Microstructure and mechanical property evolutions of bulk core-shell structured Ti-N alloys during annealing

Bulk dense core-shell structured Ti-N alloys with three different N contents were synthesized, and then annealed at different temperatures to tailor the mechanical performances. Compression tests show that with increasing N content (nitriding temperature and time), the Ti-N shell thickness and yield strength increase (from 0.9 to 1.2 GPa) with a decrease in fracture plasticity (from 27% to 3%). With increasing annealing temperature, the Ti-N shell thickness and yield strength first increase and then decrease, while fracture plasticity remains unchanged except a dramatic drop at 1500 °C. There exists a linear relationship between the yield strength and shell area fraction indicating the hardening effect of the Ti-N shell.