Effect of grain size on stress induced martensitic transformations in a Cu–Al–Be polycrystalline shape-memory alloy. Pseudoelastic cycling effects and microstructural modifications

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 609; pp. 300 - 309
• Main Authors: Sade, M., de Castro Bubani, F., Lovey, F.C., Torra, V.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.07.2014; Elsevier
• Subjects: Applied sciences; Asymptotic properties; Cross-disciplinary physics: materials science; rheology; Crystal defects; Cu-base alloys; Dislocations; Exact sciences and technology; Grain size; Grains; Martensitic transformations; Materials science; Mechanical properties; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Pseudoelasticity; Shape-memory effect; Stresses; Transformations; Transmission electron microscopy; Mechanical properties; Pseudoelasticity; Cu-base alloys; Transmission electron microscopy; Martensitic transformations; Shape-memory effect; Grain size; Asymptotic behavior; Polycrystals; Free surface; Defects; Shape memory effects; Superelasticity; Dislocation arrays; Stress effects; Microstructure; Martensite; Microelectromechanical device; Defect formation; Hysteresis
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2014.05.018

Grain size has a strong effect on the pseudoelastic properties of shape-memory alloys. Different grain sizes and several related phenomena are studied. This involves the dependence of the transformation and retransformation stresses on grain size and on the amount of transformed material. A pronounced drop of transformation stresses on cycling is observed, until an asymptotic behavior is reached. This is related to the creation of defects (dislocations and dislocation arrays) and microplates of martensite, which are the defects necessary to allow the grains to accommodate due to the shape change imposed by the martensitic transformation. The asymptotic hysteresis is related to the internal work for the grains to accommodate each other once the necessary defects were created. The asymptotic hysteresis increases linearly as the grain size decreases. A simple model shows that the slope is related to the (d/e) ratio, where d is the average grain size and e is the width of the specimen. This effect arises from the presence of the free surfaces that release the plastic work for grain accommodation.