AGING EFFECTS ON ORDERING DEGREE AND MORPHOLOGY OF 18R-TYPE MARTENSITE IN SHAPE-MEMORY CUZNAL ALLOYS

Ageing effects in CuZnAl alloys have been investigated by X-ray diffra ction and optical microscopy. The splittings observed in some selected diffraction peaks due to the monoclinicity of the martensite unit cel l by basal plane distortion are referred to as monoclinic distortion. The spacing difference, Delta d, between some selected pairs of peaks may be used as a parameter to reflect the ordering degree in CuZnAl al loys, and the extent of Delta d difference and monoclinic distortion m ay depend on the type and degree of long range order or alloy composit ion. The variation of Delta d parameters for both as-quenched and post -quench beta-phase annealed specimens show a trend to decrease with ho lding duration at room temperature. This trend is closely related to t he martensite stabilization, and this process is mainly due to the rea rrangement of atoms in martensite lattice. Self-accommodating martensi te morphology which has a diamond-like configuration has been observed in both as-quenched and post-quench heat-treated specimens. Parallel bands defined as lamellar martensite or twin-like morphologies have al so been formed on the martensite plates, and interlamellar boundaries are not as straight as twin boundaries. Copyright (C) 1997 Elsevier Sc ience Ltd.