Refining Ti2AlC in the liquid region and improving the microstructure and mechanical properties of Ti-46Al-8 Nb-2.6 C alloy by adding Y

To reveal the refinement mechanism of Ti2AlC particle by in -situ Y2O3 in the liquid region and the improvement mechanisms of refined Ti2AlC in solid-state phase transformation process, Ti-46Al-8 Nb-2.6 C-xY alloys were prepared. Microstructures were observed by SEM, XRD and TEM, and the mechanical properties were examined. Calculated results indicated that the phase boundary energy of in -situ Y2O3 combined with TiC was low in the liquid region. TiC particle was formed initially, followed by Y2O3 particle. The Y2O3 particle moved to the surface of TiC particle to inhibit its growth, which left small -sized TiC nucleation substrate for the formation of Ti2AlC. The orientation relationship was [2200]Ti2AlC//[066]Y2O3. A stepped atomic diffusion zone was formed in the interface of Y2O3 and Ti2AlC to inhibit lateral and longitudinal growth of Ti2AlC. As Y increased from 0.02 to 0.1 at%, the average aspect ratio of Ti2AlC particles decreased from 7.7 to 3.4, the Ti2AlC content with the aspect ratio of 1-5 increased from 13.7 to 91.3%. The lamellar colony size and lamellar spacing reduced from 47.5 to 26.0 mu m and 0.74 to 0.58 mu m, respectively. Both Y2O3 and refined Ti2AlC served as heterogeneous nucleation sites and inhibited the lateral thickening rate of gamma lath. The Y -type YAl2 phase was formed as Y content exceeded 0.1 at%. The compressive strength and Vickers hardness were improved from 1801 to 2201 MPa and 443.2 to 464.5 HV, respectively. However, the subsequent decrease in strength was caused by the embrittlement of grain boundary after the precipitation of YAl2 phase. The significant refinement of Ti2AlC and lamellar colony by insitu Y2O3 and the precipitation strengthening of Ti2AlC contributed to the mechanical properties.