TY - JOUR

T1 - Stress dependence of the hysteresis in single crystal NiTi alloys

AU - Hamilton, R. F.

AU - Sehitoglu, H.

AU - Chumlyakov, Y.

AU - Maier, H. J.

N1 - Funding Information: This work was partially supported by the Air Force Office of Scientific Research, Grant No. F49620-01-1-0136 and the National Science Foundation Grant, CMS-0332824. The assistance of Prof. H. S. Woo with DSC experiments is gratefully acknowledged.

PY - 2004/6/21

Y1 - 2004/6/21

N2 - We demonstrate the variation in thermal hysteresis with increasing external stress for reversible martensitic transformations. The hysteresis was measured in temperature cycling experiments under external stress and also under pseudoleastic deformation conditions. To understand the role of composition and crystal orientation effects, the study included aged and solutionized Ti-50.1, Ti-50.4, Ti-50.8 and Ti-51.5at.%Ni in the [1 1 1], [0 0 1], [0 1 1], [0 1 2], and [1 2 3] orientations. Differential scanning calorimetry was used to characterize the thermal hysteresis resulting from thermal cycling under zero stress. The results show unequivocally that the thermal hysteresis expands with increasing external stress for aged and solutionized Ti-50.1at.%Ni and Ti-50.4at.%Ni alloys, while it contracts with increasing external stress for the higher Ni alloys with 50.8 and 51.5at.%Ni compositions. The growth of temperature hysteresis was from 20 °C to as high as 80 °C for the lower Ni alloys, while the contraction of the hysteresis was from 60 to 15 °C for the higher Ni alloys. The stress dependence of the hysteresis is rationalized considering dissipation of elastic strain energy due to relaxation of coherency strains at martensite-austenite interfaces. The role of precipitates and frictional work on transformation hysteresis is also clarified based on experiments on low and high Ni alloys with heterogeneous and homogenous precipitate structures respectively. A micro-mechanical model based on reversible thermodynamics was modified to account for plastic relaxation of coherent transforming interfaces, and the predictions account for the growing hysteresis with increasing external stress.

AB - We demonstrate the variation in thermal hysteresis with increasing external stress for reversible martensitic transformations. The hysteresis was measured in temperature cycling experiments under external stress and also under pseudoleastic deformation conditions. To understand the role of composition and crystal orientation effects, the study included aged and solutionized Ti-50.1, Ti-50.4, Ti-50.8 and Ti-51.5at.%Ni in the [1 1 1], [0 0 1], [0 1 1], [0 1 2], and [1 2 3] orientations. Differential scanning calorimetry was used to characterize the thermal hysteresis resulting from thermal cycling under zero stress. The results show unequivocally that the thermal hysteresis expands with increasing external stress for aged and solutionized Ti-50.1at.%Ni and Ti-50.4at.%Ni alloys, while it contracts with increasing external stress for the higher Ni alloys with 50.8 and 51.5at.%Ni compositions. The growth of temperature hysteresis was from 20 °C to as high as 80 °C for the lower Ni alloys, while the contraction of the hysteresis was from 60 to 15 °C for the higher Ni alloys. The stress dependence of the hysteresis is rationalized considering dissipation of elastic strain energy due to relaxation of coherency strains at martensite-austenite interfaces. The role of precipitates and frictional work on transformation hysteresis is also clarified based on experiments on low and high Ni alloys with heterogeneous and homogenous precipitate structures respectively. A micro-mechanical model based on reversible thermodynamics was modified to account for plastic relaxation of coherent transforming interfaces, and the predictions account for the growing hysteresis with increasing external stress.

KW - Elastic strain energy

KW - Hysteresis

KW - Phase transformation

KW - Shape memory

UR - http://www.scopus.com/inward/record.url?scp=2642549926&partnerID=8YFLogxK

U2 - 10.1016/j.actamat.2004.03.038

DO - 10.1016/j.actamat.2004.03.038

M3 - Article

AN - SCOPUS:2642549926

VL - 52

SP - 3383

EP - 3402

JO - Acta materialia

JF - Acta materialia

SN - 1359-6454

IS - 11

ER -