Computational thermodynamics-based design of nanodispersion-strengthened shape memory alloys

3-D local electrode atom probe (LEAP) tomography (APT) is utilized to support the computational design of nanodispersion-strengthened TiNi-based shape-memory alloys. Models are developed to aid the design of a future superelastic biomedical NiTiZrAl alloy with improved fatigue resistance, strength, and radiopacity for the application of stenting a superficial femoral artery. Using LEAP tomography, the otherwise unattainable B2-L2₁ phase relations for this class of alloys at 873 K are mapped. Experimentally calibrated models are developed to describe solid solution strengthening and precipitation strengthening. Precipitate growth and coarsening was investigated with tomography, revealing that optimal microstructures occur in the early stages of precipitation rather than at equilibrium. Because peak hardness in the alloy system occurs in a non-equilibrium state, capillary equilibrium modeling of precipitation trajectory assists the design for a partially precipitated state at peak hardness. The optimal precipitate diameter of 3.08 nm is identified to achieve maximum strengthening in a NiTiZrAl alloy.