【作者】 徐睿；

【导师】 欧阳求保；

【作者基本信息】 上海交通大学 ， 材料学， 2010， 硕士

【摘要】 颗粒增强铝基复合材料已经在航空航天、半导体封装、汽车以及日常生活中得到了广泛的应用。目前,应用最为广泛的SiCp增强铝基复合材料大都采用外加法制备获得,这种复合材料由于颗粒较大并且颗粒与基体润湿性差,从而影响增强效果。于是,人们开始寻找其他优秀的增强相颗粒及制备工艺,科研工作者们发现TiB2颗粒具有优秀的力学及物理性能,而且其可以通过化学反应在铝基体中原位生成,原位自生的颗粒尺寸细小,与基体结合良好。本论文主要研究在增强相颗粒含量相近的情况下,对原位TiB2颗粒增强铝基复合材料与外加法制备的SiC颗粒增强铝基复合材料进行微观组织及力学与其他物理性能的比较并讨论原位合成复合材料的优势。本论文通过混合盐法成功原位合成7wt%TiB2颗粒增强A356铝合金复合材料。原位生成的TiB2颗粒大多呈六棱柱状,平均尺寸在300nm左右,在复合材料中大致均匀分布,晶粒呈细小等轴状或菊花状,明显比基体合金中要细小。而与之对比的是通过搅拌铸造法制备的SiCp/A356复合材料,其颗粒尺寸在15μm左右,许多颗粒带有尖棱角。7%TiB2/A356抗拉强度达到362.5MPa,弹性模量达到81.2GPa,相比基体合金分别提高了12.4%与21.6%,但塑性降低。搅拌铸造制备的SiCp/A356同样增强效果明显,且塑性下降更加明显。通过分析7%TiB2/A356与8%SiCp/A356复合材料的温度-阻尼谱线,可以得到以下结论:两种复合材料阻尼性能都随温度的上升而提高,并且在低频下能够获得更高的阻尼性能;在相同的频率和温度下,复合材料与基体合金阻尼性能比较的结果:7%TiB2/A356>8%SiCp/A356>A356,颗粒的引入使合金阻尼性能提高的原因主要是复合材料加工过程中产生的大量位错成为内耗源,而7%TiB2/A356阻尼性能比8%SiCp/A356优秀的原因是原位自生的TiB2颗粒较细小以及其晶粒细化效果,产生了更多的界面与晶界阻尼。本文同时在实验的基础上讨论了复合材料阻尼性能变化趋势:1增加颗粒含量可以提高阻尼性能;2铸态下复合材料阻尼性能比T6态更高;3挤压变形后也能获得更高的阻尼性能。本文还研究了7%TiB2/A356与8%SiCp/A356在室温下的磨损性能,发现8%SiCp/A356在整个载荷区间内,磨损率略有上升,稳定在3～6×10-6mm2,耐磨性能最好;7%TiB2/A356耐磨性能次之,磨损率也随载荷增加而增加,在载荷100N时有小幅突变;两种复合材料的耐磨性能都比基体合金A356优秀,同时也明显好于40Cr。随着摩擦终转轴速度从370rpm上升到550rpm,8%SiCp/A356的磨损率略有下降,而7%TiB2/A356则上升。分析磨损表面可知,8%SiCp/A356复合材料在低载荷下以粘着磨损机制为主,在高载荷下以粘着磨损与磨粒磨损为主,并且磨损表面容易形成机械混合层从而降低磨损量,并且在转速增加后有利于机械混合层的形成;7%TiB2/A356在低载荷下以粘着磨损为主,在高载荷下以粘着磨损与表面疲劳引起的剥层磨损为主,在转速增加后,还要考虑氧化磨损的因素。更多还原

【Abstract】 Particles Reinforced Aluminum Matrix Composites (AMCs) have been widely used in the field of aerospace, electronic packaging, automobiles and daily life. At present, SiCp reinforced ACMs which have been most extensively applied are mostly fabricated by directly adding methods. These composites do not achieve favorable effects of reinforcement due to large-sized particles and poor wet ability between particles and matrix. Therefore, people began to look for better reinforced particles and fabricating methods. Scientists find that TiB2 particles have outstanding mechanical and other physical properties, and moreover they are able to be synthesized directly in the aluminum matrix through chemical reactions. This kind of in-situ ACMs, has small and fine particles and better bond of interfaces. So the purpose of this research is to compare the microstructures and mechanical, damping and wear performances of the ACMs at similar particle contents fabricated by these two different methods and discuss the advantages of in-situ fabricating process.7wt%TiB2 reinforced A356 alloys are successfully fabricated by mixing salts method. In-situ TiB2 particles of which the average size is 300nm mostly have the shape of hexahedral prism and are well distributed within the matrix alloy. Theα-Al grains appear mostly as equal axial and the grain size is much finer than that in the base alloys. SiCp/A356 as compared material fabricated by stir casting has particles has particles of 15μm and also well distributed, but majority of SiC particles have pointed edges and corners. The tensil strength andmodulus of elasticity of 7%TiB2/A356 have reached to 362.5MPa and 81.2GPa respectively, with the increace of 12.4% and 21.6%, but the plasticity has fallen off.The damping-temperature curves of 7%TiB2/A356 and 8%SiCp/A356 are investigated in this research, and conclusions can be drawed as follows: the damping capacity of both two composites increases with the rise of temperature, and high damping capacity are more likely to emerged in low frequency; the sequence of damping capacity of composites and base alloy is: 7%TiB2/A356>8%SiCp/A356>A356. The reason why these two composites have higher damping capacity is the dislocations generated while fabricating and which become a source of damping. That 7%TiB2/A356 has higer damping capacity can be ascribed to much more interfaces and grain boundaries result from small TiB2 particles.The dry wear performances of 7%TiB2/A356 and 8%SiCp/A356 are also studied, 8%SiCp/A356 is better than 7%TiB2/A356 in wear performance. Both compostes have lower wear rate than base alloy and 40Cr, and with rise of sliding speed, the wear rate of 8%SiCp/A356 has slightly decreased and that of 7%TiB2/A356 has increased. The wear mechanism of 8%SiCp/A356 at low load is mainly adhesive wear, and abrasion wear and adhesive wear at high load. A mechanical mixed layer is able to form on the wear surface so as to prevent from abrasing, and this layer is more inclined to emerge in higer siding speed. The wear mechanism of 7%TiB2/A356 is mainly adhesive wear at low load and adhesive wear and delamination wear at high load. With sliding speed increases, oxidation wear ought to be taken into consideration.更多还原