Uncovering the role of nanoscale precipitates on martensitic transformation and superelasticity

Journal Article · 25 February 2022 · Acta Materialia

DOI: https://doi.org/10.1016/j.actamat.2022.117790 · OSTI ID:1976787

Tripathi, Shivam ^[1]; Vishnu, Karthik Guda ^[2]; Titus, Michael S.  ^[2]; Strachan, Alejandro ^[2]

---

1. Purdue University, West Lafayette, IN (United States); OSTI
2. Purdue University, West Lafayette, IN (United States)

Here we characterize the role of coherent nanoscale B2 Ni₅₀Al₅₀ precipitates on the temperature- and stress-induced martensitic phase transformation in nanocrystalline Ni₆₃Al₃₇ shape memory alloys using multi-million-atoms molecular dynamics (MD) simulations. We studied two types of precipitates: one with single crystal precipitates (SXP) and a second where grain boundaries cut through precipitates (PXP). Simulations reveal that the presence of B2 precipitates stabilizes the cyclic flag-shaped stress-strain response, characteristic of superelasticity, and reduces remnant strain. In contrast, single-phase nanocrystalline Ni₆₃Al₃₇ exhibits degradation of the reverse transformation during cyclic loading and, eventually, incomplete reversible transformation within a few cycles. This is consistent with previous experimental findings of ultra-low fatigue in Ni-Ti-Cu alloys with Ti₂Cu precipitates. The simulations reveal that the presence of precipitates significantly improves the reversibility of the transformation by acting as elastic zones that partially shield the martensitic transformation and drive the reverse transformation. A detailed analysis of the MD trajectories reveals that the martensitic transformation of the matrix induces ultra-large elastic deformation in some of the B2 precipitates (approximately 12%) to the point of resulting in a martensite-like atomic structure.

• Research Organization: Purdue University, West Lafayette, IN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: FG02-07ER46399
• OSTI ID: 1976787
• Journal Information: Acta Materialia, Journal Name: Acta Materialia Journal Issue: C Vol. 229; ISSN 1359-6454
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English