Thermophysical Properties of Alumina Particle Reinforced Glass Matrix Composites

Alumina particles incorporated glass matrix composites, which showed good prospect to be used as coating materials for high‐temperature corrosion protection on intermetallics or titanium alloys, were prepared via pressureless sintering. With increasing alumina content, the Young's modulus, fracture strength, Vickers hardness, indentation toughness, softening point, and thermal shock resistance of the composites increased monotonically. A similar increasing trend could be found for the thermal expansion coefficient of the composites, except for an abnormal drop at small amount of incorporation, which closely correlated with the Al³⁺ dissolution into the glass matrix.     

A study of the residual microstress at the matrix interface in filled epoxy resins

Using the technique of photoelasticity, we have studied in detail the magnitude of the residual microstress at the matrix interface between epoxy resin and rubber particles or glass beads. A spheric stress-optic equation applicable to these composites was derived. The photoelastic figures induced by the interfacial residual microstresses and the factors affecting the intensity of light are discussed. The experimental results show that the residual microstresses at the matrix interface are independent of the particle size of rubbers or glass beads, but depend on the nature of fillers, which have different thermal expansion coefficients and mechanical properties. Thermal history and interfacial chemical bonding of filled epoxy resins have distinct effects on the residual interfacial microstresses and the matrix internal stresses.     

Effect of Thermal Expansion Mismatch on the Thermal Diffusivity of Glass-Ni Composites

The effect of interfacial decohesion, due to the thermal expansion mismatch, on the thermal diffusivity of a hot-pressed glass matrix with a dispersed phase of nickel was investigated by the laser-flash technique at 25° to 600°C. The interfacial gap formed on cooling acts as a barrier to heat flow and lowers the thermal diffusivity to values below those predicted from composite theory and also creates a strongly positive temperature dependence of the thermdl diffusivity. Preoxidation of the Ni spheres promotes interfacial bonding and yields values of thermal diffusivity higher than those for nonoxidized spheres and a thermal diffusivity which is relatively temperature-independent. The results of the present study also confirm the criteria for the effective thermal diffusivity of composites established by Lee and Taylor.     

纳米SiC增韧Al_2O_3陶瓷复合材料的制备、表征及力学性能研究

以SiC和Si微米粉为添加剂,采用无压烧结工艺制备了纳米SiC增韧的Al2O3陶瓷复合材料,探讨了SiC含量、烧结气氛和烧结温度对复合材料的烧成收缩率、微观形貌、抗弯强度、维氏硬度及断裂韧性的影响。结果显示：SiC的添加使复合材料的烧成收缩率下降,惰性气氛下复合材料的收缩率要大于氧化气氛和还原气氛时的收缩率。在氧化性气氛下烧结时,当SiC添加量为4%时,复合陶瓷的体积密度为3.80 g·cm^-3,抗弯强度、断裂韧性及维氏硬度均达到最大值,分别为480 MPa、5.12 MPa·m1/2、16.2 GPa。添加SiC后所得复合材料的基体颗粒为椭圆状,粒径为2μm左右,颗粒与颗粒之间结合紧密,颗粒形状的改变可能是因为烧结机理发生变化所致。纳米SiC颗粒位于晶界处,形成了由Al2O3-SiC-Al2O3搭桥联结的晶界,提高了晶界强度,导致裂纹只能在晶内传播。     

Influence of diamond particles content on the critical load for crack initiation and fracture toughness of SiOC glass–diamond composites

The crack initiation load and fracture toughness were characterized as a function of diamond particle content, up to 25 vol%, in silicon oxycarbide glass matrix by means of Vickers indentation and single edge notch beam (SENB) technique, respectively. The larger fracture toughness value of 3.21 ± 0.3 MPa m^1/2 was reached for 20 vol% diamond content composites and the value was 4 times higher than that of the unreinforced glass. The addition of diamond particles greatly influenced the crack initiation load, which increased from 2.9 to 49.0 N. The enhancement in the fracture toughness and crack initiation load can be explained by both the intrinsic mechanical properties of diamond (especially the elastic properties; E ～ 1100 GPa) and the diamond/SiOC glass interfacial bonding. A clear correlation was found between the fracture energy, the reinforced interparticle spacing and the residual stress arising upon cooling due to thermal expansion mismatch between the matrix and the diamond particles.     

Interface formation in infiltrated Al(Si)/diamond composites

This study pertains to the investigation of interface formation in infiltrated Al-based composites with high-volume fractions of monocrystalline synthetic diamond particles. The interface characteristics are discussed with respect to process conditions and Al matrix chemistry. To this end, two infiltration techniques, i.e., squeeze-casting and gas pressure infiltration are compared and the effect of Si-addition to the Al matrix is addressed. Eventually, thermal properties of the composite materials are presented and are in turn related to the interface characteristics.Electron microscopy investigations reveal a distinct 50–200-nm-thick layer at the interface between the metal matrix and the diamond particle, regardless of process history and matrix chemistry. This layer is amorphous and consists of carbon, aluminium and oxygen. Additionally, nanocrystallites of Al₂OC and enrichment of Si are observed within this interface layer in the Si-free, squeeze-casted material and in the gas pressure-infiltrated material with 7 wt.% of Si, respectively. Despite the fact that no evidence of SiC is found in the Si-containing composites, the process conditions experienced in gas pressure infiltration are clearly more favourable than those experienced in squeeze casting with respect to interfacial bonding and thermal properties. Actually, between 25 and 50 °C, the gas pressure-infiltrated AlSi/diamond composite yields a thermal conductivity of 375 W/m K along with a coefficient of thermal expansion of 7 × 10^− 6/K.     

Mechanical and thermal shock properties of Cf/SiBCN composite: Effect of sintering densification and fiber coating

In this work, resin-derived carbon coating was prepared on carbon fibers by polymer impregnation pyrolysis method, then silicoboron carbonitride powder was prepared by mechanical alloying, and finally carbon fiber-reinforced silicoboron carbonitride composites were prepared by hot-pressing process. The effects of sintering densification and fiber coating on microstructure, mechanical properties, thermal shock resistance, and failure mechanisms of the composites were studied. Fiber bridging hinders the sintering densification, causing more defects in fiber-dense area and lower strength. However, higher sintering temperature (1800–2000°C) can improve mechanical properties significantly, including bending strength, vickers hardness, and elastic module, because further sintering densification enhances matrix strength and fiber/matrix bonding strength, while the change of fracture toughness is not obvious (2.24–2.38 MPa·m^1/2) due to counteraction of higher debonding resistance and less pull-out length. However, fiber coating improves fracture toughness greatly via protecting carbon fibers from chemical corrosion and damage of thermal stress and external stress. Due to lower coefficient of thermal expansion, lower fiber loading ratio, less stress concentration at the fiber/matrix interface, and better defect healing effect, lower sintering temperature favors thermal shock resistance of composites, and thermal shock recession mechanisms are the damage of interface.     

Strength and Toughness of Continuous-Alumina-Fiber-Reinforced Glass-Matrix Composites

Unidirectional, continuous-fiber composites were fabricated using polycrystalline alumina fibers and four different silicate glass matrices of differing thermal expansion. Fracture toughness measurements, strength measurements, and fractographic analysis of failed specimens are used to identify the failure mechanism. Results show that the elastic modulus mismatch between the matrix and the fibers shields the reinforcing fibers from matrix crack extension, thereby increasing composite toughness without fiber pullout. Fractographic analysis shows that fiber shielding leads to fiber failure ahead of matrix crack. Composite toughness increases linearly with increases in the residual compressive stress in the matrix phase. Ultimate composite strengths are dependent upon thermal-expansion-induced residual stresses and fiber strength.     

The role of maleic anhydride functionalized graphene oxide in improving the interfacial properties of carbon fibre/bismaleimide composites

This work aims to assess the effect of maleic anhydride functionalized graphene oxide (MAH‐f‐GO) on the interfacial properties of carbon fibre/bismaleimide (BMI) composites by experimental and finite element (FE) methods. Transverse fibre bundle (TFB) specimens with different contents of MAH‐f‐GO nanoparticles were manufactured to investigate the interfacial strength of the carbon fibre/BMI composites. The fracture surface of the TFB specimens was examined by scanning electron microscopy to observe the morphologies of the fibre ? matrix interface. The coefficient of thermal expansion, cure shrinkage and elastic modulus were measured and included in the FE simulation. An FE analysis model was established to simulate the thermal residual stress distribution around the carbon fibre and to estimate the interfacial bonding strength of the TFB specimens. The combination of experimental and FE analysis results indicated that the addition of MAH‐f‐GO nanoparticles noticeably reduced the concentration of residual stress at the fibre ? matrix interface and enhanced the interfacial properties of the carbon fibre/BMI composites.© 2017 Society of Chemical Industry     

Interface microstructure and mechanical properties of Ni–Co–P alloy coatings modified carbon fibres reinforced 7075Al matrix composites

To optimize interface microstructure between 7075Al matrix and CFs, Ni–Co–P multi-component alloy coatings coated carbon fibres were prepared by electroless plating firstly and then Ni–Co–P coated CFs reinforced 7075Al matrix composites (CF/Al(Ni–Co–P)) with high relative density were fabricated by hot pressing sintering process. After modification of Ni–Co–P coatings, Al–Co–Ni Intermetallic compounds were formed stably between matrix and reinforcement because of the smaller mixing enthalpy values of Al–Co, Al–Ni and Co–Ni, which not only restrained the generation of Al₄C₃ but also improved interfacial bonding strength. Yield strength and ultimate tensile strength of CF/Al(Ni–Co–P) composites with 30 vol% CFs had maximum improvement compared with CF/Al(U) composites than other composites reinforced by 10 vol%, 20 vol% and 30 vol%CFs, which is up to 305.8 MPa and 668.7 MPa respectively, and the fracture mode of composites from accumulation fracture to non-accumulation fracture as the existence of Ni–Co–P coatings.     

Effects of Interfacial Films on Thermal Stresses in Whisker-Reinforced Ceramics

Toughening of whisker-reinforced (or fiber-reinforced) ceramics by whisker pullout requires debonding at the whisker/matrix interface. Compressive clamping stresses, which would inhibit interface debonding and/or pullout, are expected in composites where the matrix has a higher thermal expansion coefficient than the whisker. Because such mismatch in thermomechanical properties can result in brittle composites, it is important to explore approaches to modify the thermal stresses in composites. As a result, the effects of a film at the whisker/matrix interface on the stresses due to thermal contraction mismatch upon cooling are considered in this study. Analysis of various properties of the film are considered for the whisker/matrix systems, in particular for SiC/Al₂O₃, SiC/cordierite, and SiC/mullite composites. Reduction of thermomechanical stresses is shown to occur when the interfacial film has a low Young's modulus. Also, when the whisker has a lower thermal expansion coefficient than the matrix (e.g., SiC/Al₂O₃), the interfacial stresses generated during cooling decrease as the thermal expansion coefficient of the film increases.     

Processing and properties of nano‐ and macro‐hydroxyapatite/poly(ethylene‐co‐acrylic acid) composites

Hydroxyapatite (HAp)/poly(ethylene‐co‐acrylic acid) composites have been synthesized by a solution‐based method, using nanosized (n‐HAp) and coarse hydroxyapatite (c‐HAp) particles, respectively. X‐ray diffraction study has indicated the development of compressive and tensile stresses in composites because of the thermal expansion mismatch between the particles and polymer matrix. Fourier transform infrared absorption spectra and thermal analysis have showed the presence of strong interfacial bonding between the particles and polymer. The surface roughness and the homogeneous dispersion of HAp particles in the polymer matrix have been observed by scanning electron microscopy. A comparison in mechanical properties between composites prepared with n‐HAp and c‐HAp particles, respectively, has been studied. Nanosized particles contribute excellent improvement of mechanical properties of the composites rather than the coarse particles. The uniform dispersion of HAp particles, followed by the improvement in mechanical properties of the composite, provides a means of preparing HAp/polymer composites for low load‐bearing implant applications. POLYM. COMPOS., 27:633–641, 2006. © 2006 Society of Plastics Engineers     

Effect of plate-like glass fillers on the mechanical properties of dental nanocomposites

In this study, glass flakes were incorporated into the spherical nanosilica component of the dental composites and its effect on the mechanical properties of these composites was investigated. To achieve a good interfacial adhesion between matrix resin and fillers, the particles were surface treated with a silane coupling agent (γ-MPS). Composites with different plate-like and spherical nanoparticle contents were prepared and their mechanical properties, including flexural strength, flexural modulus and fracture toughness were measured. The morphology of the particles and fracture surface of the composites were studied by SEM. The distribution of the flakes in the composite was also monitored using EDXA. Statistical analysis of the data was performed with ANOVA and the Tukey’s post hoc test was at a significance level of 0.05. The results showed that the flexural modulus and fracture toughness of specimens were improved with increasing the glass flake content up to 15 vol % which then declined upon further increase due to the stacking of the flakes on each other. A good interfacial adhesion was observed between matrix resin and particles in the SEM micrographs. The results of this study suggest that incorporation of glass flakes into the dental composites containing spherical nanosilica particles may enhance their mechanical properties.     

Measurement of Fiber/Matrix Interfacial Shear Stress at Elevated Temperatures

An apparatus for measurement of the fiber/matrix interfacial shear stress at temperatures up to 1100° is described. Equipment was used to measure interfacial properties as a function of temperature in two ceramic-matrix composites and one metal-matrix composite. In the composites where the thermal expansion of the matrix was higher than that of the fiber, the interfacial shear stress decreased with temperature. The opposite trend was observed in a system with low matrix thermal expansion. The change of the interfacial shear stress with temperature of all the composites studied can be fully explained by considering the fiber/matrix expansion differences.     

The effect of interfacial adhesion on the tensile behavior of polystyrene–glass-bead composites

The tensile behavior at 20°C of polystyrene-glass-bead composites has been studied at several glass concentrations. To gain insight into the role of interfacial adhesion, the bonding between glass and polystyrene was varied by using different silane coupling agents. In contrast to the elastic behavior, the crazing behavior of the composites was found to be considerably affected by the degree of interfacial adhesion. This is explained by means of the different mechanisms for craze formation at adhering and nonadhering glass beads, respectively. Furthermore, it was found that both elastic and crazing behavior of the composites are influenced by the glass bead concentration.     

Mechanical properties and interfacial characteristics of 2.5D SiNOf/BN wave-transparent composites

2.5D SiNO_f/BN wave-transparent composites were fabricated by borazine infiltration and pyrolysis route at 800 °C?1400 °C. The fracture behavior of the composites was investigated on the basis of the retained fiber strength, in-situ fiber and matrix mechanical properties, and fiber/matrix bonding strength. Nano-indentation were employed to determine the in-situ elastic modulus and hardness of the fiber and BN matrix, and single-fiber push-out experiments were performed to quantify the fiber/matrix bonding strength. The interfacial characteristics of the 800 °C?1200 °C fabricated composites were further studied in terms of physical bonding and chemical reaction. Physical bonding was resulted from thermal mismatch between the fiber and matrix, which induced compressive radial stress at the interface. The radial stress increased continuously with increasing fabrication temperature. Meanwhile, the TEM analysis confirmed chemical diffusion at the fiber/matrix interface, which further improved the interfacial bonding strength. The chemical reaction mechanism was proposed.     

Controlling and monitoring interfacial reactions in composites of azidosilane modified glass filled polyethylene

Model composites of spherical glass particles dispersed in a matrix of high density polyethylene were prepared with controlled variations in the interfacial structure. Dynamic-mechanical measurements of the composites in the melt state were recorded. The physical properties are found to relate to the morphology, bonding, reactivity, and other characteristics of the interfacial region which can be controlled by the applied chemistry. The interfacial reactions can be monitored in-sity by dynamic-mechanical analysis and differential scanning calorimetry.     

Thermal expansion behavior of composites based on axisymmetric ellipsoidal particles

A new model for calculating the coefficients of thermal expansion, CTE, in all three coordinate directions is developed for composites containing aligned, axisymmetric elliptical particles, i.e., characterized by a single aspect ratio, that in the limit approximate the shapes of spheres, fibers and discs. This model is based on Elshelby's method but employs a somewhat different formulation than used in prior papers; a main advantage of the current approach is that it can be readily extended to composites based on ellipsoidal particles with no axes of symmetry, i.e., all three major axes are different, as recently demonstrated for modulus. CTE predictions for the simple case of axisymmetric particles are illustrated by calculations for glass particles in the shape of spheres, fibers and discs in an epoxy resin and are compared to those from the popular Chow theory. For spherical-shaped particles, the CTEs in all directions are the same and decrease modestly as the volume fraction of filler particles increases. As the particle aspect ratio increases from unity, the thermal expansion becomes anisotropic. The coefficient of longitudinal linear thermal expansion always decreases with increasing aspect ratio and filler loading due to the mechanical constraint of the filler. For aligned axisymmetric particles, the coefficients of linear thermal expansion are always the same in two directions. The values in the transverse direction may be higher or lower than that of the matrix depending on the values of aspect ratio and filler loading; these regions are mapped out for this particular set of matrix and filler properties. The two-dimensional constraints on matrix expansion caused by discs versus the one-dimensional effects of fibers cause quantitative differences in behavior for the two shapes.     

Microstructure and properties of WB/Al nuclear shielding composites prepared by spark plasma sintering

In this paper, a novel nuclear shielding material capable of shielding neutrons and gamma rays, WB-reinforced Al (WB/Al) composites, was prepared by spark plasma sintering (SPS) process. The microstructure of the composites was characterized, and the effects of WB content, heat treatment and matrix type on the properties of the composites were discussed. The results demonstrate that the WB particles are uniformly dispersed in the aluminum matrix and formed a good binding interface with the matrix. WAl₁₂ as an interfacial reaction product is identified, and segregation of Si and Mg elements at the reinforcement/matrix interface occurs. The mechanical properties of the WB/Al composites are sensitive to the WB content. The hardness, elastic modulus and bending strength of the composites increase monotonously as the WB volume fraction increasing, up to 234%, 107% and 91.6% higher respectively than those of the monolithic 6061Al. However, the tensile strength reaches a peak point when the volume fraction is 20%. The effects of T6 treatment and matrix type are not pronounced, especially for the composites with high WB content. The thermal neutron and gamma ray shielding properties of the composites both increase with the increase of material thickness and WB content. The WB/Al composites developed in this work show good application prospects in the field of nuclear radiation protection, due to their good mechanical properties and well neutron and gamma-ray shielding performance.     

Temperature effect on interfacial bonding property of single‐carbon fiber/epoxy resin composite

The changes in interfacial fracture energy of three kinds of commercially sized carbon fiber (CF)/epoxy resin composites in the range from ambient temperature to 130°C were investigated using the single‐fiber fragmentation test to evaluate the heat resistance of the interphase. The effects of CF sizing on the interfacial bonding property were studied using desized CF/epoxy resin composites. Thermogravimetric analysis and differential scanning calorimetry of the combination of sizing and matrix were employed to investigate the role of sizing on the variations in the fiber/matrix interfacial property under elevated temperature. The interfacial fracture energy values of all the studied CF composites were found to decrease quickly during the initial stage of temperature rise and drop gradually at higher temperature. At elevated temperature, the desized CF composites had higher heat resistance than the corresponding sized fiber composites. The differences in the interfacial heat resistance among the three kinds of CF composites and the difference in the interfacial thermal stability between the sized and the desized fiber composites were related to different glass transition temperatures of the interphases. The interaction between sizing and the matrix and the chain motion of the crosslink structure of the interphase has been suggested to determine the interfacial heat resistance. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers