Coherency strains of H-phase precipitates and their influence on functional properties of nickel-titanium-hafnium shape memory alloys

Abstract A Ni 50.3 Ti 41.7 Hf 8 alloy was studied after two-step aging treatments consisting of 300 °C for 12 h followed by 550 °C for different times. An anomalous change in transformation temperatures was observed as the second aging time was increased from 7.5 to 13.5 h. Initially with increased aging time (0.5–7.5 h) at 550 °C, coherency strain fields about H-phase precipitates increased. The corresponding backstress favored martensite formation, hence an increase in transformation temperatures. However, a point was eventually reached where misfit dislocations relaxed those strain fields and the effect was reduced, resulting in a decrease in transformation temperatures.

[1]  M. Mills,et al.  Role of aging time on the microstructure and shape memory properties of NiTiHfPd single crystals , 2013 .

[2]  Fan Yang,et al.  Structure analysis of a precipitate phase in an Ni-rich high-temperature NiTiHf shape memory alloy , 2013 .

[3]  Haluk E. Karaca,et al.  TEM study of structural and microstructural characteristics of a precipitate phase in Ni-rich Ni–Ti–Hf and Ni–Ti–Zr shape memory alloys , 2013 .

[4]  Ze Zhang,et al.  A new precipitate phase in a TiNiHf high temperature shape memory alloy , 1998 .

[5]  K. Gall,et al.  The influence of aging on critical transformation stress levels and martensite start temperatures , 1999 .

[6]  Ibrahim Karaman,et al.  Microstructural characterization and shape memory characteristics of the Ni50.3Ti34.7Hf15 shape memory alloy , 2015 .

[7]  K. Bhattacharya,et al.  Transformation strains and temperatures of a nickel–titanium–hafnium high temperature shape memory alloy , 2014 .

[8]  S. Padula,et al.  Mechanical and functional behavior of a Ni-rich Ni50.3Ti29.7Hf20 high temperature shape memory alloy , 2014 .

[9]  Haluk E. Karaca,et al.  Effects of nanoprecipitation on the shape memory and material properties of an Ni-rich NiTiHf high temperature shape memory alloy , 2013 .

[10]  M. Hÿtch,et al.  Measurement of the displacement field of dislocations to 0.03 Å by electron microscopy , 2003, Nature.

[11]  D. J. Gaydosh,et al.  Load-biased shape-memory and superelastic properties of a precipitation strengthened high-temperature Ni50.3Ti29.7Hf20 alloy , 2011 .

[12]  Othmane Benafan,et al.  Microstructural Response During Isothermal and Isobaric Loading of a Precipitation-Strengthened Ni-29.7Ti-20Hf High-Temperature Shape Memory Alloy , 2012, Metallurgical and Materials Transactions A.

[13]  Ronald D. Noebe,et al.  Effect of a pre-aging treatment on the mechanical behaviors of Ni50.3Ti49.7 − xHfx (x ≤ 9 at.%) Shape memory alloys , 2018 .

[14]  Anita Garg,et al.  Characterization of the microstructure and mechanical properties of a 50.3Ni–29.7Ti–20Hf shape memory alloy , 2012 .

[15]  G. S. Bigelow,et al.  Structure–property relationships in a precipitation strengthened Ni–29.7Ti–20Hf (at%) shape memory alloy , 2015 .