Abstract
The present study utilizes molecular dynamics simulations to study the athermal and stress-induced martensitic transformation of B2 to B19′ phase in a Ni-Ti alloy and the effect of precipitates on the phase transformation. The simulations demonstrate the existence of an intermediate B19 phase between martensite and austenite phases. The Nickel-Titanium shape memory alloy with precipitates is studied by introducing Ni3Ti, NiTi2 and Ni4Ti3 precipitates individually using atomistic simulations. The results show that the phase transition temperature decreases in the presence of a large volume fraction of precipitates. A blended precipitates model with Ni3Ti and NiTi2 is simulated to study the phase transformation in equiatomic NiTi alloy. The results indicate that the precipitates would initiate the emergence of the B19 phase and reduce the transition temperature. In addition, the variation of Nickel content by embedded precipitates would lead to a change in the microstructural phenomena.
Highlights
Ni-Ti shape memory alloy (SMA) is extensively used in biomedical treatments (Duerig et al 2003), automation, manufacturing and aerospace (Hartl and Lagoudas 2007) applications due to their diverse mechanical properties
Observation of martensite phase austenite start temperature (As) the SME is related to martensite and austenite phase transformation, the material data can be gathered from a simulation where the system is cooled and heated which can reproduce the martensite and austenite phases
The change in atomic structure is shown in figures 4, (a)–(d) that show different phases in the range of 500 K and 100 K in cooling and heating respectively, where green and grey are identified as Ni and Ti atoms
Summary
Ni-Ti shape memory alloy (SMA) is extensively used in biomedical treatments (Duerig et al 2003), automation, manufacturing and aerospace (Hartl and Lagoudas 2007) applications due to their diverse mechanical properties. The mechanism of recoverable strain in SMA is controlled by the martensitic transformation with applied stress or change in temperature (Wei et al 1998). The present work focuses on the factors influencing Ni-Ti SMA properties during athermal and stress induced martensitic transformation. Zhong et al (2011) and Chen et al (2018) studied the stress-induced martensitic transformation and phase recovery phenomenon of B2 and B19′ phase in Ni-Ti SMA at the nanoscale. MD simulations using a high accuracy interatomic potential, derived from Lai and Liu (2000), showed the formation of B19 phase in the middle of martensitic transformation (Ko et al 2015). Sewak and Dey (2019) had recognized the intermediate phase as the B19 phase instead of R phase, according to the crystal structure parameter and the perturbed angular correlation (PAC)
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