Towards enhancing the hot deformability of Ti₂AlN/Ti46Al4Nb1Mo composites via melt hydrogenation

A new strategy called melt hydrogenation was introduced in this study to improve the hot deformability of Ti₂AlN/Ti46Al4Nb1Mo composites, which was directly melting materials in mixed gas of H₂ and Ar with different ratios (H₂ percentage: 0, 20% and 40%). XRD results showed that melt hydrogenation decreased the proportion of α₂ phase, which was due to the narrowed α phase region and enlarged β phase region since hydrogen acting as β stable element. The length of Ti₂AlN particles in as-cast composites increased, because hydrogen induced overheat on melt surface and then promoted the growth rate of Ti₂AlN particles along their long axis. Hot compression results indicated melt hydrogenation effectively reduced the peak stress from 695 MPa to 605/603 MPa at 1100 °C/0.1 s⁻¹ when H₂ percentage was 20% and 40%, respectively. Deformed microstructure indicated that hydrogen accelerated dynamic recrystallization (from 55.6% to 74.7%) and increased the fraction of area with low density of dislocations (from 82.3% to 87.8%). In addition, hydrogen facilitated the formation of deformed nano-twins, which was probably due to hydrogen reducing the stacking fault energy. Therefore, the increased DRX, decreased dislocations density and more deformed nano-twins all contributed to the enhanced hot deformability of Ti₂AlN/Ti46Al4Nb1Mo composites.