Process and materials science aspects for the development of hard coatings for cutting tools

Research output: ThesisDoctoral Thesis

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The present thesis highlights selected process and materials science aspects for the development of advanced hard coatings for cutting tools. As a proper hard coating adhesion is crucial for the wear performance, interface engineering was performed to foster local epitaxial growth of Ti1-xAlxN on Fe-25%Co-15%Mo, which is an auspicious novel tool material. Plasma-assisted nitriding during sputter etching yielded the formation of cubic Mo2N in the topmost few nanometres of the substrate surface, significantly increasing the adhesion strength of the subsequently deposited Ti1-xAlxN coatings. The coating crystallinity increased with increasing nitriding time, while a change in preferred orientation from (111) to (110) was observed. Tribological tests revealed a high potential of duplex Ti1-xAlxN coated Fe-25%Co-15%Mo for severe cutting applications especially after shorter nitriding pre-treatments. Furthermore, the beneficial influence of increased deposition temperatures on structure, properties, thermal stability and wear resistance of multilayered Ti1-xAlxN/TiN coatings was investigated. Increasing the substrate temperature from 375 to 575 °C resulted in a higher coating thickness along with a preferred (111) orientation. In the as-deposited state, the formation of sharper layer interfaces and domain boundaries at the highest substrate temperature yielded enhanced mechanical properties in spite of distinctly rising domain sizes. Vacuum annealing experiments revealed a by 50 °C retarded onset of the detrimental wurtzite AlN formation subsequent to spinodal decomposition. Tribological investigations, where special emphasis was also laid on the hot hardness of the coated powder-metallurgical high-speed steel substrates, indicated significantly increased wear resistance. The superior coating performance was furthermore corroborated in cutting tests, where an enhancement in tool lifetime of about 40% was demonstrated. Finally, newly developed triangle-like segmented sputter targets and their high potential to distinctly reduce the workload in coating material development were presented. Cr1-xAlxN coatings with 0.21 ≤ x ≤ 0.74 were synthesized at a high compositional resolution within two deposition runs. The obtained coating compositions were supported with sputtering simulations, and the metastable AlN solubility limit in cubic Cr1-xAlxN was detected at x = 0.61 for the chosen process parameters. Tribological test revealed excellent performance of the Cr1-xAlxN coatings with low friction down to µ ≈ 0.4 and outstanding wear resistance. Consequently, the presented approach was proven as an auspicious tool for efficient coating material development.
Translated title of the contributionProzesstechnische und werkstoffwissenschaftliche Aspekte für die Entwicklung von Hartstoffschichten für Zerspanungswerkzeuge
Original languageEnglish
  • Mitterer, Christian, Supervisor (internal)
  • Keckes, Jozef, Assessor A (internal)
Publication statusPublished - 2013

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