【作者】 杨莹；

【导师】 沈强；

【作者基本信息】 武汉理工大学 ， 材料加工工程， 2011， 硕士

【摘要】 SiC泡沫陶瓷具有耐高温、耐腐蚀、低热导率及低热膨胀系数等优异的物理性能,孔隙高度连通,是熔融金属过滤器的最佳候选材料之一。SiC泡沫陶瓷增强Al基复合材料具有高比强度、比模量、良好的导热导电性、高的尺寸稳定性等优异的综合性能,在航空航天、电子、汽车、先进武器装备系统中具有广泛的应用前景。本论文针对SiC泡沫陶瓷力学强度较低、孔隙结构难以控制、SiC泡沫陶瓷增强Al基复合材料界面不能良好结合的问题,制备出孔隙结构和显微结构可控的SiC泡沫陶瓷及其增强Al基复合材料,重点研究了材料的结构控制方法及增强方式。首先,利用有机泡沫复制法和常压烧结技术制备了轻质高强且结构可控的SiC泡沫陶瓷。采用Al2O3、Y2O3和MgO、Al2O3、SiO2作为烧结助剂,调配SiC陶瓷料浆,采用有机泡沫复制法,通过改变浸渍涂覆次数、烧结工艺等合理控制了SiC泡沫陶瓷的孔隙结构和显微结构,并建立了力学抗压强度与其结构之间的相互关系。研究表明：SiC陶瓷料浆的粘度呈现剪切变稀特性,有利于有机泡沫浸渍过程；采用50%的固相含量的非水基SiC陶瓷料浆,在600℃下排除有机泡沫体,制备得到棱杆饱满的SiC泡沫陶瓷预制体。SiC泡沫陶瓷的孔隙结构中孔穴分布均匀,气孔连通性好；孔隙率为77～97%,孔径大小为1.08～2.20mm,随选用有机泡沫PPI(pores per inch,每英寸宏孔数)值的增大、浸渍涂覆次数的增加而降低,孔棱直径为260～690μm,随PPI值的降低、浸渍涂覆次数的增加而增加；1500℃烧结前后SiC泡沫陶瓷的平均线性收缩为15%。SiC泡沫陶瓷的显微结构中未添加烧结助剂的SiC泡沫陶瓷孔棱存在大量无法消除的气孔；添加Al2O3、Y2O3为烧结助剂的SiC泡沫陶瓷在1700℃烧结后所含液相为Y3Al5O12,实现了孔棱显微结构的完全致密化；添加MgO、Al2O3、SiO2为烧结助剂的SiC泡沫陶瓷在1300℃烧结后所含液相为Mg2Al4Si5O18和MgSiO3,高温时液相分解,SiC颗粒依靠玻璃相黏结为大颗粒,但气孔无法有效消除。SiC泡沫陶瓷的抗压强度随相对密度的增加而增大；在相对密度基本一致的情况下,当PPI值由15、20增加到40时,SiC泡沫陶瓷的抗压强度值从0.60MPa、1.22MPa升高至2.14MPa；在PPI值为20,相对密度基本都为0.20的情况下,随孔棱气孔减少、显微致密程度的升高,SiC泡沫陶瓷的抗压强度明显增大。然后,研究了SiC泡沫陶瓷增强Al基复合材料的制备及结构形成机理。利用无压浸渗工艺成功实现了SiC泡沫陶瓷高温浸渗熔融金属Al液,表征了复合材料的物相组成、显微结构和显微硬度。研究表明：SiC泡沫陶瓷增强Al基复合材料的主相为Al、SiC,并存在少量高温浸渗过程反应生成的Si和MgAl2O4。950℃氮气气氛下,SiC泡沫陶瓷增强Al基复合材料中泡沫陶瓷体的宏观轮廓清晰,SiC与Al界面结合良好,陶瓷体中空孔道中渗入了金属Al,增强相SiC和基体Al起到了相互约束的作用,有利于整体力学性能的提高。SiC泡沫陶瓷增强Al基复合材料中基体Al的硬度值为700MPa,靠近界面的SiC侧区域的显微硬度值为10GPa,在SiC增强体中略微升高至11GPa。在Al熔体中加入Mg元素,同时升高熔体的温度,可以起到改善Al与SiC润湿性的作用。反应生成液态Si进入Al合金液,在冷却时以粗大片状晶体Si相析出,可以进一步改善Al基复合材料的力学性能。更多还原

【Abstract】 SiC ceramic foams are one of the most suitable candidates for the filtration of molten metals due to their excellent properties such as high temperature resistance, corrosion resistance, low thermal conductivity, low thermal expansion coefficient and the unique structures of extremely interconnected cell. SiC ceramic foam reinforced Al matrix composites have wide application prospects in aerospace, electronics, automobile and advanced weapon system based on the high relative strength, relative modulus, good thermal and electric conductivity and size stability. According to the problems that the strength of SiC ceramic foams is relatively low, the cell structure is difficult to control and the related composite interface is not well bonded, in this paper SiC ceramic foams and related reinforced Al matrix composites are fabricated, and the ways of structure controlling and the methods of strengthening are mainly focused on.First, by polymer templates replica method and pressureless sintering technique, SiC ceramic foams with light weight, high strength and controllable structure are fabricated. By using sintering aids of Al2O3, Y2O3 or MgO, Al2O3 and SiO2, SiC slurry and ceramic foams are prepared. The cell structure and microstructure is adjusted, and the relationship between compressive strength and the structure is established. The results suggest that the viscosity of SiC slurry appears shear thinning behavior which is good for the polymeric sponge immersing process. The SiC ceramic foam preforms with plump cell strut are prepared using non-water based SiC slurry of 50% solid content, after the sponge is burnt out at 600℃. The cell is uniformly distributed and well interconnected. The porosity is 77～97%, the cell size is 1.08-2.20mm which decrease with the increasing PPI values of and the coating time. The cell strut diameter is 260-690μm, rising with the decreasing PPI values and the increasing coating time. The average linear contraction of SiC ceramic foams is 15% before and after sintering at 1500℃. According to the microstructure, the SiC ceramic foams with no sintering aids contain a lot of unavoidable pores. Those with Al2O3 and Y2O3 as sintering aids achieve fully dense strut, the liquid phase of which is Y3Al5O12 after sintering at 1700℃. And the SiC particle of those with MgO, Al2O3 and SiO2 as sintering aids is tied by glass phase, which are Mg2Al4Si5O18 and MgSiO3 after sintering at 1300℃and then decompose during high temperatures. The compressive strength of SiC ceramic foams increases with the increasing relative density. With the same relative density, the bigger the PPI values (or the smaller the cell sizes) of polymer templates are chosen, the higher the compressive strength presents. The scatters of the compressive strength distribute in the much higher numerical range with the same relative density of 0.2, which is contributed to the corresponding increase in microstructure densification degree.And then, the preparation and structure formation mechanisms of SiC ceramic foam reinforced Al matrix composites are investigated. The SiC ceramic foams are pressurelessly infiltrated by molten Al under high temperature. The phase compositions, microstructure and micro hardness are characterized. The results suggest that the main phases are Al and SiC, while the rest Si and MgAl2O4 phases are formed by infiltration reaction. The macroscopic contour of SiC reinforcement in the composites is clear and the interface of Al and SiC is well bonded. The infiltration of Al into the hollow strut of SiC ceramic results in the mutual restriction, which is beneficial to the entire strength of the composites. The hardness of Al is 700MPa, that of the SiC side near the interface is lOGPa, and that inside the SiC strut slightly increases to 11GPa. The bringing of Mg into the molten Al with high temperature improves the wettability of Al and SiC. The liquid Si phase formed by reaction enters into the molten Al and separates out when cooling down, which will further boost the mechanical strength of Al matrix composites.更多还原