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 degrees 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, a(2) lamellae thinned and were broken down, and became discontinuous with increasing aging time. The decomposition of a(2) lamella to gamma which was characterized by parallel decomposition and breakdown of a(2) lamellae led to the degradation of the lamellar structure. While in the composite, lamellar structure remained relatively stable even after aging at 900 degrees C for 100 h. No breakdown of a(2) 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 a(2)/gamma interface which played an important role in retarding the coarsening of lamellar microstructure in the matrix of composite.