PSI - Issue 69

Carlo Alberto Biffi et al. / Procedia Structural Integrity 69 (2025) 61 – 68

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In fact, the stress/strain curve of the NiTa alloy shows a plateau with a small stress reduction (about 150 MPa), meaning probably the propagation of the cracks in the sample during the compression. On the contrary, the B addition increased the plateau stress by 300-400 MPa. The value of d s /d e was calculated to be about 38,2 GPa for the ternary alloys while about 30,7 GPa for the binary one. The calculated strain hardening coefficients of such alloys are significantly higher than other HT SMAs, discussed in literature. Firstov et al. [3] proposed a comparison in terms of mechanical properties between CuZr based alloys and NiTi based alloys, showing that d � /d �� was approximately in the range 10-30 GPa.

Fig. 5. Thermal hysteresis of the alloys

Fig. 6. Compression response on the alloys at room temperature

Table 2. Characteristic stress and strain values of the alloys during compression testing. Alloy Plateau stress [MPa] Recovered strain [%] Residual strain [%]

d s /d e [GPa]

NiTa

150 300 400

0.6

0.9

30.7 38.2 38.2

NiTaBA1 NiTaBA2

0.75

0.75

1.0

0.5