Approach to the Theoretical Strength of Ti-Ni-Cu Alloy Nanocrystals by Grain Boundary Design

The grain boundary design was used to introduce boride Ti2B and TiB2 nanoparticles of 5 nm in size into grain boundaries of nanocrystalline Ti50Ni25Cu25 alloy. As a result, the maximum normalized microhardness was increased by 20% and the theoretical limit of hardness is substantially approached. It is proposed that boride nanoparticles suppressed low-temperature grain-boundary sliding and, therefore, shifted the range of the anomalous behavior of Hall-Petch relation toward smaller sizes of the Ti-Ni-Cu nanocrystals.