TiAl-based composite sheet with multi-layer distributed reinforcement prepared by solid-liquid reaction

TiAl-based alloy have potential as high temperature structural materials for aerospace applications, especially for thermal protection systems in aerospace vehicles including skin materials. Unfortunately, the ductility and formability of TiAl-based alloys are rather poor and thus γ-TiAl sheets or foils are quite difficult to be manufactured by traditional methods and still far from practical applications. In the present work, commercial pure Ti foils and in-house fabricated TiB₂/Al composite foils were alternately stacked and rolled to prepare Ti-(TiB₂/Al) laminates, and then heat treatment was utilized to make liquid Al react with solid Ti, and finally TiAl-based composite sheet with multi-layer distributed reinforcement TiB₂ particles were achieved. This method avoided the direct deformation of brittle TiAl billets and thus the near-net-shape processing of TiAl-based alloys sheets was feasible. Phase transformation and microstructure evolution during heat treatment were investigated and mechanical properties of the resulting micro-laminated TiB₂-TiAl composite sheets were evaluated. The results showed that porous TiAl₃ layers were produced by the reaction between liquid Al and solid Ti because of Kirkendall effect, and the following densification treatment under 50 MPa at 1300°C for 2 h significantly improved the relative density of material. Subsequently, the reaction diffusion between TiAl₃ and residual Ti proceeded in the following heat treatment, and finally fully lamellar (α₂~-Ti₃Al+γ-TiAl) layers were obtained. TiB₂ particles did not participate in any reaction and remained, and displayed multi-layered distribution in the matrix (α₂-Ti₃Al+γ-TiAl) layers. TiB₂-rich layer hindered the coarsening of lamellar colony of (α₂-Ti₃Al+γ-TiAl) layer. Tensile properties at 800°C of multi-layered TiB₂-TiAl composite sheets remarkably increased because of an increase of energy dissipation caused by plastic deformation.