TY - JOUR

T1 - Pseudoelasticity and cyclic stability in Co49Ni21 Ga30 shape-memory alloy single crystals at ambient temperature

AU - Dadda, J.

AU - Maier, H. J.

AU - Niklasch, D.

AU - Karaman, I.

AU - Karaca, H. E.

AU - Chumlyakov, Y. I.

N1 - Funding Information: The present study was supported by Deutsche For-schungsgemeinschaft, United States Army Research Office, Contract No W911NF-06-1-0319, and the United States Civilian Research and Development Foundation, Grant No RUE1-2690-TO-05.

PY - 2008/9

Y1 - 2008/9

N2 - As-grown Co49Ni21Ga30 [001]- and [123]-oriented single crystals were subjected to cyclic compression loading at room temperature above the austenite finish temperature of 15 °C. Strain-controlled experiments were performed using both incremental strain steps and constant strain amplitudes. Cyclic deformation with a maximum strain amplitude of 2.5 pct resulted in rapid accumulation of irrecoverable strains in the [123]-oriented crystals. However, after a few cycles, the samples demonstrated cyclic stability with fully recoverable transformation. By contrast, the [001]-oriented crystals displayed excellent cyclic stability with hardly any change in stress-strain characteristics. In-situ optical microscopy and electron backscattered diffraction analysis were employed to clarify the events that take place at different stages of a typical loading-unloading history. The in-situ observations also revealed that the initiation and growth characteristics of stress-induced martensite (SIM) are heterogeneous on the microscopic scale in CoNiGa alloys. In addition, theoretical transformation and detwinning strains, and resolved shear stress factors (RSSFs), were calculated based on the energy minimization theory and are compared to the experimentally obtained orientation-dependent transformation stress and strain levels. It is shown that the selection of an appropriate orientation is one of the key criteria to optimize the pseudoelastic (PE) response and cyclic stability of CoNiGa alloys.

AB - As-grown Co49Ni21Ga30 [001]- and [123]-oriented single crystals were subjected to cyclic compression loading at room temperature above the austenite finish temperature of 15 °C. Strain-controlled experiments were performed using both incremental strain steps and constant strain amplitudes. Cyclic deformation with a maximum strain amplitude of 2.5 pct resulted in rapid accumulation of irrecoverable strains in the [123]-oriented crystals. However, after a few cycles, the samples demonstrated cyclic stability with fully recoverable transformation. By contrast, the [001]-oriented crystals displayed excellent cyclic stability with hardly any change in stress-strain characteristics. In-situ optical microscopy and electron backscattered diffraction analysis were employed to clarify the events that take place at different stages of a typical loading-unloading history. The in-situ observations also revealed that the initiation and growth characteristics of stress-induced martensite (SIM) are heterogeneous on the microscopic scale in CoNiGa alloys. In addition, theoretical transformation and detwinning strains, and resolved shear stress factors (RSSFs), were calculated based on the energy minimization theory and are compared to the experimentally obtained orientation-dependent transformation stress and strain levels. It is shown that the selection of an appropriate orientation is one of the key criteria to optimize the pseudoelastic (PE) response and cyclic stability of CoNiGa alloys.

UR - http://www.scopus.com/inward/record.url?scp=49049089323&partnerID=8YFLogxK

U2 - 10.1007/s11661-008-9543-0

DO - 10.1007/s11661-008-9543-0

M3 - Article

AN - SCOPUS:49049089323

VL - 39

SP - 2026

EP - 2039

JO - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

JF - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

SN - 1073-5623

IS - 9

ER -