SiC泡沫陶瓷/Fe基双连续相复合材料的制备和性能

将SiC泡沫陶瓷氧化,用挤压铸造法制备SiC泡沫陶瓷/Fe基双连续相复合材料并对其退火,研究了制备工艺和SiC泡沫陶瓷的体积分数对其微观组织和力学性能的影响。结果表明,在1250℃氧化48 h后在SiC泡沫陶瓷表面生成了厚度为1 mm的SiO2反应阻挡层。在双连续相复合材料的制备过程中,SiO2反应阻挡层抑制Fe与SiC的化学反应,避免了脆性化合物Fe3Si的生成,改善了基体与增强体的界面,使复合材料的抗弯强度提高2倍,压缩强度提高18%。当SiC泡沫陶瓷的氧化时间增至72 h时,SiC泡沫陶瓷表面SiO2的厚度过大。SiO2与基体和增强体热膨胀系数不匹配,使复合材料内相界面间的残余应力增加,导致其性能下降。将SiC泡沫陶瓷/Fe基双连续相复合材料在600℃退火4 h,可降低复合材料中的残余应力,提高复合材料的性能。SiC的体积分数较低时,金属基体的桥接、偏转裂纹的作用比较大,复合材料的弯曲强度高,变形程度大。随着复合材料中SiC体积分数的增大,SiC骨架筋增粗,其承载能力加强,复合材料的压缩强度呈提高的趋势。     

包套热挤压SiCp/6066铝基复合材料断裂机制和强化机制的研究

采用包套热挤压工艺制备了不同体积分数SiC颗粒增强的6066铝基复合材料,结合其断口形貌及微观组织,分析了材料的断裂机制及抗拉强度和屈服强度随SiC增强颗粒体积分数变化的规律.结果表明,材料的断裂机制为颗粒与基体间的界面脱粘以及SiC团聚体的脆性开裂.当SiC颗粒的体积分数小于12%时,随着SiC颗粒增强相的增加,SiCp/6066铝基复合材料的抗拉强度和屈服强度增加.当SiC颗粒的体积分数大于12%时,材料的强度增加减缓或略有下降,其主要强化机制是位错强化和弥散强化.     

界面改性对SiC_p/Cu复合材料热物理性能的影响

采用热压烧结法成功制备SiC_p/Cu复合材料。采用溶胶-凝胶工艺在SiC颗粒表面制备Mo涂层,研究Mo界面阻挡层对复合材料热物理性能的影响。结果表明:过氧钼酸溶胶-凝胶体系能够在SiC颗粒表面包覆连续性、均匀性较好的MoO_3涂层,最佳工艺配比为SiC∶MoO_3=5∶1(质量比)、过氧化氢∶乙醇=1∶1(体积比),SiC表面丙酮和氢氟酸预清洗处理有利于MoO_3涂层的沉积生长。MoO_3在540℃第一步氢气还原后转变为MoO_2,MoO_2在940℃第二步氢气还原后完全转变为Mo,Mo涂层包覆致密完整。热压烧结SiC_p/Cu复合材料微观组织致密均匀,且相比原始SiC颗粒增强的SiC_p/Cu,经溶胶-凝胶法界面改性处理的SiC_p/Cu复合材料热导率明显提高,SiC体积分数约为50%时,SiC_p/Cu复合材料热导率达到214.16W·m~(-1)·K~(-1)。     

Al_(72)Ni_(12)Co_(16)/A365准晶颗粒增强铝基复合材料的制备及其力学性能

制备了增强相体积分数为5%~20%的系列Al72Ni12Co16P/A356准晶增强铝基复合材料。其中增强相Al72Ni12Co16通过将严格按化学成分配比的Al72Ni12Co16浇于水冷铜基板上激冷凝固而获得。TEM和XRD分析结果表明所获得的材料为单相准晶材料。准晶增强铝基复合材料经热挤压处理后,绝大部分的铸造缺陷被消除,力学性能测试显示当准晶相的加入量为20%时,铝基复合材料的抗拉强度、屈服强度、弹性模量等性能分别从基体材料的275 MPa、200 MPa和70 GPa提高至410 MPa、350 MPa和102 GPa,而延伸率却从6%降低至3%。分析了准晶增强铝基复合材料的断裂机制和增强机制,准晶颗粒增强铝基复合材料的断裂机制可能有如下3种:界面及其附近区域脱粘、基体在集中的滑移带内撕裂和颗粒断裂,而其增强机制主要是细晶强化、弥散强化和固溶强化。     

超声外场对SiCp/7085复合材料界面及拉伸性能的影响

为研究超声辅助制备工艺对SiC_p/7085复合材料界面结合及拉伸性能的影响,用机械搅拌、机械搅拌+超声施振、超声施振3种工艺制备体积分数为10%的SiC_p/7085复合材料.采用扫描电子显微镜(SEM)、能谱(EDS)研究各工艺对SiC_p/7085复合材料的界面微观组织和拉伸性能的影响.实验结果表明:机械搅拌工艺促进大颗粒(80μm)与熔体结合,但产生了粗大Al4C3界面产物包裹层,且难改善小颗粒(37μm)与熔体界面结合差的问题;超声施振能促进界面反应,生成尺寸细小、排列规整、紧密的Mg O、Mg Al2O4界面强化相覆盖层,有效改善小颗粒与熔体界面结合;相比于7085铝合金,机械搅拌不能改善SiC_p/7085复合材料拉伸性能,而超声施振的加入能显著提升材料拉伸性能.     

高体分SiC颗粒增强镁基复合材料的显微组织与力学性能EI北大核心

预先对SiC颗粒增强体进行表面氧化处理,然后采用压铸浸渗法制备了体积分数为51.5%的SiCp/Mg-6Al-0.5Mn复合材料。通过压缩性能测试、扫描电镜、透射电镜等方法,研究了复合材料的显微与力学性能。结果表明,在基体Mg-6Al-0.5Mn合金掺入51.5%体积分数的SiC颗粒预制块后,复合材料的组织致密,分布均匀,其断裂方式包括界面脱开、基体韧断和增强体开裂。SiC颗粒与基体之间发生了界面反应,生成了纳米级的Mg2Si化合物。同时,适度的预氧化可以提高基体与颗粒之间的界面结合强度,从而使复合材料抗拉强度得到提高。     

碳化硅颗粒增强铝基复合材料颗粒表面改性技术研究现状

SiC颗粒增强铝基复合材料因具有高的比强度、比刚度、耐磨性及较好的高温稳定性而被广泛应用于航空航天、电子、医疗等领域,但由于SiC颗粒高熔点、高硬度的特点以及SiC颗粒与铝基体间存在界面反应,碳化硅铝基复合材料存在加工性差、界面结合力不足等问题,已无法满足航天等领域对材料性能更高的要求,因此开展如何改善基体与颗粒之间界面情况的研究对进一步提升复合材料综合性能具有重要的科学意义。结合国内外现有研究成果,总结了SiC颗粒与铝基体界面强化机制、界面反应特点、表面改性技术原理及数值建模的发展现状,结果表明,现有经单一表面改性方法处理后的增强颗粒对铝基复合材料性能的提升程度有限,因此如何采用新的手段使复合材料性能进一步提升将成为后续研究热点,且基于有限元数值模拟方法进行复合材料设计也是必然趋势。最后针对单一强化性能提升有限的问题,提出了基于表面改性的柔性颗粒多模式强化方法,同时针对现有的技术难点展望了后续的研究方向,以期为颗粒增强复合材料的制备提供理论参考。     

高强度阻尼铝基复合材料研究

基于多相结构阻尼原理,根据阻尼混合原则,通过激冷金属基体提高其阻尼行为的同时添加合理的合金元素、具有不同截面滑动能耗的增强相以及改变增强相的体积分数,采用高速小漩涡剪切搅拌制备的混杂颗粒增强铝基复合材料,既获得高的比强度和比刚度同时,也有优异的阻尼性能,实现了在不降低A356性能的同时,开发出一种以A356为基的低密度高强度高阻尼结构-功能一体化的新型结构材料。     

高体积分数SiCp/Al复合材料的微观组织与导热性能

选用两种粒径的SiC颗粒,采用挤压铸造方法制备了体积分数为70％的SiCp／LD11（Al-12％Si）复合材料,研究了材料的微观组织和导热性能．研究表明：复合材料组织均匀、致密;SiC—Al界面干净,而基体中的Si相分别存在从铝中直接析出和依附SiC颗粒表面生长这两种分布形态;复合材料导热性能优异,其导热率大于基体LD11铝合金的导热率．     

反应熔渗SiC/MoSi_2和SiC/Mo(Si,Al)_2复相材料抗氧化行为

研究了低成本制备技术反应熔渗方法制备的SiC/MoSi2和SiC/Mo(Si,Al)2复合材料高温氧化行为。表面氧化物的形态和氧化增重的研究结果表明,所制备复合材料高温氧化3 h后即发生钝化现象,继续在500℃再进行低温氧化试验,发现限制该材料使用的"Pest"现象消失。其中渗铝复合材料SiC/Mo(Si,Al)2高温增重较渗硅SiC/MoSi2严重。当后者中形成的SiC增强相全部为原位反应生成时,由于界面结合力提高,抗氧化能力更强。     

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.     

Fabrication of SiC particles-reinforced magnesium matrix composite by ultrasonic vibration

Magnesium matrix composites reinforced with two volume fractions (1 and 3%) of SiC particles (1 μm) were successfully fabricated by ultrasonic vibration. Compared with as-cast AZ91 alloy, with the addition of the SiC particles grain size of matrix decreased, while most of the phase Mg₁₇Al₁₂ varied from coarse plates to lamellar precipitates in the SiCp/AZ91 composites. With increasing volume fraction of the SiC particles, grains of matrix in the SiCp/AZ91 composites were gradually refined. The SiC particles were located mainly at grain boundaries in both 1 vol% SiCp/AZ91 composite and 3 vol% SiCp/AZ91 composite. SiC particles inside the particle clusters may be still separated by magnesium. The study of the interface between the SiC particle and the alloy matrix suggested that SiC particles bonded well with the alloy matrix without interfacial reaction. The ultimate tensile strength, yield strength, and elongation to fracture of the SiCp/AZ91 composites were simultaneously improved compared with that of the as-cast AZ91 alloy.     

Microstructure and mechanical properties of cast (Al–Si)/SiCp composites produced by liquid and semisolid double stirring process

Abstract

A stirring process containing two steps, i.e. liquid and then semisolid stirring, was used to produce SiC particle reinforced aluminium matrix composites. The major advantages of this process are that full wetting of SiC particles by molten aluminium can be readily achieved at relatively low stirring rates, and undesirable Al₄ C₃ is not formed at the Al/SiC interface due to lower processing temperatures. Cast Al–Si matrix composites reinforced with 15 and 20 vol.-%SiC particles were produced in the present work. The mechanical properties of the composites were evaluated under the conditions of investment mould casting and heat treatment. For the composites obtained without employing semisolid stirring, the aggregation of SiC particles observed in the microstructure of composites resulted in quite poor mechanical properties. Observations and analyses indicated that some Al/SiC interfaces were very clean, and a reaction product of spinel MgAl₂O₄ was also found at some Al/SiC interfaces. Silicon dioxide (SiO₂ ) was found to exist on the surface of as purchased and 250°C dried SiC powders. This SiO₂ is involved in the spinel reaction at the interface between the SiC particles and the matrix in the present Al/SiC composites.     

Effect of re-melting on particle distribution and interface formation in SiC reinforced 2124Al matrix composite

The interface between metal matrix and ceramic reinforcement particles plays an important role in improving properties of the metal matrix composites. Hence, it is important to find out the interface structure of composite after re-melting. In the present investigation, the 2124Al matrix with 10 wt.% SiC particle reinforced composite was re-melted at 800 °C and 900 °C for 10 min followed by pouring into a permanent mould. The microstructures reveal that the SiC particles are distributed throughout the Al-matrix. The volume fraction of SiC particles varies from top to bottom of the composite plate and the difference increases with the decrease of re-melting temperature. The interfacial structure of re-melted 2124Al–10 wt.%SiC composite was investigated using scanning electron microscopy, an electron probe micro-analyzer, a scanning transmission electron detector fitted with scanning electron microscopy and an X-ray energy dispersive spectrometer. It is found that a thick layer of reaction product is formed at the interface of composite after re-melting. The experimental results show that the reaction products at the interface are associated with high concentration of Cu, Mg, Si and C. At re-melting temperature, liquid Al reacts with SiC to form Al₄C₃ and Al–Si eutectic phase or elemental Si at the interface. High concentration of Si at the interface indicates that SiC is dissociated during re-melting. The X-ray energy dispersive spectrometer analyses confirm that Mg- and Cu-enrich phases are formed at the interface region. The Mg is segregated at the interface region and formed MgAl₂O₄ in the presence of oxygen. The several elements identified at the interface region indicate that different types of interfaces are formed in between Al matrix and SiC particles. The Al–Si eutectic phase is formed around SiC particles during re-melting which restricts the SiC dissolution.     

Thermal conductivities of Ti-SiC and Ti-TiB2 particulate composites

Composites of commercial-purity titanium reinforced with 10 and 20 vol % of SiC and TiB₂ particulates were produced by powder blending and extrusion. Heat treatments were conducted on each of these composites. The thermal diffusivities of the composites were measured as a function of temperature using the laser flash technique. Thermal conductivities were inferred from these measurements, using a rule-of-mixtures assumption for the specific heats. It has been shown that, while an enhancement of the thermal conductivity is expected to arise from the presence of both types of reinforcement, this behaviour is in fact observed only with the Ti-TiB₂ composites. The thermal conductivity of Ti-TiB₂ composites is significantly greater than that of the unreinforced matrix and rises with increasing volume fraction of reinforcement. In contrast, the conductivities of the Ti-SiC composites were considerably lower than that of the unreinforced titanium and decreased with increasing volume fraction of SiC reinforcement. These results have been interpreted in terms of the thermal resistance of the reaction layers which exist between the matrix and two types of particulate reinforcements. The faster reaction kinetics between SiC and Ti gives rise to a thicker reaction layer for a given heat treatment than that between Ti and TiB₂ and is also accompanied by a much larger volume change (– 4.6%). It is proposed that this volume decrease, giving rise to interfacial damage and a network of microcracks, is at least partly responsible for a high interfacial thermal resistance, reducing the conductivity of the Ti-SiC composite. These results indicate that TiB₂ would be preferable to SiC as a reinforcement in Ti for situations where a high thermal conductivity would be beneficial.     

Incorporation of new technique for processing of Al/SiCp composites based on evaporative pattern casting (EPC) method

Abstract

A336 Al matrix composites containing different volume fraction and mean mass particle size of SiC particles as the reinforcing phase were synthesised by evaporative pattern casting (EPC) route. The process consisted of fabricating of EPS/SiC_p composite pattern followed by EPC of A336 Al alloy. The EPS/SiC_p pattern was made by blending SiC particles with expandable polystyrene (EPS) beads and placing them in expanding mould heating with steam until EPS beads expand completely. Uniform distributed SiC particles around the EPS beads and locally movement of them during pouring and degradation leads to homogenous distribution of particles in final Al/SiC_p composite. Higher modulus, strength and hardness were observed in the composites than the unreinforced Al alloy part. The fracture surfaces of the composite samples exhibited dimple surfaces and fracture in SiC particles.     

Pressure infiltration casting process and thermophysical properties of high volume fraction SiCp/Al metal matrix composites

Abstract

SiC_p/Al composites containing high volume fraction SiC particles were fabricated using a pressure infiltration casting process, and their thermophysical properties, such as thermal conductivity and coefficient of thermal expansion (CTE), were characterised. High volume fraction SiC particulate preforms containing 50–70 vol.-%SiC particles were fabricated by ball milling and a pressing process, controlling the size of SiC particles and contents of an inorganic binder. 50–70 vol.-%SiC_p/Al composites were fabricated by high pressure infiltration casting an Al melt into the SiC particulate preforms. Complete infiltration of the Al melt into SiC preform was successfully achieved through the optimisation of process parameters, such as temperature of Al melt, preheat temperature of preform, and infiltration pressure and infiltration time after pouring. Microstructures of 50–70 vol.-%SiC_p/Al composites showed that pores resided preferentially at interfaces between the SiC particles and Al matrix with increasing volume fraction of SiC particles. The measured coefficients of thermal expansion of SiC_p/Al composites were in good agreement with the estimated values based on Turner's model. The measured thermal conductivity of SiC_p/Al composites agreed well with estimated values based on the 'rule of mixture' up to 70 vol.-% of SiC particles, while they were lower than the estimated values above 70 vol.-% of SiC particles, mainly due to the residual pores at SiC/Al interfaces. The high volume fraction SiC_p/Al composite is a good candidate material to substitute for conventional thermal management materials in advanced electronic packages due to their tailorable thermophysical properties.     

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.     

Thermal conductivity of Al–SiC composites with monomodal and bimodal particle size distribution

The thermal conductivity of aluminum matrix composites having a high volume fraction of SiC particles is investigated by comparing data for composites fabricated by infiltrating liquid aluminum into preforms made either from a single particle size, or by mixing and packing SiC particles of two largely different average sizes (170 and 16 μm). For composites based on powders with a monomodal size distribution, the thermal conductivity increases steadily from 151 W/m K for particles of average diameter 8 μm to 216 W/m K for 170 μm particles. For the bimodal particle mixtures the thermal conductivity increases with increasing volume fraction of coarse particles and reaches a roughly constant value of 220 W/m K for mixtures with 40 or more vol.% of coarse particles. It is shown that all present data can be accounted for by the differential effective medium (DEM) scheme taking into account a finite interfacial thermal resistance.     

Investigation of thermal conductivity and dielectric properties of LDPE-matrix composites filled with hybrid filler of hollow glass microspheres and nitride particles

The hybrid filler of hollow glass microspheres (HGM) and nitride particles was filled into low-density polyethylene (LDPE) matrix via powder mixing and then hot pressing technology to obtain the composites with higher thermal conductivity as well as lower dielectric constant (D_k) and loss (D_f). The effects of surface modification of nitride particles and HGMs as well as volume ratio between them on the thermal conductivity and dielectric properties at 1 MHz of the composites were first investigated. The results indicate that the surface modification of the filler has a beneficial effect on thermal conductivity and dielectric properties of the composites due to the good interfacial adhesion between the filler and matrix. An optimal volume ratio of nitride particles to HGMs of 1:1 is determined on the basis of overall performance of the composites. The thermal conductivity as well as dielectric properties at 1 MHz and microwave frequency of the composites made from surface-modified fillers with the optimal nitride to HGM volume ratio were investigated as a function of the total volume fraction of hybrid filler. It is found that the thermal conductivity increases with filler volume fraction, and it is mainly related to the type of nitride particle other than HGM. The D_k values at 1 MHz and microwave frequency show an increasing trend with filler volume fraction and depend largely on the types of both nitride particles and HGMs. The D_f values at 1 MHz or quality factor (Q × f) at microwave frequency show an increasing or decreasing trend with filler volume fraction and also depend on the types of both nitride particle and HGM. Finally, optimal type of HGM and nitride particles as well as corresponding thermal conductivity and dielectric properties is obtained. SEM observations show that the hybrid filler particles are agglomerated around the LDPE matrix particles, and within the agglomerates the smaller-sized nitride particles in the hybrid filler can easily form thermally conductive networks to make the composites with high thermal conductivity. At the same time, the increase of the value D_k of the composites is restricted due to the presence of HGMs.