Effects of aging on the microstructure of a Cu-Al-Ni-Mn shape memory alloy

Abstract

The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy (SMA) was studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometer, and differential scanning calorimeter (DSC). Experimental results show that bainite, γ₂, and α phase precipitates occur with the aging effect in the alloy. After aging at 300dgC, the bainitic precipitates appear at the early stages of aging, while the precipitates of γ₂ phase are observed for a longer aging time. When the aging temperature increases, the bainite gradually evolves into γ₂ phase and equilibrium α phase (bcc) precipitates from the remaining parent phase. Thus, the bainite, γ₂, and α phases appear, while the martensite phase disappears progressively in the alloy. The bainitic precipitates decrease the reverse transformation temperature while the γ₂ phase precipitates increase these temperatures with a decrease of solute content in the retained parent phase. On the other hand, these precipitations cause an increasing in hardness of the alloy.

Keywords

copper alloys / shape memory effect / martensitic transformations / aging / precipitates

References

[1] Pérez-Landazábal J.I., Recarte V., Sánchez-Alarcos V., et al. Study of the stability and decomposition process of the β phase in Cu-Al-Ni shape memory alloys. Mater. Sci. Eng. A, 2006, 438–440, 734.

[2] Zak G., Kneissl A.C., Zatulskij G. Shape memory effect in cryogenic Cu-Al-Mn alloys. Scripta Mater., 1996, 34, 363.

[3] Wei Z.G., Peng H.Y., Yang D.Z., et al. Reverse transformations in CuAlNiMnTi alloy at elevated temperatures. Acta Mater., 1996, 44, 1189.

[4] Morris M.A. Influence of boron additions on ductility and microstructure of shape memory Cu-Al-Ni alloys. Scripta Metall. Mater., 1991, 25, 2541.

[5] Morris M.A. High temperature properties of ductile Cu-Al-Ni shape memory alloys with boron additions. Acta Metall. Mater., 1992, 40, 1573.

[6] Morris M.A., Lipe T. Microstructural influence of Mn additions on thermoelastic and pseudoelastic properties of Cu-Al-Ni alloys. Acta Metall. Mater., 1994, 42, 1583.

[7] Adachi K., Shoji K., Hamada Y. Formation of X phases and origin of grain refinement effect in Cu-Al-Ni shape memory alloys added with titanium. ISIJ Int., 1989, 29, 378.

[8] Wei Z.G., Peng H.Y., Zou W.H., Yang D.Z. Aging effects in a Cu-12Al-5Ni-2Mn-1Ti shape memory alloy. Metall. Mater. Trans. A, 1997, 28, 955.

[9] Sari U. Influences of 2.5wt% Mn addition on the microstructure and mechanical properties of Cu-Al-Ni shape memory alloys. Int. J. Miner. Metall. Mater., 2010, 17(2): 192.

[10] Miyazaki S., Otsuka K. Development of shape memory alloys. ISIJ Int., 1989, 29, 353.

[11] Saburi T., Wayman C.M. Crystallographic similarities in shape memory martensites. Acta Metall., 1979, 27, 979.

[12] Sari U., Aksoy I. Electron microscopy study of 2H and 18R martensites in Cu-11.92wt% Al-3.78wt% Ni shape memory alloy. J. Alloys Compd., 2006, 417, 138.

[13] Sari U., Kirindi T. Effects of deformation on microstructure and mechanical properties of a Cu-Al-Ni shape memory alloy. Mater. Charact., 2008, 59, 920.

[14] Cheniti H., Bouabdallah M., Patoor E. High temperature decomposition of the β1 phase in a Cu-Al-Ni shape memory alloy. J. Alloys Compd., 2009, 476, 420.

[15] Zou W., Gui J., Wang R., et al. Bainitic precipitation and its effect on the martensitic transformation in the Cu-Al-Ni-Mn-Ti shape-memory alloy. J. Mater. Sci., 1997, 32, 5279.

[16] Suresh N., Ramamurty U. Effect of aging on mechanical behavior of single crystal Cu-Al-Ni shape memory alloys. Mater. Sci. Eng. A, 2007, 454–455, 492.

[17] Recarte V., Pérez-Sáez R.B., Bocanegra E.H., et al. Influence of Al and Ni concentration on the martensitic transformation in Cu-Al-Ni shape-memory alloys. Metall. Mater. Trans. A, 2002, 33, 2581.

[18] Sari U., Aksoy I. Micro-structural analysis of self-accommodating martensites in Cu-11.92wt% Al-3.78wt% Ni shape memory alloy. J. Mater. Process. Technol., 2008, 195, 72.

[19] Aydogdu A., Aydogdu Y., Adiguzel O. Long-term ageing behaviour of martensite in shape memory Cu-Al-Ni alloys. J. Mater. Process. Technol., 2004, 153-154, 164.