SiC颗粒增强Al基复合材料中有害界面反应的控制

对有害界面化学反应的控制 ,是当前SiC颗粒增强Al基复合材料研究中的主要问题之一。本文对近年来国内外研究工作者 ,通过添加Si元素及对SiC颗粒进行表面处理来控制SiC Al之间有害界面反应的研究进展进行了评述     

扭转圈数对高压扭转SiC_P/Al复合材料界面扩散行为和组织性能的影响

采用OM和EDS研究不同扭转圈数下高压扭转法制备SiC_P/Al复合材料的显微组织和界面扩散行为,并结合组织特点和界面特征分析扭转圈数对复合材料拉伸性能和断裂机理的影响。结果表明:扭转圈数的增加可以有效提高SiC颗粒分布的均匀性,闭合孔隙,界面处Al元素扩散能力增强,扩散距离增大,Al扩散系数实际计算值较理论值增大了10~(17)倍,形成以元素扩散和界面反应为主的强界面结合,试样抗拉强度和伸长率不断提高,少量的SiC颗粒均匀分布在断口韧窝中,断裂主要以基体的韧性断裂为主;当扭转圈数较大时,SiC颗粒在剧烈剪切作用下破碎加剧,颗粒"再生团聚"导致孔隙率增大,潜在裂纹源增多,形成大量结合强度较低的断裂新生界面,试样抗拉强度和伸长率显著降低,在团聚位置易形成尺寸较大的深坑韧窝,复合材料断裂呈现韧性断裂与脆性断裂的混合模式。     

SiC颗粒增强Al基复合材料中有害界面反应的控制

对有害界面化学反应的控制，是当前SiC颗粒增强Al基复合材料研究中的主要问题之一，本文对近年来国内外研究工作者，通过添加Si元素及对SiC颗粒进行表面处理来控制SiC/Al之间有害界面反应的研究进展进行了评述。     

Ti基复合材料界面反应扩散的微观分析

通过SiC连续纤维增强Ti基复合材料的制备及在不同条件下的热处理试验,利用TEM,SEM,EDS及XRD分析技术研究复合材料的界面反应以及产物相的形成.研究结果表明:SiC /Ti复合材料界面发生了反应扩散,反应元素C,Ti,Si在界面反应层中出现浓度波动;界面反应产物被确认为是Ti3SiC2 ,TiC和 Ti5Si3,在靠近SiC侧出现Ti3SiC2和Ti5Si3单相区,靠近Ti基体侧为Ti5Si3单相区,中间为TiC Ti5Si3双相区;SiC/Ti复合材料界面相序列为SiC┃Ti3SiC2┃Ti5Si3┃TiC Ti5Si3┃Ti5Si3┃Ti.     

无压浸渗法制备氧化态SiC颗粒增强铝基复合材料

研究了SiC颗粒在1000~1200℃的氧化行为, 其氧化增重率与保温时间符合抛物线规律, 氧化增重受扩散过程控制, 氧化激活能为219 kJ/mol. 采用预氧化处理的SiC颗粒为增强体, 含Si、Mg的铝合金为基体, 通过无压浸渗方法制备了SiC_p/Al复合材料, 分析了复合材料的微观组织与界面形貌, 探讨了无压浸渗机理. 复合材料中颗粒分布均匀, 无偏聚现象. 材料制备过程中存在界面反应, SiC颗粒表面的氧化层与铝合金中的Mg、Al反应形成了一定数量的MgAl₂O₄. 界面反应的存在提高了润湿性, 促进了无压自发浸渗.     

高体积分数SiCp/A356复合材料的显微组织和电导率

铝基复合材料在电子封装领域存在着潜在的应用前景。为获得高体积分数的铝基复合材料,利用压力浸渗法制备了高体积分数SiC颗粒增强A356复合材料(SiC_p/A356),通过金相显微镜、XRD、SEM和EDS等分析手段对其物相、显微结构和电导率进行了表征。结果表明:用该方法制备的SiC_p/A356复合材料组织致密,颗粒分布均匀,界面结合性能较好;SiC增强颗粒与A356基体界面反应控制良好,仅有少量Al4C3脆性相生成。SiC粉体经颗粒表面氧化处理在其表面生成一层SiO_2薄膜,虽抑制了界面反应的发生,但也使复合材料的收缩减小,电阻率增大,导电性能变差。     

增强颗粒在铝基复合材料中的作用

主要讨论了铝基复合材料中常用的几种增强颗粒SiC、B4C、TiC、Al2O3、TiB2、AlN的特性及制备中可能与基体发生的界面反应和改善方法,从而可选取适当的铝基体与增强颗粒组合,通过适当的方法,制备出高性能的复合材料.     

高压扭转对SiC_P/Al复合材料微观组织和力学性能的影响

为研究大塑性变形对金属基复合材料微观组织和力学性能的影响,利用高压扭转工艺(HPT)在200℃下将纯Al粉末和经氧化处理的SiC粉末混合固结成10wt%SiC_P/Al复合材料。采用TEM观察HPT变形后不同圈数试样的SiC-Al界面及Al基体微观组织,采用EDS能谱仪分析界面处原子扩散现象,采用万能拉伸试验机测试研究不同扭转圈数试样的力学性能。结果表明:不同圈数试样Al基体内出现大量位错、非平衡晶界等晶格缺陷;组织内存在两种SiC-Al界面,含SiO_2层的原始界面和因颗粒破碎而新生成的界面。两种界面结合良好,界面处元素相互扩散;随着扭转圈数的增加,10wt%SiC_P/Al复合材料抗拉强度增加,延伸率得到较大提高。分析发现高压扭转后不同圈数组织内产生的大量晶格缺陷和细小晶粒,促进界面处元素的相互扩散,使界面结合良好,同时大量晶格缺陷和细小晶粒的产生以及结合良好的SiC-Al界面是SiC_P/Al复合材料力学性能大幅提升的主要原因。     

碳化硅颗粒增强铝基复合材料的无压浸透反应机理探讨

为探讨SiCp/Al基复合材料无压浸渗反应机理,利用XPS鉴定了SiC预制体浸渗前沿界面上的反应产物结构.采用HRTEM研究了SiCp/Al基复合材料的界面结构.结果表明,浸渗与未浸渗部分之间的界面上存在MgO.Al2O3和ZnO诸化合物,没有发现氮的化合物.在SiC相与铝相的界面上仅存在MgAl2O4相,MgAl2O4相几乎连续地包敷在SiC颗粒上.这表明,高温下SiC与熔Al合金接触后,SiC颗粒表面上的SiO2与Al,Mg,Zn诸元素发生了放热反应,从而降低了表面张力,提高了湿润性.促进了自发浸渗.     

高导热金属基复合材料的热物理性能

分别采用无压浸渗、气压浸渗、内氧化技术制备了高导热Al/SiC、Al/C、Cu/Al2O3复合材料.研究了增强相和界面对这三种复合材料的热导率和热膨胀系数的影响,并对这些性能进行了理论分析和数值模拟.当颗粒尺寸与界面层厚度之比固定时,颗粒尺寸对Al/SiC复合材料热导率影响很小,但界面热导率对其影响很大;Al/SiC复合材料的CTE随温度的升高而增加,随SiO2层厚度的增加而减小;碳纤维中混杂3%SiC颗粒有利于改善纤维的分布,降低Al/C复合材料的缺陷,并提高其热导率;压力加工增加了Cu/Al2O3的致密度,也提高了其热导率;可用Schapery和Kerner模型计算复合材料的热膨胀系数,用Hasselman-Johnson模型计算热导率.     

Processing and interfacial bonding strength of 2014 Al matrix composites reinforced with oxidized SiC particles

The SiC powder with a SiO₂ protective layer is used as the reinforcements for 2014 Al/SiC_p composites to suppress the reaction between the Al matrix and the SiC particle. 2014 Al/SiC_p composites were fabricated by vacuum hot pressing (VHP) and subsequent extrusion using 2014 Al powders and the SiC particles covered with a SiO₂ layer. The interfacial product was found to be Mg spinel (MgAl₂O₄) formed mainly by the chemical reactions of the SiO₂ layer covered on SiC particles with the Mg, Al in the 2014 Al alloy matrix. Also the interfacial bonding strength of the composites was investigated using push-out tests of SiC rods with the SiO₂ oxidation layer, which were processed within 2014 Al alloy.     

热轧高含量B4C颗粒增强Al基复合材料的成形性能

高含量B₄C (B₄C≥30wt%)颗粒增强Al基(B₄C_P/Al)复合材料具有优异的结构和功能特性,尤其是具有优异的中子吸收性能,在核防护领域被用做屏蔽材料使用。但由于高含量B₄C颗粒的加入,使B₄C_P/Al复合材料变形困难。采用ABAQUS数值模拟方法对不同变形量下B₄C_P/Al复合材料的热轧过程进行数值模拟分析,在480℃温度下对热压烧结的B₄C_P/Al复合材料坯料进行轧制,并对其微观组织和力学性能进行分析。数值模拟结果表明,热轧变形量达到60%以上时,B₄C_P/Al复合材料板材表面中间区域应力较小,侧面应力较大,在板材边缘容易产生残余应力。研究结果表明,随轧制下压量的增加,B₄C_P/Al复合材料中B₄C颗粒分布明显均匀,位错密度增加。当轧制变形量达到70%时,B₄C_P/Al复合材料的屈服强度提高至249.46 MPa,极限抗拉强度提高至299.56 MPa。在拉伸过程中,B₄C颗粒优先断裂,但并未与基体界面脱黏,B₄C颗粒承受了主要载荷,Al基体发生塑性流动,从而提高了B₄C_P/Al复合材料的强度。      

SiC颗粒增强铝基复合材料的纯铜中间层液相扩散焊

采用Cu箔中间层在Ar气氛保护、550℃条件下过渡液相扩散焊(TLP)焊接SiC颗粒(SiC_P)增强Al基复合材料SiC_P/ZL101和SiC_P/Al (SiC_P 10vol%),对母材与焊接接头的微观组织、剪切强度、焊接接头剪切断面与断裂路径等进行分析。结果表明:在铸Al(ZL101)与纯Al(Al)基体中,分别通过共晶温度较低的Al-Si-Cu(524℃)三元共晶反应与Al-Cu(548℃)二元共晶反应实现中间层金属/基体金属(M/M)界面润湿。其中铸Al基体焊接接头中虽有颗粒偏聚,但由于Al-Si-Cu三元共晶反应的Cu含量(26.7wt%)低于Al-Cu二元共晶反应的Cu含量(33wt%),SiC_P/ZL101焊接接头焊缝中CuAl₂相少于SiC_P/Al焊接接头焊缝中的CuAl₂相,且未出现CuAl₂相的聚集,故其强度较高。Cu中间层形成的金属间化合物CuAl₂相是影响焊接接头力学性能的重要因素,两种复合材料焊接接头的剪切强度分别为85.4 MPa和73 MPa。      

SiC/SiC-哈氏合金异质连接机制及其氟熔盐腐蚀特性分析

以Cu-2.67Ni钎料, 采用钎焊工艺获得了SiC/SiC复合材料-哈氏合金异质接头, 并研究了其在800 ℃的FLiNaK熔盐中的腐蚀行为。利用不同手段表征了接头微观结构和氟熔盐腐蚀行为。结果表明, Ni、Cr、Mo等合金元素以及SiC中的Si元素发生互扩散。Cr元素替代Ni元素, 在焊料-复合材料界面富集并形成不连续碳化物层。高温钎焊加速Ni扩散并侵蚀SiC, 低温钎焊导致焊料熔融不充分。钎焊过程中的元素扩散改变了哈氏合金的组成,导致其耐腐蚀性能恶化。Cr与Si的选择性溶出导致钎焊接头及合金的腐蚀损伤, 这与热力学计算结果一致。     

Investigation on diffusion bonding characteristics of SiC particulate reinforced aluminium metal matrix composites (Al/SiCp-MMC)

Joining characteristics of SiC particulate reinforced aluminium metal matrix composites (Al/SiC_p-MMC) were investigated by vacuum diffusion bonding process. The joining performances of the similar and dissimilar composites were studied, and the influences of SiC_p volume percentage and the insert alloy layer on bonding quality and properties of the bonded joints were also estimated. The experimental results indicate that the strength of vacuum diffusion bonded joints decreases with increasing SiC_p volume percentage, and obtaining satisfactory bonding quality in the diffusion bonded joints of the dissimilar Al/SiC_p-MMC is much more difficult than that of the similar Al/SiC_p-MMC. Moreover, the results still manifest that the diffusion bonding either for the similar or for the dissimilar Al/SiC_p-MMC, the suitable insert alloy layer can improve evidently the joining quality of joints, and the strength of diffusion bonded joints corresponding to using the insert alloy layer is apparently higher than that of no insert layer.     

Behaviour of coatings on reinforcements in some metal matrix composites

Coating on reinforcements affects the interface bonding of a composite, and is therefore usually used for improving the composite's properties. The behaviour of SiC coating on carbon fibre in reinforced aluminium metal castings, Fe on carbon fibre-reinforced copper and alumina coating on K₂O · 6TiO₂ whisker-reinforced aluminium composites were investigated, respectively, by modern techniques such as TEM, SEM etc. with the goal of controlling the interfacial interaction and wettability of reinforcement with the matrices. SiC coating produced by a polycarbosilane solution process effectively improved the strength because it successfully controlled oxidation of the carbon fibres themselves and the harmful reaction between the carbon fibres and molten aluminium during the fabrication process and heating process of the composites. The metal coating, Fe, made by electrical plating, strengthened the bonding of carbon fibres with copper by changing the bonding state of the interface from a mechanical one to a partly chemical one. Therefore the strengths of the resulting composites were improved. The alumina coating on K₂O · 6TiO₂ also controlled the diffusion of the K element from the whiskers into the aluminium matrix and altered the reaction with aluminium, and led to the optimization of interfacial bonding between the whiskers and a superior composite.     

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.     

Mechanical property improvements in Nicalon SiC fibre reinforced silicon nitride ceramics by oxide coating of Si3N4 starting powders

Ceramic matrix composites are attractive as candidate materials for high-temperature applications offering some advantages compared to monolithic ceramics and high-temperature metal alloys. SiC fibre reinforced silicon nitride is one such composite system. However, the processing route is critical to the production of a reliable composite. In this study, silicon nitride matrix densification was improved and sintering temperature was lowered by coating of Si₃N₄ particles with oxides deposited from hydrolysed metal alkoxides. The solution containing oxide coated Si₃N₄ powders was used as a slurry to infiltrate Nicalon SiC fibre tows. Following previous studies, the fibres were heat-treated in carbon monoxide to improve mechanical and surface properties. Infiltrated green bodies were hot-pressed at elevated temperatures to produce dense composites. The results showed that particle coating accelerated densification kinetics, eliminated pores and reduced the required hot-pressing temperature. There was also less fibre degradation as a result of the lower temperature of densification. Bending strength and fracture toughness of the composites were measured and fractography was conducted using scanning electron microscope. Composites manufactured using coated Si₃N₄ powders showed improved properties, specifically matrix stiffening and delayed crack initiation under load.