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 gamma-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 degrees 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 (alpha(2)-Ti3Al+gamma-TiAl) layers were obtained. TiB2 particles did not participate in any reaction and remained, and displayed multi layered distribution in the matrix (alpha(2)-Ti3Al+gamma-TiAl) layers. TiB2 rich layer hindered the coarsening of lamellar colony of (alpha(2)-Ti3Al+gamma-TiAl) layer. Tensile properties at 800 degrees C of multi layered TiB2 TiAl composite sheets remarkably increased because of an increase of energy dissipation caused by plastic deformation.