两级网状结构(TiBw+Ti5Si3)/TC4复合材料设计与强化机理

Inspired by natural multi-scale hierarchical structures, in order to further improve combination property of titanium matrix composites, fine TiB2 powders and Si powders are simultaneously adhered onto the surface of TC4 particles by low-energy milling process. Micro TiB whiskers (TiBw) are in-situ synthesized by the reaction between TiB2 and Ti in the process of hot pressing sintering, and distributed around TC4 particles, which forms the first-scale network structure with about 150μm diameter. Subsequently, nano Ti5Si3 needles are formed by Si solid solution and precipitation, and distributed around α grains in the interior of the first-scale network structure, which forms the second-scale network structure with about 10μm diameter. The parameters of the second-scale network structure and microstructure characteristics of Ti5Si3 can be controlled by subsequent heat treatment. The delicate design of two-scale network structures and macro control of mechanical property of (TiBw+Ti5Si3)/TC4 composites will be achieved by designing and optimizing the composite structure parameters, fabrication parameters and heat treatment parameters. The relationships between microstructure and property of the composites will be clarified. The formation and evolution mechanisms of two-scale network structure and Ti5Si3 reinforcement will be further revealed. Combining with analysis on fracture and in-situ tensile observation, the strengthening mechanisms of (TiBw+Ti5Si3n)/TC4 composites with two-scale network microstructure can be finally revealed. Therefore, the present work will provide experimental and theoretical guides for multi-scale hierarchical structure design of metal matrix composites and toughening mechanisms investigation on composites.

受自然界多级多尺度结构启发，为提高钛基复合材料综合性能，通过低能球磨在TC4颗粒周围同时镶嵌细小TiB2粉与Si粉，在热压烧结过程中TiB2与Ti反应形成微米TiB晶须(TiBw)，分布在TC4颗粒周围形成一级网状结构(约150μm)。Si通过固溶和脱溶，在一级网状结构内部的α相周围析出纳米针状Ti5Si3，形成二级网状结构(约10μm)，其结构参数与组织特征可通过热处理得到调控。通过对复合材料结构参数、制备参数与热处理参数的设计与优化，实现(TiBw+Ti5Si3)/TC4复合材料两级网状结构精确设计与综合性能宏观调控，阐明复合材料微观结构与性能的内在关系，揭示两级网状结构与纳米针状Ti5Si3形成与演变机制。结合断裂与原位拉伸分析，揭示两级网状结构(TiBw+Ti5Si3)/TC4复合材料强化机理。为金属基复合材料多级多尺度结构设计与复合材料强韧化理论研究提供试验与理论指导。

受自然界多级多尺度结构启发，为进一步提高钛基复合材料综合性能，在一级网状结构TiBw/TC4复合材料基础上，采用大尺寸TC4粉与细小TiB2粉和Si粉为原料，通过低能球磨与真空热压烧结方法，结合原位自生反应与固溶和脱溶析出，制备出了系列两级网状结构(TiBw+Ti5Si3)/TC4复合材料。原位反应自生形成的TiBw增强相分布在钛合金颗粒周围，形成一级网状结构，而固溶和脱溶析出的纳米针状Ti5Si3增强相分布在α-Ti相周围，形成了二级网状结构，从而构成了两级网状结构。阐明了制备参数与结构参数对两级网状结构钛基复合材料组织与性能的影响规律，并优化了相应的参数。优化后的两级网状钛基复合材料在550℃-650℃/(100-350MPa)蠕变条件下，与烧结态TC4合金相比，蠕变速率可降低一个数量级，蠕变断裂时间最大可提高20倍，复合材料的抗蠕变性能大幅度提高。阐明了热处理参数对(TiBw+Ti5Si3)/TC4复合材料组织与性能的影响规律，热处理后的两级网状结构钛基复合材料在550℃和600℃条件下的高温抗拉强度分别达到了1050MPa和880MPa，高温强度大幅提升。通过组织分析与性能表征，揭示出了(TiBw+Ti5Si3)/TC4复合材料结构参数及组织特征与性能的内在关系及影响规律。结合相变理论分析，揭示出了两级网状结构与纳米针状Ti5Si3增强相的形成及演变机理。通过断口、侧断面、拉伸、蠕变等力学行为分析，结合组织与性能分析，揭示出了两级网状结构(TiBw+Ti5Si3)/TC4复合材料强化机理，以及一级网状结构抑制“晶界”滑动而二级网状结构阻碍相界滑移的高温抗蠕变机理。为金属基复合材料多级多尺度结构设计与复合材料强韧化理论研究提供试验与理论指导。

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