L Journal of Alloys and Compounds 336 (2002) 196–201 www.elsevier.com / locate / jallcom Formation of nickel aluminides by mechanical alloying and thermodynamics of interaction a, b b a c * V.K. Portnoy , A.M. Blinov , I.A. Tomilin ,V.N. Kuznetsov , T. Kulik a Department of Chemistry, Moscow Lomonosov State University, Leninskie Gory, Moscow, GSP-3, 119899, Russia b Moscow State Steel and Alloys Institute, Leninsky prosp. 4, Moscow 117936, Russia c Department of Materials Science and Engineering, Warsaw University of Technology, Warsaw, Poland Received 6 August 2001; accepted 25 September 2001 Abstract Structure and temperature stability of Ni–Al alloys obtained by mechanical alloying (MA) were studied using X-ray diffraction and differential scanning calorimetry (DSC). MA of Ni–Al powders produces the B2 phase for the composition range 40–61 at.% Ni, and a nanocrystalline supersaturated solid solution Ni(Al) in the range 65–85 at.% Ni. MA of Ni Al leads to a nanocrystalline phase, 62.5 37.5 probably with L1 structure. The NiAl (B2) phase is formed through direct rapid exothermic solid state reaction without formation of 0 intermediate solid solutions. Formation of the ordered tetragonal Ni Al phase occurs after prolonged deformation of the nonstoich- 5 3 iometric B2 phase with 62.5 at.% Ni. The results of MA were compared with calculated Gibbs energies of principal phases namely FCC, L1 and B2 using the results of computer assessment of the system. The final product of MA is always single phase which has minimal 2 Gibbs energy of the competing phases at alloy composition. This indicates a leading role of the thermodynamic factors on phase formation by MA.  2002 Elsevier Science B.V. All rights reserved. Keywords: Transition metal alloys; High temperature alloys; Mechanical alloying; Crystal structure; X-ray diffraction 1. Introduction aluminide NiAl (B2 structure) is formed by an explosive exothermal reaction. Pabi and Murty [4] suggest the NiAl 3 Intermetallics of the nickel–aluminium system existing phase to be formed by the same diffusionless mechanism. in the composition region 40–75 at.% Ni attract significant In both cases the reaction starts when, as a result of ball attention due to a promising combination of properties like milling, the particles of aluminum and nickel achieve high melting temperature, low density, high corrosion minimal critical sizes. resistance, and good high-temperature strength. The attain- According to the equilibrium diagram [8], between 60 ment of those properties stems from their microstructure. and 75 at.% Ni the orthorhombic phase Ni Al exists at 5 3 Using mechanical alloying (MA) for the preparation of temperatures below 7008C, and there is a two-phase region such alloys results in the occurrence of metastable states, NiAl1Ni Al at higher temperatures. In [1] the formation 3 and dispersed microstructures, that significantly changes of amorphous-like structure was found after MA of the properties of the alloys. mixtures with 65–73 at.% Ni. However, in later work [3] it The synthesis of nickel aluminides by MA of the was revealed that for the composition 67 at.% Ni, being components using various ball mills was reported in a inside that limit, the solid solution Ni(Al) is formed. By number of works [1–7]. For alloys with the higher nickel MA of alloys richer in aluminum namely Ni Al 33–40 67–60 contents, 73 at.% and more, MA produces a supersaturated [1,3] the B2 phase was obtained as a final product, whereas solid solution Ni(Al) [1,3]. Pabi and Murty [4] treat the Coreno-Alonso et al. [7] obtained the equilibrium Ni Al 2 3 supersaturated solid solution with Ni Al composition as phase. These studies have allowed some conclusions to be 75 25 disordered Ni Al. In Refs. [1,2] it was shown that during drawn about the mechanisms and kinetics of the solid- 3 MA of the mixtures Al Ni (46,x,60) the mono- phase interaction of the components during MA. However, 1002x x the published data concerning the phase composition of nickel–aluminum alloys after MA remain inconsistent and *Corresponding author. E-mail address: portnoy@general.chem.msu.ru (V.K. Portnoy). requires refining. 0925-8388 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388(01)01905-3