Abstract
Co–Ni–Ga high-temperature shape memory alloys (HT-SMAs) are well-known candidate materials for damping applications at elevated temperatures. Recent studies showed that upon heat treatment in stress-induced martensite under compressive loads transformation temperatures can be increased significantly, qualifying Co–Ni–Ga for HT-actuation. The increase in transformation temperatures is related to a change in chemical order recently validated via neutron diffraction experiments. Since SMAs show distinct tension–compression asymmetry in terms of theoretical transformation strains and bearable stresses, understanding the impact of martensite aging in tension is crucial for future applications. The current results indicate that martensite aging in tension provides for a further improvement in functional properties.
Highlights
The increase in transformation temperatures is related to a change in chemical order recently validated via neutron diffraction experiments
The current results indicate that martensite aging in tension provides for a further improvement in functional properties
By means of neutron diffraction, the underlying microstructural mechanism responsible for this martensite stabilization has been identified as change of chemical order in the martensitic phase.[18]
Summary
Shape memory alloys (SMAs) have received considerable attention over the last decades.[1,2,3,4,5] Their unique functional properties are based on a thermo-elastic, fully reversible phase transformation from a high-temperature austenitic phase to a low-temperature martensitic phase, being characterized by a high and low degree of symmetry, respectively.[1,4,5] As is known from literature, the thermoelastic nature of martensitic transformation strongly affects phase transition,[1] such that findings available for martensitic phase transformation in non-thermo-elastic alloys, e.g. in Ref. 6, cannot be directly transferred to SMAs, e.g. Co–Ni– Ga being in focus of the current study. Recent studies showed that upon heat treatment in stress-induced martensite under compressive loads transformation temperatures can be increased significantly, qualifying Co–Ni–Ga for HT-actuation.
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