Effect of metalloid silicon addition on densification,microstructure and thermal–physical properties of Al/diamond composites consolidated by spark plasma sintering

Aluminum matrix composites reinforced with diamond particles were consolidated by spark plasma sintering. Metalloid silicon was added (Al–Si/diamond composites) to investigate the effect. Silicon addition promotes the formation of molten metal during the sintering to facilitate the densification and enhance the interfacial bonding. Meanwhile, the alloying metal matrix precipitates the eutectic-Si on the diamond surfaces acting as the transitional part to protect the improved interface during the cooling stage. The improved interface and precipitating eutectic-Si phase are mutually responsible for the optimized properties of the composites. In this study, for the Al–Si/diamond composite with 55 vol.% diamonds of 75 μm diameter, the thermal conductivity increased from 200 to 412 Wm⁻¹ K⁻¹, and the coefficient of thermal expansion (CTE) decreased from 8.9 to 7.3 × 10⁻⁶ K⁻¹, compared to the Al/diamond composites. Accordingly, the residual plastic strain was 0.10 × 10⁻³ during the first cycle and rapidly became negligible during the second. Additionally, the measured CTE of the Al–Si/diamond composites was more conform to the Schapery’s model.     

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.     

Preparation of high thermal conductivity copper–diamond composites using molybdenum carbide-coated diamond particles

Molybdenum carbide (Mo₂C) coatings on diamond particles were proposed to improve the interfacial bonding between diamond particles and copper. The Mo₂C-coated diamond particles were prepared by molten salts method and the copper–diamond composites were obtained by vacuum pressure infiltration of Mo₂C-coated diamond particles with pure copper. The structures of the coatings and composites were investigated using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicated that the Mo₂C coatings effectively improved the wettability between diamond particles and copper matrix, and Mo₂C intermediate layers were proved to decrease the interfacial thermal resistance of composites. The thermal conductivity of the composite reached 608 Wm^?1 K^?1 with 65 vol.% Mo₂C-coated diamond, which was much higher than that with uncoated diamond. The greatly enhanced thermal conductivity is ascribed to the 1-μm-thick Mo₂C coatings. Mo₂C coatings on diamond particles are proved to be an effective way to enhance the thermal conductivities of copper–diamond composites.     

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.     

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.     

放电等离子烧结制备Diamond/Al复合材料

采用放电等离子烧结法（SPS）制备了Diamond/Al复合材料,研究了金刚石粒径、成分配比、工艺参数等对复合材料的导热性能的影响。结果表明,SPS可以得到导热性能较好的Diamond/Al复合材料,致密度是影响该材料导热性能的最重要因素。在实验确定的金刚石体积分数50%,金刚石粒径70 μm,温度550℃、压力30 MPa的工艺条件下,所制备的材料致密度较高,热导率为182 W/(m·K),比相同条件下纯铝粉烧结体的热导率提高了34.8%,表明金刚石的添加对烧结铝基材料导热性能有明显的改善作用。      

Numerical investigation of the effect of interfacial thermal resistance upon the thermal conductivity of copper/diamond composites

Copper/diamond (Cu/D) composites are known for their applications in thermal management systems. This paper investigates the effect of interfacial thermal resistance (TR) upon the effective thermal conductivity of Cu/D composites through experimental and numerical means. The composite samples were made using uncoated, Cu-coated, and Cr-coated diamond particles. The transient plane source method was used to measure the thermal conductivity of the composite samples, while the micrographs of the specimens were used to develop the finite element models. Together with the experimental and numerical results, the interfacial TR was identified in each sample. Although Hasselman–Johnson model calculated the conductivity values with significant error, the trend shown by experimental results is still followed. The finite element model, however, led to an error of less than 1%. The numerical analysis showed that the TR depends not only upon the diamond volume fraction but also upon the coating material. Finally, it has been demonstrated that numerical simulation may be employed to reveal the appropriate combinations of diamond fraction and the coating material in order to attain the desired level of effective thermal conductivity.     

Influence of interfacial carbide layer characteristics on thermal properties of copper–diamond composites

Copper–diamond composites are increasingly being considered for thermal management applications because of their attractive combination of properties, such as high thermal conductivity (λ) and low coefficient of thermal expansion (CTE). In this research, thermal properties of Cu–diamond composites with two different types of interfacial carbides (Cr₃C₂ and SiC) were studied. The interface thermal conductance (h _c) was calculated with Maxwell mean-field and differential effective medium schemes, wherein experimentally measured λ was entered as an input parameter. The λ and h _c of both the Cu–Cr₃C₂–diamond and Cu–SiC–diamond composites are higher than those reported in previous studies for Cu–diamond composites with no interfacial carbides. The value of h _c is intimately related to the morphology and thickness of the interface carbide layer, with the highest h _c being associated with a thin and continuous interface carbide layer. A lower h _c resulting from a thicker Cr₃C₂ layer can provide an alternate explanation for a previously reported trend in λ of Cu–Cr₃C₂–diamond composites with different Cr-contents. The experimentally measured CTE was compared with the Turner and Kerner model predictions. The CTE of both the Cu–Cr₃C₂–diamond and Cu–SiC–diamond composites is lower and better matches the model predictions than the previously reported CTE of Cu–diamond composite with no interfacial carbides. The CTE of Cu–Cr₃C₂–diamond composites agrees better with the Kerner model than the Turner model, which suggests that deformation during temperature excursions involves shear.     

金刚石/Al(或AlSi合金)复合材料性能衰退及抑制

采用气体压力浸渗法制备了金刚石/Al、金刚石/AlSi7和金刚石/AlSi9复合材料,对比研究了其暴露在空气中的性能衰退行为。研究表明,界面反应产物Al₄C₃会潮解生成Al（OH）₃,增大界面热阻,导致金刚石/Al复合材料性能衰退。Al基体中添加Si元素可以显著降低其性能衰退速率,其机制为:金刚石中C元素在Al液中溶解度的降低和Si在金刚石颗粒表面的优先析出,抑制了Al₄C₃的生成量;此外,金刚石/AlSi复合材料致密度的提高,对Al₄C₃与水汽的接触起到阻碍作用。讨论了抑制金刚石/Al复合材料性能衰退的几种可行方法,有望进一步提高其在潮湿环境中的使用寿命。      

Effect of copper content on the thermal conductivity and thermal expansion of Al–Cu/diamond composites

Al–Cu matrix composites reinforced with diamond particles (Al–Cu/diamond composites) have been produced by a squeeze casting method. Cu content added to Al matrix was varied from 0 to 3.0 wt.% to detect the effect on thermal conductivity and thermal expansion behavior of the resultant Al–Cu/diamond composites. The measured thermal conductivity for the Al–Cu/diamond composites increased from 210 to 330 W/m/K with increasing Cu content from 0 to 3.0 wt.%. Accordingly, the coefficient of thermal expansion (CTE) was tailored from 13 × 10⁻⁶ to 6 × 10⁻⁶/K, which is compatible with the CTE of semiconductors in electronic packaging applications. The enhanced thermal conductivity and reduced coefficient of thermal expansion were ascribed to strong interface bonding in the Al–Cu/diamond composites. Cu addition has lowered the melting point and resulted in the formation of Al₂Cu phase in Al matrix. This is the underlying mechanism responsible for the strengthening of Al–Cu/diamond interface. The results show that Cu alloying is an effective approach to promoting interface bonding between Al and diamond.     

Thermal conductivity of Cu–Zr/diamond composites produced by high temperature–high pressure method

Copper matrix composites reinforced with about 90 vol.% of diamond particles, with the addition of zirconium to copper matrix, were prepared by a high temperature–high pressure method. The Zr content was varied from 0 to 2.0 wt.% to investigate the effect on interfacial microstructure and thermal conductivity of the Cu–Zr/diamond composites. The highest thermal conductivity of 677 W m⁻¹ K⁻¹ was achieved for the composite with 1.0 wt.% Zr addition, which is 64% higher than that of the composite without Zr addition. This improvement is attributed to the formation of ZrC at the interface between copper and diamond. The variation of thermal conductivity of the composites was correlated to the evolution of interfacial microstructure with increasing Zr content.     

界面反应对Cu35Ni25Co25Cr15多主元合金/金刚石复合材料磨损性能的影响

金刚石超硬磨具在高端芯片加工、3C陶瓷等领域发挥的作用日益重要,粘结相与金刚石的界面结合情况在很大程度上影响了金刚石超硬复合材料的力学和磨损性能。为了研究粘结相和金刚石的界面结合情况,采用放电等离子烧结方法制备了Cu₃₅Ni₂₅Co₂₅Cr₁₅多主元合金/金刚石复合材料,通过热力学计算和实验研究了粘结相和金刚石颗粒的界面反应。结果表明：烧结过程中,金属粘结相中的Cr元素与金刚石在界面处发生了化学反应,生成Cr-C化合物,且Cr-C化合物层的厚度随着烧结温度的升高而增加。当烧结温度达到950℃时,Cr-C化合物反应层均匀连续,厚度大约为1.1μm。复合材料粘结相与金刚石颗粒的粘结系数随着Cr-C化合物层厚度的增加而增大。摩擦磨损测试表明,在900℃和950℃烧结的样品表面,粘结相在摩擦过程中首先被磨除,金刚石随后露出,而Cr-C界面反应层有助于保持对金刚石颗粒的把持能力,提高复合材料的磨削性能。因此,适当的界面反应可提升金刚石复合材料的服役性能。     

高压熔渗金刚石/铜复合材料的低温导热特性

为研究高压熔渗金刚石/铜复合材料导热率在低温区的变化规律,采用高压熔渗（HRF）的方法分别制备了不同粒度（100 μm,250 μm,400 μm）的金刚石/铜复合材料,利用扫描量热法分析评价了高压熔渗法制备的不同粒度金刚石/铜复合材料的低温导热特性,采用扫描电子显微镜（SEM）分析其显微组织。研究结果表明：由于高压熔渗制备的金刚石/铜复合材料中的部分金刚石发生聚晶反应,导致金刚石颗粒间晶界传热的热阻远小于界面传热热阻;高压熔渗条件下,金刚石颗粒内部变形破碎导致缺陷增多,且100~150 K低温下以声子为主要热载子的传热对裂纹和间隙等缺陷敏感,导致在较低温区内金刚石/铜复合材料的导热率低于普通压力熔渗（PF）所制备的金刚石/铜复合材料的导热率。     

The effect of Si upon the interfacial reaction characteristics in SiCp/Al-Si system composites during multiple-remelting

The composite interfaces play an important role in determining the resultant composite properties, especially the development of interfacial reaction during remelting is critical to the commercialization and sustainable-development of metal matrix composites. In this paper, the interfacial reaction characteristics of SiCp/Al-Si system composites during multiple-remelting were investigated by Differential Scanning Calorimeter (DSC). It was found that the interfacial reactions were not sensitive to remelting number, remelting temperature and reinforcement volume fraction after a degree of reaction, and the results also suggested that the preventation effects of Si upon the interfacial reaction SiCp/Al were mainly attributed to the Si released from the interfacial reaction, while the original Si content in the master alloy also has the same effect only after a given Si content.     

Investigation of thermal properties of Al–Si matrix reinforced fine SiCp composites

Abstract

The characterisation of thermal expansion coefficient and thermal conductivity of Al–Si matrix alloy and Al–Si alloy reinforced with fine SiC_p (5 and 20 wt-%) composites fabricated by stir casting process are investigated. The results show that with increasing temperature up to 350°C, thermal expansion of composites increases and slowly reduces when the temperature reaches to 500°C. The values of both thermal expansion and conductivity of composites are less than those for Al–Si matrix. Microstructure and particles/matrix interface properties play an important role in the thermal properties of composites. Thermal properties of composites are strongly dependent on the weight percentage of SiC_p.     

Mechanical properties of a diamond–copper composite with high thermal conductivity

Using pressureless infiltration of copper into a bed of coarse (180 μm) diamond particles pre-coated with tungsten, a composite with a thermal conductivity of 720 W/(m K) was prepared. The bending strength and compression strength of the composite were measured as 380 MPa. As measured by sound velocity, the Young's modulus of the composite was 310 GPa. Model calculations of the thermal conductivity, the strength and elastic constants of the copper–diamond composite were carried out, depending on the size and volume fraction of filler particles. The coincidence of the values of bending strength and compressive strength and the relatively high deformation at failure (a few percent) characterize the fabricated diamond–copper composite as ductile. The properties of the composite are compared to the known analogues — metal matrix composites with a high thermal conductivity having a high content of filler particles (~ 60 vol.%). In strength and ductility our composite is superior to diamond–metal composites with a coarse filler; in thermal conductivity it surpasses composites of SiC–Al, W–Cu and WC–Cu, and dispersion-strengthened copper.     

Thermal conductivity of diamond/Ag composites with chromium carbide coated diamonds for the building materials of high power modules

Abstract

This paper reports on a study of the preparation and characterisation of diamond/Ag composites for the building materials of high power modules. The Cr₇C₃ coated diamond particles are utilised to improve the interfacial bonding between the Ag and diamond and composites are prepared by hot pressing technique. The characteristics of Cr₇C₃ coating layers were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the Cr₇C₃ coatings on the diamonds result in a strong interfacial bonding and a greatly enhanced thermal conductivity of the composites. A largely enhanced thermal conductivity of 768 W m^?1 K^?1 is obtained in Cr₇C₃ coated composites, which increases 168% relative to that of uncoated composites at 65% diamond volume fraction. The measured thermal conductivity agrees reasonably well with the predictions by a differential effective-medium (DEM) model.     

Effect of coating on the microstructure and thermal conductivities of diamond-Cu composites prepared by powder metallurgy

Diamond-Cu composites from the direct combination of diamond and Cu show low thermal conductivities due to weak interface and high thermal resistance as a result of chemical incompatibility. In this paper, a new method is proposed to strengthen interfacial binding between diamond and Cu by coating strong carbide-forming elements, e.g., Ti or Cr on the surface of the diamond through vacuum micro-deposition. Interfacial thermal resistance of diamond-Cu composites is greatly decreased when diamond particles are coated by a Cr or Ti layer of a certain thickness before combining with Cu. Thermal conductivity is also increased several times. Cr coating can reduce more effectively interface thermal resistance between diamond and Cu than Ti coating. Moreover, it has a smaller negative impact on the thermal conductivity of the Cu matrix, resulting in higher thermal conductivity of Cr-coated diamond-Cu composites. Through the vacuum micro-deposition technology, Cr on the diamond particle surface is present in the form Cr₇C₃ near diamond and a pure Cr outer layer at 2:1. The optimum thickness is within 0.6-0.9 μm; at this depth, the thermal conductivities of 70 vol% diamond-Cu composites can be increased four times and reach as high as 657 W/m K. In this work, an original theoretical model is proposed to estimate the thermal conductivities of composite materials with an interlayer of a certain thickness. The predicted values from this model are in good agreement with the experimental values.     

Fabrication process and thermal properties of SiCp/Al metal matrix composites for electronic packaging applications

The fabrication process and thermal properties of 50–71 vol% SiC_p/Al metal matrix composites (MMCs) for electronic packaging applications have been investigated. The preforms consisted with 50–71 vol% SiC particles were fabricated by the ball milling and pressing method. The SiC particles were mixed with SiO₂ as an inorganic binder, and cationic starch as a organic binder in distilled water. The mixtures were consolidated in a mold by pressing and dried in two step process, followed by calcination at 1100 °C. The SiC_p/Al composites were fabricated by the infiltration of Al melt into SiC preforms using squeeze casting process. The thermal conductivity ranged 120–177 W/mK and coefficient of thermal expansion ranged 6–10 × 10^–6/K were obtained in 50–71 vol% SiC_p/Al MMCs. The thermal conductivity of SiC_p/Al composite decreased with increasing volume fraction of SiC_p and with increasing the amount of inorganic binder. The coefficient of thermal expansion of SiC_p/Al composite decreased with increasing volume fraction of SiC_p, while thermal conductivity was insensitive to the amount of inorganic binder. The experimental values of the coefficient of thermal expansion and thermal conductivity were in good agreement with the calculated coefficient of thermal expansion based on Turner's model and the calculated thermal conductivity based on Maxwell's model.     

Microstructure and properties of Sip/Al–20 wt% Si composite prepared by hot-pressed sintering technology

In the present work, 50 vol% Sip/Al–20Si composite was prepared by hot-pressed sintering technology. Si particles were uniformly distributed in the Sip/Al–20Si composite, and only the presence of Si and Al phases were detected by XRD analysis. Dislocations, twins, and stacking faults were found in the Si particles. Several Si phases were found to be precipitated between Al matrix and Si particles. Si/Al interface was clean, smooth, and free from interfacial product. HRTEM indicated that the Si/Al interface was well bonded. The average CTE and thermal conductivity (TC) of Sip/Al–20Si composite were 11.7 × 10^?6/°C and 118 W/(m K), respectively. Sip/Al–20Si composite also demonstrated high mechanical properties (bending strength of 386 MPa). Thus, the comprehensive performance (low density and CTE, high TC, and mechanical properties) makes the Sip/Al–20Si composite very attractive for application in electron packaging.