizes(8 and 1.5μm)could significantly enhance the micro-hardness of the Ni composite coatings.Nevertheless,electrochemical measurements demonstrate that micron-sized SiC particles would weaken the corrosion resistance of Ni composite coatings ascribed to the structure defects induced.In contrast,the combined incorporation of nanosized(50 nm)SiC particles with medium micron(1.5μm)ones is capable of promoting the compactness of the composite coatings,which is beneficial to the long-term corrosion resistance with negligible micro-hardness loss.

Effect of SiC particles on microstructure and mechanical property of friction stir processed AA6061-T4

Friction stir processing of AA6061-T4 alloy with SiC particles was successfully carried out.SiC particles were uniformly dispersed into an AA6061-T4 matrix.Also SiC particles promoted the grain refinement of the AA6061-T4 matrix by FSP.The mean grain size of the stir zone (SZ) with the SiC particles was obviously smaller than that of the stir zone without the SiC particles.The microhardness of the SZ with the SiC particles reached about HV80 due to the grain refinement and the distribution of the SiC particles.

60%SiCp/2009铝基复合材料表面等离子体电解氧化膜的生长和表征

在硅酸盐溶液中采用等离子体电解氧化技术在60%SiCP(体积分数)/2009铝基复合材料表面制备陶瓷膜。研究氧化膜的显微组织、成分、润湿性及其耐腐蚀性能,探讨SiC颗粒表面火花放电的产生机理。结果表明,来自硅酸盐溶液的不溶性化合物(SiO_(2))使SiC颗粒表面产生火花放电,Al-Si-O化合物中的缺陷为SiC颗粒表面放电电流的传导提供优先路径。1200s时铝基复合材料表面形成5.5μm厚的均匀膜层,膜层的表面自由能在40s时达到最大值37.10 m J/cm^(2),并在1200 s时下降到25.95 m J/cm^(2)。此外,等离子体电解氧化处理可以显著提高复合材料的耐蚀性。

Preparation and Mechanical Properties of Micro- and Nano-sized SiC/Fluoroelastomer Composites

Microand nano-sized SiC/fluoroelastomer （FKM） composites were prepared by a mechanical mixing method. These composites were first characterized by a rotorless rheometer. Then the effects of micro- and nano-sized SiC on hardness, static and dynamic mechanical properties of the composites were investigated. The increasing amount of the SiC filler increased the curing efficiency of the biphenyl curing system, which was evident from the rheometric properties of the resulting composites. The tensile properties of composite increased with the increasing of micro- and nano-sized SiC content. When the micro- and nano-sized SiC content was higher than 20 phr, the composites showed almost unchanged tensile properties. The increasing of the tensile property was mainly attributed to the well dispersed micro- and nano-sized SiC particles characterized by SEM images. Compared to pure FKM, the composites exhibited a higher glass transition temperature and lower tan peak value.

Distribution of SiC particles in semisolid electromagnetic-mechanical stir-casting Al-SiC composite

The distribution of SiC particles in Al-SiC composite can greatly influence the mechanical performances of Al-SiC composite. To realize the homogeneous distribution of SiC particles in stir-casting Al-SiC composite, semisolid stir casting of Al-4.25 vol.%SiC composite was conducted using a special electromagneticmechanical stirring equipment made by our team, in which there are three uniformly-distributed blades with a horizontal tilt angle of 25 ° to mechanically raise the SiC particles by creating an upward movement of slurry under electromagnetic stirring. The microstructure of the as-cast Al-SiC composites was observed by Scanning Electron Mcroscopy(SEM). The volume fraction of SiC particles was measured by image analysis using the Quantimet 520 Image Processing and Analysis System. The tensile strength of the Al-4.25 vol.%SiC composites was measured by tensile testing. Results show that the Al-4.25 vol.%SiC composites with the homogeneous distrbutin of SiC particles can be obtained by the electromagnetic-mechanical stirring casting with the speed of 300 and 600 r·min-1 at 620 °C. The differences between the volume fraction of Si C particles at the top of ingot and that at the bottom are both ~0.04 vol.% with the stirring speed of 300 and 600 r·min-1, which are so small that the distribution of SiC particles can be seen as the homogeneous. The tensile strength of the Al matrix is enhanced by 51.2% due to the uniformly distributed SiC particles. The porosity of the composite mainly results from the solidification shrinkage of slurry and it is less than 0.04 vol.%.

基于神经网络的混杂SiC颗粒增强铝基复合材料力学性能预测

目的提高混杂SiC颗粒增强铝基复合材料的韧性,利用卷积神经网络预测其力学性能,以得到力学性能关键因素的影响规律。方法首先,通过实验得到了铝基复合材料的力学性能数据。其次,基于相场裂纹扩展本构,采用Python代码批量生成了不同构型参数的代表性体积单元,并利用Abaqus软件进行了有限元仿真(FEM)。通过代码实现了建模与仿真的一体化构建,利用得到的仿真数据,建立了神经网络模型,并实现了对复合材料力学性能的预测。建模前,对数据进行预处理和筛选,以提高数据质量并降低模型复杂度。最后,建立卷积神经网络,并优化模型的超参数。结果通过建立的神经网络模型,实现了对复合材料力学性能的有效预测。极限强度的预测误差保持在−7%~8.5%,能耗的预测误差保持在−5%~6%,预测精度较高。结论通过结合实验、仿真和卷积神经网络模型,可以更有效地预测混杂SiC颗粒增强铝基复合材料的力学性能,从而为材料设计和制备提供指导。

SiC量子点颗粒间距估算及其对光学性能的影响

以氢氟酸、硝酸和分析纯硫酸组成的混合液为腐蚀剂,通过简单、过程可控的化学腐蚀制备出光学性能优异的碳化硅量子。利用扫描电镜分析检测碳化硅量子点在腐蚀进程中微观形貌的演变过程,通过Auto-CAD计算机辅助设计建立了碳化硅量子点颗粒间距的数学模型,估算了量子点水相溶液在不同稀释程度下颗粒间平均间距。结果表明,随着碳化硅量子点颗粒平均间距的单调增加,其光致发光强度呈现先增后减的变化规律,且光致发光相对强度峰值出现在颗粒间距为26 nm处,该变化规律源自淬灭效应、光吸收与荧光竞争效应的综合作用。

Influence of stirring speed on SiC particles distribution in A356 liquid

A straight-blade mechanical stirrer was designed to stir A356-3.5vol%SiCp liquid in a cylindrical crucible with the capability of systematically investigating the influence of rotating speed of stirrer on the distribution of SiC particles in A356 liquid. The experimental results show that the vertical distribution of SiC particles in A356 liquid can be uniform when the rotating speed of stirrer is 200 rpm, but the radial distribution of SiC particles in A356 liquid is always nonhomogeneous regardless of the rotating speed of stirrer. The radial centdfugalization ratio of SiC particles in A356 liquid between the center and the periphery of crucible increases with the rotating speed of stirrer. The results were explained in the light of SiC particles motion subject to a combination of stirring and centrifugal effect.

Removal of SiC particles from solar grade silicon melts by imposition of high frequency magnetic field

Non-metallic particles and metallic impurities present in the feedstock affect the electrical and mechanical properties of high quality silicon which is used in critical applications such as photovoltaic solar cells and electronic devices. SiC particles strongly deteriorate the mechanical properties of photovoltaic cells and cause shunting problem. Therefore, these particles should be removed from silicon before solar cells are fabricated from this material. Separation of non-metallic particles from liquid metals by imposing an electromagnetic field was identified as an enhanced technology to produce ultra pure metals. Application of this method for removal of SiC particles from metallurgical grade silicon （MG-Si） was presented. Numerical methods based on a combination of classical models for inclusion removal and computational fluid dynamics （CFD） were developed to calculate the particle concentration and separation efficiency from the melt. In order to check efficiency of the method, several experiments were done using an induction furnace. The experimental results show that this method can be effectively applied to purifying silicon melts from the non-metallic inclusions. The results are in a good agreement with the predictions made by the model.

搅拌铸造结合搅拌摩擦加工制备不同体积分数SiC_(p)/Al复合材料的摩擦磨损行为

采用搅拌铸造结合搅拌摩擦加工方法制备了SiC颗粒体积分数分别为20%,25%,30%的SiC_(p)/Al复合材料,研究了复合材料的显微组织和力学性能,并基于市域列车的实际运行工况(制动压力0.57,0.67,0.72MPa)设计摩擦磨损试验,研究了不同复合材料的摩擦磨损行为。结果表明:所得SiC_(p)/Al复合材料均组织致密,无裂纹和气孔缺陷,SiC颗粒均匀分布在铝合金基体中,无团聚现象;复合材料的抗拉强度、断后伸长率和硬度均满足制动盘行业标准要求,随SiC颗粒体积分数的增加,抗拉强度变化幅度较小,断后伸长率呈降低趋势,硬度呈升高趋势;当SiC颗粒体积分数为25%和30%时,复合材料的平均摩擦因数稳定在0.3~0.5,满足市域列车高速制动要求,磨损表面未发现明显的犁沟和分层,表面形成了完整的摩擦膜,但是SiC颗粒体积分数为30%的复合材料对偶闸片的磨损量较高,且在0.57MPa制动压力下的摩擦稳定系数较低,摩擦副的匹配性差;当SiC颗粒体积分数为20%时,最大平均摩擦因数大于0.55,磨损表面犁沟和分层现象明显,磨粒磨损严重,最大犁沟深度达到45μm,无法满足市域列车高速制动要求。

45#钢表面Ni-P-nano-SiC复合化学镀层的制备

在优化设计的化学镀基础镀液中通过添加不同含量的纳米SiC颗粒,研究在45#钢表面制备具有纳米SiC颗粒增强的复合镀层及形成机理.利用SEM,XRD和显微硬度计等方法对实验样品的组织结构、形貌、显微硬度及其镀层形成机理进行了研究,结果表明:实验制备的Ni-P,Ni-P-SiC镀层镀态时硬度分别为572 HV,649 HV,热处理后其表面硬度在400℃时达到最大值1 045 HV和1 341 HV.纳米SiC颗粒在镀液中不参与化学反应,只是与化学反应所产生的Ni和P共同沉积在镀层中起到了复合强化的作用.Ni-P-nano-SiC镀层的生长机理是按层状方式生长,生长方向垂直于钢基体表面.纳米SiC提高了复合化学镀层的生长速度,促进了复合镀层以较薄的分层方式生长.

Particle Removal Mechanism of High Volume Fraction SiCp/Al Composites by Single Diamond Grit Tool

Particle removal mechanism was presented during machining particle SiC/Al composites with diamond grinding tool. The relevant removal modes and their mechanisms were discussed considering the impact and squeezing effect of diamond grit on the SiC particle. The experimental results show that the aluminum matrix has larger plastic deformation, so the aluminum mixed with the surplus SiC particles is cut from the surface. The SiC particles can be removed in multiple ways, such as broken/fractured, micro cracks, shearing and pulled out, etc. More particles removed by shearing, and less particles removed by fractured during material removal progress can produce a better machined surface.

Microstructure and mechanical properties of SiC-particle-strengthening tri-metal Al/Cu/Ni composite produced by accumulative roll bonding process

In this study, a multilayer Al/Ni/Cu composite reinforced with Si C particles was produced using an accumulative roll bonding(ARB) process with different cycles. The microstructure and mechanical properties of this composite were investigated using optical and scanning microscopy and hardness and tensile testing. The results show that by increasing the applied strain, the Al/Ni/Cu multilayer composite converted from layer features to near a particle-strengthening characteristic. After the fifth ARB cycle, a composite with a uniform distribution of reinforcements(Cu, Ni, and SiC) was fabricated. The tensile strength of the composite increased from the initial sandwich structure to the first ARB cycle and then decreased from the first to the third ARB cycle. Upon reaching five ARB cycles, the tensile strength of the composite increased again. The variation in the elongation of the composite exhibited a tendency similar to that of its tensile strength. It is observed that with increasing strain, the microhardness values of the Al, Cu, and Ni layers increased, and that the dominant fracture mechanisms of Al and Cu were dimple formation and ductile fracture. In contrast, brittle fracture in specific plains was the main characteristic of Ni fractures.

Effect of second-phase particle size and presence of vibration on AZ91/SiC surface composite layer produced by FSP

An improved method of friction stir processing(FSP)was introduced for the processing of AZ91 magnesium alloy specimens.This novel process was called“friction stir vibration processing(FSVP)”.FSP and FSVP were utilized to develop surface composites on the studied alloy while SiC nanoparticles were applied as second-phase particles.The effect of reinforcing SiC particles with different sizes(30 and 300 nm)on different characteristics of the composite surface was studied.The results indicated that the microstructure was refined and mechanical properties such as hardness,ductility,and strength were enhanced as FSVP was applied.Furthermore,it was concluded that the effect of reinforcing particles with a size of 30 nm on the microstructure and mechanical properties of the surface composite was more obvious than that of particles with a size of 300 nm.It was also found that mechanical properties and microstructure of FSV-processed specimens were improved as vibration frequency increased.The hardness value in the stir zone was about 157 MPa for the FSV-processed specimen at a vibration frequency of 50 Hz,while this value was around 116 MPa for the FSV-processed specimen at a vibration frequency of 25 Hz.

Effect of SiC particle addition on microstructure of Mg_2Si/Al composite

In the present study, by adding SiC particles into AI-Si-Mg melt, Mg2Si and SiC particles hybrid reinforced AI matrix composites were fabricated through the Mg2Si in situ synthesis in melt combined with the SiC ex situ stir casting. The as-cast microstructure containing primary Mg2Si and SiC particles that distribute homogenously in AI matrix was successfully achieved. The effects of SiC particle addition on the microstructure of Mg2Si/AI composites were investigated by using scanning electron microscopy （SEM） and XRD. The results show that, with increasing the fraction of the SiC particles from 5wt.% to 10wt.%, the morphologies of the primary Mg2Si particulates in the prepared samples remain polygonal, but the size of the primary phase decreases slightly. However, when the SiC particle addition reaches 15wt.%, the morphologies of the primary Mg2Si particulates change partially from polygonal to quadrangular with a decrease in size from 50 pm to 30 μm. The size of primary AI dendrites decreases with increasing fraction of the SiC particles from 0wt.% to 15wt.%. The morphology of the eutectic Mg2Si phase changes from a fiber-form to a short fiber-form and/or a dot-like shape with increasing fraction of the SiC particles. Furthermore, no significant change in dendrite arm spacing （DAS） was observed in the presence of SiC particles.