Tribological performance of additive manufactured metallics with carbide-rich microstructures for wear-related applications

  • Eleftherios Iakovakis

Student thesis: Phd

Abstract

Developing materials for applications requiring wear resistance is an ongoing and active field. Additive manufacturing (AM) may provide wear-resistant metallic materials with microstructures that are finer than those produced using conventional manufacturing technologies. Despite this potential, the understanding about the tribological performance of AM-processed metallics is still limited and a deeper understanding is required prior to their implementation in industrial applications. The present thesis aims to reveal the tribological performance of a series of electron-beam powder bed fusion-processed metallics, more specifically, three tool steels (8%, 20% and 25% volume carbides), a cemented carbide (65% volume carbides) and a martensitic stainless steel (22.5% volume carbides) with carbide-rich microstructures. Performance was assessed through microstructural, topographical, and tribological characterisation. Among the AM-processed tool steels, the grade with 20% volume carbides have shown the best friction and wear performance via macro- and micro-scale tribological tests and surface topography mapping. This has indicated a limit where the carbide addition is beneficial to improve the tribological performance. The predominant wear mechanism was oxidation against bearing steel for all carbide-rich tool steels at the macro-scale. An increase in carbide content significantly changed the abrasive mechanism at the micro-scale level. The overall wear and friction performance of the AM-processed cemented carbide was similar to conventionally processed cemented carbides under similar testing conditions. The wear mechanisms changed explicitly depending on the counterbody employed during testing. A friction reduction effect was detected when the cemented carbide slid against alumina, while a reduced wear rate was observed against bearing steel. The order of the wear mechanisms over time was revealed at the micro-scale level through videos from in-situ scratching tests. The characterisation of the martensitic stainless steel indicated that the wear rate was nearly identical with a similarly processed tool steel under low load. Abrasion, oxidation, and three-body abrasion were observed as dominant wear mechanisms against alumina. Furthermore, the stainless steel candidate had a plastically deformed zone identified beneath the wear track using micro-hardness mapping. This research provides a better understanding of the tribological performance of AM-processed tool steels, cemented carbide and martensitic stainless steel as well as recommendations for future research. In a wider context, the tribological understating of these AM-processed metallics contributes to broaden their usage for demanding environments and applications. Further, this work presents characterisation approaches for better understanding the wear performance of materials.
Date of Award31 Dec 2022
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorAllan Matthews (Supervisor) & Matthew Roy (Supervisor)

Keywords

  • Electron beam melting
  • Cemented carbides
  • Tool steel
  • Martensitic stainless steel
  • Plastic deformation
  • Additive manufacturing
  • Micro-tribology
  • Abrasive wear

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