NiTi-Nb in-situ Nanowire Composite: Extending the Boundaries of Materials Elastic Strain Limit, Young’s Modulus and Strength

This paper reports the creation of a NiTi-Nb nanowire in-situ composite of remarkable mechanical properties. This composite is based on a new materials design concept of elastic strain coupling between a NiTi matrix and Nb nanowires. It is challenging to develop bulk materials that exhibit large elastic strains, low Young's moduli and high strengths because of the intrinsic trade-off relationships among these properties. A low Young's modulus in a single-phase material usually means weak interatomic bonding and thus low strength. Due to the initiation of dislocation activity and early failure caused by structural flaws, the elastic strain of bulk metals is usually limited to less than 1%. On the other hand, freestanding nanowires have ultrahigh elastic strain limits (4-7%) and yield strengths [1,2]. As a result, much effort has been given to develop bulk composites with nanowires for exceptional mechanical properties. However, results obtained so far in the past two decades have been disappointing [3], primarily because the intrinsic mechanical properties of nanowires have not been successfully exploited in bulk composites [3-5]. This situation has been commonly known as "the valley of death" in nanocomposite design. This work has overcome this long-standing challenge by using a new composite materials design concept utilizing the martensitic phase of NiTi