Effects of lamellar spacing on mechanical properties of fully lamellar Ti–39.4mol%Al alloy

Effects of lamellar spacing on mechanical properties of a fully lamellar TiAl alloy were investigated at room temperature and at 950K by compression tests. Lamellar spacing was varied from 20 to 590 nm, keeping the same grain size of 90 μm. The Hall–Petch relation holds between lamellar spacing and yield stress of the alloy. However, the yield stress saturates at a value of about 1 GPa below a critical lamellar spacing of about 100 nm. The Hall–Petch slope, critical lamellar spacing and saturation stress can be explained consistently by the pile-up model of dislocations at lamellar interfaces. Contrary to the beneficial effect on yield stress, the refinement of lamellar spacing deteriorates ductility of the alloy probably due to the suppression of the hard deformation modes.