Effect of aging treatment on mechanical properties of (SiCw+SiCp)/2024Al hybrid nanocomposites

2024Al based composites reinforced by a hybrid of SiC whisker and SiC nanoparticle were fabricated by a squeeze casting route. In the (SiCw+SiCp)/Al composites, the volume fraction of SiC whisker is 20% and that of SiC nanoparticle is 2%, 5% and 7%, respectively. The as cast composites were solution treated followed by aging treatment. The experimental results show that the SiC nanoparticles are more effective in improving the hardness and tensile strength of the composites than SiC whiskers. The hardening kinetics of the composites is enhanced by reinforcements addition and the peak aging time is 4-5 h. The hardness of all the hybrid composite decreases at the initial aging stage, suggesting that dislocation recovery softening process coexists with precipitation hardening. DSC study shows that the GP zone formation of the hybrid composites is suppressed.

Effects of thermal oxidation on microwave-absorbing and mechanical properties of SiC_f/SiC composites with PyC interphase

The SiCf/SiC composites containing PyC interphase were prepared by chemical vapor infiltration process. The influences of thermal oxidation on the complex permittivity and microwave absorption properties of Si Cf/Si C composites were investigated in the frequency range of 8.2-12.4 GHz. Both the real and imaginary parts of the complex permittivity decreased after thermal oxidation. The composites after 100 h thermal oxidation showed that reflection loss exceeded-10 d B in the frequency of 9.7-11.9 GHz and the minimum value was-11.4 d B at 11.0 GHz. The flexural strength of composites decreased but fracture behavior was improved obviously after thermal oxidation. These results indicate that the SiCf/SiC composites containing PyC interphase after thermal oxidation possess good microwave absorbing property and fracture behavior.

Microstructure and mechanical properties of 3D fine-woven punctured C/C composites with P_yC/SiC/TaC interphases

The 3D fine-woven punctured C/C-(PyC/SiC/TaC)composites,composed of PyC/SiC/TaC interphases and pyrocarbon (PyC)matrix,were synthesized by isothermal chemical vapor infiltration(ICVI)methods.The alternating layers and the structure of these composites were examined by polarized light microscopy(PLM),X-ray diffractometry(XRD)and scanning electron microscopy(SEM).It is found that the PyC matrix has rough laminar(RL)structure,the TaC layer has NaCl-type cubic structure,and the SiC layer has few wurtzite type 10H-SiC besidesβ-SiC structure.The effects of fiber coating and the bulk density on the tensile and flexural properties of composites along X or Y and Z direction were investigated.It is shown that fiber coated 3D woven punctured C/C composites have good tensile and flexural strength,and the maximum of flexural strength is 375 MPa in X or Y direction at density of 1.89 g/cm 3 ,which is about three times higher than that of samples without TaC/SiC fiber coating.The flexural strength and bending strength increase with increasing the density of the composites.The analysis of fracture surfaces reveals that fibers and fiber bundles are pulled out in composites,indicating that the composite exhibits a non-linear failure behavior through propagation and deflection of the cracks.

INVESTIGATION ON MECHANICAL PROPERTIES OF ZN-AL/SIC PARTICULATE COMPOSITES

In order to improve the properties of ZA 27 and ZA4-3 zinc alloys and broaden their application ranges,SiC particlj1Ale composites, prepared by means of rheological casting technology, are investigated individually on their rT..t'llanical properties. The results of ne-cural strength, impact strensttl, compressive strength, hardness values and wear rate of the composites show that the addition of SiCp, leads to the increase of the compressive strength and hardness values at both room and higher temperature, and wear resistance of the materials, accompanying with the slight decrease of the fie-cural strength and sharp reduction of the impacttoughness. The factors affecting the mechanical properties of the composites are discussed in the paper.

Microstructure and Mechanical Properties of Si_3N_4 Composites Containing SiC Platelet

Hoppressed Si3N4/SiC platelet composites had been investigated with respect to their microstructure and mechanical properties. The results indicate that Vickers hardness, elastic modulus and fracture toughness of the composites were increased by the addition of SiC platelet until the content up to 20 vol pct. A slight decrease in flexural Strength was measured at room temperature with increasing SiC platelet content. The high temperature flexural strength tests at 1150, 1250, and 1350℃ were conducted. It was found that the flexural strength at elevated temperature was degraded with the rising temperature, and the downward trend of flexural strength for the composite containing 10 vol. pct SiC platelet was less. The results indicate that SiC platelet had a positive influence on the high temperature strength. Effects of SiC platelet reinforcement were presented

Controlling the Si/C ratio in SiC matrix based on the modified polymethysilane for C/C-SiC composites with enhanced mechanical properties

Fabricating SiC matrix with controllable Si/C ratio for C/C-SiC composites via precursor infiltration and pyrolysis is difficult to realize due to the absence of suitable precursors.Here,SiC precursors with Si-rich(Si/C=1.23),nearstoichiometric(Si/C=1.01),and C-rich(Si/C=0.88)pyrolyzed ceramics at 1200℃ were successfully synthesized by the novel modification of polymethysilane.The structure and ceramization of synthesized SiC precursors were studied,and C/C-SiC composites with similar Si/C ratio in SiC matrix were also fabricated.The results revealed that the defects and Young’s modulus of SiC matrix and the thermal residual stress on pyrolytic carbon coated carbon fiber were determined by the Si/C ratio.As a result,the Si/C ratio exerted significant effects on the crack deflection behavior and the mechanical properties of the composites.The composites with near-stoichiometric SiC matrix showed excellent mechanical properties because of the effective crack deflection and the moderate Young’s modulus of their SiC matrix.The flexural strength,flexural modulus,and compressive strength were 423±27 MPa,33.41±4.52 GPa,and 393±8 MPa,respectively.Meanwhile,after a heat treatment at 1600℃,the role of carbon fiber toughening was improved and accompanied by a decrease in mechanical properties for all composites,which was attributed to the increased defects in SiC matrix and the damaged interfaces by the thermal residual stress.

Effects of dip-coated BN interphase on mechanical properties of SiC_f/SiC composites prepared by CVI process

BN interphase was successfully synthesized on SiC fiber fabrics by dip-coating process using boric acid and urea as precursors under N2 atmosphere. The morphology of BN interphase was observed by SEM, and the structure was characterized by XRD and FT-IR spectra. The SiCf/SiC composites with dip-coated BN interphase were fabricated by chemical vapor infiltration （CVI） process, and the effects ofBN interphase on the mechanical properties of composites were investigated. The results show that the SiC fibers are fully covered by BN interphase with smooth surface and turbostratic structure （t-BN）, and the thickness is about 0.4 μm. The flexural strengths of SiCf/SiC composites with and without BN interphase are about 180 and 95 MPa, respectively. Compared with the as-received SiCf/SiC composites, the composites with BN interphase exhibit an obvious toughened fracture behavior. From the microstructural analysis, it can be confirmed that the BN interphase plays a key part in protecting the fibers from chemical attack during matrix infiltration and weakening interfacial bonding, which can improve the mechanical properties of SiCf/SiC composites remarkably.

Microstructure and Mechanical Properties of Dy-α-sialon/Nano-size SiC Composites

The composite of Dy-α-sialon/10 wt pct nano-size SiC particles has been prepared from precursor powders of Si3N4, AIN, Al2O3, Dy2O3 and nano-size β-SiC. The hardness, toughness and bending strength of the composite at ambient temperature are a little higher than those of Dy-α-sialon.while the bending strength is maintained up to 1000℃ and about 2 times more than that of Dy-α-sialon at the same temperature. The fracture surfaces show that the grain size of the composite is smaller than that of Dy-α-sialon, and both Of them have predominately transgranular mode of fracture. It is believed that the decrease of the bending strength of Dy-α-sialon at elevated temperature is caused by the viscous flow of the grain boundary phase, while the addition of nanosize SiC particles effectively increases the viscosity of the grain boundary phase and therefore prevents the strength loss of Dy-α-sialon/nano-size SiC composites at elevated temperature

Effects of Mg content on microstructure and mechanical properties of SiC_p/Al-Mg composites fabricated by semi-solid stirring technique

10%(volume fraction) SiCp/Al-Mg composites with different Mg contents were successfully fabricated by semi-solid mechanical stirring technique under optimum processing conditions.Effects of Mg content on microstructure and mechanical properties were studied by scanning electron microscopy(SEM),X-ray diffractometry(XRD) and transmission electron microscopy(TEM).The results indicate that SiC particles disperse homogeneously in Al-Mg matrix and interfacial reaction between Al matrix and SiC particles is effectively controlled.Distribution of SiCp reinforcement and interfacial bonding are improved by adding Mg.Additionally,the mechanical properties of composites are remarkably improved with the Mg content increasing.

Effect of rare earth La_2O_3 on the microstructure and mechanical properties of TiC/W composites

In this study, La2O3 was investigated as an additive to TiC/W composites. The composites were prepared by vacuum hot pressing, and the microstructure and mechanical properties of the composites were investigated. Experimental results show that the grain size of the TiC/W composites is reduced by TiC particles. When 0.5 wt.% La2O3 is added to the composites, the grain size is reduced further. According to TEM analysis, La2O3 can alleviate the aggregation of TiC particles. With La2O3 addition, the relative density of the TiC/W composites can be improved from 95.1% to 96.5%. The hardness and elastic modulus of the TiC/W ＋ 0.5 wt.% La2O3 composite are little improved, but the flexural strength and the fracture toughness increase to 796 MPa and 10.07 MPa·m^1/2 respectively, which are higher than those of the TiC/W composites.

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.

Microstructure, sintering behavior and mechanical properties of SiC/MoSi_2 composites by spark plasma sintering

SiC/MoSi2 composites were synthesized at different temperatures by spark plasma sintering using Mo, Si and SiC powders as raw materials. The phase composition, microstructure and mechanical properties of the as-prepared composites were investigated and the sintering behavior was also discussed. Results show that SiC/MoSi2 composites are composed of MoSi2, SiC and trace amount of Mo4.8Si3C0.6 phase and exhibit a fine-grain texture. During the synthesis process, there was an evolution from solid phase sintering to liquid phase sintering. When sintered at 1600 °C, the SiC/MoSi2 composites present the most favorable mechanical properties, the Vickers hardness, bending strength and fracture toughness are 13.4 GPa, 674 MPa and 5.1 MPa·m^1/2, respectively, higher 44%, 171%, 82% than those of monolithic MoSi2. SiC can withstand the applied stress as hard phase and retard the rapid propagation of cracks as second phase, which are beneficial to the improved mechanical properties of Si C/MoSi2 composites.

Microstructures and mechanical properties of 2024Al/Gr/SiC hybrid composites fabricated by vacuum hot pressing

The 2024Al/Gr/SiC hybrid composite plates with 5%-10% SiC particles （volume fraction） and 3%-6% flaky graphite （Gr） （volume fraction） were fabricated by vacuum hot pressing and hot extrusion processing. The effects of SiC and Gr on the microstructures and mechanical properties of the composites aged at 160, 175 and 190℃ were studied by optical microscopy, scanning electron microscopy （SEM）, and hardness and tensile tests. The results indicate that the SiC particles have a more obvious effect on accelerating the aging response as compared with the Gr. Both the tensile strength and elongation are reduced by the Gr and SiC particles added into the matrix, while the Gr has a more negative influence on the elongation than the SiC particles. The tensile strength （ab）, yield stress （as） and elongation （δ） of the 2024Al/3Gr/10SiC composite aged at 165℃ for 8 h are 387 MPa, 280.3 MPa and 5.7%, respectively. The hybrid composites are characterized by ductile fracture, which is associated with the ductile fracture of the matrix and the tearing of the interface between the matrix and the particles.

Engineered Wood/Bamboo Laminated Composites for Outdoor Hydrophilic Platforms:Structural Design and Performance

Landscape designers increasingly prefer to use wood/bamboo-based composites for outdoor hydrophilic platforms owing to their natural surface texture,high performance,and sustainability to facilitate extensive interaction between people and water and enable the full range of ecological functions of water resources.In this study,four laminated composite(LC)structures were designed and manufactured using fluffed bamboo and wood veneers.Their surface textures,profile densities,water resistances,and mechanical properties were then evaluated.The type of fluffed veneer of the surface layer determined the texture of the LC surface.The specific structures of fluffed bamboo and wood veneer laminations were found to affect the LC profile density variability,water resistance,and mechanical properties owing to the differences in the strength and interfacial properties of bamboo and wood fibers.Finally,the water resistance and mechanical properties of all four LCs were found to be much higher than the highest level specified in GB/T 20241-2006 for“laminated veneer lumber”and GB/T 30364-2013 for“bamboo scrimber flooring”,indicating that they are promising materials for structures and flooring,particularly for outdoor hydrophilic platforms.

Effects of volume fraction of SiC particles on mechanical properties of SiC/Al composites

SiC particle reinforced pure aluminum composites were fabricated using a powder metallurgy method.The effect of the volume fraction of the SiC particles on the mechanical properties of the composites was studied by both model simulation and experiment.The results indicate that the yield strength and tensile strength increase,but the elongation decreases with the increase in the volume fraction of the SiC particles.Both the modified shear lag model and the multi-scale model predicted yield strength and normalized elongation show similar evolution trends with the experimental data.However,the modified shear lag model underestimates the yield strength due to the ignorance of the strengthening mechanisms caused by grain refinement and dislocations interaction by the introduction of the SiC particles,and the multi-scale model overestimates the normalized elongation due to the ignorance of the pores distributed in the matrix.

A Review of Basic Mechanical Behavior of Laminated Bamboo Lumber

Over the past decade,the physical and mechanical performances of laminated bamboo lumber(LBL)–a bamboo-based structural material,have been extensively studied using experimental,analytical,and numerical approaches.This paper presents a review of existing knowledge in the literature about the mechanical properties of LBL.The paper involved the review of the response of LBL to different types of loading such as tension,bending,compres-sion,and shear.Based on results of the literature reviewed,the strength of LBL parallel to grain was 90–124 MPa with MOE of 10700 MPa in tension,29.55–72.60 MPa,and MOE of 8396–11022 MPa in compression,63.87–128.4 MPa,and MOE of 8320–10912 MPa in bending,and 7.15–17.5 MPa in shear.The average strength of LBL was similar and in some cases exceeded the average values of bamboo-or wood-based materials,while the variability of its mechanical parameters was lower.The variability in strength values of LBL was affected by bamboo species,density and thickness of bamboo strips,growth portion,type of treatment,strips arrange-ments,and type of adhesive which in turn calls for classification of LBL by strength grades,degree of hardness,the capability of impregnation and penetration,as well as by areas of application in construction.The study pro-vided and discussed concluding observations,the current research gap,and future research directions on the mechanical properties of LBL.

Effects of addition of rare earth on properties and structures of Ni-W-B-SiC composite coatings

The effects of rare earth (RE) on the composition, phase structures, surface morphologies and hardness of electrodeposited RE Ni W B SiC composite coatings were discussed. The results show that W and SiC contents in the coatings increase with the increase of RE in the bath. When RE is added in the coatings, the grains are refined and the trend of formation of amorphous coatings is increased. Moreover, the thermal stability of the RE Ni W B SiC composite coatings is enhanced. The hardness of the coatings is increased with the increase of heat treatment temperature, and it reaches the peak value when heated at 400 ℃. Besides, the hardness of the RE Ni W B SiC coatings is higher than that of the Ni W B SiC coatings.

Preparation and mechanical properties of SiC/2024 composite by semisolid casting

A SiC/2024 composite was made by semisolid casting. The wetting between SiC and Al matrix is improved by treating SiC particles at a high temperature, coating K2ZrF6, and adding Mg to the Al melt. An effective way to remove the gas around SiC particles was also found. Microstructures were observed under optical microscope (OM) and scanning electron microscopy (SEM). The results show that SiC particles and Al matrix are well bonded and no gaps or cavities around the particles are observed. SiC particles distribute homogeneously in the Al matrix. The existence of SiC particles results in the increase of wear resistance and strength.

SiC-W层状复合材料增韧机理分析

为分析 Si C W层状复合材料增韧机理 ,对以 Si C陶瓷胶片为基体层 ,金属 W为夹层的 Si C W层状复合材料进行了力学性能测试 ,并用电镜法得到其断面显微结构照片。试验结果表明 :1)与 Si C单材料断裂韧性相比 ,Si C W层状复合材料的断韧性增大 ;2 )在基体层厚度不变 ,夹层厚度为 10～ 5 0μm时 ,Si C W层状复合材料的断裂韧性随夹层厚度的增加而增大 ,而抗弯强度随之下降 ;3)材料在不同方向断裂韧性不同。 Si CW层状复合材料裂韧性增大的原因是 :1)夹层晶体颗粒大于基体层的 ,其沿晶断裂形式延长了裂纹扩展路径 ;2 )断裂过程中有晶片拨出消耗了能量 ;3)

Mechanical Properties of Laminated Aluminum-Based Plates with Gradient Interface

Two laminated composites, 2024/3003 and 7075/6009 aluminum alloys were prepared by double-stream-pouring continuous casting (DSPCC) followed by plastic deformation and heat treatment. The interface characteristics between the external and internal layers of the composites in the as-cast and plastic deformation conditions were analyzed. The results show that the macrostructure difference between the external and internal layers of both composite ingots in the as-cast condition can be clearly clarified but the gradient interfaces are not distinct. However, the macro-scale gradient layers can be demonstrated from the hardness distribution in the cross sections of the composite ingots. After plastic deformation, the gradient characteristic of the interface in the laminated composites maintains except for the decrease in the interface thickness. After plastic deformation and T6 heat treatment, the ultimate strength, yield strength and elongation of 2024/3003 composite plate are 2.35, 3.10 and 0.9 times of that of 3003 aluminum alloy, respectively. The ultimate strength and yield strength of 7075/6009 composite plate increase 47 % and 82 % of that of 6009 aluminum alloy, respectively and the elongation of the composite is still as high as 15.3 %.