Modeling the thermal conductivity of diamond reinforced aluminium matrix composites with inhomogeneous interfacial conductance

A reasonable model for describing the thermal conductivity of diamond reinforced aluminium matrix composites behaving a distinctive character of inhomogeneous distribution of interfacial thermal conductance on diamond surfaces is proposed in terms of an equivalent diameter approach combined with a double effective-medium approximation scheme. Theoretical analyses for the thermal conductivity of diamond reinforced Al (Si) composites prepared by different infiltration techniques (squeeze casting (SQ), gas pressure infiltration (GPI)) are given for rediscovering the existing experimental results considering inhomogeneous conductance behavior. Numerical results using present model agree reasonably well with the experimental observations and explore new findings, i.e. the diffusion bonding also occurs at Al–diamond {1 1 1} interfaces of GPIed composites; the interconnected particles is possibly existed in GPIed Al/diamond composites.     

On the thermal conductivity of Cu–Zr/diamond composites

Interfaces and close proximity between the diamond and the metal matrix are very important for their thermal conductance performance. Matrix-alloying is a useful approach to greatly enhance the interfacial bonding and thermal conductivity. In this study, the copper–diamond (Cu/Dia) composites with addition of 0.8, 1.2 and 2.4 wt.% zirconium (Zr) are prepared to investigate the influence of minor addition of Zr on the microstructure and thermal conductivity of the composites. The thermal conductivity of the composites is analyzed both experimentally and theoretically. It is demonstrated that moderate interfacial modification due to the Zr added is beneficial to improve the thermal conductivity of the Cu/Dia composites.     

Phonon Contribution to Thermal Boundary Conductance at Metal Interfaces Using Embedded Atom Method Simulations

The phonon contribution to the thermal boundary conductance (TBC) at metal–metal interfaces is difficult to study experimentally, and it is typically considered negligible. In this study, molecular dynamics simulations (MDS), employing an embedded atom method (EAM) potential, are performed to study the phonon contribution to thermal transport across an Al–Cu interface. The embedded atom method provides a realistic model of atomic behavior in metals, while suppressing the effect on conduction electrons. In this way, measurements on the phonon system may be observed that would otherwise be dominated by the electron contribution in experimental methods. The relative phonon contribution to the TBC is calculated by comparing EAM results to previous experimental results which include both electron and phonon contributions. It is seen from the data that the relative phonon contribution increases with decreasing temperature, possibly accounting for more than half the overall TBC at temperatures below 100 K. These results suggest that neglect of interfacial phonon transport may not be a valid assumption at low temperatures, and may have implications in the future development of TBC models for metal interfaces.     

Fabrication and thermal conductivity of copper matrix composites reinforced with Mo2C or TiC coated graphite fibers

Graphite fiber reinforced Cu-based composites have good thermal conductivity, low coefficient of thermal expansion for heat sink applications. In these composites, the quality of interfacial bonding between the copper matrix and the graphite fibers has significant influence on the thermal properties of composites. In this study, two different carbide coatings (Mo₂C or TiC) were synthesized on graphite fiber to promote the interfacial bonding in composites. Fibers/Cu composites had been produced by spark plasma sintering process. The results showed that the densification, interfacial bonding and thermal conductivity of coated composites were improved distinctly compared to that of uncoated ones. The enhanced composites present 16–44% increase of thermal conductivity in X–Y plane. An original theoretical model was proposed to estimate the interface thermal resistance. The result showed that the interfacial thermal resistance was largely reduced by one order of magnitude with the introduction of carbide interlayer.     

Interfaces in discontinuously reinforced metal matrix composites: An overview

The fundamental and engineering aspects pertaining to the matrix-reinforcement interfaces in discontinuously reinforced metal matrix composites are presented in this overview. The interfaces play a key role in determining mechanical properties, namely Young’s modulus, yield strength, elongation, creep and fracture behaviour, as well as physical properties like coefficient of thermal expansion, thermal conductivity and damping characteristics of metal matrix composites; these are discussed in detail. The ratio of the experimental value of the Young’s modulus to that predicted from the rule of mixtures has been used as a measure of interfacial bond strength. Various issues such as the nature of the interfacial bond, chemical reaction at the interfaces, and effect of alloying and processing on the structure of the interfaces and the properties of the composite are examined. In order to exploit the full potential of reinforcing the metallic matrix, the suggested strategies include creation of metallic bonding at the interface, use ofin situ processing, choice of right type of alloying elements, and heat treatments and engineering of interfaces.     

Ultra-High Interfacial Thermal Conductance via Double hBN Encapsulation for Efficient Thermal Management of 2D Electronics

Heat dissipation is a major limitation of high-performance electronics. This is especially important in emerging nanoelectronic devices consisting of ultra-thin layers, heterostructures, and interfaces, where enhancement in thermal transport is highly desired. Here, ultra-high interfacial thermal conductance in encapsulated van der Waals (vdW) heterostructures with single-layer transition metal dichalcogenides MX₂ (MoS₂, WSe₂, WS₂) sandwiched between two hexagonal boron nitride (hBN) layers is reported. Through Raman spectroscopic measurements of suspended and substrate-supported hBN/MX₂/hBN heterostructures with varying laser power and temperature, the out-of-plane interfacial thermal conductance in the vertical stack is calibrated. The measured interfacial thermal conductance between MX₂ and hBN reaches 74 ± 25 MW m⁻² K⁻¹, which is at least ten times higher than the interfacial thermal conductance of MX₂ in non-encapsulation structures. Molecular dynamics (MD) calculations verify and explain the experimental results, suggesting a full encapsulation by hBN layers is accounting for the high interfacial conductance. This ultra-high interfacial thermal conductance is attributed to the double heat transfer pathways and the clean and tight vdW interface between two crystalline 2D materials. The findings in this study reveal new thermal transport mechanisms in hBN/MX₂/hBN structures and shed light on building novel hBN-encapsulated nanoelectronic devices with enhanced thermal management.     

金属基复合材料界面导热性能的扫描热探针测试

利用扫描热探针方法,以微米级的空间分辨率,分析测试了三种馆长在复合材料（ＭＭＣ）界面特征和界面导热性能,应用数学统计方法对扫描热显微镜（ＳＴhM)的形貌和热电压数据进行处理和转换,获得 面宽度和界面导热率数据,结果表明,金属基复合材料宏观导热性能与增强相一基体界面的导热性能密切相关。     

Interfacial microstructure and its effect on thermal conductivity of SiCp/Cu composites

Thermal conductivity of SiCp/Cu composites was usually far below the expectation, which is usually attributed to the low real thermal conductivity of matrix. In the present work, highly pure Cu matrix composites reinforced with acid washed SiC particles were prepared by the pressure infiltration method. The interfacial microstructure of SiCp/Cu composites was characterized by layered interfacial products, including un-reacted SiC particles, a Cu–Si layer, a polycrystalline C layer and Cu–Si matrix. However, no Cu₃Si was found in the present work, which is evidence for the hypothesis that the formation of Cu₃Si phase in SiC/Cu system might be related to the alloying elements in Cu matrix and residual Si in SiC particles. The thermal conductivity of SiCp/Cu composites was slightly increased with the particle size from 69.9 to 78.6 W/(m K). Due to high density defects, the real thermal conductivity of Cu matrix calculated by H–J model was only about 70 W/(m K). The significant decrease in thermal conductivity of Cu matrix is an important factor for the low thermal conductivity of SiCp/Cu composites. However, even considered the significant decrease of thermal conductivity of Cu matrix, theoretical values of SiCp/Cu composites calculated by H–J model were still higher than the experimental results. Therefore, an ideal particle was introduced in the present work to evaluate the effect of interfacial thermal resistance. The reverse-deduced effective thermal conductivities of ideal particles according to H–J model was about 80 W/(m K). Therefore, severe interfacial reaction in SiCp/Cu composites also leads to the low thermal conductivity of SiCp/Cu composites.     

碳/铝复合材料界面反应对抗拉强度的影响

本文对Ti-B法制备的碳—铝合复材料经各种处理后产生的不同程度的界面反应与其纵向抗拉强度的关系进行了研究。碳—铝界面反应主要从三方面影响复合材料的抗拉强度:①界面结合强度;②界面脆性层;⑨纤维损伤。这三者的作用程度与界面反应程度有关。界面反应不严重时,主要是界面结合强度起作用;反应较严重时,界面脆性层的影响增大;反应很严重时,纤维发生严重损伤,对材料的抗拉强度产生很大的影响。      

Thermal conductivity of polymer composites based on the length of multi-walled carbon nanotubes

The anisotropic development of thermal conductivity in polymer composites was evaluated by measuring the isotropic, in-plane and through-plane thermal conductivities of composites containing length-adjusted short and long multi-walled CNTs (MWCNTs). The thermal conductivities of the composites were relatively low irrespective of the MWCNT length due to their high contact resistance and high interfacial resistance to polymer resins, considering the high thermal conductivity of MWCNTs. The isotropic and in-plane thermal conductivities of long-MWCNT-based composites were higher than those of short-MWCNT-based ones and the trend can accurately be calculated using the modified Mori-Tanaka theory. The in-plane thermal conductivity of composites with 2 wt% long MWCNTs was increased to 1.27 W/m·K. The length of MWCNTs in polymer composites is an important physical factor in determining the anisotropic thermal conductivity and must be considered for theoretical simulations. The thermal conductivity of MWCNT polymer composites can be effectively controlled in the processing direction by adjusting the length of the MWCNT filler.     

Interfacial characterization and thermal conductivity of diamond/Cu composites prepared by two HPHT techniques

With the aim of obtaining materials with high-thermal conductivities (TCs) for heat sink applications, diamond/Cu composites were produced via two different high-pressure-high-temperature (HPHT) techniques: powder metallurgy method (HPHT–PM) and infiltration method (HPHT–IM). The interfacial characteristics of composite materials are compared with respect to the sintering process and their effect on thermal properties is addressed. The HPHT–IM process is clearly more favorable than that of HPHT–PM and the obtained composites exhibited TCs as high as 717 W/mK for the former, but also as low as 200 W/mK for the latter. The advanced thermal property of HPHT–IM composites is attributed to a well-bonded interface layer with gradual and continuous element transition probably due to amorphous carbon detected by Raman spectra. EDS analysis indicate selective interfacial bonding between diamond {100} faces and Cu. Diamond skeleton with connected particles have been observed in this case, also resulting in enhanced interfacial bonding and thermal properties. The HPHT–PM composites with isolated diamond particles feature visible macro interfacial debonding, leading to rather low TC less than that of pure Cu.     

Thermal conduction across the one-dimensional interface between a MoS<Subscript>2</Subscript> monolayer and metal electrode

The thermal conductance across the one-dimensional (1D) interface between a MoS2 monolayer and Au electrode (edge-contact) has been investigated using molecular dynamics simulations.Although the thermal conductivity of monolayer MoS2 is 2-3 orders of magnitude lower than that of graphene,the covalent bonds formed at the interface enable interfacial thermal conductance (ITC) that is comparable to that of a graphene-metal interface.Each covalent bond at the interface serves as an independent channel for thermal conduction,allowing ITC to be tuned linearly by changing the interfacial bond density (controlling S vacandes).In addition,different Au surfaces form different bonding configurations,causing large ITC variations.Interestingly,the S vacancies in the central region of MoS2 only slightly affect the ITC,which can be explained by a mismatch of the phonon vibration spectra.Further,at room temperature,ITC is primarily dominated by phonon transport,and electron-phonon coupling plays a negligible role.These results not only shed light on the phonon transport mechanisms across 1D metal-MoS2 interfaces,but also provide guidelines for the design and optimization of such interfaces for thermal management in MoS2-based electronicdevices.     

Fabrication and thermal conductivity of near-net-shaped diamond/copper composites by pressureless infiltration

Near-net-shaped diamond/copper composites with a relative density of over 99% and thermal conductivity of over 350 Wm⁻¹ K⁻¹ are successfully fabricated by powder press-pressureless infiltration processing. The effects of infiltration temperature, infiltration time, interfacial thickness, and type of protective atmosphere on the thermal conductivity of the diamond/copper composites were investigated. The results showed that the diamond-copper composites with complicated shape exhibited better thermal properties, which can be widely used in electronic packaging field. It was found that the properties of diamond-copper composites infiltrated in high vacuum atmosphere were better than that of composites infiltrated in other atmospheres. The thickness of interface showed great effects on the properties of composites. The carbide interfaces were attributed to the decrease of interfacial thermal resistance and enhancement of wetting properties between the diamonds and copper.     

Interfacial role and properties in model composites: Fracture surfaces by scanning electron microscopy

The fracture surfaces of glass sphere-filled polyethylene model composites with varying degrees of interfacial modification were examined by scanning electron microscopy. The micrographs give a qualitative view of the bonding process and the nature of the region of modified matrix surrounding the glass spheres. Adhesive failure is seen for the unmodified composites, and also for the composites with near monolayer modification. At higher degrees of interfacial modification a layer of bound modified matrix is formed around the glass surface and the failure is cohesive. The micrographs demonstrate that the properties of the modified interfacial layer are dependent on the volume fraction of glass. The micrographs also show that the mechanism of bonding the matrix to the glass surface is through the thermally activated azide moeity.     

The effect of interfacial state on the thermal conductivity of functionalized Al2O3 filled glass fibers reinforced polymer composites

Rapidly increasing packaging density of electronic devices puts forward higher requirements for thermal conductivity of glass fibers reinforced polymer (GFRP) composites, which are commonly used as substrates in printed circuit board. Interface between fillers and polymer matrix has long been playing an important role in affecting thermal conductivity. In this paper, the effect of interfacial state on the thermal conductivity of functionalized Al₂O₃ filled GFRP composites was evaluated. The results indicated that amino groups-Al₂O₃ was demonstrated to be effective filler to fabricate thermally conductive GFPR composite (1.07 W/m K), compared with epoxy group and graphene oxide functionalized Al₂O₃. It was determined that the strong adhesion at the interface and homogeneous dispersion of filler particles were the key factors. Moreover, the effect of interfacial state on dielectric and thermomechanical properties of GFRP composites was also discussed. This research provides an efficient way to develop high-performance GFRP composites with high thermal conductivity for integrated circuit packaging applications.     

Thermal Conductivity and Interfacial Thermal Resistance in Bilayered Nanofilms by Nonequilibrium Molecular Dynamics Simulations

A nonequilibrium molecular dynamics study of the cross-plane thermal conductivity and interfacial thermal resistance of nanoscale bilayered films is presented. The films under study are composed of argon and another material that is identical to argon except for its atomic mass. The results show that a large temperature jump occurs at the interface and that the interfacial thermal resistance plays an important role in heat conduction for the whole films. The cross-plane thermal conductivity is dependent on the average temperature. The interfacial thermal resistance is found to be dependent apparently on the atomic mass ratio of the two materials and the temperature, but to be independent of the film thickness. A linear relationship is observed between the reciprocal of the cross-plane thermal conductivity and that of the film thickness with the film thickness between 5.4 nm and 64.9 nm, which is in good agreement with results in the literature for a single film.     

Structural Insight in the Interfacial Effect in Ferroelectric Polymer Nanocomposites

Both experimental results and theoretical models suggest the decisive role of the filler–matrix interfaces on the dielectric, piezoelectric, pyroelectric, and electrocaloric properties of ferroelectric polymer nanocomposites. However, there remains a lack of direct structural evidence to support the so-called interfacial effect in dielectric nanocomposites. Here, a chemical mapping of the interfacial coupling between the nanofiller and the polymer matrix in ferroelectric polymer nanocomposites by combining atomic force microscopy–infrared spectroscopy (AFM–IR) with first-principles calculations and phase-field simulations is provided. The addition of ceramic fillers into a ferroelectric polymer leads to augmentation of the local conformational disorder in the vicinity of the interface, resulting in the local stabilization of the all-trans conformation (i.e., the polar β phase). The formation of highly polar and inhomogeneous interfacial regions, which is further enhanced with a decrease of the filler size, has been identified experimentally and verified by phase-field simulations and density functional theory (DFT) calculations. This work offers unprecedented structural insights into the configurational disorder-induced interfacial effect and will enable rational design and molecular engineering of the filler–matrix interfaces of electroactive polymer nanocomposites to boost their collective properties.     

Interfacial fracture of dentin adhesively bonded to quartz-fiber reinforced composite

The paper presents the results of an experimental study of interfacial failure in a multilayered structure consisting of a dentin/resin cement/quartz-fiber reinforced composite (FRC). Slices of dentin close to the pulp chamber were sandwiched by two half-circle discs made of a quartz-fiber reinforced composite, bonded with bonding agent (All-bond 2, BISCO, Schaumburg) and resin cement (Duo-link, BISCO, Schaumburg) to make Brazil-nut sandwich specimens for interfacial toughness testing. Interfacial fracture toughness (strain energy release rate, G) was measured as a function of mode mixity by changing loading angles from 0° to 15°. The interfacial fracture surfaces were then examined using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) to determine the failure modes when loading angles changed. A computational model was also developed to calculate the driving forces, stress intensity factors and mode mixities. Interfacial toughness increased from ≈ 1.5 to 3.2 J/m² when the loading angle increases from ≈ 0 to 15°. The hybridized dentin/cement interface appeared to be tougher than the resin cement/quartz-fiber reinforced epoxy. The Brazil-nut sandwich specimen was a suitable method to investigate the mechanical integrity of dentin/cement/FRC interfaces.     

Thermal properties of diamond/SiC/Al composites with high volume fractions

The diamond/SiC/Al composites with high volume fractions and a large ratio of diamond to SiC particle size (7.8:1) were fabricated by gas pressure infiltration. The results show that the fine SiC particles occupy efficiently the interstitial positions around coarse diamond particles; the main fracture mechanism of the composite is matrix ductile fracture, and diamond brittle fracture was observed which confirms a high interfacial bonding strength; the diamond/SiC/Al composites with 80% and 66.7% volume fraction of diamond in the reinforcement have the higher volume fraction in the reinforcement and lower coefficient of thermal expansion compared to the diamond/Al composite. Turner and Kerner models are not in good agreement with the experimental data for the composites based on reinforcement with two phases different in shape and component. When the effect of the coating layer considered, differential effective medium (DEM) model is confirmed a reliable model in designing a composite with a given thermal conductivity based on reinforcement with two phases different in size.     

新一代高导热金属基复合材料界面热导研究进展

热物理性质不同的材料之间存在界面热阻,界面热阻对热传输过程产生极大的影响,并在很大程度上决定了复合材料的导热性能。金刚石颗粒增强金属基复合材料(Metal matrix composites,MMCs)充分发挥了金刚石的高热导率和低热膨胀系数的优点,有望获得高的热导率以及与半导体相匹配的热膨胀系数,可满足现代电子设备在散热能力上提出的越来越高的要求,作为新一代电子封装材料已引起广泛关注。界面热导(界面热阻的倒数)既是决定复合材料导热能力的关键因素,也是研究的难点,复合材料制备工艺、界面改性方式(金属基体合金化或金刚石表面金属化)以及改性金属种类均会影响界面热导。详细论述了界面热导理论及实验研究的最新成果,并对金刚石/金属复合材料在未来研究中面临的主要问题进行探讨。