Mechanism of mechanical alloying in NiAl and CuZn systems

✍ Scribed by S.K. Pabi; B.S. Murty

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 586 KB
• Volume: 214
• Category: Article
• ISSN: 0921-5093
• DOI: 10.1016/0921-5093(96)10224-0

✦ Synopsis

Nanocrystalline A13Ni, NiA1 and Ni3A1 phases in the Ni-AI system and the c~,/7, 7 and e phases in the Cu-Zn system were synthesized by mechanical alloying of elemental blends in a planetary mill. In the as-milled state, A13Ni and AINi were always ordered, while Ni3A1 was disordered. MA results in a large extension of the NiA1 and Ni3A1 phase fields particularly towards Al-rich compositions. The crystallite size was finest (~ 6 nm) when NiA1 and Ni3AI phases coexist after prolonged milling. In contrast, in all Cu-Zn blends containing 15-85 at.% Zn, the Zn-rich phases were first to form and final crystallite sizes were coarser (15-80 nm). Two different modes of alloying have been identified. In the case of NiA1 and AI3Ni, where the ball milled product is ordered and the heat of formation is large (JHr > 120 kJ mol -1), a rapid discontinuous mode of alloying accompanied with an additive increase in crystallile size is detected. In all other cases irrespective of the magnitude of zlItr, gradual diffusive mode of intermixing during milling ~eems to be the underlying mechanism of alloying.