We report results from a systematic program of alloy development in the system TiNiX, X = Cu, Pt, Pd, Au, to pursue certain special lattice parameters that have been identified previously with low hysteresis. We achieve λ2 = 1, where λ2 is the middle eigenvalue of the transformation stretch matrix, for alloys with X = Pt, Pd, Au. In all cases there is a sharp drop in the graph of hysteresis vs. composition at the composition where λ2 = 1. When the size of the hysteresis is replotted vs. λ2 we obtain a universal graph for these alloys. Motivated by these experimental results, we present a new theory for the size of the hysteresis based on the growth from a small scale of fully developed austenite martensite needles. The energy of the transition layer plays a critical role in this theory. Overall, the results point to a simple systematic method of achieving low hysteresis and a high degree of reversibility in transforming materials.
Bibliographical noteFunding Information:
We wish to acknowledge valuable discussions with John Ball, Rémi Delville, Eckhard Quandt, Nick Schryvers, Doron Shilo, Thomas Waitz, Barbara Zwicknagl, the comments of an anonymous reviewer and the assistance of Sakthivel Kasinathan. This work was supported by the ARO-MURI W911NF-07-1-0410, the MULTIMAT RTN network MRTN-CT-2004-505226, AFOSR (GameChanger, GRT00008581/ RF60012388) and DOE DE-FG02-05ER25706. The work also benefited from the support of NSF-NIRT DMS-0304326, ONR-MURI N000140610530, NIH Z196601 and the Humboldt Foundation.
- Continuum mechanics
- Martensitic phase transformation
- Nickel-titanium alloys
- Nucleation and growth