Systematic study and characterization of silicon carbide films produced via micro cold spray

Micro cold spray (MCS) has emerged in the past three decades as a novel technology for depositing dense, patterned, thick films without the need for high temperature treatments or chemical precursors. MCS film deposition has been demonstrated with a number of ceramics, but very limited work has been published on the deposition of silicon carbide (SiC), which possesses a high melting temperature and notable wear and chemical resistance properties. This dissertation aims to understand particle deformation and film formation mechanisms that occur during MCS through computational and experimental studies of SiC deposition. A molecular dynamics simulation study is first presented of SiC particle impact on an atomically flat SiC substrate by systematically varying particle impact velocity, impact angle, and particle orientation. Quantitative analysis of the simulations indicates that impact conditions favoring amorphization also favor increased deformation and deposition efficiency, establishing amorphization as the primary mechanism for SiC particle deformation during MCS deposition. The remaining studies focus on SiC films experimentally deposited using a custom MCS machine. In the next chapter, observation of SiC film deposition by multiple powder feedstocks of different particle size distributions is discussed. Additionally, the effect of particle impact velocity is explored by systematic variation of MCS processing conditions using powder feedstock with a nominal size of 500 nm to deposit SiC films on 304 stainless steel. Imaging performed via scanning electron microscopy (SEM) and atomic force microscopy indicate that the films contain larger microstructural features and lower porosity with increasing particle impact velocity. Further characterization is performed on 25 × 25 mm films. Optical profilometry and ion milling with SEM imaging is used to characterize film thickness and x-ray diffraction is used to characterize crystallinity. Adhesion and wear/erosion testing is used to assess the strength and wear resistance of the films. Results indicate that the films are primarily amorphous, consolidated, and are 2–11 μm thick. The adhesion strength of the films exceeds 5 MPa, but measured wear/erosion exceeded that of the reference substrate. The low wear resistance was attributed to the significant roughness of the substrate which suggests improved properties may be possible.