Zero thermal expansion and high Young's modulus in Ti-Nb achieved by concurrent α′′iso and ω precipitation

This work develops a novel and efficient processing strategy for creating multi-phase Ti-alloys with zero thermal expansion and enhanced rigidity. By heating to between the start and finish temperatures for martensite reversion, the cold-rolled, alpha '' martensitic microstructure in Ti22Nb mostly transforms to austenite beta, which in turn facilitates the simultaneous precipitation of nano-scale alpha '' isoand omega phases during aging. The diffusional partitioning of Nb leads to the formation of beta + alpha '' iso+omega multi-phase microstructures. The crystal-level thermal expansion of alpha '' isois analogous to athermal alpha '' martensite, featuring negative thermal expansion along [010]alpha ''. Macroscopic expansion behavior and Young's modulus are related to the microstructural evolution during aging. Holding at 250 degrees C increases the initially negative sample-level coefficient of thermal expansion and makes it become zero after aging for 1000 h. A considerable improvement in Young's modulus of 44% could be verified.

Automated summary

This study develops a novel and efficient processing strategy for creating multi-phase Ti-alloys with zero thermal expansion and enhanced rigidity. By heating to specific temperatures, the microstructure of Ti22Nb transforms and precipitates nano-scale phases, resulting in the formation of multi-phase microstructures. The thermal expansion and Young's modulus of the alloy can be modified through aging process, leading to improved properties.