1. Coherency strains of H-phase precipitates and their influence on functional properties of nickel-titanium-hafnium shape memory alloys
- Author
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Ali Shamimi, Aaron P. Stebner, Ronald D. Noebe, Joseph Pauza, Behnam Amin-Ahmadi, and Tom Duerig
- Subjects
010302 applied physics ,Materials science ,Strain (chemistry) ,Mechanical Engineering ,Alloy ,Metals and Alloys ,chemistry.chemical_element ,Coherency strain ,02 engineering and technology ,Shape-memory alloy ,engineering.material ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Hafnium ,chemistry ,Mechanics of Materials ,Nickel titanium ,Phase (matter) ,Martensite ,0103 physical sciences ,engineering ,General Materials Science ,Composite material ,0210 nano-technology - Abstract
A Ni50.3Ti41.7Hf8 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.
- Published
- 2018
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