Structure and properties of NiAl-TiC nanocomposites obtained by mechanical alloying and powder consolidation
Dariusz Oleszak*, Andrzej Michalski*, Andrzej Olszyna*, Stanisław Gierlotka**, Józef Paszula*** *Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa **Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa ***Wojskowa Akademia Techniczna, Wydział Uzbrojenia i Lotnictwa, ul. Kaliskiego 2, 00-908 Warszawa
Annals 3 No. 7, 2003 pages 172-175
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abstract In order to obtain nanocrystalline NiAl-TiC composites, mechanical alloying and powder consolidation methods were applied. Mechanical alloying processes were performed in a Fritsch P5 planetary ball mill. Mixtures of powders of pure elements, i.e. Ni, Al, Ti and graphite, giving 40 wt.% of TiC, were subjected to milling. Due to highly negative values of enthalpies of formation of NiAl and TiC (–118 and –184 kJ/mol, respectively), after several hours of milling, NiAl+TiC composite powder was obtained, as a result of solid state reaction. Three different methods of powder consolidation were employed: explosive compaction (velocity of detonation wave about 3500 m/s), pulse current sintering (1000 pulses, current 700 A, duration of pulse 0.2 s) and hot pressing under very high pressure (7.7 GPa, 1000oC, 5 min). The obtained densities of compacts after various consolidation methods were: 86, 92 and 98% of theoretical density, respectively. The sample after 7.7 GPa pressing exhibited very high microhardness 1370 HV01, while the hardness after pulse current sintering was 750 HV1. High pressure and explosive compaction methods allowed to preserve a nanocrystalline size of crystallites of both phases (NiAl and TiC). However, at least partial decomposition of TiC was observed as a result of explosive compaction. On the other hand, pulse current sintering resulted in the increase of crystallite size up to about 100 nm. Key words: mechanical alloying, powder consolidation, nanocomposites, intermetallic NiAl, TiC