Material deformation and removal mechanism of SiCp/Al composites in ultrasonic vibration assisted scratch test

The material removal process of SiCp/Al composites is a result of synergetic deformation and interaction among Al matrix, SiC particles and interface. The non-homogeneity of microscopic mechanical properties due to the inherent polyphase heterogeneity of SiCp/Al composites will directly affect the removal mechanism and surface integrity in the machining process. This paper aims to gain further insight of the material deformation and removal mechanism of SiCp/Al composites in ultrasonic vibration assisted machining process. The elastic modulus and hardness of SiCp/Al composites were determined through the indentation test by loading on Al matrix and SiC particles, respectively. Due to the interaction effects of the three phases during the deformation process, when the indenter is on a single phase, the influence of the other phases cannot be neglected and is reflected in the P-h curves. Scratch force, friction coefficient and material removal behavior were investigated in traditional scratch (TS) and ultrasonic vibration assisted scratch (US) tests. In most cases, with the assistance of ultrasonic vibration, scratch force and friction coefficient in US process are smaller than those in TS process, and the reduction of them is modeled and analyzed. The material removal behavior of SiCp/Al composites is similar to metal at the macroscale, and a high material removal rate is achieved in US process. SiC particles tend to maintain the structural integrity rather than be fractured or pulled out in US process. The scratched surface in TS process is damaged to a greater degree than that subjected to US process.     

SiCp/Al复合材料的自发熔渗机理

以Mg为助渗剂,采用液态铝自发熔渗经氧化处理的SiC粉体压坯的方法,制备出高增强体含量的SiCp/Al复合材料.通过考察铝液在SiC粉体压坯中的渗入高度与温度、时间的关系来研究铝液的熔渗机理,并对SiCp/Al复合材料进行X射线衍射、能量散射谱和金相分析.结果表明:在熔渗前沿发生的液-固界面化学反应促进两相润湿,毛细管力导致铝液自发渗入到SiC多孔陶瓷中;熔渗高度与时间呈抛物线关系.熔渗激活能为166 kJ/mol,这表明渗透过程受界面反应控制.经氧化处理的SiC粉体均匀地分布在金属基体中,其轮廓清晰.在SiCp/Al复合材料中未发现Al4C3的存在.     

Surface and subsurface formation mechanism of SiCp/Al composites under ultrasonic scratching

Rotary ultrasonic machining (RUM) is an effective method of high-quality and high-efficiency machining for advanced composites. However, the machining mechanism and kinematic characteristics of ultrasonic machining of SiC particles-reinforced aluminum matrix (SiC_p/Al) composites are yet unclear, limiting the applications of RUM in composites machining. In this study, a rotary ultrasonic vibration-assisted scratch (RUVAS) test was designed for the high-volume fraction of SiC_p/Al composites. The kinematic and scratch force model of RUVAS was developed to describe the scratch process of SiC_p/Al. Both RUVAS and conventional scratch (CS) tests were performed under various scratch speeds on SiC_p/Al. The scratch trajectory was divided into three modes: continuous, semi-continuous, and intermittent. We observed the formation of different surface morphology under different modes. The scratch force difference between RUVAS and CS was insignificant when the scratch speed is high, which indicated that the effect of ultrasonic vibration diminished at a high speed when the ultrasonic frequency was fixed. When assisted by ultrasonic vibration, the scratch morphology of SiC_p/Al indicated that the matrix has undergone significant plastic deformation. While the hard SiC particles tended to be ruptured and pressed into the plastic matrix, this mechanism can effectively suppress the initiation and propagation of cracks, which is beneficial to reducing the stress influence zone, healing the surface defects, and improving the surface integrity. The subsurface morphology indicates that the subsurface damage under CS and RUVAS mainly includes particle cracking, matrix tearing, and interface failure. Our experimental result shows that ultrasonic vibration can effectively reduce the subsurface damage of SiC_p/Al composites, bringing insight into fundamental mechanisms of ultrasonic machining and providing guidance for the vibration-assisted processing of SiC_p/Al composites.     

低体积分数SiCp/Al复合材料封装盒体搅拌摩擦焊研究

碳化硅颗粒增强铝基复合材料具有优异的性能,在许多领域都备受青睐,然而焊接性较差,成为制约其广泛应用的瓶颈难题.本文采用搅拌摩擦焊的方法,实现了低体积分数SiCp/Al复合材料封装盒体的连接.试验中采用圆锥形WC-Co合金搅拌头,搅拌头轴肩直径为10 mm,锥头直径3 mm,锥尾直径5 mm,搅拌针高度2.5 mm,采用下压力控制方式,焊接工艺参数为:下压力控制在2 kN,搅拌头倾角为3°,搅拌头转速为1500 RPM,焊接速度保持在120 mm/min,下压深度为2.55 mm,能够获得表面及内部质量良好的焊接接头.经过搅拌摩擦焊后,搅拌区的碳化硅颗粒尺寸更加细小,分布也更加均匀,搅拌区中没有出现孔洞、沟槽等搅拌摩擦焊常见缺陷.热机影响区内部分布着大量严重变形的结构,这主要是由于母材组织被拉长后伴随着塑性流动而产生的较大变形.母材区的平均硬度值最高,为61.9 HV3,搅拌区的平均硬度为58.3 HV3,热机影响区的平均硬度最低,为55.4 HV3.     

二硼化锆基超高温陶瓷的制备及性能

用碳化硅(SiC)颗粒增韧二硼化锆(ZrB2)陶瓷,在氩气流中热压烧结温度为1 950℃、保温1 h,20 MPa压力下成功制备出了致密的ZrB2/SiCp复合材料.ZrB2/SiCp复合材料的致密度随着SiC颗粒添加量的增加而增加.当SiC颗粒的体积分数(下同)为15%时,相对致密度达到100%.ZrB2/SiCp复合材料的抗弯强度和断裂韧性都随着SiC添加量的增加成上升趋势,当SiC颗粒的添加量在15%时同时达得最大值,分别为646 MPa和8.52 MPam·m1/2.SiCp的添加还提高了ZrB2/SiCp复合材料的耐氧化烧蚀性能.     

半固态搅拌制SiC颗粒增强镁基复合材料过程的数值模拟

采用商用的计算流体动力学(CFD)计算软件Fluent对SiC颗粒增强镁基复合材料搅拌过程进行动态模拟,研究了不同搅拌速度、搅拌时间及温度对于SiCp/AZ91(SiC颗粒增强镁合金AZ91)组织的影响。研究结果表明,搅拌时间和搅拌速度对于SiCp/AZ91材料成品质量有显著的影响,搅拌速度的增加有助于SiC颗粒的分散,但速度过快导致液面起伏较大,大量气体进入镁液中,最终使成品中气孔较多。而在搅拌时间方面,当时间较短时,SiC颗粒未充分与合金液混合,因此出现大片SiC颗粒团聚现象。随着搅拌时间的延长,团聚的颗粒逐渐向镁合金液中均匀分散,当搅拌时间为15 min时,SiC固相颗粒与镁合金液所组成的混合相最为均匀,此时继续延长搅拌时间,其固相颗粒的宏观均匀性并未发生进一步变化。根据模拟和试验的结果得出最佳的搅拌时间为15 min,搅拌速度为300 r/min。     

温度及表面金属化对铝基复合材料与可伐合金真空钎焊的影响

采用Al63-Cu22-Ti5-Si10钎料,研究了55%SiCp/6063Al复合材料和可伐合金之间的真空钎焊工艺,分析了钎焊温度和复合材料表面镀层材料对接头抗剪强度和显微硬度的影响规律,并对接头的显微组织进行了研究。结果表明钎焊温度和复合材料表面镀层对接头的力学性能影响很大,在同样的焊接参数下,复合材料表面镀铜的试样,其抗剪强度要高于无镀层和镀镍的试样,镀铜试样的最高抗剪强度为92.8 MPa。当钎焊温度从560℃增加到580℃时,接头的抗剪强度逐渐降低再上升,经过不同表面处理的试样均在钎焊温度为560℃时达到最大抗剪强度。钎焊温度相同时,镀铜试样的显微硬度均最高,而镀镍试样的显微硬度最低。焊缝组织致密,没有出现孔洞和未润湿等钎焊缺陷,钎焊完成后,接头中镀层被钎料取代而消失。在保温时间为30 min、真空度6.5×10-3 Pa条件下,采用Al63-Cu22-Ti5-Si10钎料,55%SiCp/6063Al复合材料与可伐合金真空钎焊合理钎焊温度为560℃,合理镀层为镀铜。     

SiC／Al复合材料的组织与力学性能研究

采用无压浸渗法制备了SiC／Al复合材料．研究不同颗粒大小的复合材料的抗弯强度、金相组织和断裂机理。结果表明：颗粒尺寸为20um的SiC／Al复合材料抗弯强度最高：小颗粒复合材料的断裂以沿晶断裂为主，局部有韧性撕裂的特征，而大颗粒还伴有穿晶解理特征。     

Effect of Interfacial Reaction on the Thermal Conductivity of Al–SiC Composites with SiC Dispersions

The effect of interfacial reactions between Al and SiC on the thermal conductivity of SiC-particle-dispersed Al-matrix composites was investigated by X-ray diffraction and transmission electron microscopy (TEM), and the thermal barrier conductance ( h _c) of the interface in the Al–SiC composites was quantified using a rule of mixture regarding thermal conductivity. Al–SiC composites with a composition of Al (pure Al or Al–11 vol% Si alloy)–66.3 vol% SiC and a variety of SiC particle sizes were used as specimens. The addition of Si to an Al matrix increased the thermal barrier conductance although it decreased overall thermal conductivity. X-ray diffraction showed the formation of Al₄C₃ and Si as byproducts in addition to Al and SiC in some specimens. TEM observation indicated that whiskerlike products, possibly Al₄C₃, were formed at the interface between the SiC particles and the Al matrix. The thermal barrier conductance and the thermal conductivity of the Al–SiC composites decreased with increasing Al₄C₃ content. The role of Si addition to an Al matrix was concluded to be restraining an excessive progress of the interfacial reaction between Al and SiC.     

Microstructure evolution of SiC/SiC joints during ultrasonic-assisted air bonding using a Sn–Zn–Al alloy

Direct soldering of SiC ceramic in air at 230 °C was achieved using a Sn–9Zn–2Al alloy assisted by ultrasonic wave within seconds. Experimental results indicated that a sound metallurgical bond was formed between the SiC ceramic and Sn–9Zn–2Al alloys. The dependence of interfacial microstructure evolution on ultrasonic action duration time was investigated. Two types of interfacial structures at the interface were observed as the ultrasonic action duration time increased. An amorphous SiO₂ layer was identified at the interface for ultrasonic exposures of 1 s, which was the oxide layer formed on the SiC ceramic surface during heating. A layer of amorphous alumina with a thickness of ~ 6.8 nm formed at the interface under ultrasonic action for over 4 s. The shear strength of joints could reach up to 44 MPa. The formation of the alumina layer at the interface was attributed to the redox reaction of Al from the filler metal and SiO₂ on the SiC ceramic surface under the action of ultrasonic waves. The rapid interfacial reaction was principally induced by the acoustic cavitation and streaming effects at the liquid/solid interface.     

Investigation on ultrasonic vibration-assisted femtosecond laser polishing of C/SiC composites

This paper proposed a novel ultrasonic vibration-assisted femtosecond laser polishing method for C/SiC composites. The effect of near-field convection enhancement of ultrasonic vibration can improve the cooling of ablated particles and reduce their tendency of bonding to the material surface, reducing surface oxidation and improving the machined surface quality, removal depth and material removal rate. Through optimizing defocusing distance and scanning speed, a specific relationship between ultrasonic amplitude, pulse energy density, and spot overlap rate was established, obtaining a smooth and flat surface without defects. The residual stress of carbon fibers was investigated, and found that the coupling effect of ultrasonic energy and laser energy fields can enhance the residual compressive stress of carbon fibers. The formation of typical features of fiber fracture and pulling-out, banded pits, voids and deposition, was explained. This paper proposes new research ideas for better understanding of the removal mechanism of C/SiC composites using ultrasonic vibration-assisted femtosecond laser.     

Micromechanical modeling of thermo-mechanical properties of high volume fraction particle-reinforced refractory composites using 3D Finite Element analysis

Previously, we have developed several particle-reinforced castable ceramic composites for refractory applications with exposure to thermal shock and measured their effective thermo-elastic properties experimentally. These composites contained silicon-carbide (SiC) solid particles, zirconia (ZrO₂) bubbles, and ZrO₂ solid particles, dispersed in an alumina (Al₂O₃) matrix. The present work aims to implement representative volume element (RVE) approach and periodic boundary condition (PBC) to accurately predict those properties, namely elastic and shear modulus, thermal conductivity, and coefficient of thermal expansion (CTE), using three-dimensional (3D) Finite Element (FE) simulations while accounting for the effect of porosity. In comparison to established micromechanical schemes and two-dimensional (2D) FE predictions, 3D FE simulations specifically show more accuracy in prediction of elastic properties and thermal conductivity. This novel and thorough comparison across various thermo-mechanical properties for complex microstructures (with up to three types of inclusions) can be valuable for designing comparable high volume fraction (VF) composites.     

Revealing the dimensional stability mechanisms of SiC/Al composite under long-term thermal cycling

Long-term thermal cycling causes irreversible dimensional changes of the material, which in turn affects the reliability of precision instruments. In this paper, dimensional stability mechanisms of SiC/Al composites during thermal cycling were revealed using high-precision thermal dilatometer, XRD and spherical aberration correction transmission electron microscope (Cs-TEM). First, how the factors including dislocations, internal stress and precipitates affect the dimensional change of SiC/Al composites were separately introduced. Then, the integrated effect of these factors affecting the dimensional stability of SiC/Al composites was further discussed. Among them, the integrated effect of dislocation-internal stress in SiC/pure Al composites leads to an increase in dislocation density and average lattice constant, which leads to an increase in dimensional change. The integrated effect of dislocation-internal stress-precipitates in SiC/2024Al composites leads to a decrease in the average lattice constant and some changes in the precipitation behavior (including the type, density and lattice constant of the precipitates), which ultimately leads to a decrease in dimensional change. The dimensional change of the two types of composites was semi-quantitatively estimated. Finally, the reasons for the significantly higher dimensional stability of the SiC/2024Al composites were given.     

Interconnected SiC–Si network reinforced Al–20Si composites fabricated by high pressure solidification

The microstructures and mechanical properties of the interconnected SiC–Si network reinforced Al–20Si composites solidified under high pressures were investigated. The results demonstrate that the complete interconnected SiC–Si network can be obtained by high pressure solidification, and the connected micron-sized pores are uniformly distributed in the interconnected SiC–Si network. The compressive strength and microhardness of the SiC/Al–20Si composites solidified under 3 GPa were 723 MPa and 229 HV_0.05, respectively. Furthermore, the fracture process of SiC/Al–20Si composites was studied by in situ TEM tensile testing. The result shows that the crack first initiated and propagated at the Al/Si interface under an external load, and the SiC particles in the interconnected SiC–Si network can effectively hinder the crack propagation, thus enhancing the strength.     

In situ reaction synthesis and characterization of Ti3Si(Al)C2/SiC composites

The reaction route, microstructure, and properties of Ti₃Si(Al)C₂/SiC composites with 5–30 vol.% SiC content prepared by in situ hot pressing/solid–liquid reaction synthesis process are investigated. In contrast to monolithic Ti₃Si(Al)C₂, the SiC particle-reinforced composites exhibit higher elastic modulus, Vickers hardness, fracture toughness, improved wear, and oxidation resistance, but have a slight loss in flexural strength. The improvement in the properties is mainly ascribed to the contribution of SiC particles, and the strength degradation is due to the residual tensile stresses in the matrix.     

Properties of Hybrid-Reinforced Aluminum Matrix Composites for Precision Instruments

Hybrid-reinforcement SiC/Gr/Al composites were fabricated by squeeze-casting technology, to provide a novel solution to machinable materials for precision instruments. The effect of flake graphite particles on mechanical properties, machinability, dimensional stability and coefficient of thermal expansion was studied. With the addition of 5% graphite particles in the SiC/Al composites, the tool life during cutting is prolonged by 40% and the tensile strength, elastic modulus and specific modulus are 405 MPa, 150 GPa and 51 GPa cm³/g respectively. The micro-yield stress of SiC/5%Gr/Al composite is higher than 300 MPa and the linear CTE is 11.6 × 10⁻⁶ °C⁻¹. The properties of SiC/Gr/Al composite were in contrast to conventional materials of precision instruments and the advantages in application are discussed.     

SiC particle reinforced Al matrix composites brazed on aluminum body for lightweight wear resistant brakes

Aluminum alloys are well known light-weight alloys and very interesting materials to optimize the strength/weight ratio in order to reduce automotive vehicle weight, fuel consumption and CO₂ emissions; unfortunately, they are also relatively soft and therefore cannot be used for high wear applications.The aim of this work was to develop an aluminum alloy brake disc with wear-resistant SiC particle reinforced aluminum matrix composites (SiC/Al) joined on to its surface.Different approaches based on brazing or shrink fitting joining technologies were used to join SiC/Al to the aluminum alloy surface.A functional graded structure was built by brazing thin layers of aluminum matrix composites reinforced with progressively higher amount of SiC particles by using a Zn–Al based alloy as joining material. Several samples were prepared by shrink fitting and brazing: 40 mm x 40 mm x 10 mm samples and a 100 mm diameter brake disc with 68% SiC particle reinforced Al matrix surface and aluminum alloy A365 body. Tribological tests demonstrated that an aluminum alloy brake disc with wear-resistant SiC particle reinforced aluminum matrix composites (SiC/Al) brazed on its surface is a promising technical opportunity.     

SiC改性C/C复合材料的制备及其烧蚀性能

采用超声波震荡法将SiC微粉添加到二维针刺碳毡预制体中,利用热梯度化学气相浸渗工艺沉积热解碳制备了SiC改性碳纤维增强碳基(carbon fiber reinforced catbon,C/C)复合材料.借助x射线衍射与扫描电子显微镜检测和观察材料的微观结构,利用氧-乙炔烧蚀实验测试材料的抗烧蚀性能.结果表明:SiC微...     

Chemical vapor infiltration of additively manufactured preforms: Pore-resolved simulations and experimental validation

The densification of additively manufactured porous preforms by chemical vapor infiltration (CVI) is studied using pore-resolved simulations and experiments. Experimentally, 3D printed silicon carbide (SiC) preforms are subject to CVI synthesis using methyltrichlorosilane (MTS) precursor to obtain high purity SiC/SiC composites. Optical images of the cross sections of the processed preforms are analyzed to obtain the spatial porosity distribution. The numerical method is based on a level set formulation to capture the spatial distribution and time evolution of the pore scale microstructural characteristics. The coupled transport and kinetic effects are represented using a dimensionless Thiele modulus. Simulations are initialized using representative synthetic preform geometries comprising of packed particles based on the size distribution of the powder used for 3D printing. The simulation results are validated against the experimental observations in terms of total density and the distribution of residual porosity. The densification characteristics, porosity classification, concentration profiles, and structure functions are analyzed as functions of processing temperature and Thiele modulus.     

Ti3SiC2/Al2O3复合材料的制备与性能研究

以TiC／TiO2/Si／Al／Ti等为主要原料，采用热压法原位合成Ti2SiC2／Al2O3复合材料，分别探讨了Al掺入量和工艺制度对Ti3SiC2/Al2O3复合材料物相、显微结构以及性能的影响。结果表明：原位合成制备的Ti3SiC2/Al2O3复合材料与传统方法合成制备的纯Ti3SiC2材料相比，材料的硬度和致密度均有很大的提高。