Design, Fabrication and Characterization of Advanced Metal Matrix Composites with Bimodal Size Distributions of Ceramic Particulates

本研究旨在开发一种新型的颗粒陶瓷增强铝基金属基复合材料（MMCs）作为高级高温结构材料。我们特别关注不同尺寸的陶瓷颗粒在传统颗粒增强mmc和分散增强合金中的不同作用，并计划在设计新型“混合”颗粒mmc时，研究颗粒尺寸对含有细（<1μm）和粗（【约等于】10μm）陶瓷颗粒的mmc的高温刚度和抗蠕变性能的影响。为此，本研究首先从Al- ti - b混合元素粉末反应合成TiB_2 /Al MMCs开始，因为这种反应粉末工艺可以在铝基体中原位生成亚微米级的TiB_2颗粒。在这里，我们涉及到一个问题，即在加热温度高达1000℃的通常加工条件下，中间形成的不良化合物Al_3Ti通常会在最终产品中残留更多。我们的详细研究表明，已知的两种中间化合物al_2和Al_3Ti在熔融铝存在下会发生分解，生成TiB_2和Al，即al_2 +Al_3Ti→TiB_2+4Al。结果表明，制备TiB_2 /Al两相mmc所需的反应物组成为xAl-Ti-2B， x【大于或等于】4，其临界组成x=4对应的TiB_2 vol.%最大为27.9。然后，工作继续进行制备三种不同的20 vol.% TiB_2/Al mmc，其中颗粒增强要么是非常细的（<1μm）原位形成的TiB_2，要么是粗的（【大约等于】10μm）非原位形成的TiB_2，或者两者都是等量的（10 vol,%）。这三种材料都在基本相同的加工条件下成功地制造出来，从而我们在动态拉伸模量和蠕变试验的温度依赖性测量方面的最终实验工作圆满完成。根据我们基于微观力学的mmc高温变形描述，对结果进行了详细分析，其中强调了增强颗粒的强尺寸依赖性应力松弛的重要性。“混合”颗粒设计和反应合成路线的制造是有前途的高温mmc的先进技术。少

This research has been done in an attempt to develop a new type of aluminum-base metal matrix composites (MMCs) with particulate ceramic reinforcements as advanced high-temperature structural materials. Paying special attention to different roles of ceramic particles with much different sizes in conventional particulate-reinforced MMCs and dispersion-strengthened alloys, we have planed to examine, toward the design of novel 'hybrid' particulate MMCs, the effects of particle size on elevated-temperature stiffness and creep resistance in MMCs which contain either one or both of fine (<1μm) and coarse (【approximately equal】10μm) ceramic particles. To this end, the present work begins with reactive synthesis of TiB_2 /Al MMCs from Al-Ti-B mixed elemental powders because this reactive powder processing can produce submicron-size TiB_2 particulates in situ in aluminum matrices. Here, we are much involved in a problem as to the undesirable compound Al_3Ti that forms intermediately and often r … More emains in final products under the usual processing conditions with heating temperatures of up to 1000℃. Our detailed study has shown that two intermediate compounds AlB_2 and Al_3Ti, known previously, can decompose in the presence of molten aluminun, forming TiB_2 and Al, i.e. AlB_2 +Al_3Ti→ TiB_2+4Al. This reveals a proper range of reactant compositions, xAl-Ti-2B with x【greater than or equal】4 for making the desired TiB_2 /Al two-phase MMCs, the critical composition x=4 corresponding to a maximum of 27.9 vol.% TiB_2. Then, the work proceeds to the fabrication of three different 20 vol.% TiB_2/Al MMCs wherein the particulate reinforcement is either one of very fine (<1μm) in situ and coarse (【approximately equal】10μm) 'ex situ' formed TiB_2, or both of these at equal amounts (10 vol,%). All the three have been successfully fabricated under essentially the same processing condition, and thereby our final experimental work on the measurement of temperature dependence of dynamic tensile modulus and creep tests is satisfactorily accomplished. Results are analyzed in detail in light of our micromechanics-based description of high-temperature deformation of MMCs, wherein the importance of strongly size-dependent stress relaxation of reinforcing particles is emphasized. The 'hybrid' particulate design and reactive synthesis route to fabrication is promising as advanced technology of high-temperature MMCs. Less