Electron beam melted TiC/high Nb–TiAl nanocomposite: Microstructure and mechanical property

Abstract

To enhance the process stability and densification, semi-melt step has been introduced when fabricating the TiC/high Nb–TiAl nanocomposite via electron beam melting. The homogenous TiAl matrix microstructure with dispersed nano-scale carbides was realised. During the EBM melt, most TiC nanoparticles dissolved and Ti2AlC formed with near-spherical and rod-like shapes. The particles had an influence on solidification behaviour and the subsequent microstructural degradation. High Nb–TiAl nanocomposites with 1.2 wt% TiC addition exhibited a duplex microstructure with dispersed carbides, while a nearly lamellar microstructure (carbide-free) was found in samples with 0.6 and 0.8 wt% TiC. Furthermore, a lower scanning speed resulted in higher relative density, greater Al loss, increased α2-phase but reduced carbide fractions. The microhardness of 433 ± 10 HV0.2, ultimate tensile strength of 657 ± 155 MPa and fracture toughness of 8.1 ± 0.1 MPa√m in 1.2 wt% TiC/high Nb–TiAl nanocomposite processed by EBM are very promising. In addition, the compressive yield strength of 1085 ± 55 MPa, fracture strength of 2698 ± 34 MPa and strain to fracture of 26.1 ± 1.0%, are superior to those processed by conventional means. The strengthening and toughening mechanisms have been interpreted on the basis of crack path observation.