硼化钛基原位纳米复合涂层的组织结构和性能调控机理研究

Plasma sprayed TiB2 coatings have high porosity, low toughness and poor thermal shock resistance. Preparation and research of in-situ titanium diboride matrix nanocomposite coatings have important theory significance and practical value for improving the properties of TiB2 coatings. Based on the principle of reaction among TiO2, B4C and Al, in-situ titanium diboride matrix nanocomposite coatings were prepared by plasma spraying TiO2-B4C-Al composite powders. The main phases of the as-prepared coatings were TiB2, TiC and Al2O3, and the grain sizes of the in-situ phases are less than 100 nm. The in-situ nanocomposite coatings had dense microstructure, and obviously improved performance. The reaction thermodynamics and kinetics of TiO2-B4C-Al system in plasma jet and the deposition and solidification rule of the phases formed by the reaction of TiO2-B4C-Al system will be investigated, and the in-situ formation mechanism of the TiB2 matrix nanocomposite coatings could be revealed. The relationship between preparation process, microstrcuture and properties of the in-situ TiB2 matrix nanocomposite coatings will be investigated, and the strengthening and toughening mechanism of the in-situ TiB2 matrix nanocomposite coatings could be revealed. The project proposed a new method for the preparation of TiB2 matrix nanocomposite coatings, and put forward a new idea of toughening TiB2 ceramics with in-situ nanocomposites. The research results had important theoretical guiding significance for toughening of TiB2 ceramics and preparing of in-situ nanocomposites.

等离子喷涂硼化钛（TiB2）涂层的孔隙率高，韧性、抗热震性差，TiB2基原位纳米复合涂层的研制对改善TiB2涂层性能具有重要理论意义和实用价值。依据TiO2、B4C和Al间可发生反应的原理，采用等离子喷涂TiO2-B4C-Al复合粉，成功制备出以TiB2、TiC和Al2O3为主相的硼化钛基复合涂层，原位形成的各相晶粒尺寸均在100nm以下，涂层致密，性能优异。本项目主要研究TiO2-B4C-Al体系在等离子焰流内的反应热力学与动力学，探讨TiO2-B4C-Al体系反应产物的沉积凝固规律，揭示TiB2基原位纳米复合涂层的形成机制；研究原位纳米复合涂层的制备工艺—组织结构—性能间关系，揭示TiB2基原位纳米复合涂层的强韧化机理。本项目提出一种制备TiB2基纳米复合涂层的新方法，提出用原位纳米复合材料实现对TiB2陶瓷韧化的新思路，对TiB2陶瓷的韧化和原位纳米复合材料的制备有重要理论指导意义。

等离子喷涂硼化钛（TiB2）涂层的孔隙率高，韧性、抗热震性差，TiB2基原位纳米复合涂层的研制对改善TiB2涂层性能具有重要理论意义和实用价值。依据TiO2、B4C和Al间可发生反应的原理，采用等离子喷涂TiO2-B4C-Al复合粉，成功制备出以TiB2、TiC和Al2O3为主相的硼化钛基复合涂层，原位形成的各相晶粒尺寸均在100nm以下，涂层致密，性能优异。本项目主要研究TiO2-B4C-Al体系在等离子焰流内的反应热力学与动力学，探讨TiO2-B4C-Al体系反应产物的沉积凝固规律，揭示TiB2基原位纳米复合涂层的形成机制；研究原位纳米复合涂层的组织结构—性能间关系，揭示TiB2基原位纳米复合涂层的强韧化机理。通过系统、完整地研究，取得以下创新性研究成果：（1）TiO2-B4C-Al体系反应的热力学计算结果表明，在等离子焰流内一定成分的TiO2-B4C-Al体系可以发生反应。（2）采用喷雾干燥技术成功制备出了球形的TiO2-B4C-Al复合粉，每个球形颗粒内部Al、B4C和TiO2分布较均匀，这保证了Al、B4C和TiO2能构成独立反应单元在高速等离子焰流内发生反应的可能性。（3）阐明了原料成分、喂料粒度、浆料固含量、等离子喷涂工艺参数等因素对TiO2-B4C-Al体系在等离子喷涂条件下反应形成硼化钛基原位纳米复合涂层的影响规律。（4）TiO2-B4C-Al在等离子焰流内的反应过程为：复合粉进入等离子焰流后，随着温度升高，Al和TiO2发生反应生成Al2O3和Al3Ti，随后Al3Ti继续与B4C反应生成TiB2和TiC。（5）TiO2-B4C-Al体系在等离子焰流中反应原位形成硼化钛复合涂层的机制为：熔化—扩散—液固反应—沉积。首先是反应孕育期；其次是固-液反应阶段；再次是液-液反应阶段；最后是熔融液滴沉积凝固过程。（6）等离子喷涂反应合成的硼化钛基原位纳米复合涂层的硬度、韧性、摩擦磨损性能和抗热震性明显优于直接喷涂TiB2-TiC体系和TiB2-TiC-Al2O3体系复合涂层。揭示了硼化钛基原位纳米复合涂层的强韧化机理为：细晶强韧化，颗粒弥散增韧和裂纹偏转。本项目提出一种制备TiB2基纳米复合涂层的新方法，提出用原位纳米复合材料实现对TiB2陶瓷韧化的新思路，对TiB2陶瓷的韧化和原位纳米复合材料的制备有重要理论指导意义。

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