Nanostructured TiN/ZrAlN and HfAlN Thin Films : Effect of Structure on Mechanical Properties

Abstract

Transition metal nitrides are a remarkable group of ceramic materials that offer exceptional properties such as high hardness, low tribological wear, excellent thermal stability, and high oxidation resistance. Alloys such as TiN, CrN, VN, ZrN, and HfN have been identified as ideal candidates for protective coatings on cutting tool inserts in the metal processing industry. While TiAlN has been widely accepted, ZrAlN and HfAlN alloys have much unexplored potential. With a melting point of HfN at 3300 °C, approximately 400 °C higher than TiN, HfAlN shows great potential for age-hardening at even higher temperatures. These remarkable materials inspire us to push the limits of what is possible, and to continue to innovate materials science.The work performed in this thesis focuses on the development of hard coatings using ionassisted reactive magnetron sputtering. The coatings are based on group IV TM-Al-N, where TM is either Ti, Zr, or Hf. The aim is to enhance the performance of these ceramic coatings by simultaneously increasing their hardness and toughness. To achieve this, the growth mechanisms, structure, and mechanical properties of the films were studied in detail. The coatings were deposited onto single crystal Si(001) and MgO(001) substrates.I have been fortunate to work at a place with brilliant people at Linköping University. My journey had a rocky start in the middle of a global pandemic but despite this I got a superb reception at the department, largely thanks to my supervisor Naureen Ghafoor. We had to meet online mostly and keep our distance in physical meetings, but that didn't stop Naureen from making me feel warmly welcomed at IFM, and quickly brought me up to speed. You have always been available for support, suggestions, feedback, and new perspectives on any problem that came up during this time. We have also had some very nice trips to conferences and experiments abroad which were both productive and fun. Thank you! A big thank you to my co-supervisors Jens Birch and Johanna Rosén for happily sharing your vast knowledge. The support is greatly appreciated! I also want to express my gratitude to Per Sandström. You are an indispensable help in the lab and a superb colleague and friend. I really enjoy our conversations and topics ranging from high and low. I have also been lucky to get to teach on two of your courses. To Fredrik Eriksson, you have been a great support, in particular for solving problems in the labs. You even put up with my calls in the evening or when you're under the weather.Big thanks to Michael Meindlhumer, Naoki Takata and Tianqi Zhu for your expertise and collaboration in discovering the mechanical response of my films using advanced microcantilever bending and micropillar compression techniques. Your support has been critical to this work. A big thank you to Justinas Palisaitis for all the help and amazing times in Arwen and the beautiful STEM micrographs, and to Grzegorz Greczynski for the help with XPS. With your support this work is elevated to a higher level. To Lars Hult...