Multi-scale Modeling and Finite Element Analyses of Thermal Conductivity of 3D C/SiC Composites Fabricating by Flexible-Oriented Woven Process

Thermal conductivity is one of the most significant criterion of three-dimensional carbon fiber-reinforced SiC matrix composites(3D C/SiC).Represent volume element(RVE)models of microscale,void/matrix and mesoscale proposed in this work are used to simulate the thermal conductivity behaviors of the 3D C/SiC composites.An entirely new process is introduced to weave the preform with three-dimensional orthogonal architecture.The 3D steady-state analysis step is created for assessing the thermal conductivity behaviors of the composites by applying periodic temperature boundary conditions.Three RVE models of cuboid,hexagonal and fiber random distribution are respectively developed to comparatively study the influence of fiber package pattern on the thermal conductivities at the microscale.Besides,the effect of void morphology on the thermal conductivity of the matrix is analyzed by the void/matrix models.The prediction results at the mesoscale correspond closely to the experimental values.The effect of the porosities and fiber volume fractions on the thermal conductivities is also taken into consideration.The multi-scale models mentioned in this paper can be used to predict the thermal conductivity behaviors of other composites with complex structures.

3D Evaluation Method of Cutting Surface Topography of Carbon / Phenolic (C/Ph) Composite

3D evaluation method of cutting surface topography for C/Ph composites was established.The cutting surface was measured by Talyscan 150,using 3D non-contact measurement.Through the results of 2D and 3D roughness evaluating for C/Ph composite and Duralumin,the 2D evaluation method of the cutting surface topography of C/Ph composite loses a lot of information,the characteristics of the surface topography of C/Ph composite can be comprehensively and authentically evaluated only by 3D evaluation method.Furthermore,3D amplitude and spatial parameters were adopted to evaluate the surface.The results show that： the topography of the C/Ph composite is anisotropic,there are more valleys in the machined surface of C/Ph than that of duralumin,and there are not obvious feeding textures for C/Ph,which indicates the machining mechanism is different from the metal.In conclusion,the topography of the C/Ph composite cutting surface is anisotropic;the cutting surface of C/Ph composite needs 3D evaluation method.

Tensile Properties of 3-Dimension-4-directional Braided C_f/Si C Composite based on Double-scale Model

The longitude tensile properties of 3-Dimension-4-directional（3D-4d） braided C/Si C composites（CMCs） were investigated with the help of a double scale model. This model involves micro-scale and unit-cell scale. In micro-scale, the tensile properties of fiber tows which involves matrix cracking, interfacial debonding, and fiber failure are studied. The unit-cell scale model can reflect the braided structure and simulate the tensile properties of 3D-4d CMCs by introducing the tensile properties of fiber tows into it. Quasi-static tensile tests of 3D-4d braided CMCs were performed on a PWS-100 test system. The predicted tensile stressstrain curve by the double scale model is in good agreement with that of the experimental results.

A 3D evaluation method of cutting surface topography of carbon/carbon(C/C) composite

This paper aims to establish a 3D evaluation method for cutting surface topography of C/C composites. The cutting surface is measured by Talyscan 150, using 3D non-contact measurement. By evaluating 2D and 3D roughness of C/C composite and Duralumin, the 2D evaluation method of the cutting surface topography of C/C composite loses a lot of information, and the characteristics of the surface topography of C/C composite can be comprehensively and authentically evaluated only by the 3D evaluation method. Furthermore, 3D amplitude and spatial parameters are adopted to evaluate the surface and the results show that： the topography of the C/C composite is anisotropy and there are no obvious feeding textures but abrupt peaks and valleys on surface of the C/C composite, which indicates that the machining mecha- nism is different from that of the metal. In conclusion, The C/C composite surface is evaluated using a 3D evaluation method, the roughness error is small, and the unique topography characteristics earl be au- thentically evaluated.

Thermodynamic Analysis of Combusion Synthesis and Reaction Hot Pressing of Al_2O_3/B_4C Composite

The equilibrium phases and adiabatic temperature for combustion synthesis and reaction hot pressing of Al 2O 3/B 4C employing ① Al, B 2O 3 and C ② C, B, Al 2O 3 as starting reactants were analyzed by the CALPHAD technique. It is shown that the equilibrium phases at the adiabatic temperature in the combusion system (1) are not the intended composite Al 2O 3/B 4C but other phases. Good agreement with the experimental data was achieved for the calculated adiabatic temperature. The results were discussed with respect to the elimination of the by product in the combustion synthesis. It also revealed that the reactant mixture (2) is a weak exothermic or endothermic reaction system, which can be employed in the reaction hot pressing.

Al_4C_3对AZ91D镁合金铸态显微组织与性能的影响

借助SEM、EDS、XRD、DTA研究Al4C3对AZ91D镁合金铸态显微组织与性能的影响。结果表明,少量Al4C3对合金铸态组织具有明显的细化作用,而且共晶组织形貌发生明显改变,由完全离异的骨骼状β相共晶组织和共生生长的层片状共晶组织α+β转变为蜂窝状的部分离异共晶组织α+β,同时β相的尺寸变小、分布更趋弥散。通过能谱分析、差热分析以及错配度的计算,证实Al4C3可成为初生α-Mg的良好异质核心。显微组织的细化使强度性能明显提高,延伸率的提高幅度有限,耐腐蚀性能改善。

Al_4C_3和Ce对AZ91D镁合金铸态显微组织和性能的影响

借助SEM、EDS、XRD、DTA等研究了Al4C3和Ce加入对AZ91D镁合金铸态组织和性能的影响。结果表明:加入0.6%Al4C3能显著细化合金晶粒,使粗大骨骼状β相和层片状α+β共晶组织转变为蜂窝状的部分离异共晶组织,同时β相的尺寸变小、分布较均匀。在此基础上,复合添加0.2%Ce后细化效果更好,β相分布更趋均匀且含量减少。此外,组织中有少量针状化合物Al4Ce形成。通过错配度计算、能谱分析以及差热分析,证实了Al4C3可成为初生α-Mg的良好异质核心。显微组织的细化有利于合金强度性能及耐腐蚀性能的明显提高。

Mg-Al_4C_3中间合金在AZ91D镁合金中的细化效果及机理

采用SEM、EDS和XRD等测试手段研究粉末原位合成法制备的Mg-50%Al4C3中间合金对AZ91D镁合金显微组织的细化效果。结果表明:中间合金的加入可显著细化AZ91D镁合金的α-Mg晶粒。当Al4C3的含量为1.0%时,α-Mg晶粒的尺寸由基体合金的142.9μm降至63.2μm,降低幅度约为56%,且共晶组织形貌发生明显改变,由完全离异的骨骼状β共晶组织和共生生长层片状α+β共晶组织转变为蜂窝状的α+β部分离异共晶组织,同时β相的尺寸变小、分布更趋弥散。通过能谱分析、面错配度计算及差热分析,证实Al4C3可成为初生α-Mg晶粒的良好异质核心。此外,显微组织的细化导致合金力学性能的提高。

Elastic Modulus Prediction of Three-dimension-4 Directional Braided C_f/SiC Composite Based on Double-scale Model

Double-scale model for three-dimension-4 directional（3D-4d） braided C/SiC composites has been proposed to investigate its elastic properties. The double-scale model involves micro-scale that takes fiber/ matrix/porosity in fibers tows into consideration with unit cell which considers the 3D-4d braiding structure. Micro-optical photographs of composites have been taken to study the braided structure. Then a parameterized finite element model that reflects the structure of 3D-4d braided composites is proposed. Double-scale elastic modulus prediction model is developed to predict the elastic properties of 3D-4d braided C/SiC composites. Stiffness and eompliance-averaging method and energy method are adopted to predict the elastic properties of composites. Static-tension experiments have been conducted to investigate the elastic modulus of 3D-4d braided C/SiC composites. Finally, the effect of micro-porosity in fibers tows on the elastic modulus of 3D-4d braided C/SiC composites has been studied. According to the conclusion of this thesis, elastic modulus predicted by energy method and stiffness-averaging method both find good agreement with the experimental values, when taking the micro-porosity in fibers tows into consideration. Differences between the theoretical and experimental values become smaller.

Fabrication and evaluation of high-performance 3D interpenetrated network structures SiC/Al composites with high-purity plate-like a-SiC framework

To reinforce compatibility with the thermophysical and mechanical properties of SiC/Al composites for electronic packaging to improve the stability and reduce fatigue failure of electronic integrated devices,a novel 3D SiC reinforced framework with interpenetrated plate-like a-SiC grains was synthesized.A small amount of doped a-SiC was seeded to induce the transformation of b-SiC to plate-like a-SiC at 2,300℃,forming a high-purity a-SiC strongly bonded framework.Vacuum/gas pressure infiltration of Al alloy was subsequently used to manufacture the 3D interpenetrated network structure SiC/Al(SiC3D/Al)composite.Characterization results showed that 15%(in mass)seeds provided the composite with the optimal comprehensive performance,including a low coefficient of thermal expansion(CTE)of 5.54×10^(-6)K^(-1),a high thermal conductivity(l)of 239.08 W·m^(-1)·K^(-1),the highest flexural strength of 326.84 MPa,and a low thermal deformation parameter(TDP)of 0.023.High-purity plate-like grains enhanced the purity of the framework promoting a significant improvement in l.As the seed content increased to 20%(in mass),both CTE and l reached optimal values of 5.22×10^(-6)K^(-1)and 243.14 W·m^(-1)·K^(-1),but the mechanical properties declined by 10.30%.The synergistic effect of the well-bonded interface and the high-purity 3D SiC framework balanced excellent mechanical properties and multiple thermal functions.

Mn、Fe对AZ91D镁合金中Al_4C_3细化效率的影响

采用OM、SEM、EDS等测试手段研究了Mn、Fe对Al4C3细化AZ91D镁合金显微组织的影响。结果表明,经0.6%Al4C3细化后,基体合金的平均晶粒尺寸由360μm减小至215μm。在此基础上,将基体合金的Mn含量由0.23%增至0.5%,可使合金的平均晶粒尺寸进一步降至130μm。继续增加Mn量至0.7%时,其晶粒尺寸变化不大。当基体合金中Fe含量由0.0021%增至0.1%时,晶粒尺寸由215μm减小至123μm。Mn、Fe对AZ91D合金中Al4C3细化效率的影响机制可能是,三者共同作用形成的Al-C-O-Mn-Fe复杂颗粒可作为α-Mg晶粒的异质核心。

3D printing of PEEK–cHAp scaffold formedical bone implant

The major drawback associated with PEEK implants is their biologically inert surface,which caused unsatisfactory cellular response and poor adhesion between the implants and surrounding soft tissues against proper bone growth.In this study,polyetheretherketone(PEEK)was incorporated with calcium hydroxyapatite(cHAp)to fabricate a PEEK-cHAp biocomposite,using the fused deposition modeling(FDM)method and a surface treatment strategy to create microporous architectures onto the filaments of PEEK lattice scaffold.Also,nanostructure and morphological tests of the PEEK-cHAp biocomposite were modeled and analyzed on the FDM-printed PEEK-cHAp biocomposite sample to evaluate its mechanical and thermal strengths as well as in vitro cytotoxicity via a scanning electron microscope(SEM).A technique was used innovatively to create and investigate the porous nanostructure of the PEEK with controlled pore size and distribution to promote cell penetration and biological integration of the PEEK-cHAp into the tissue.In vivo tests demonstrated that the surface-treated micropores facilitated the adhesion of newly regenerated soft tissues to form tight implant-tissue interfacial bonding between the cHAp and PEEK.The results of the cell culture depicted that PEEK-cHAp exhibited better cell proliferation attachment spreading and higher alkaline phosphatase activity than PEEK alone.Apatite islands formed on the PEEK-cHAp composite after immersion in simulated body fluid of Dulbecco’s modified Eagle medium(DMEM)for 14 days and grew continuously with more or extended periods.The microstructure treatment of the crystallinity of PEEK was comparatively and significantly different from the PEEK-cHAp sample,indicating a better treatment of PEEK-cHAp.The in vitro results obtained from the PEEK-cHAp biocomposite material showed its biodegradability and performance suitability for bone implants.This study has potential applications in the field of biomedical engineering to strengthen the conceptual knowledge of FDM and medical implants fabricated from PEEK-cHAp biocomposite materials.

SiC晶须和Ti(C,N)颗粒协同增韧Al_2O_3陶瓷刀具的研究

采用热压工艺烧结制备了SiCW Ti(C ,N) Al2 O3(Y2 O3)陶瓷刀具复合材料。研究了不同烧结温度(16 0 0～ 175 0℃ )下 ,材料的致密度和力学性能 (断裂韧性KIC ,维氏硬度HV和抗弯强度σf)随晶须含量 (10 %～4 0 % )的变化关系 ;探讨了SiC晶须和Ti(C ,N)颗粒对Al2 O3基体的协同增韧机理。同时与SiCW Al2 O3陶瓷及Ti(C ,N) Al2 O3陶瓷作对比研究。结果表明 :SiCW Ti(C ,N) Al2 O3(Y2 O3)陶瓷材料在 175 0℃ ,晶须含量为 2 0 %时获得最佳的综合力学性能 :KIC =7 11MPa m1 2 ,HV =2 1 16GPa ,σf=82 0MPa ;明显高于SiCW 含量为 2 0 %的SiCW Al2 O3陶瓷和不加晶须的Ti(C ,N) Al2 O3陶瓷。第三相Ti(C ,N)颗粒的加入与晶须一起产生明显的迭加增韧效果 ,而且对SiCW 的各种增韧机制起到了促进作用。

3D-C／SiC复合材料的高温疲劳性能

采用应力比为0.1和0.5,频率为60和20Hz的正弦波从室温至1500℃,在10-4Pa真空中对3D-C/SiC复合材料进行拉—拉疲劳实验;获得其在应力比0.1频率60Hz条件下室温、1100、1300和1500℃的疲劳曲线,以及应力比0.1频率20Hz和应力比0.5频率20Hz条件下1500℃的疲劳曲线。结果表明,若取循环基数为106周,应力比0.1频率60Hz条件下,3D-C/SiC复合材料在室温、1100、1300和1500℃的疲劳极限分别为235、350、285和240MPa,约为其拉伸强度的87%、97%、94%和90%;疲劳极限与比例极限和拉伸强度随温度有相似的变化规律,即随温度升高而增加,在1100℃达到最大值,尔后随温度增加而下降;但是S—Nf曲线的斜率的变化规律恰好与此相反。应力比的增加和频率的降低,均使复合材料1500℃的疲劳极限有所减小。

Effect of Al_(2)O_(3)on the Mechanical Properties of(B_(4)C+Al_(2)O_(3))/Al Neutron Absorbing Materials

B_(4)C/Al composites are widely utilized as neutron absorbing materials for the storage and transportation of spent nuclear fuel.In order to improve the high-temperature mechanical properties of B_(4)C/Al composites,in-situ nano-Al_(2)O_(3)was introduced utilizing oxide on Al powder surface.In this study,the Al_(2)O_(3)content was adjusted by utilizing spheroid Al powder with varying diameters,thereby investigating the impact of Al_(2)O_(3)content on the tensile properties of(B_(4)C+Al_(2)O_(3))/Al composites.It was found that the pinning effect of Al_(2)O_(3)on the grain boundaries could hinder the recovery of dislocations and lead to dislocation accumulation at high temperature.As the result,with the increase in Al_(2)O_(3)content and the decrease in grain size,the high-temperature strength of the composites increased significantly.The finest Al powder used in this investigation had a diameter of 1.4μm,whereas the resultant composite exhibited a maximum strength of 251 MPa at room temperature and 133 MPa at 350℃,surpassing that of traditional B_(4)C/Al composites.

Numerical simulation on thermal expansion coefficient of 3D braided C/C composites

To effectively get the thermal expansion coef- ficient （CTE） of three-dimensional （3D） braided C/C composites and study the variations, a VC＋＋ program with graphical user interfaces was obtained, based on the yam unit model and numerical analysis. With the limited basic properties of carbon fibers and carbon matrix, CTE of 3D braided C/C composites is obtained at 85 ~C. The deviation between the simulated and exl^erimental axial CTE of 3D braided C/C composites is no more than 11%. The effects of different parameters （including the braiding angle of 3D braided preform, the fiber volume fraction and the porosity of 3D braided C/C composites, and the elastic modulus, Poisson＇s ratio and CTEs of carbon fibers and carbon matrix） were analyzed with the program. The results show that the axial CTE of C/C composites decreases with the increase of the braiding angle, the fiber volume fraction, and the porosity of 3D braided C/C composites. The transverse elastic modulus of carbon fibers has the greatest effect on the axial CTE among the studied mechanical parameters, followed by the elastic modulus and Poisson＇s ratio of carbon matrix.

Microstructure and mechanical properties of Al-B4C composite at elevated temperature strengthened with in situ Al2O3 network

This study evaluated the mechanical properties and thermal properties of Al-12 vol%B4 C composite at elevated temperature strengthened with in situ Al2 O3 network.The composite was fabricated using powder metallurgy(PM)with raw materials of fine atomized aluminum powders,and the associated microstructures were observed.At 350℃,the composite had ultimate tensile strength of UTS=137 MPa,yield strength of YS0.2=118 MPa,and elongation ofε=4%.Besides,the mechanical properties of the composite remained unchanged at 350℃after the long holding periods up to 1000 h.The excellent mechanical properties and thermal stability at 350℃were secured by in situ am-Al2O3 network that strengthened the grain boundaries.The interfacial debonding and brittle cracking of B4 C particles were the main fracture mechanisms of the composite.In addition,the influence of sintering temperature and rolling deformation on the microstructures and mechanical properties was studied.

Mechanical properties and frictional resistance of Al composites reinforced with Ti3C2Tx MXene

Two-dimensional(2D)Ti3C2Tx MXene is an attractive additive not only used in base oil due to its low friction coefficient,but also used in composites due to its high aspect ratio and rich surface functional groups.So far there has been intense research into polymer matrix composites reinforced with Ti3C2Tx,Here we report on the use of 2D Ti3C2Tx to enhance the mechanical and frictional properties of Al matrix composites.Ti3C2Tx/Al composites were designed and prepared by pre s sureless sintering followed by hot extrusion technique.The prepared composites exhibit a homogeneous distribution of Ti3C2Tx.The Vickers hardness and the tensile strength continuously increase with increasing Ti3C2Tx content.A hardness of 0.52 GPa and a tensile strength of 148 MPa were achieved in the 3 wt%Ti3C2Tx/Al composite.The frictional properties of pure Al and the Ti3C2Tx/Al composite were comparably studied under dry sliding.A low friction coefficient of 0.2,twice lower than that of pure Al,was achieved in the 3 wt%Ti3C2Tx/Al composite.Ti3C2Tx acting as a solid lubricant reduces the abrasive wear in the composite,improving the frictional properties of Al matrix composites.

Microstructure evolution of nanostructured ferritic alloy with and without Cr3C2c oated SiC at high temperatures

This work focuses on fundamental understanding of microstructure evolution of nanostructured ferritic alloy(NFA) and 25 vol.% Cr3C2 coated Si C(Cr3C2@Si C)-NFA composite during spark plasma sintering at950°C and the following thermal treatment at 1000°C. A unique bi-phase microstructure with distinct Cr-rich and Si-rich phases has been observed for the 25 vol.% Cr3C2@Si C-NFA composite, while for the NFA sample, the traditional large grain microstructure remains. Grain sizes are significantly smaller for the25 vol.% Cr3C2@Si C-NFA composite compared to those for the pure NFA, which can be attributed to the presence of grain boundary phases in the composite sample. During the thermal treatment, microstructure features can be directly correlated with the dissolution kinetics and phase diagrams calculated using Thermo-Calc/DICTRA/PRISMA~?.

The effect of applied stress on damage mode of 3D C/C composites under bend-bend fatigue loading

The bend-bend fatigue behavior of 3D integral braided carbon/carbon composites (3D C/C) was examined. Fatigue test was conducted under load control at a sinu-soidal frequency of 10 Hz to obtain stress-fracture cycles (S-N) relationship. The fatigue limit of the C/C was found to be 203 MPa (92% of the static flexural strength), the lag loops of fatigue load-displacement were transformed from elasticity to anelasticity and the flexibility of specimens were enhanced with increase in applied stress. It is revealed that the interfacial sliding abrasion played an important role in the fatigue failure process, and the extent and speed of sliding abrasion were con-trolled by the level of applied stress.