【作者】 王慧远；

【导师】 姜启川；

【作者基本信息】 吉林大学 ， 材料加工工程， 2004， 博士

【摘要】 进入 21 世纪以来，资源和环境已成为人类可持续发展的首要问题。因此，目前世界工业发展的趋势是节省能源、资源和绿色生产。镁合金作为最轻的工程结构金属材料，具有许多优异的独特性能，如比强度高、比刚度高、导电导热性好，兼有良好的阻尼减震和电磁屏蔽性能，易于加工成形，良好的再生回用等优点，在汽车、通讯设备、航空等领域中得到了广泛的应用。因此，镁基材料被认为是本世纪最有开发前途和应用潜力的“绿色工程材料”。但是，镁合金存在弹性模量小、高温强度和抗蠕变性低、耐磨性差等严重的不足，而且仅仅通过合金化技术又不能加以解决，因此大大限制了镁合金的进一步发展及其工业应用。如何解决这一问题自然成为镁合金研究领域的瓶颈问题。众所周知，镁基复合材料具有低的温度膨胀系数、高的杨氏模量和耐磨性等优点。因此，从材料的内在属性出发，作者认为，解决镁合金性能方面存在的不足的最佳途径之一就是走复合材料的道路。按照增强体的形态特征，镁基复合材料主要有纤维、晶须和颗粒增强三种。连续纤维增强镁基复合材料沿纤维方向强化效果显著，引起人们的广泛兴趣，但是制备工艺复杂，而且产品难以回收再用；晶须增强镁基复合材料强度高、工艺性能优良、可进行二次加工，而且材料可以回收再用，但是其成本很高，大大限制了其应用范围。颗粒增强镁基复合材料具有制备工艺简单、成本低廉以及各向同性的性能，已成为镁基复合材料的研究热点之一。目前，颗粒增强镁基复合材料主要是通过外加方式制备的，即增强体在制备复合材料之前需单独合成，然后通过混料方式引入镁基体或者通过搅拌方式直接加入镁熔体中。在这种情况下，增强体的尺寸受其原材料尺寸的影响，往往在几微米至几十微米级，很少小于 1.0 微米。其它的不足，如增强体和基体之间的界面反应以及由于增强体表面易受污染从而导致与基体之间的润湿性差等问题也是困扰材料科学工作者的重大难题。金属基复合材料（MMCs）的性能受增强体的类型、尺寸、分布、体积分数以及增强体和基体界面的本质特征所控制。当尺寸细小和大体积分数且热力学上稳定的增强体均匀分布在基体中时可以获得某些独特的性能。为了 - I -<WP=187>摘 要满足以上要求，近年来人们开发了一种新的复合材料—原位（In situ）MMCs，即增强体是在复合材料制备过程中通过两种或多种元素或化合物之间的化学反应生成的。与传统上的外加 MMCs 的制备技术相比，原位 MMCs 具有以下优点：①增强体在基体中热力学是稳定的，有利于高温服役工况；②增强体与基体的界面干净，润湿性好，故界面结合强度高；③增强体尺寸细小，分布均匀，增强效果明显提高。因此，从工业应用前景的长远利益来看，原位陶瓷颗粒增强方式是镁基复合材料的理想选择和最佳落脚点之一。 然而，目前的原位 MMCs 制备技术主要集中在 Al 基、Ti 基和 Fe 基之上；适用于镁基体的制备技术及相应的增强体极其有限。对于金属结构材料中的质量最轻、比强度极高的镁及其合金，由于其熔点低，极易氧化燃烧，增强颗粒难以引入，给原位镁基复合材料的研究和开发带来了极大的困难。 本文通过实验研究，针对镁合金的自身特点，首次采用镁熔体内 SHS 反应法，成功地制备了原位 TiC 和 TiB2颗粒增强镁基复合材料，在解决原位镁基复合材料制备过程中的关键科学问题即原位增强颗粒的引入与界面污染等方面取得了突破，开发了适合于镁基合金的增强体（TiC、TiB2）和相关制备技术；在此基础上，利用 Al-Ti-C-B、Al-Ti-B、Al-Ti-C-Mg、Al-Ti-B4C 等体系，采用镁熔体外（真空下和气氛保护下）的 SHS 反应合成了含有原位增强颗粒的中间相载体，并借助于搅拌铸造法将原位颗粒引入镁熔体中，成功地制备了 TiC、TiB2和 TiC+TiB2颗粒增强镁基复合材料。本文的主要研究工作如下： (1) 镁熔体内形成原位增强颗粒的 SHS 反应机理 通过差热分析和淬熄实验，对 Al-Ti-C 和 Al-Ti-B 体系的 SHS 反应进行了深入研究，在此基础上给出了原位 TiC 和 TiB2颗粒增强镁基复合材料的形成机制，并建立了其形成模型。实验发现，在 Mg 熔体内 Al-Ti-C 体系的 SHS反应过程中，除了 Al、Ti 和 C 之间通过 Al-Ti 反应形成 TiAlx过渡相，然后TiAlx 进一步和 C 反应形成 TiC 以外，Ti 和 C 之间的直接反应也能够进行，并形成 TiC。研究表明，Al-Ti-B 体系中反应形成 TiB2 的可能途径有：AlB2(s)-TiAl3(s)、Ti(s)-AlB2(s)和 B(s)-TiAl3(s)之间的反应，其中，B(s)-TiAl3(s)之间的反应在热力学上最有利；此外，固溶态的[B]和[Ti]之间的反应也可以形成TiB2。 (2) 镁基复合材料原位增强颗粒 SHS 反应动力学的影响因素 对于形成原位增强颗粒的 SHS 反应动力学的影响因素进行了细致的实验研究，分别优化并给出了适合于镁熔体内 SHS 反应法和熔体外反应法两种制备技术的实验参数。研究发现，微米级粒度的 Al、Ti 和 C 粉体系，压坯的预热温度决定了熔体内能否发生 SHS 反应，当预热温度低于 400℃时反应难?更多还原

【Abstract】 With the entrance to 21st century the resource and environment problemshave become the principle problems in the sustainable development of humanbeings. Therefore in the long term, the trends of the industrial development allover the world can be reduced to the saving of energy and resource, and what ismore, the pursuit of natural production. Magnesium alloys are kind of the lighteststructural metal alloys, which have many excellent and unique properties, such ashigh specific strength and stiffness, high heat and electrical conductivity, gooddamping and shock absorption, excellent electromagnetic shielding capability andeasy processing, as well as a good recovery capability, and therefore, increasingattention has been paid to magnesium and its alloys in automotive, communicationapparatus and aerospace applications. Consequently, it is considered thatmagnesium alloys are the most worthy and exploitative “natural engineeringmaterials” with greatly potential application in this century. However, the further development and commercial application of magnesiumalloys have been limited because of its low elastic modulus, poor tensile strengthand creep resisting especially at elevated temperatures, as well as low wearresistance. Moreover, these disadvantages can not be overcome only by using costintensive magnesium alloys. As a result, it has become a bottleneck problem thathow to solve these problems in the field of magnesium alloys. It is widely recognized that excellent properties such as a lower coefficient ofthermal expansion, a higher Young’s modulus and a higher wear resistance etc. canbe realized only by magnesium metal matrix composites (MMCs). As aconsequence, the best routes are the selection of magnesium MMCs to solve theproblems of magnesium and its alloys on the basis of the internal attribute ofmaterial system. According to the morphological feature of reinforcement, - VI -<WP=192>吉林大学博士学位论文magnesium MMCs can be grouped under three heads, i.e. fiber, whisker andparticulate reinforced magnesium matrix composites. The strengthening effect offibre reinforced composites is evident along the fiber direction, attracting moreextensive interest; however, the fabrication processing is very complex and theproduction can not be reutilized. Although, the strength of whisker reinforcedmagnesium MMCs is very high and the production with excellent fabricating andreprocessing properties can be reutilized, the range of application of the compositehas been limited due to a high cost starting material. Recently, the particulatereinforced magnesium matrix composites have been becoming one of the hotspotin the research field of magnesium MMCs due to its significant inherent simplicityand potential cost-effectiveness in scale-up manufacturing, as well as its isotropyproperties. Presently, the particulate reinforced magnesium MMCs are mainly fabricatedby ex situ manner, namely, the reinforcements are prepared separately prior to thecomposite fabrication, and then the reinforcements are mixed into the magnesiummatrix by powder blends or directly added to the molten magnesium. In this case,the scale of the reinforcement is limited by the starting powder size, which istypically of the order of microns to tens of microns and rarely below 1.0 μm.Other main drawbacks that have to be overcome are the interfacial reactionsbetween the reinforcements and the matrix, and poor wettability between thereinforcements and the matrix due to surface contamination of the reinforcements.It is a puzzle, therefore, for the materials science researchers to find a solution tothe inherent problems that are associated with conventionally processed MMCs. It is well known that the properties of MMCs are controlled by the type, sizeand volume fraction of the reinforcement phase as well as the nature of thematrix-reinforcement interface. A unique or an optimum set of mechanicalproperties更多还原