Microstructure stability of Ti₂AlN/Ti-48Al-2Cr-2Nb composite at 900 °c

Microstructure stability of in situ synthesized Ti₂AlN/Ti-48Al-2Cr-2Nb composite during aging at 900 °C was investigated by XRD, OM and TEM, and the unreinforced Ti-48Al-2Cr-2Nb alloy was also examined for comparison. The result showed that in the TiAl alloy, α₂ lamellae thinned and were broken down, and became discontinuous with increasing aging time. The decomposition of α₂ lamella to γ which was characterized by parallel decomposition and breakdown of α₂ lamellae led to the degradation of the lamellar structure. While in the composite, lamellar structure remained relatively stable even after aging at 900 °C for 100 h. No breakdown of α₂ lamellae except parallel decomposition and precipitation of fine nitride particles was observed. The better microstructural stability of the composite was mainly attributed to the precipitation of Ti₂AlN particles at the α₂/γ interface which played an important role in retarding the coarsening of lamellar microstructure in the matrix of composite.