Controlling Stress Evolution in Ceramic Thin Films and Coatings: Investigations of Mechanical and Chemical Responses

控制陶瓷薄膜和涂层中的应力演变：机械和化学响应的研究

• 批准号: 0305418
• 负责人: Brian Sheldon
• 金额: $ 56万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-06-01 至 2008-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0305418&HistoricalAwards=false
• 关键词: Controlling; Stress; Evolution; Ceramic; Thin

This research focuses on controlling intrinsic stresses in several different polycrystalline ceramic films and coatings where residual stresses have an important effect on key materials properties. The intrinsic stresses are produced by the film growth process, and can thus be controlled during processing. While previous work has examined intrinsic stresses in metal films, ceramics have been investigated in far less detail. Four inter-related efforts will lead to a significant increase in both knowledge and our ability to control stress-related effects. First, in MEMS devices, residual stress effects at small length scales are critical. By controlling stress gradients in polycrystalline SiC, we expect to eliminate bending problems in free standing SiC films for MEMS applications. Secondly, non-stoichiometric oxide films are important for a variety of electrochemical applications. Initial work with TiO2-X shows that stresses due to compositional variations can be accurately measured, and that the defect chemistry of the material determines the type of stress changes observed. Additional work on oxides will explore yittria stabilized zirconia and CeO2-X, both of which are used as electrolytes in solid oxide fuel cells. As well, new models of tensile and compressive intrinsic stresses have been developed with previous NSF funding. These will be integrated into a unified model, applicable to a broad range of vapor-deposited polycrystalline films. Finally, the fracture resistance and adhesion of SiC coatings will be measured as a function of residual stresses and stress gradients. Our demonstrated ability to vary the film microstructure and stress independently during deposition will make it possible to isolate the effects of residual stresses. All three investigators are engaged in significant educational activities. Profs. Rankin and Sheldon will continue to promote several different K-12 outreach activities. Prof. Rankin is also the Associate Director of the Sheridan Center for Teaching and Learning at Brown, where she is regularly engaged in advancing the teaching skills of faculty and graduate students from a wide range of different disciplines. During the academic year, Prof. Walden is on the faculty at Trinity College, an undergraduate teaching institution. We will employ Trinity undergraduates in research efforts, providing them with experience in a research setting. This research will provide new knowledge and materials fabrication capabilities for controlling the mechanical stresses that invariably exist in coatings and thin-films of ceramic materials. These stresses can be either detrimental to the materials performance (e.g., by promoting failure) or beneficial (e.g., by improving toughness). Thus, proper control of these stresses is critical. Work is focused on two types of materials, silicon carbide that is of interest in miniature machines (so-called micro-electro-mechanical systems or MEMS), and oxide ceramics that are useful for electrochemical applications such as fuel cells. Much of the knowledge that is obtained from these investigations will also be broadly applicable to thin-films and coatings that are used for a wide variety of other applications, including microelectronic devices, jet engines, and hard coatings that are used to extend the life of different types of machinery.

本研究的重点是控制几种不同的多晶陶瓷薄膜和涂层的残余应力有重要影响的关键材料的性能的内在应力。 内在应力由膜生长过程产生，并且因此可以在处理期间被控制。 虽然以前的工作已经研究了金属薄膜中的内应力，但陶瓷的研究却少得多。 四个相互关联的努力将导致知识和我们控制压力相关影响的能力的显着增加。 首先，在MEMS器件中，小长度尺度下的残余应力效应是关键的。 通过控制多晶SiC中的应力梯度，我们期望消除MEMS应用中独立SiC膜的弯曲问题。 其次，非化学计量的氧化物膜对于各种电化学应用是重要的。 使用TiO 2-X的初步工作表明，可以准确测量由于成分变化引起的应力，并且材料的缺陷化学性质决定了观察到的应力变化类型。 氧化物的其他工作将探索氧化钇稳定的氧化锆和CeO 2-X，这两者都被用作固体氧化物燃料电池的电解质。 此外，拉伸和压缩内应力的新模型已经开发与以前的NSF资金。 这些将被集成到一个统一的模型，适用于广泛的气相沉积多晶薄膜。 最后，SiC涂层的抗断裂性和附着力将被测量为残余应力和应力梯度的函数。 我们所证明的在沉积过程中独立改变薄膜微观结构和应力的能力将使隔离残余应力的影响成为可能。 所有三名调查员都参与了重要的教育活动。 教授兰金和谢尔顿将继续推动几个不同的K-12外展活动。 兰金教授也是布朗大学谢里丹教学中心的副主任，在那里她经常从事提高教师和来自各种不同学科的研究生的教学技能。 在学年期间，瓦尔登教授是Trinity学院，本科教学机构的教师。 我们将聘请Trinity本科生从事研究工作，为他们提供研究环境的经验。 这项研究将提供新的知识和材料制造能力，以控制机械应力，总是存在于涂层和薄膜的陶瓷材料。 这些应力可能对材料性能有害（例如，通过促进失败）或有益（例如，通过提高韧性）。 因此，适当控制这些应力至关重要。 工作集中在两种类型的材料上，碳化硅在微型机器（所谓的微机电系统或MEMS）中很有意义，氧化物陶瓷可用于电化学应用，如燃料电池。 从这些研究中获得的许多知识也将广泛适用于用于各种其他应用的薄膜和涂层，包括微电子设备，喷气发动机和用于延长不同类型机器寿命的硬涂层。