Design and investigation of strength-ductility TiAl matrix composites with a novel dual-layers couple reinforced structure

Abstract

TiAl matrix composites with a novel dual-layers couple reinforced structure have been designed and successfully prepared by the combination of plasma rotating electrode process (PREP) and spark plasma sintering (SPS) in this study. The dual-layers reinforced TiAl composites consisted of the fully lamellar TiAl matrix units that were reinforced by dispersed carbides and the outer reinforced network structures that were composed of TiB and Ti₂AlC. The growth mechanisms of TiB and Ti₂AlC in the outer network reinforced structures have been revealed. The orientation relationships were indicated as (0001)[11–20]_Ti2AlC||(111)[10-1]_TiAl, [011]_TiB||[210]_TiAl and [-100]_TiB||[11–20]_Ti2AlC. The introduction of dual-layers couple reinforced structures significantly enhanced the ultimate tensile strength (UTS) at 900 °C and the elongation at room temperature (RT). Especially, the composites with 0.5 wt% B₄C addition represented the UTS and elongation as 424.36MPa/1.42 % at RT and 497.32MPa/4.12 % at 900 °C. The growths of outer network reinforced structures enhanced the connectivity of adjacent TiAl matrix units, and triggered off the transformation of fracture modes from intergranular to translamellar. Additionally, the plastic deformation of TiAl matrix composites mainly stemmed from γ phase and refined lamellae. The fractures usually propagated along the (101)_TiB and (100)_TiB planes in TiB crystals during the loading. Dislocations pile-ups led to the activation of slipping along the (0001)_Ti2AlC in carbides, especially at high temperatures. The dual-layers couple reinforced structures resulted in the coordination of strengthening and toughening within TiAl matrix units and the interfaces, which contributed to the balance between the UTS at 900 °C and the elongation at RT of the composites.