Study of Shape Memory Alloys
Metal alloys are indispensable in a variety of industrial application areas, and research into their properties is critical for engineering and manufacturing. One area is the link between microstructure and properties, where most of the information to date comes from complex and expensive experiments. The use of computational tools can, however, help to solve some problems related to ICME (Integrated Computational Materials Engineering).One example is the phase-field method application that combines first-principles calculations with the continuum representation of the order parameter. A recent application of this methodology of this is the study of the prototypical shape memory alloy, Ni-Ti, as presented in the recent paper “Study on Ni-Ti alloys around equiatomic composition by the first-principles phase field method” published in Computational Materials Science. Shape memory alloys can be deformed when cold, and they return to their original shape when heated. This property is beneficial in various applications in medicine – and of course, only a few such alloys have sufficient biocompatibility to be inserted into a human body for long-term service. The biocompatibility of Ni-Ti makes it so valuable, and still, information about its full map of structure-properties data is missing.
A group of authors, including BIOVIA’s Riichi Kuwahara, applied the first principles phase-field method to this system with 45-55% Ni to predict the microstructure and time evolution of precipitate particles for different Ni concentrations. These calculations did not use any empirical input parameters. All necessary data was generated by density functional code. You can find more information about CASTEP in BIOVIA Materials Studio, and a workflow to construct cluster expansions from CASTEP results has been developed with BIOVIA Pipeline Pilot. The method has promise for creating a coherent workflow for more complex alloy compositions, impacting on the rational design of future experiments in metal alloy developments.
This methodology was further validated in the study of Pt-Ti alloys, as presented in the Acta Materialia paper “Effect of the Pt concentration on microstructures of Ti-Pt alloys using the first-principles phase field method”. Simulations confirmed that increasing the Pt concentration to 5, 10, 15 and 20 wt% causes a drastic change in the microstructure of Ti-Pt alloys in accord with the experimental observations. In the case of the Pt concentration of less than 10 wt%, the microstructure is lamellar- or wavy-shaped everywhere. When the Pt concentration is 15 and 20 wt%, spot-like TiPt precipitates appear in the -Ti phases with lamellar- or wavy-shaped patterns. Simulations in both 2D and 3D confirm these findings.
This series of papers continues an important collaboration that combines Materials Studio DFT calculations, Pipeline Pilot protocol to combine the results, and the academic phase-field approach to microstructure simulation. In a topical application area, it’s reassuring to see that BIOVIA tools can be successfully applied in multiscale simulations.
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