Effect of carbon nanotube content on the microstructure and mechanical properties of CNTs/TiAl alloys

TiAl alloys are ideal high-temperature structural materials for aerospace applications. However, their ductility, bending strength and machinability are poor at room temperature, thus severely limiting their practical application. In this study, carbon nanotubes (CNTs) were used as additives, and Ti-48Al-2Cr-8Nb was used as the original powder to prepare CNTs/TiAl alloys by employing spark plasma sintering. The effects of different CNT contents on the microstructure, hardness and bending strength of CNTs/TiAl alloys were investigated. The results indicated that CNTs reacted with the matrix to generate granular TiC and Ti2AlC reinforced phases stacked into bands at the grain boundaries, limiting grain growth. The Ti2AlC phase content increased with increasing CNT content. When the contents of the TiC and Ti2AlC phases were high, agglomeration occurred, leading to defects such as pits and cracks on the surface, which explains the weakened mechanical properties of the CNTs/TiAl alloys at room temperature. When the CNT content was 0.4 wt%, the average grain size was approximately 32 mu m under the effects of fine grain strengthening and second phase strengthening. Moreover, the mechanical properties of the composite were the best at room temperature. The Vickers hardness and bending strength at room temperature were 377 HV and 879 MPa, respectively, and the compressive strength and strain were 2554 MPa and 31.86%, respectively. The fracture mode was mainly transgranular.