Temperature dependent atomic-scale modeling of interfaces in cemented carbides
Doctoral thesis, 2020
Cemented carbides, or hardmetals, are composite materials manufactured by means of powder metallurgy, where carbide and binder metal powders are mixed, pressed, and sintered into a dense material. In this way the material gets a unique combination of hardness from the carbide and toughness from the binder. Cemented carbide is, therefore, an excellent choice of material in application where high hardness, wear-resistance, and toughness are crucial.
In this thesis bulk, interface, and surface thermodynamics in cemented carbides are studied using DFT, but also using other atomistic descriptions derived from DFT including analytical bond order potential (ABOP), cluster expansions (CE) and force constant (FC) models. Further, free energies are calculated using methods such as thermodynamic and temperature integration from both molecular dynamics (MD) and Monte Carlo (MC) simulations, quasi harmonic approximation (QHA), effective harmonic models (EHM) from ab-initio molecular dynamics (AIMD), surface stress for liquid surface free energy and calculation of work of adhesion from separation and joining simulations.
Wetting of WC surfaces and WC/WC grain boundaries is investigated in WC-Co and WC-Ni cemented carbides at elevated temperatures and it is concluded that, at liquid sintering temperatures, wetting of WC surfaces is only partial in C-rich materials while perfect in W-rich materials. Further, WC/WC grain boundaries are predicted to be stable also at liquid phase sintering temperatures. WC/WC grain boundary sliding is shown to be facilitated by infiltration of binder phase of only a few atomic layers proportion. Moreover, the hexagonal and cubic WC phases are investigated at high temperatures and a phase diagram is generated. Finally, the formation of thin cubic carbide films (complexions) in WC/Co phase boundaries is studied in both undoped and Ti-doped cemented carbides. These films are predicted at liquid phase sintering temperatures in both cases and also at solid state sintering temperatures in the Ti-doped case. In Ti-doped cemented carbides, the Ti atoms are found to mostly segregate to the second layer of the thin film and leave an essentially pure W layer towards Co.
analytical bond order potential
density functional theory
Condensed Matter and Materials Theory
Wetting of surfaces and grain boundaries in cemented carbides and the effect from local chemistry
Materialia,; Vol. 8(2019)
A computational study of the temperature dependence of interface and surface energies in WC–Co cemented carbides
International Journal of Refractory Metals and Hard Materials,; Vol. 87(2020)
Molecular dynamics simulation of WC/WC grain boundary sliding resistance in WC–Co cemented carbides at high temperature
International Journal of Refractory Metals and Hard Materials,; Vol. 49(2015)p. 75-80
Martin Gren, Erik Fransson, Mattias Ångqvist, Paul Erhart och Göran Wahnström. Modeling of vibrational and configurational degrees of freedom in hexagonal and cubic tungsten carbide
Erik Fransson, Martin Gren och Göran Wahnström. Modeling of thin cubic film thermodynamics in undoped WC-Co cemented carbides
Martin Gren, Erik Fransson och Göran Wahnström. Modeling of thin cubic film thermodynamics in Ti-doped WC-Co cemented carbides
Sintring av inhomogena strukturer för förbättra prestanda. Materials Science 2015.
Swedish Foundation for Strategic Research (SSF), 2016-05-01 -- 2021-06-30.
Effect of interface chemistry and structure on grain morphology and plastic deformation of cemented carbides
Swedish Research Council (VR), 2014-01-01 -- 2016-12-31.
Seco Tools AB, 2014-01-01 -- 2015-12-31.
Sandvik, 2014-01-01 -- 2015-12-31.
Flerskalsmodellering av plastisk deformation av hårdmetaller.
Swedish Research Council (VR), 2017-01-01 -- 2020-12-31.
Areas of Advance
Condensed Matter Physics
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4786
Chalmers University of Technology
Opponent: Dr. Hannu-Pekka Komsa, Institutionen för teknisk fysik, Aalto universitet, Finland