Growth kinetics and martensitic transformation of large Fe particles in a Cu-1.5 mass% Fe alloy

Abstract

The growth kinetics and martensitic transformation induced by simple cooling of large Fe particles in Cu-1.5 mass % Fe single crystals aged at 973 K for up to 60 days are examined by transmission electron microscopy and magnetic measurement. The growth kinetics of large Fe particles can be described by the Lifshitz-Slyozov-Wagner theory and the interfacial energy between the Fe particles and the Cu matrix is estimated as 0.24 to 0.40 J m⁻². The volume fraction of α-Fe particles increases with the mean particle size and with lowering of the cooling temperature. The critical sizes below which the transformation by simple cooling does not occur, are found to be 290 and 350 nm for specimens cooled to 77 K and room temperature, respectively. The saturation magnetization of the Cu-Fe alloy containing large α-Fe particles increases by further annealing of the cooled specimens. These facts imply that α-Fe particles are not produced during the prolonged ageing but are formed martensitically during the cooling process.