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

本研究试图开发一种新型的铝基金属基复合材料(MMCs)，其中颗粒陶瓷增强体是一种先进的高温结构材料。特别关注不同尺寸的陶瓷颗粒在传统颗粒增强MMC和弥散强化合金中的不同作用，我们计划在设计新型的“混合”颗粒MMC时，研究颗粒尺寸对细(&lt；1μm)和粗([约等于]10μm)陶瓷颗粒中的一种或两种的MMC的高温硬度和蠕变性能的影响。为此，本工作首先从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中原位生成亚微米级的TiB_2颗粒。在这里，我们涉及到一个关于中间体和通常是r…形成的不良化合物Al_3Ti的问题在通常的加工条件下，加热温度高达1000℃时，最终产品中会有更多的残留物。我们的详细研究表明，已知的两种中间化合物AlB_2和Al_3Ti在铝熔体的存在下可以分解，形成TiB_2和Al，即AlB_2+Al_3Ti→TiB_2+4Al。这揭示了用于制备所需的TiB_2/Al两相MMC的合适的反应物成分范围，XAl-Ti-2B的x[大于或等于]4，临界成分x=4，最大对应于27.9体积%TiB_2。然后，工作进行到三种不同的20体积%TiB_2/Al MMC的制备，其中颗粒增强体是非常细小(约1μm)原位和粗大([约等于]10μm)形成的TiB_2，或者这两者以相等的量(10体积，%)形成。这三种材料都是在基本相同的工艺条件下成功制备的，从而圆满地完成了动态拉伸模数和蠕变测试的温度依赖性实验工作。根据我们对复合材料高温变形的细观力学描述，对结果进行了详细的分析，其中强调了增强颗粒强烈依赖于尺寸的应力松弛的重要性。“混合”颗粒设计和反应合成路线作为高温金属基复合材料的先进技术是很有前途的。较少

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