The effect of texture on stress-induced martensite formation in nickel–titanium

Abstract

An experimental study was performed to investigate the effect of texture on stress-induced martensitic phase transformation in the shape memory alloy Nickel-Titanium (Nitinol). Thin sheet specimens of Nitinol were examined under uniaxial tensile loading using three-dimensional digital image correlation in order to spatially and temporally track strain localization indicative of martensitic transformation. Tensile specimens were fabricated along directions oriented 0° (RD), 45°, and 90° (TD) to the rolling direction of the sheet and subjected to 50 cycles at prescribed strain rates of-4-3-2-1 g ε = 10 ,10 , and 10 s. It was found that upon loading, specimens unfavorably oriented for transformation (TD specimens) nucleated a greater number of deformation bands due to a smaller difference between nucleation and propagation stresses, and also accommodated less axial strain inside the band and more axial strain outside of the band. The unfavorable (TD) specimens also exhibited a stronger cycle-to-cycle similarity in the strain accommodated inside the deformation band, which has important implications for the design of SMA structures for fatigue applications. Finally, the (primarily martensite) region of the deformation band(s) consistently showed significantly stronger cycle-to-cycle similarity than the (primarily austenite) region outside of the band(s), regardless of specimen texture.

A review of elastocaloric cooling: Materials, cycles and system integrations

“…The reverse phase change from B19' back to B2 is a single step process. This is consistent with the DSC measured results reported in literature (Uchil et al, 2001, Kim and Daly, 2013, Ossmer et al, 2014. This intrinsic two-steps phase change and asymmetric phase change path on the phase diagram determine that Ni-Ti has higher hysteresis during the phase transformation.…”

Deformation Mechanisms in NiTi-Al Composites Fabricated by Ultrasonic Additive Manufacturing

“…In this case, NiTi fibers were purchased from the same source (Nitinol Devices & Components, Inc.) as used by Kim and Daly [43]. That work reports a h110i B2 crystallographic texture along the fiber axis based on RD inverse pole data provided in Fig.…”

“…The experimental curves are from so-called ''stabilized'' fibers and represent the response after ten cycles. In principle, such cycling can introduce additional defect accumulation and plastic strain [43]. However, stabilized fibers tend to have greater hardening and reduced incremental plastic ratcheting [26].…”

Recent Developments in Assessing Microstructure-Sensitive Early Stage Fatigue of Polycrystals (Postprint)

“…El Bartali et al [7] quantified plastic strain at the grain scale in a duplex stainless steel and measured a high degree of strain heterogeneity within some grains, attributed to local constraint and resulting triaxiality. Daly and coworkers [8][9][10] coupled DIC methodologies with infrared thermography and stereo digital imaging to characterize the behavior of shape memory alloys with resolution on the order of several microns. DIC has become an important validation tool for grain scale crystal plasticity models, but it still has its challenges, including the resolution necessary to resolve fine slip band structures and high-intensity illumination, heat haze and degradation of the speckle pattern at high temperature.…”