Ti基非晶/纳米晶复合材料冷静液机械压制变形机理及光化学性能

Ti-based bulk metallic glasses (BMGs) are a class of advanced materials which have drawn extensive attention due to their high specific strength and superior corrosion resistance. However, the widespread engineering applications of Ti-based BMGs are severely hindered by the size limitation and lack of ductile deformation at room temperature. To overcome these restrictions, various powder-consolidation methods have been employed to obtain large-sized BMGs and their composites with enhanced mechanical properties. Moreover, the developing of advanced photochemical properties further contributes to offer opportunities for the functional applications of Ti-based BMG composites. In this project, large-sized Ti-based BMG composites will be fabricated using the cold hydro-mechanical pressing technique and the deforming densification mechanism of the gas atomized Ti-based metallic glassy/nanocrystalline composite powders will be comprehensively studied. We will systematically reveal the effect of the in-situ formed nanocrystals, as well as the interfaces between the glassy matrix and the nanocrystals, on the densification behavior of the composite powders during pressing. In addition, the mechanical and photochemical properties of the sintered bulk composites will be also investigated, leading to intrinsic understanding of the deforming and the dealloying mechanisms for the bulk composites in atomic scale. Based on the above results, this project aims to clarify the relationships among the deforming densification, microstructure, mechanical behavior and photochemical properties, which will help to provide more basically theoretical details for the exploitation of novel Ti-based metallic glassy composites and further accelerate their promising applications in the high technological field.

Ti基非晶合金因比强度高、耐腐蚀性能好等优势而备受关注，而玻璃形成能力有限及室温塑性较小制约了其进一步工程化应用。采用粉末固结方法制备Ti基大块非晶合金复合材料，可以达到增大尺寸并提高单一材料力学性能的目的。另外，探索Ti基大块非晶合金复合材料先进的光化学性能，可以拓宽其功能化应用范围。本项目拟深入研究气雾化内生Ti基非晶/纳米晶复合粉末在冷静液机械压制过程中的变形致密化机理，揭示内生纳米晶及非晶/纳米晶界面对复合粉末变形过程的影响规律，表征大块非晶/纳米晶复合材料的力学及光化学性能，从原子尺度上阐明大块复合材料的变形机理及退合金化机制，从而建立变形致密化－组织结构－力学行为及光化学性能之间的本构关系，为新型Ti基非晶合金复合材料的开发提供理论指导依据，并进一步推动其在高新技术产业中的应用。

本项目以无毒、成本低廉的Ti（Al）基非晶合金为对象，采用氩气雾化方法制备了非晶/纳米晶合金粉末。采用粉末固结方法突破了非晶合金形成的尺寸瓶颈问题，制备了大尺寸非晶/纳米晶合金材料，并对非晶/纳米晶复合材料的固结致密化机理及变形行为进行了系统的研究。.采用放电等离子烧结方法成功制备了大尺寸、高强度Ti基非晶/纳米晶合金，样品尺寸为直径20 mm、高度10 mm。在440 °C的烧结温度下，可以得到非晶态合金材料。烧结态合金材料的维氏硬度6.6 GPa，断裂强度可以达到1.65 GPa。根据自由体积模型，在烧结压力作用下，由烧结温度引起的充分粘性流动是非晶合金粉末高温烧结致密化过程的微观机制。在此过程中，原子的迁移能力与流动缺陷密度是决定最终烧结密度的关键因素。采用新型冷静液机械压制成形方法制备了Al基非晶/纳米晶复合材料，样品尺寸为直径30 mm、高度30 mm。块体复合材料由晶体相与非晶相共同组成，说明采用冷态压制成形的方法可以保留粉末中的非晶态特征。在三轴压制状态下，非晶/纳米晶粉末的大变形是导致材料冷压致密化过程的主要原因。由于纳米晶的强化作用，即对剪切带的阻碍作用，块体复合材料表现出优异的综合力学性能，其断裂强度可达到1.0 GPa，塑性变形可达到2%，上述结果说明内生纳米晶对单相非晶合金起到了补强增塑的强化作用。此外，采用冷静液机械压制工艺制备了Al基非晶合金复合材料齿轮形预成形件。.以Ti基非晶/纳米晶合金为原料，采用一步式水热反应-退合金化方法制备了Zr离子改性钛酸钠纳米带材料，研究了所制备半导体材料的微观组织及光催化制氢性能。结果表明：在反应过程中，多组元Ti基合金成分发生了选择性退合金化，Ti与Zr原子溶解到氢氧化钠溶液中，并与之反应，而其它组元则留在合金基体与纳米带之间的过渡区域内。Zr离子改性钛锆酸钠纳米带具有比传统方法制备的钛酸纳米带更为优异的光催化活性。基于实验及第一性原理计算结果，分析了Zr离子掺杂对半导体纳米带材料能带结构及特征的影响规律。由于Zr原子4d轨道对半导体纳米材料价带及导带的杂化作用，使得其具有优异的光催化性能。此外，更强的热力学驱动力（即导带底位置越负、氢离子还原电位越正）和更多的有效反应位置有利于光催化制氢反应的进行，即制氢性能越优异。