Microstructural evolution in silicon alloyed gamma-Ti-Al alloys after thermomechanical processing

The microstructures of silicon alloyed gamma-Ti-Al alloys containing silici de particles have been studied after thermomechanical treatments to investi gate microstructural evolution. Important parameters including temperature forging strain, and sequence of thermomechanical treatments were systematic ally studied. Isothermal forging below the eutectoid temperature resulted i n inhomogeneous dynamic recrystallisation with fine equiaxed grains in recr ystallised areas and residual alpha(2) + gamma lamellae elsewhere. Eutectic silicides play an important role in destruction of the as cast structure b y promoting dynamic recrystallisation during deformation and static recryst allisation on subsequent annealing. There is evidence that silicon, in solu tion, also enhances recrystallisation. The presence of fine silicides produ ced by precipitation in the solid state restricts fire size of grains produ ced by both dynamic and static recrystallisation. Silicon also alter's sign ificantly the phase equilibrium between the alpha and gamma phases.