Modification of transverse creep behavior of an orthorhombic titanium aluminide based Ti–22Al–23Nb/SiCf composite using heat treatment

The feasibility of improving the transverse creep properties of an orthorhombic titanium aluminide matrix composite reinforced with unidirectional SCS-6 SiC fiber via modification of matrix microstructure was investigated using post-consolidation heat treatments. A Ti–22Al–23Nb/SCS-6 4-ply composite was subjected to heat treatments which consisted of solutionizing at either above or below the β-transus temperature of the matrix alloy, followed by controlled cooling and aging within the orthorhombic (O) phase field. Mechanical testing showed that the transverse (90°) creep behavior of the titanium alloy composite in the temperature range 650–760°C is significantly improved by a supra-transus solution heat treatment followed by the aging, without any adverse effect on the longitudinal (0°) tensile strength of the composite. This improvement in the creep response was attributed to an increase in the volume fraction of the orthorhombic phase and the lath morphology of the (O+β) two-phase regions in the matrix microstructure. The effect of sub-transus heat treatment was less pronounced and the transverse creep resistance of the composite decreased with increasing volume fraction of the α2 phase in the matrix. Examination of creep ruptured 90° composite specimens showed that transverse creep damage in the form of fiber/matrix interfacial debonding occurs predominantly at very closely spaced or touching fibers.