Deformation, fracture, and fatigue crack growth behavior in TiB-reinforced near-α Ti matrix composites fabricated using powder metallurgy technique

Abstract

Titanium matrix composites with TA15 alloy as the matrix and TiB (ranging from 0 to 4 vol.%) as reinforcement were produced via powder metallurgy-based hot press sintering, employing AlB2 precursor. The addition of TiB to TA15 led to a substantial reduction in the colony and prior β grain sizes, and an increase in the lath thickness in the composites. Plastic deformation due to planar slip, which traverses across the α/β-ligament phase boundaries within each colony, may cause TiB particles located on colony boundaries to break, potentially more so than those within the colony. The composite containing 1 vol.% TiB exhibited simultaneous improvements in strength, ductility, and strain hardening rate, attributed to colony refinement and possibly a sizable amount of intra-boundary TiB. Further increase in the TiB content led to significant drops in ductility, which was further exacerbated by the precipitation of α2-Ti3Al phase. A substantial decrease in the mode I fracture toughness, attributed to reduced colony size and diminished crack deflection, was noted in the composite with 1 vol.% TiB. The colony size refinement also contributed to a reduction in the threshold stress intensity factor range, ΔK0, for the fatigue crack growth, owing to the decreased tortuosity of the fatigue crack front. This study elucidates the intricate relationship between TiB location, microstructure, and mechanical properties, providing insights for the design of TiB-reinforced titanium alloys with both α and β phases.