MECHANICAL ALLOYING OF IMMISCIBLE CU(70)TM(30) ALLOYS (TM=FE,CO)

Four series of copper-based alloys with compositions Cu70Co30, Cu70Fe3 0Cu70Co15Fe15 and Cu-70(CoFe)(30) were synthesized by mechanical alloy ing (MA). The interest in these materials is as parents of alloys whic h will show the giant magnet resistance (GMR) effect. The structural e volution was studied as a function of the MA time by means of Mossbaue r spectroscopy, X-ray and neutron diffraction techniques and different ial scanning calorimetry (DSC). In spite of the positive heat of mixin g of the alloy constituents, the complete dissolution of the minority phases (iron and/or cobalt) into the copper f.c.c. lattice was observe d for each specimen after 16 h of MA. This alloying was accompanied by changes in lattice parameter \Delta a(0)/a(0)\ of up to 0.5% with res pect to pure copper. Analysis of the crystallization products arising from DSC treatments up to 600 degrees C revealed a separation into cop per f.c.c. and iron-based b.c.c, phases. In the case of the ternary Cu -70(FeCo)(30) alloys, the FeCo intermetallic compound was obtained by heating both alloys which originated as ternaries and also as pseudo-b inaries based on copper plus the intermetallic phase. Mossbauer spectr a of the annealed Cu70Fe30 specimens also revealed a non-magnetic phas e of iron with a f.c.c. environment, which was probably stabilized by the presence of copper and small quantities of nitrogen.