Effect of thermomechanical treatment on the structural, phase transformations and properties of the Cu~--- Al~--- Ni shape memory alloys

A. E. Svirid ; A. V. Luk’yanov ; V. V. Makarov ; V. G. Pushin ; A. N. Uksusnikov

Čelâbinskij fiziko-matematičeskij žurnal, Tome 4 (2019) no. 1, pp. 108-117.

Résumé

The optical and electron microscopy, electron diffraction and X-ray diffraction have been used to study the effect of thermomechanical processing on grain structure, average grain size, structural and phase transformations in ternary shape memory Cu-Al-Ni alloys. In the studied alloys with a fixed content of Ni in an amount of 3 wt.%, the concentration of aluminum varied from 9 to 14 wt.%. It is shown that in the alloys after thermomechanical processing, including forging and homogenizing annealing using controlled recrystallization in austenite state and also subsequent quenching, grain-boundary decay and segregation are eliminated. It was found that the microstructure of alloys in a hot-tempered and quenched state with an aluminum content of 9–10 wt.%. is represented by grains with an average size of 60–80 $\mu$, with a content of 10–12% by weight of aluminum 100–350 $\mu$, whereas in alloys with an aluminum content of up to 14% by weight, the average grain size reaches 0.5–1 mm. At the same time, according to the mechanical tests at room temperature, as the aluminum content decreases, the tensile strength $\sigma_{u}$, the yield strength $\sigma_{m}$, the elongation $\delta$ increase. The increase in the mechanical properties of alloys is due to the refinement of the grain structure of the $\beta_{2}$-austenite and the package substructure of $\beta_{1}^{'}$- and $\gamma_{1}^{'}$ -martensites with decreasing aluminum content in alloys. Thus, for fine-grained alloys with 9.2 and 9.5% Al, the value of the relative elongation remains at a good level (grater than 10%), and for the remaining alloys with an aluminum content of 10–14 wt.% it does not exceed 5%. With an increase in the aluminum content in alloys, character of failure changes (from viscous to brittle) of samples under uniaxial tension.

Détail

Keywords: shape memory effect, mechanical properties, structure, martensitic phases, thermomechanical processing.

Bibliographie

[1] (In Russ.)

[2] S. Miyazaki, T. Kawai, K. Otsuka, “On the origin of intergranular fracture in $\beta$ phase shape memory alloys”, Scripta Metallurgica, 16:4 (1982), 431–436 | DOI

[3] Likhachev V.A., Kuzmin S.L., Kamentseva Z.P., The effect of shape memory, Leningrad State University, Leningrad, 1987, 218 pp. (In Russ.)

[4] Otsuka K., Shimidzu K., Suzuki Yu., et al., Alloys with shape memory effect, Metallurgiya Publ., Moscow, 1990, 224 pp. (In Russ.)

[5] Y. S. Sun, G. W. Lorimer, N. Ridley, “Microstructure and its development in Cu-Al-Ni alloys”, Metallurgical Transactions A., 21:2 (1990), 575–588 | DOI

[6] Khachin V.N., Pushin V.G., Kondratiev V.V., Nickel Titanium: Structure and properties, Nauka Publ., Moscow, 1992, 160 pp. (In Russ.)

[7] V.A. Likhachev (ed.), Materials with shape memory effect, in 4 volumes, Research Institute of Chemistry of Saint-Petersburg State University, Saint-Petersburg, 1997, 1998 (In Russ.)

[8] Pushin V.G., Kondratiev V.V., Khachin V.N., Pretransitional phenomena and martensite transformations, Ural Branch of Russian Academy of Sciences, Yekaterinburg, 1998, 368 pp. (In Russ.)

[9] K. Otsuka, C. M. Wayman, Shape Memory Materials, Cambridge University Press, Cambridge, 1999, 284 pp.

[10] P. Sedlak, H. Steiner, M. Landa, V. Novak, P. Sittner, L. I. Manosa, “Elastic constants of bcc austenite and 2H orthorhombic martensite in Cu-Al-Ni shape memory alloy”, Acta Materialia, 53:13 (2005), 3643–3661 | DOI

[11] L. A. Matlakhova, E. C. Pereira, A. N. Matlakhov, S. N. Monteiro, R. Toledo, “Mechanical behavior and fracture characterization of a monocrystalline Cu–Al–Ni subjected to thermal cycling treatments under load”, Materials Characterization, 59:11 (2008), 1630–1637 | DOI

[12] J. San Juan, M. L. No, C. A. Schuh, “Superelastic cycling of Cu–Al–Ni shape memory alloy micropillars”, Acta Materialia, 60:10 (2012), 4093–4106 | DOI

[13] N. Resnina, V. Rubanik (eds.), Shape memory alloys: properties, technologies, opportunities, Trans Tech Publication Ltd, Switzerland, 2015, 645 pp.