基于原位反应铌基/SiC-Mo(Si,Al)2涂层扩散障的制备及其作用效应和机理研究

The interface reaction between the Nb-based matreial and silicide coating accelerates the degradation of the silicide coating for the function of oxidation resistance.It is a very important problem to inhibit interdiffusion between the substrate and silicide coating. The MoSi2 powder is used as a spray powder reinforced with the alloying elements Al and SiC particles. A Al2O3 layer is prepared between the surface of pre-oxidized Nb-based material and the oxidation resistance coating during the course of high temperature insostatic pressing.The influence of parameters of pre-oxidation,high temperature insostatic pressing and the content of Al of SiC-Mo(Si,Al)2 coating on the former of Al2O3 layer are studied, the formation mechanism of Al2O3 layer is also to be explained.The rule of oxidation kinetics and microstructure during the oxidation course at the temperature from 1100 to 1300℃ are studide.The oxidation resistance mechanism and diffusion barrier mechanism are also discussed.The influence rules of the microstructure of Al2O3 layer on the barrier effect,the oxidation resistance capaxity and the stability of interface are also to be revealed.This study can provide guidance and basis for improving the performance of Nb-based high temperature oxidation resistance coating.It also has a good reference to solve the high temperature oxidation resistance problem for the other refractory metals.

铌基/硅化物高温抗氧化涂层的界面反应加速了涂层功能的退化，抑制基体与涂层元素互扩散是铌合金抗氧化涂层亟待解决的重要问题。本项目选用合金化元素Al协同SiC颗粒共同强韧化的MoSi2作为喷涂粉末，首次尝试采用热喷涂协同热等静压技术，借助SiC-Mo(Si,Al)2涂层中的"铝池"作用，创造性地提出在预氧化铌基表面与涂层界面处原位生成Al2O3薄膜。系统研究铌基预氧化工艺、热等静压参数和涂层中Al含量对生成Al2O3扩散障的影响规律并揭示其形成机制；详细研究涂层在1100～1300℃的氧化动力学和微观组织演变规律，阐明Al2O3陶瓷层在氧化过程中的功能效应与作用机制，诠释涂层的高温抗氧化机理；厘清Al2O3阻挡层的微观组织（包括厚度）与阻挡效果、涂层抗氧化性能以及涂层界面稳定性之间的内在关系。本研究可为铌合金抗氧化性能的提高提供科学依据，对解决其它难熔金属的高温抗氧化问题具有较好的借鉴意义。

防护涂层是提高铌基抗高温氧化性能的重要途径。本项目选用MoSi2及其复合材料作为铌基高温防护涂层。研究了不同Al含量的Mo(Si,Al)2的微观结构、力学性能和抗氧化性能；探讨了Nb/MoSi2涂层的抗氧化性能和界面扩散行为，研究了Al2O3、W、Al对Nb/MoSi2涂层氧化和界面扩散行为影响。本研究可为铌基抗高温氧化MoSi2涂层的应用和性能提升提供指导和依据。主要学术成果如下：（1）Mo(Si1-x,Alx)2中Al含量为0.05时，材料由MoSi2（C11b）组成；Al含量x=0.1时，为C40结构Mo(Si,Al)2和MoSi2相；x=0.2~0.4时，为C40结构Mo(Si,Al)2。Al元素对MoSi2的强韧化机制为裂纹偏转和微接桥。随着Al含量的增加，Mo(Si1-x,Alx)2膨胀系数增加。（2）Mo(Si1-x,Alx)2的复合材料在1200℃的氧化动力学都遵守抛物线规律。随着Al含量的增加，Mo(Si,Al)2抗氧化能力逐渐降低，其抗氧化机理与Al含量相关。随着Al含量的增加，氧化膜按SiO2→SiO2-Al2O3→Al2O3规律演变。（3）Nb/MoSi2涂层在1200~1500°C高温氧化研究结果表明，氧化温度越高，涂层抗氧化性能降低，基体与涂层界面互扩散越严重。Nb基与MoSi2涂层界面结构为MoSi2/(Mo,Nb)5Si3/Nb5Si3/Nb。（4）MoSi2涂层中加入Al、W合金化元素后，降低了MoSi2涂层的高温抗氧化能力。Al抑制Nb/MoSi2界面的扩散，W加速Nb/MoSi2界面的扩散。在Nb基和MoSi2涂层中间引入Al2O3层后，抑制了Nb/MoSi2界面扩散，证明Al2O3中间层具有良好的界面阻扩散性能，作用效果与Al2O3层特性有关。