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研究了热压烧结的Al2O3/TiAl基复合材料在900℃静止空气中的断续氧化行为.结果表明,随着Nb2O5掺量的增加,氧化增重减小,氧化抗力明显改善,其初始氧化动力学符合线性规律,断续氧化动力学服从抛物线规律.Nb2O5掺量大的材料,因氧化产物中含有TiAl和Ti2AlN相,显示其良好的抗高温氧化性.在900℃温度断续氧化120h后,氧化膜主要由TiO2外表层、Al2O3次表层以及TiO2和Al2O3的混合内层构成,由外向内为富Al向富Ti的氧化物混合层过渡.靠近基体TiO2和Al2O3混合内层为多孔疏松状结构,孔洞是由于形成Ti的氧化物后生成的.整个氧化层厚约20μm.氧化膜表面均未形成均一的Al2O3保护膜,但形成的内层Al2O3膜与外层TiO2膜粘附性高,没有发生氧化膜脱落现象.原位自生的Al2O3微细颗粒,高温下促使其本身成核与生长,使得热力学形成其膜所需的最低Al含量降低;同时,增加了Ti离子由M/MO界面向O/MO界面扩散的势垒,从而降低了TiO2的生成率,提高了抗氧化性能;另外,形成从外向内由富Al向富Ti氧化物混合层过渡的复层结构,降低了O2?的内扩散,改善了复合材料的抗氧化性能.
The intermittent oxidation behavior of hot-pressed Al2O3 / TiAl matrix composites in still air at 900 ℃ was studied. The results showed that with the increase of Nb2O5 content, the oxidation weight gain decreased and the oxidation resistance significantly improved. The initial oxidation kinetics According to the law of linearity, the kinetics of discontinuous oxidation obeys the parabolic law.The material with large amount of Nb2O5, which contains TiAl and Ti2AlN phases, shows good high temperature oxidation resistance.After intermittent oxidation at 900 ℃ for 120h, The oxide film is mainly composed of TiO2 outer layer, Al2O3 subsurface layer and a mixed inner layer of TiO2 and Al2O3, which is rich in Al to Ti-rich oxide mixed layer from the outside to the inside. The mixed inner layer near the matrix TiO2 and Al2O3 is porous and loose structure , The hole is formed by the formation of Ti oxide.The entire oxide layer thickness of about 20μm oxide film surface are not formed uniform Al2O3 protective film, but the formation of the inner Al2O3 film and the outer TiO2 film adhesion is high, there is no The phenomenon of oxide film shedding occurs.The in situ self-generated Al2O3 micro-particles promote their own nucleation and growth under high temperature, which reduces the minimum Al content needed to form their films by thermodynamics. Meanwhile, Ti ions increase from M / MO interface to O / MO sector Diffusion barrier, thereby reducing the generation rate of TiO2 and improving the oxidation resistance. In addition, the formation of a multi-layer structure from the outside to the inside of the mixed layer rich in Al to Ti-rich oxide reduces the internal diffusion of O2 and improves Antioxidant properties of composite materials.