Phase Formation, Microstructure and Mechanical Properties in Mixed Metal/Silicon Carbide Films

本课题主要研究过渡金属碳化物/碳化硅混合薄膜的结构和力学性能。金属碳化物与碳化硅之间强烈的化学不混溶性以及低温沉积工艺的使用将促进异相纳米级微观结构的形成。将研究这些薄膜中相形成和微观结构演变的基本机制，特别强调在金属碳化物晶界上a-SiC渗透阈值附近形成的结构。表征方法将包括高分辨率透射电子显微镜和x射线光电子能谱。此外，表面与体扩散过程的模型将用于合理化观察到的微观结构，包括相分离的观察。这些薄膜的力学性能，特别是通过观察压痕后存在的微观变形结构来研究这些薄膜的变形机制，也将被研究。最近关于具有纳米级异相结构的混合金属氮化硅/氮化硅薄膜的力学性能的研究报告称，其性能得到了显着的增强，包括硬度水平超过金刚石和高断裂韧性。制造硬度高于钻石的材料是材料科学家长期以来的追求。如果这一目标能够实现，它将使切削工具和轴承涂层等应用取得重大进展。在这个研究项目中，我们将研究过渡金属碳化物/碳化硅涂层，类似于氮化体系，这是最近研究兴趣的主题。利用先进的表征和测试方法，以及热力学和动力学建模，我们希望更好地理解这些材料的强化机制，以及用于改进工业涂料的新候选陶瓷材料

In this research program the structural and mechanical properties of mixed transition metal carbide/silicon carbide thin films will be studied. The strong chemical immiscibility between the metallic carbides and SiC, as well as the use of low-temperature deposition processes will promote the formation of heterophase nano-scale microstructures. Fundamental mechanisms of phase formation and microstructural evolution in these films, with particular emphasis on the structures formed near the percolation threshold of a-SiC on the grain boundaries of the metallic carbides, will be examined. Characterization methods will include high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. In addition, models of surface vs. bulk diffusion processes will be used to rationalize the observed microstructures, including observations of phase separation. The mechanical properties of these films, particularly the deformation mechanisms operating in these films by observing the microscopic deformation structure present after indentation, will also be investigated.%%%Recent research reports on the mechanical properties of mixed metal nitride/silicon nitride thin films with nano-scale heterophase structures have claimed dramatic property enhancements, including hardness levels exceeding that of diamond and high fracture toughness. The ability to create materials with hardness levels above that of diamond is a long-standing quest for materials scientists. If this objective can be achieved, it would allow significant advances in applications such as coatings for cutting tools and bearings. In this research program we will study transition metal carbide/silicon carbide coatings that are analogous to the nitride systems that have been the subject of much recent research interest. Using advanced characterization and testing methods, along with thermodynamic and kinetic modeling, we hope to achieve an improved understanding of strengthening mechanisms in these materials, along with new candidate ceramic materials for improved industrial coatings.***