Jakob Kübarsepp

Behaviour of TiC-base cermets in different wear conditions

TiC-base cermets are in advantage compared with WC-base hardmetals because of their lower friction coefficient and higher oxidation resistance. At the same time, the diversity of alloys based on TiC, wear and loading conditions contributes substantially to problems in material selection. Present research focuses on testing of TiC-based cermets of different composition in different wear conditions and on material selection. Tribological characteristics, wear mechanisms and rational application areas of TiC-base cermets will be compared with those of WC- base hardmetals.

Structure sensitivity of wear resistance of hardmetals

The influence of the structure of hardmetals of two classes, tungsten carbide-base cobalt bonded and titanium carbide-base steel bonded, in two different wear conditions, erosive and adhesive wear, has been investigated. It has been shown that the wear resistance is much more structure sensitive than any single mechanical property. The structure sensitivity of adhesive wear is much higher than that of erosive and this is related to differences in stress-strain states and fracture mechanics during wear. At equal levels of hardness and approximately equal levels of strength, the adhesive wear resistance of TiC-base steel bonded hardmetals (on the contrary to their resistance to erosion) is as good as that of conventional WC-base cobalt bonded hardmetals.

Characterization of the serviceability of steel-bonded hardmetals

Abstract Mechanical properties of steel-bonded hardmetals have been investigated to characterize their serviceability as instrumental material for plastic forming of metals. The content of TiC in steel-bonded hardmetals investigated was 40 to 80 wt.% (51–86 vol.%). Hardenable martensitic steel austensitic steel and steel with intermediate structure were used as metallic binders. The study of different properties such as hardness, strength, plasticity, strain energy and fracture toughness of these alloys and the comparison with conventional WCCo and TiC(Ni,Mo) hardmetals enables one to recommend their application fields.

Mechanical properties and wear performance of compression sintered TiC based cermets

Abstract The present paper analyses mechanical properties and wear performance in different wear conditions of prospective for metalforming TiC based cermets sintered by two different techniques – ordinary vacuum sintering and compression sintering (sinter/hipping). It was found that the sinter/hipping technology enhances cermet resistance to a brittle failure in terms of transverse rupture strength and to wear, especially in the conditions of prevailing surface adhesion failure. The results are described by the classical Griffiths strength theory of brittle materials.

Direct CVD Growth of Multi-Layered Graphene Closed Shells around Alumina Nanofibers

In this work, a catalyst-free direct deposition of multi-layered graphene closed shells around highly aligned alumina nanofibers with aspect ratio of 107 is demonstrated for the first time. A single – step chemical vapor deposition process of specified parameters was used for development of hybrid structures of carbon shells around the core alumina nanofibers. Transmission electron microscopy and Raman spectroscopy were used to confirm formation of graphene layers and to understand the morphology of the various structures. The developed routine for growth of peculiar carbon nanostructures opens new opportunities for deposition of the tailored carbon structures on dielectric substrates.

Strength and failure of TiC based cermets

Abstract The strength and failure of TiC based cermets (designed for metalforming) under monotonously increasing and cyclic loading conditions were investigated. Comparative trials with an ordinary WC hardmetal (widely used in metalforming) complemented with XRD studies were performed. It is shown that the failure of the carbide composite is preceded by local plastic strain taking place in its both phases in the ductile binder and in the brittle carbide phase. Under cyclic loading conditions the plasticity of carbide composites decreases. The intensity in decrease depends on alloy composition.

Performance of Cemented Carbides in Cyclic Loading Wear Conditions

The present study describes the wear and mechanical behaviour of some carbide composites (TiC-base cermets and WC-base hardmetals) in cyclic loading applications (blanking of sheet metal). Adhesive wear as well as fatigue endurance were tested, followed by XRD measurements. The results show that the blanking performance of a carbide composite is dependent on its level of resistance to adhesion wear and fatigue sensitivity. XRD measurement revealed that fatigue damage is preceded by plastic strain in both the ductile binder and the brittle carbide phase.

Influence of Pressurized Sintering on Performance of TiC-Based Cermets

This paper discusses the effect of advanced sintering technologies – sinter + hot isostatic pressing (HIP) and sinter/HIP on the performance of TiC-based cermets. The performance was evaluated by strength (transverse rupture strength), adhesive wear resistance and durability. Adhesive wear was performed by a turning method (turning of mild steel at low speed) while durability was evaluated by functional testing – wear of tools during blanking of sheet metal. It was found that sinter/HIP ensures a higher positive effect than sinter + HIP in different cycles.

Students’ Self-management: E-course, E-tutoring and Online Support System

This paper discusses designing of an E-course and the Students’ E-tutoring and Support System (the SEOS System) at Tallinn University of Technology (TUT). There was a pressing need for such a system since the student drop-out rate at TUT is high (40%), especially among the first-year students. The general purpose of the E-course “Self-management” and the SEOS System is to decrease the drop-out rate among first-year students through individual assistance in problem solving. The first steps were interviewing tutors and doing a Pilot Study in order to map the problems first-year students have at TUT. We designed and introduced the self-management E-course since it became evident that students at TUT often had problems that fell outside the scope of TUT student support sources such as problems concerning knowledge and skills of time management and personal finance management. The SEOS System was developed for decreasing the first-year students’ drop-out rate trough offering them individual assistance, advice and guidance.

Developments in cermet design, technology and performance

This paper reviews developments in the research of cermets, related technologies and their mechanical and tribological (erosion abrasive wear resistance) characterisation. The aim is to enhance the performance and reliability of cermets and widen their application areas. Cermet technologies (ceramic-metal composites), such as TiC-based bonded with Ni- and Fe-alloys and Cr3C2-based bonded with Ni-alloys, are analysed. Focus is on the influence of different sintering modes: vacuum sintering, sinter/HIP and sinter + HIP (in different cycle) on the performance and reliability of TiC- and Cr3C2-based cermets. The structure, mechanical characteristics (hardness, transverse rupture strength) and wear resistance (erosive and abrasive wear) of the developed cermets are characterised.