Cermets for a wide range of temperatures
Development of new advanced materials in particular powder metallurgy (PM) materials and related technologies is one of the major factors for industrial success. Combination of desirable properties of advanced PM materials is met in multiphase material structures including ceramic-metal composites - cermets and cemented carbides ( hardmetals). One of the promising fields of cermets application is their use in tribological application where resistance to monotonic and cyclic loading and corrosion becomes an important factor to improve durability of tools and wear resistant parts.
The research in the field of wear resistant composites (tribocomposites ) of enhanced mechanical and corrosion reliability produced by advanced PM manufacturing methods has been carried out in TTÜ for many decades. Latest research has been focused on development of tribocomposites for a wide range of temperatures, characterization of these composites based on carbides, carbonitrides, nitrides and establishment of the generic relationships between materials performance, structure and processing route. The aim is development and/or optimization of ceramic-metal composites of high hardness and strength, enhanced fracture toughness and excellent wear or corrosive-wear resistance that is sustainable in a wide range of temperatures. The research program is mostly focused on titanium carbide, carbonitride, nitride ( TiC, TiCN, TiN ), chromium carbide ( Cr3C2 ) and tungsten carbide ( WC ) based composites.
Examples of the latest research activities and results for industrial applications are as follows:
• Development and use of ceramic-metal composites ( cermets and hardmetals ) as tool materials for friction stir welding (FSW) of aluminium alloys and low-carbon steels. It has been revealed that prevailing degradation mechanism of tools during FSW is adhesion. It has been also established that WC-Co hardmetals and TiC-Fe alloy ( steel ) cermets compare favourably with other ceramic –metal composites in adhesive wear conditions.
• Development of Ni- and Co-free ceramic-metal composites ̶ TiC-, TiN- and Cr3C2-based cermets and WC-based cemented carbides. Iron based binders binders with different structure are used to replace toxic metals (Ni, Co) in these composites. The focus of research is at present prevalently on utilisation of Ni- and Co-free high-chromium corrosion resistant ferritic steels as alternative metallic binders. The phase transformations and microstructural evolution ( see Figures 1 and 2 ) ) during sintering as well as mechanical and corrosion behaviour of these composites have been revealed.
• Investigation of contact fatigue behaviour of ceramic-metal composites on basis of TiC, Cr3C2 and WC of different composition produced using different technological routes ( vacuum sintering, Sinter/HIP, reactive sintering , spark plasma sintering ( SPS ) ). Contact loads of cyclic nature between contacting surfaces are common e.g. in cold forming tools and machine components. The mechanical response and the damage mechanism during contact fatigue have been disclosed.
• Development of reliable technology of induction air brazing of titanium carbide- based cermets to steels using commercially available Ag – and Cu- based filler materials and fluxes. Advanced testing methods have been utilized for estimation of quality and characteristics of brazed joints.
Figure 1. SEM image (a) and EDS mapping results of TiC-430L high chromium steel cermets sintered at 1500 °C during 30 min (b): blue – titanium, red – chromium and green – iron
Figure 2 . SEM image of regular WC-Co hardmetal (a) and experimental WC hardmetal with high chromium steel (AISI430L) and titanium (b). Wear rate (mass loss) of hardmetals during erosion wear test at room and elevated temperatures (c).
Head of research:
Professor Jakob Kübarsepp
jakob dot kubarsepp at ttu dot ee