Microstructure, mechanical and functional properties of NiTi-based shape memory ribbons

• Published in: Journal of alloys and compounds Vol. 526; pp. 45 - 52
• Main Authors: Mehrabi, K., Bruncko, M., Kneissl, A.C.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15-06-2012; Elsevier
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Elasticity, elastic constants; Exact sciences and technology; Intermetallic compounds; Intermetallics; Martensitic transformations; Materials science; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Melt-spinning; Microstructure; Nickel base alloys; Nickel compounds; Nickel titanides; NiTi-based alloys; Other heat and thermomechanical treatments; Physics; Ribbons; Shape memory alloys; Thermomechanical training; Titanium compounds; Treatment of materials and its effects on microstructure and properties; Two-way effect; NiTi-based alloys; Melt-spinning; Shape memory alloys; Microstructure; Two-way effect; Thermomechanical training; Nickel alloys; Ruptures; Tensile tests; Thermal cycle; Elasticity; Melt spinning; Shape memory effects; Titanium alloys; Shape memory alloy; Rapid solidification; Thermomechanical treatments; Flow planar casting; Two way shape memory effect; Bending test
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2012.02.097

► Melt-spun samples exhibited martensite structure and shape memory effects immediately after processing at room temperature. ► Using a new etchant and interference contrast, it is possible to reveal the fine microstructures and grain boundaries. ► The martensite structure in NiTi is very fine, and nano-sized twin boundaries could be revealed using TEM only. ► Two-way effects have been successfully introduced by different thermomechanical training methods in NiTi, NiTiCu and NiTiW alloys, which can be used for several applications, e.g. microsensors and microactuators.
The present work has been aimed to study the microstructures, functional properties and the influence of different thermomechanical training methods on the two-way shape memory effect in NiTi-based melt-spun ribbons. In order to get small-dimensioned shape memory alloys (SMAs) with good functional and mechanical properties, a rapid solidification technique was employed. Their fracture and elasticity characteristics have been determined, as well as shape memory properties by thermomechanical cycling. The ribbons were trained under tensile and bending deformation by thermal cycling through the phase transformation temperature range.
The results displayed that all different training methods were effective in developing a two-way shape memory effect (TWSME). The influence of copper (5–25at.% Cu) and tungsten (2at.% W) on the microstructure, and the functional and mechanical behavior of NiTi thin ribbons was also investigated. All samples show a shape memory effect immediately after processing without further heat treatment. The melt-spun ribbons were trained under constant strain (bending and tensile deformation) by thermal cycling through the phase transformation temperature range. The addition of copper was effective to narrow the transformation hysteresis. The W addition has improved the TWSME stability of the NiTi alloys and mechanical properties. Results about microstructures, functional and mechanical properties will be presented.