Improving the high-temperature tensile properties of titanium alloys by elemental enrichment at grain boundaries

Abstract

Titanium alloys are widely used in aerospace applications due to their excellent heat resistance and high specific strength. However, their high-temperature strength enhancement is constrained by grain boundary slip phenomena at elevated temperatures. In this study, a TA0-(9 wt%) NiAlCrMoZr titanium alloy was fabricated via laser-directed energy deposition (LDED) to systematically investigate the formation mechanism of interfacial element enrichment and its influence on high-temperature tensile properties. Owing to the different diffusion rates of elements in β-Ti, Ni and Mo were enriched at the grain boundary of α phase and β phase interfaces by tailoring the heat treatment temperature. Notably, the specimen heat-treated at 900 °C demonstrated a 9.0 % enhancement in high-temperature tensile strength and an 88.6 % improvement in elongation at 600 °C compared to its counterpart treated at 800 °C. These significant improvements in high-temperature mechanical properties are primarily attributed to interfacial element enrichment. On one hand, the strengthening effect by grain boundary element enrichment on grain boundaries is greater than the weakening effect caused by grain boundary coarsening, thereby increasing the high-temperature strength. On the other hand, the strengthening of grain boundaries by element enrichment promotes the synergistic deformation of grain boundaries and grain interiors, significantly increasing the elongation of the alloy. Furthermore, the interfacial enrichment of Ni and Mo is ascribed to the epitaxial growth of the α phase during high-temperature processing and the mismatch in atomic diffusion rates during rapid cooling. This work may provide valuable insights into microstructure design strategies for optimizing the high-temperature performance of titanium alloys.