Superelastic Properties of Aged FeNiCoAlTaB Cold-Rolled Shape Memory Alloys
Journal
Metals
Series/Report No.
Metals
Journal Volume
14
Journal Issue
6
Start Page
643
ISSN
2075-4701
Date Issued
2024-06
Author(s)
DOI
10.3390/met14060643
Abstract
In the present study, microstructure and cyclic tensile tests were used to measure the superelastic responses of Fe40.95Ni28Co17Al11.5Ta2.5B0.05 (at.%) shape memory alloys after 97% cold rolling. Cold-rolled samples underwent annealing heat treatment (1250 °C/1 h) followed by quenching in water or aging heat treatment (700 °C/6 h and 700 °C/12 h) followed by quenching in water. The microstructure results showed that the average grain size increased from 210 μm to 1570 μm as annealing times increased from 0.5 h to 1 h. X-ray diffraction (XRD) spectra for FeNiCoAlTaB (NCATB) showed that in cold-rolled alloys after solution, the strong peak was in the face-centered cubic (γ, FCC) <111> structure. In aged samples, a new peak (γ’, FCC) emerged, the intensity of which increased as aging times rose from 6 to 12 h. Transmission electron microscope (TEM) images showed that the average precipitate size was around 10 nm in 700 °C/6 h specimens and 18 nm in 700 °C/12 h specimens. The precipitate was enriched in Ni, Al, and Ta elements and exhibited an L12 crystal structure. Tensile samples aged at 700 °C for 6 and 12 h exhibited recoverable strains of 1% and 2.6%, respectively, at room temperature. Digital image correlation (DIC) results for the sample aged at 700 °C for 12 h showed that two martensite variants were activated during the superelastic test. Such variants can form corresponding variant pairs (CVPs), which promote tensile deformation. The tensile sample exhibited a gradual cyclic degradation, and a large irrecoverable strain was observed after the test. This irrecoverable strain was the result of residual martensite, which was pinned by dislocations.
Subjects
FeNiCoAlTaB
grain size
precipitate
recoverable strain
superelastic properties
Publisher
MDPI AG
Type
journal article