Development of High Fracture Toughness Hard Coatings

2021-9-2
Kaygusuz, Burçin
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Improving the machining performance of cutting tools is critical for increasing product quality and decreasing production cost and time. For this purpose, hard coatings on cutting tools are widely utilized in the industry. These hard coatings increase the lifetime of cutting tools by improving their wear resistance and allow higher cutting speeds. One of the primary drawbacks of these hard coatings is their brittle nature, which occasionally results in premature failure. This thesis investigated a solution to this problem through the development of new generation hard coatings. For this purpose, W and Mo alloying additions were made to conventional coating compositions such as AlTiN and AlCrN, based on the predictions of density functional theory calculations (DFT). The thesis study considered two different coating methods: magnetron sputtering (MS), suitable for lab-scale studies, and cathodic arc evaporation (CAE), suitable for industrial purposes. X-ray Diffraction, Scanning Electron Microscopy, and Energy Dispersive X-ray Spectroscopy characterized the coatings and nanoindentation measurements provided the hardness and fracture toughness values. In addition, new generation fracture toughness measurements based on microcantilever bending tests were employed for more accurate quantification of the fracture behavior. Lastly, selected coatings were subjected to drilling and ball-on disc tests to clarify their performance in actual working conditions. The results show that especially W additions provide at least an order of magnitude increase in fracture toughness combined with dramatic increases in tool lifetime. Therefore, the thesis results demonstrated an effective route to the development of new high-performance coatings for wear resistance applications. Future studies on optimizing the process parameters for cathodic arc evaporation will enable the wider utilization of the developed coatings in industry.
hard coatings, fracture toughness, wear resistance, nanoindentation, cutting tools
https://hdl.handle.net/11511/92221
Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats
B. Kaygusuz, “Development of High Fracture Toughness Hard Coatings,” Ph.D. - Doctoral Program, Middle East Technical University, 2021.
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