Mechanically alloyed Ti-20Si3N4 based composites
[ 1 ] Instytut Inżynierii Materiałowej, Wydział Inżynierii Materiałowej i Fizyki Technicznej, Politechnika Poznańska | [ S ] student | [ D ] phd student | [ P ] employee
EN Silicon-based non-oxide ceramics (Si3N4+TiN) have attracted much attention as engineering materials, mainly due to their good mechanical and chemical properties such as high hardness, chemical stability and corrosion resistance, high melting point and reliablity at elevated temperatures. Si3N4 based composites have great potential as cutting-tool and other high temperature applications. Other authors have reported that TiN/Si3N4 based nanocomposites with excellent mechanical properties and conductivity can be processed through a chemical route, as well as, mechanical milling and sintered by SPS. They applied Si3N4 and TiN nano powders as a precursors. In this work authors investigate mechanical alloying process of Ti-20Si3N4 powders. The specimens were than consolidated by high frequency induction heating sintering and cold pressing followed by free-sintering. The structure, microstructure and porosity, hardness were investigated by XRD, SEM and Vickers tester, respectively. After mechanical alloying nearly amorphous structure was obtained which could be interesting precursor for consolidation, due to higher reactivity than standard microstructure. The MA process takes 30h, using Spex shaker-type mill, under argon atmosphere. Authors decided to investigate the consolidation process using two techniques: traditional cold pressing (1000 MPa) followed by free-sintering (1300°C/120min) and high frequency induction heating sintering (50MPa, 1000°C/3min). Free-sintering results in highly porous samples (porosity level was over 30%). HFIH samples despite lower sintering parameters (pressure, temperature and time) showed nearly full densification (0,4% porosity). Moreover, after HFIH the grain size was almost two times lower than after traditional consolidation. The phase compositions were the same for both consolidation techniques and consist of Si3N4, Ti5Si3, TiN. The obtained composites show relatively high hardness of about 1650 HV.
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