Insights into in-situ TiB/dual-phase Ti alloy interface and its high load-bearing capacity

Abstract

To better understand the strengthening mechanism of in-situ formed TiB reinforcements in dual-phase Ti6Al4V alloy, the interface characters and properties of α-Ti/β-Ti/TiB system were thoroughly investigated with the combined use of high-resolution transmission electron microscopy (HRTEM), ab-initio calculations, and indentation tests. The ab-initio calculations suggest that the highly coherent (100)TiB/(1¯21)β-Ti phase boundary (PB) has fairly low interface energy of 0.082 J/m2 with an exceptionally high adhesion strength of 6.04 J/m2, owing to the formation of strong interfacial Ti–B ionic bonds. The semi-coherent (201¯)TiB/(0001)α-Ti interface shows a relatively higher interface energy of 1.442 J/m2 but still with a fairly high adhesion strength of 4.95 J/m2. With the obtained interfacial energetics, thermodynamics analyses were further carried out to explore the nucleation mechanism of α-Ti in TiB reinforced Ti6Al4V composite. Superior to the heterogeneous nucleation at TiB/β-Ti interface, the homogeneous nucleation of α-Ti within the β-Ti phase can be more energy-preferred, due to its lower nucleation energy barrier and critical radius. Further indentation tests under various loads of different modes confirmed a remarkably enhanced load-bearing capacity of dual-phase Ti6Al4V alloys, under the critical significance of the strong interfacial bonding achieved by reinforcements of in-situ formed TiB.