Shape Memory Alloy Transformations Open access Peer reviewed

Improving Mechanical Properties of CoNiAl(-Fe) Shape Memory Alloys through Controlled γ-Phase Evolution

Christian Hinte, Henri Heimers, E. Holzmann, Sebastian Herbst and 1 more

Shape Memory and Superelasticity | Oct 26, 2026

Abstract

Abstract

Polycrystalline CoNiAl-based shape memory alloys offer promising functional properties but are limited by poor mechanical properties. This study investigates the influence of alloy composition and processing history on γ-phase formation, spatial distribution, and mechanical response in CoNiAl(-Fe) alloys. Six compositions with varying Fe contents were analyzed in the as-cast and homogenized condition. Despite substantial variations in alloy composition, elemental partitioning between the γ and B2 phases remained essentially consistent. In contrast, the γ -phase fraction and spatial distribution varied substantially with alloy composition. γ -phase fractions below 0.2% were associated with low ductility and compressive strengths below 500 MPa, yet relatively small γ -phase fractions enabled pronounced deformation when favorably distributed along grain boundaries. However, increasing the γ -phase fraction did not inherently improve the mechanical response. Co 35 Ni 35 Al 28 Fe 2 was selected for detailed investigations on processing-induced γ-phase evolution. Variations in solidification rate, homogeneity, and aging substantially modified the γ -phase fraction and spatial distribution while maintaining largely unchanged γ -phase compositions. Aging at 1100 °C for 0.5 h promoted preferential γ -phase formation along grain boundaries while limiting intragranular precipitation and provided the most favorable combination of strength and ductility. The results demonstrate that controlling γ -phase distribution enables tailoring the mechanical response without requiring high overall γ -phase fractions.

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Authors

Researchers on this paper

Christian Hinte

first | Leibniz University Hannover | ORCID 0000-0001-7319-3905

Henri Heimers

middle | Leibniz University Hannover | ORCID 0009-0005-7302-6214

E. Holzmann

middle | Leibniz University Hannover | ORCID 0009-0007-8615-181X

Sebastian Herbst

middle | Leibniz University Hannover | ORCID 0000-0002-3351-2550

Hans Jürgen Maier

last | Leibniz University Hannover | ORCID 0000-0003-2119-824X

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Citation

BibTeX

@article{Hinte2026Improving,
  title = {Improving Mechanical Properties of CoNiAl(-Fe) Shape Memory Alloys through Controlled γ-Phase Evolution},
  author = {Christian Hinte and Henri Heimers and E. Holzmann and Sebastian Herbst and Hans Jürgen Maier},
  journal = {Shape Memory and Superelasticity},
  year = {2026},
  doi = {10.1007/s40830-026-00646-0},
  url = {https://doi.org/10.1007/s40830-026-00646-0}
}

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