The effects of heat treatment on the microstructure and mechanical property of laser melting deposition γ-TiAl intermetallic alloys

Ti–47Al–2.5V–1Cr and Ti–40Al–2Cr (at.%) intermetallic alloys was fabricated by the laser melting deposition (LMD) manufacturing process. The microstructure was characterized by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The room-temperature (RT) tensile properties and Vickers hardness of the as-deposited and heat-treated specimens were evaluated on longitudinal directions. Results shows that full density columnar grain with fully lamellar (FL) microstructure consisted of γ-TiAl and α2-Ti3Al was formed in the as-deposited γ-TiAl samples. The room-temperature tensile strength of the as-deposited Ti–47Al–2.5V–1Cr alloy is up to approximately 650 MPa in the longitudinal direction and 600 MPa for the as-deposited Ti–40Al–2Cr alloy, while the tensile elongation is approximately 0.6% at most. Different microstructure types were obtained in the Ti–47Al–2.5V–1Cr and Ti–40Al–2Cr alloy after heat treatment. The stress–strain curve and the tensile fracture sub-surface indicate that the fracture manner of the as-deposited and heat-treated specimens was inter-granular manner.