热浸渗硅制备W基W-WSi2功能梯度材料及其性能表征

The hypersonic aerodynamic heating will lead to the aircraft leading edge components appear large temperature gradient and thermal stress, reduce the cycle service life of the component significantly. Therefore, metallic wolfram and WSi2 ceramics as ultra high temperature structural materials has aroused worldwide concern in the aerospace field. However, the problems of oxidation invalidation of metallic matrix, poor machinability of WSi2 ceramics and the thermal properties mismatch between W and WSi2 have severely limits their application. Therefore, this research intends to adopt the hot dip siliconizing method to prepare a W-WSi2 functional gradient materials which has a continuous distribution of W, Si element. Giving full play to the special advantages of metal tungsten and WSi2 ceramics, solving the oxidation invalidation problem of wolfram matrix at the high temperature oxidizing atmosphere and overcoming the disadvantages of poor toughness and machinability of WSi2 ceramics. Based on the gradient layer microstructure, phase composition, element distribution and diffusion controlling, to eliminate the stress and thermal expansion mismatch problem of local phase boundary between matrix and wolfram disilicide. The effects of different heat treatment, diffusion annealing and pre oxidation treatment on the properties of W-WSi2 will be investigated, such as toughness, high temperature strength, thermal shock resistance, ablation resistance and oxidation resistance etc. Obtaining the optimal microstructure and preparation technology. Building the thermodynamics and dynamics model of W-Si reaction diffusion and high temperature oxidation process, revealing the growth mechanism of tungsten silicide functionally graded layer. Revealing the growth mechanism, phase transition and composition rules of gradient layer, and the diffusion characteristics of silicon in wolfram matrix.

金属钨和WSi2陶瓷作为超高温结构材料在航空航天领域引起了广泛关注。然而，金属钨的氧化失效、WSi2陶瓷的难切削加工以及两者间的热膨胀不匹配问题限制了它们的应用。为此，本项目拟采用热浸渗硅的方法，制备一种W、Si元素连续分布的W-WSi2功能梯度材料。充分发挥金属钨和WSi2陶瓷的特殊优点，克服金属钨的高温氧化失效和WSi2陶瓷韧性差、难切削加工的缺点。通过对梯度层微观结构、物相组成、元素分布和扩散行为的调控，来消除WSi2与钨基体相边界间的局部应力和热膨胀不匹配问题。研究不同热浸渗硅、扩散退火、预氧化处理工艺对W-WSi2功能梯度材料室温韧性、高温强度、抗热震、抗烧蚀和抗氧化等性能的影响，确定W-WSi2功能梯度材料的最佳组态和最佳制备工艺。建立W-Si反应扩散和梯度层高温氧化过程的热力学和动力学模型，揭示硅在钨基体中的扩散特性、梯度层的生长机理、物相变迁和组成规律。

本项目针对金属钨的氧化失效以及涂层和基体间的热膨胀不匹配问题，提出了一种新型抗氧化W-WSi2功能梯度材料，即首先采用热浸渗硅工艺（HDS）在钨基体上沉积硅化钨涂层（W5Si3及WSi2），获得组元成分、元素分布、涂层厚度以及微观形貌可控的W-WSi2功能梯度材料；再通过高温扩散退火工艺对W-WSi2功能梯度材料进行处理，旨在改善界面层中的元素渐变行为，增大涂层厚度，缓解WSi2涂层与钨基体之间的热膨胀失配，避免涂层的开裂与剥落。本项目获得了W-WSi2功能梯度材料的制备工艺条件和形成机理，阐明了WSi2及W5Si3在钨表面的作用机制和生长规律，确立了各组元分布、比例、界面状态及组织结构与制备工艺参数之间的关系，发现W-WSi2功能梯度材料主要由钨基体、界面层（W5Si3层）以及涂层（WSi2层）构成，WSi2涂层在（211）和（206）晶面上具有很强的择优取向。随着热浸时间和温度的增大，硅化钨涂层的厚度显著增大，而界面层（W5Si3层）的厚度随着热浸温度和时间的增大，则表现为一个抛物线规律。此外，当热浸温度和时间较大时，涂层表面的硅浓度较高，显著改善了涂层的高温抗氧化性能。采用热浸硅技术制备的W-WSi2功能梯度材料具有非常良好的表面形貌，涂层表面晶粒大小均匀、表面形貌光滑平整，最佳工艺条件下的涂层表面粗糙度可控制在50 nm以下，显著改善了涂层的力学性能。本项目还揭示了W-WSi2功能梯度材料在不同服役环境下的氧化烧蚀机理，在高温氧化过程中，光滑致密的SiO2薄膜能够有效防止氧原子的扩散，能够保护钨及其合金在高温氧化环境中长时间服役。因此，W-WSi2功能梯度材料能够在航空航天、电子、化工、冶金等领域发挥其巨大作用，具有很好的国防和工业应用前景。