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Open Access Thesis
Master of Science in Mechanical Engineering (M.S.M.E.)
Year Degree Awarded
Month Degree Awarded
Cold spray (CS) deposition of metals is a process involving deposition of materials in the solid or semi-solid state. It also has lower operating temperatures, and oxidation is greatly reduced in the process. The process is beneficial for refractory metals, such as tantalum, which are tough and difficult to machine. The interface between the CS powder and the substrate is the most important region for the study of mechanical properties as it is where the bonding process occurs first; studying mechanical properties at the nanoscale will give us a better idea of the mechanical properties of the coated surface. The present work investigates multiple-sprayed conventional and low-hydrogen treated tantalum powders on stainless steel substrates and also single-sprayed nitrogen-treated tantalum powders on aluminum substrate using Atomic force microscopy (AFM). It also discusses the effects of topography on the local changes in modulus.
AFM is an instrument that measures the site-specific property of the sample. In this work, the local Young's modulus is studied using force-distance curves. Calibration of the AFM cantilever and the photodetector used to measure the cantilever, is a vital step before the actual process. The conventional method of calibration can cause damage to the tip as it arbitrarily penetrates into the sample creating a cantilever deflection vs. tip penetration curve, giving the sensitivity of the photodetector.
AFM is highly dependent on topographical features as the cantilever tip-sample interaction can vary, causing variations in the property mapped. This work, however uses a non-contact method of calibration which saves the cantilever tip from potential damages, saving the results from the detrimental effects of tip topography. The work also discusses the effects of local sample deformation and volume of tip-surface contact on local changes in Young's modulus at the interface of coating and substrate.
This work uses Electron micro-probe analysis (EPMA) to show the presence of oxides at the interface. The presence of oxides changes the bond energy as compared to a pure tantalum bond, ultimately affecting the local modulus mapped using AFM. The effect of oxides on the local modulus at the coating-substrate interface is theoretically discussed.
Stephen S. Nonnenmann
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Chowdhury, Dhrubajyoti, "Local Nanomechanical Variations of Cold-sprayed Tantalum Coatings" (2022). Masters Theses. 1176.