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Study of kinetics of phase transitions in the CuMnAl alloys
Author(s) -
Soltys J.,
Kozubski R.,
Meres K.,
Holender J.
Publication year - 1985
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.2170200424
Subject(s) - metastability , phase (matter) , precipitation , materials science , thermodynamics , decomposition , type (biology) , crystallography , phase transition , chemistry , physics , geology , paleontology , organic chemistry , meteorology
The alloys of the system CuMnAl have been extensively investigated. The results of systematic studies of phase equilibria in those alloys have been recapitulated by West, Thomas, and by Köster, Gödecke. However, the alloys of the composition approximating Cu 2 MnAl have been drawing special attention. At high temperatures the alloys of such composition are comprised in a range of equilibrium of the β‐phase which has simple crystalline structure and is often called the Heusler phase. The properties of the above alloys are very interesting due to the simultaneous occurrence of two kinds of structural phase transitions: the “order‐disorder” transformations in the range of β‐phase and the decomposition of the β‐phase in the temperature range of its metastability. It was indicated that above 1050 K the β‐phase has cubic disordered structure of the type A2 while, when cooled, it transforms at 1050 K into partially ordered B2‐type structure and at about 950 K into completely ordered L2 1 ‐type one, Dubois (Lisse). On the other hand, the β‐phase is metastable at temperatures below 970 K and decomposes into three phases of the types β MN , γ‐Cu 9 Al 4 and T‐Cu 3 Mn 2 Al (West, Thomas; Köster, Gödecke). The simultaneous occurrence of the ordering and decomposition processes may be an interesting subject of theoretical considerations (Nishizawa et al.). The processes may be considered either on microscopic level requiring various simplifying assumptions or through the study of processes of precipitation in real structure. The aim of the presented work was the detailed research of the process of decomposition of β‐phase in the stoichiometric alloy Cu 2 MnAl (Kozubski et al. 1982, 1983a, b, c). During the investigations the methods of X‐ray diffraction and the measurement of electrical resistivity as well as electron microprobe were applied. The X‐ray diffraction and microprobe measurements were performed at room temperature and the specimens quenched in water after the desired annealing were examined. All samples of the alloy were at first homogenized at 1123 K and then annealed at various temperatures between 423 and 973 K.