Solid State Ionics 60 (1993) 299-304 North-Holland SOLID STATE IONICS Formation of new metastable transition metal alloys by combination of mechanical alloying and chemical leaching E. Ivanov TOSOH SMD, 3515 Grove City Road, Grove City, OH 43123, USA K. Suzuki, K. Sumiyama, S.A. Makhlouf and H. Yamauchi Institute for Materials Research, Tohoku University, Katahira 2-1- I, 980 Sendal Japan Received 21 August 1992; accepted for publication 7 December 1992 The leaching of A1atoms from B2 structures of mechanically alloyed Ni and Co aluminides led to the formation of metastable B2 Ni and Co. B2 Ni is strong paramagnet not stable above 470 K. The magnetic moment of Co atom in ferromagnetic B2 phase is smaller than in fcc one. B2 Ni demonstrates high catalytic activity in hydrogenation of organic compounds. There is a considerable interest on producing and studying nanocrystalline materials because of the size sensitivity of their structure, physical and chemical properties (Gleiter [ 1 ] ). Mechanical alloying (MA) has served for preparing nanocrystalline powders with nonequilibrium structures in several metal and alloy systems. In solid-state chemistry a technology of topotactic reactions combined with MA opens a possibility to prepare new materials with unusual structures. Since aluminum can be leached out of the aluminides of 3d-metals by basic solution, Ivanov et al. [2 ] have used a combination technique of MA and leaching and carried out a topotactic transfor- mation of mechanically alloyed Ni35AI6s and CO4oA16o of the B2 type into metastable nanocrystalline B2 Ni (Raney nickel) and Co. The structure of Ni2A13 (D513) is closely related to that of NiA1 (B2), i.e., the former is derived by replacing one third of Ni atoms by ordered vacancies in ( 11 1 ) plane of the NiA1 structure as shown in fig. 1. Ivanov et al. [3] showed that since shear dis- placement and atomic mixing take place during the MA leading to the formation of the NiA1 (B2), the homogeneity range of NiA1 becomes wider from equilibrium 45-59.2 at.% Ni to metastable 35-60 at.% Ni and the concentration ranges of disordered Ni2A13 and NiA1 phases overlap. Fig. 2 shows X-ray [OOll Q) AI 0 Ni I [111l D513 B2 a b Fig. 1. Comparison of Ni2AI3 and NiAI structures: (a) pseudo cubic cell (heavy bonding) surrounded by neighboring body cen- tered Ni atoms, dashed line indicates the missing plane of Ni at- oms; (b) bcc cell and neighboring atoms. diffraction pattern of as-milled Ni3sA16s and Raney Ni before and after annealed at 770 K under 2.0 MPa H2 gas pressure. Previously Mikhailenko et al. [4] showed that the lattice parameter, crystalline size and strains did not change (see table 1 ) after leaching. 0167-2738/93/$ 06.00 © 1993 Elsevier Science Publishers B.V. All rights reserved.