钇氧化物薄膜的热稳定性与力学性能的研究

发布时间：2018-05-29 22:34

本文选题：钇氧化物薄膜 + 高温保护涂层　；参考：《吉林大学》2017年硕士论文

【摘要】：Y_2O_3由于其高温稳定性、高熔点而具有作为高温复合材料的反应障涂层的巨大应用潜力,高温相结构稳定性和与结构相关机械性能是本应用的关键参数。在本工作中,首先我们采用直流磁控溅射,以不同的氧分压和基片偏压将Y_2O_3薄膜沉积在硅(100)基片上,然后在1000?C进行真空退火以研究其相结构稳定性。通过X射线衍射,透射电子显微镜和纳米压痕仪研究了退火前后的Y_2O_3薄膜的微观结构,应力和硬度。结果表明,当基片偏压为-60V,无论氧分压大小,均有立方晶相形成,并且在1000?C退火后立方晶相保持稳定,结晶度提高。另外,硬度和模量也只是作为氧分压的函数发生微小的变化。元素含量表征分析发现,氧分压的提升并没有影响到薄膜的氧化程度,原因是该条件下氧化学势对各种缺陷态形成能的影响不大。当氧分压保持在约0.043Pa时,随着衬底偏压的增加,薄膜中形成更多的单斜相,硬度和模量也有所提高,并且1000?C的高温退火导致沉积态的单斜相转变为立方相。氧空位是控制着Y_2O_3形核与相变行为的一个关键因素。通过采用不同的基片温度(Ts)成功调制出了具有不同氧空位含量的Y_2O_3薄膜。随着温度由25?C升高到600?C,O/Y原子比从1.52连续下降到1.37,这对应着氧空位浓度的增加。对于沉积态的Y_2O_3薄膜,在高的基片温度下存在的氧空位可以促进单斜相的成核,而另一方面,高的基片温度也可以导致单斜相的不稳定。因此,我们观察到的结构演化主要是二者之间的竞争结果。其中在25?C下存在的立方相在200?C下转化为单斜晶相,然后在较高的Ts(400?C,600?C)下改变为立方晶相和单斜相的混相。在退火处理后,立方结构保持稳定,而存在于沉积Y_2O_3膜中的缺氧单斜相在高温下是一种热力学亚稳定态,转变为更稳定的相,包括立方或贫氧相,具体取决于氧空位含量。我们发现氧空位含量存在一个临界值,在Ts=400?C下生长的薄膜中,氧空位含量低于这个值,单斜晶相转变为立方相;而在Ts=600?C下生长的薄膜中,氧空位含量高于这个值,单斜相转变为的贫氧相。退火处理中,压应力通过由晶粒生长和相变引起的薄膜体积水平收缩得到释放,应力硬化和晶粒尺寸强化效应的减弱引起了硬度的下降。在Ts=400?C和600?C得到的沉积态薄膜和在Ts=600?C沉积的退火后薄膜中不同相之间的界面可以阻止位错运动并产生增强的硬度,而只有在600?C下沉积的高氧空位含量的钇氧化物组织能够在高温下维持高的硬度。为了在较大的温度范围内保持稳定和良好的机械性能,可以引入氧空位来帮助维持Y_2O_3薄膜中的多相结构。
[Abstract]:Because of its high temperature stability and high melting point, Y_2O_3 has great potential as a reactive barrier coating for high temperature composites. The structure stability and mechanical properties of high temperature phase are the key parameters of this application. In this work, the Y_2O_3 thin films are deposited on Si / 100) substrates by DC magnetron sputtering at different oxygen partial pressures and substrate bias voltages. Then vacuum annealing at 1000C is carried out to study the phase structure stability. The microstructure, stress and hardness of Y_2O_3 films before and after annealing were investigated by X-ray diffraction, transmission electron microscopy and nano-indentation. The results show that when the substrate bias is -60V, no matter the oxygen partial pressure, the cubic crystal phase is formed, and after annealing at 1000C, the cubic crystal phase remains stable and the crystallinity increases. In addition, the hardness and modulus as a function of the partial pressure of oxygen only a small change. Element content analysis showed that the increase of oxygen partial pressure did not affect the oxidation degree of the film, because the oxidation potential had little effect on the formation energy of various defect states under these conditions. When the oxygen partial pressure is kept at about 0.043Pa, with the increase of substrate bias, more monoclinic phases are formed in the films, and the hardness and modulus of the films are also increased, and the monoclinic phase in the deposited state is transformed into cubic phase after high temperature annealing at 1000C. Oxygen vacancy is a key factor controlling the nucleation and phase transition behavior of Y_2O_3. Y_2O_3 thin films with different oxygen vacancy content were successfully prepared by using different substrate temperatures. With the increase of temperature from 25C to 600C / Y, the atomic ratio decreases from 1.52 to 1.37, which corresponds to the increase of oxygen vacancy concentration. For the deposited Y_2O_3 films, the oxygen vacancy at high substrate temperature can promote the nucleation of monoclinic phase, on the other hand, the high substrate temperature can also lead to the instability of monoclinic phase. Therefore, we observe that the evolution of the structure is mainly the result of competition between the two. Among them, the cubic phase existing at 25C is transformed into monoclinic phase at 200C, and then changed into cubic phase and monoclinic phase at higher TsC400C (C600 ~ (600) C). After annealing, the cubic structure remains stable, while the anoxic monoclinic phase in the deposited Y_2O_3 film is a thermodynamic metastable state at high temperature, which changes to a more stable phase, including cubic or oxygen-poor phase, depending on the oxygen vacancy content. We find that there is a critical value of oxygen vacancy content in the films grown under Ts=400?C, and the monoclinic phase is transformed into cubic phase, while in the films grown under Ts=600?C, the oxygen vacancy content is higher than this value. The monoclinic phase is transformed into an oxygen-poor phase. During annealing, the compressive stress is released by the horizontal shrinkage of film volume caused by grain growth and phase transformation, and the hardness decreases with the decrease of stress hardening and grain size strengthening effect. The interface between the deposited films obtained at Ts=400?C and 600C and the different phases in the annealed films deposited by Ts=600?C can prevent dislocation movement and produce enhanced hardness. However, only yttrium oxide with high oxygen vacancy content deposited at 600C can maintain high hardness at high temperature. In order to maintain stability and good mechanical properties in large temperature range, oxygen vacancies can be introduced to help maintain the polyphase structure in Y_2O_3 films.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ133.23;TB383.2

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