Improvement in microstructure and high-temperature brittleness of laser-welded Ti-22Al-25Nb joints with the addition of TiB2 powder

A Review—Additive Manufacturing of Intermetallic Alloys Based on Orthorhombic Titanium Aluminide Ti2AlNb

“…Titanium alloys containing the O-phase developed based on the Ti-Al-Nb system usually contain 18–30% of Al and 12.5–30% of Nb [ 4 , 20 ]. The equilibrium phase composition of O-phase alloys is based on the isopleth sections of the Ti-Al-Nb phase diagram, which corresponds to constant Al content (22, 23, 25, 27.5 at%) and varied Nb content [ 21 , 22 , 23 , 24 ].…”

“…However, these powders have not yet been used for additive manufacturing due to their non-spherical shape. In addition, from 2008 to 2018, only Ti-22Al-25Nb powders were produced, and since 2018, more complex compositions that include Mo [ 20 , 64 , 65 , 66 ] and, in some cases, V, Zr, Si and Hf have been reported [ 12 , 55 , 56 ]. Note that the best combination of mechanical properties of AM orthorhombic titanium aluminides was obtained using pre-alloyed powders, rather than elemental powders, apparently due to the additional operations needed (mixing, spheroidization, mechanical alloying, etc.)…”

“…Numerous results on tensile mechanical properties at room temperature have been obtained [ 10 , 11 , 12 , 14 , 20 , 51 , 52 , 54 , 56 , 59 , 62 , 64 , 65 , 66 , 67 , 70 , 93 ] and less research is devoted to elevated temperatures of 650 °C [ 13 , 20 , 62 , 64 , 66 ] and 750 °C [ 59 ]. A wide range of values characterizes the strength and ductility of MAM O-phase alloys—from ultimate tensile strength (UTS) and elongation (EL) of 220 MPa and 0% after L-PBF [ 12 ] to 1258 MPa after heat treatment [ 13 ] and 25.7% after DED accompanied by point forging [ 54 ].…”

“…The authors of [ 70 ] considered the effects of the hatching distance (HD), inhomogeneity of the properties throughout the part height [ 10 ], the orientation of the sample on the building platform [ 52 ] and doping [ 20 ]. The superior properties for L-PBF were obtained at HD 0.12 and 0.16 mm in [ 70 ] ( Table 6 ).…”

“…However, considering the dispersion of properties, the values overlap in both directions ( Table 6 ). In [ 20 ], the effect of the TiB 2 addition to Ti 2 AlNb powder on the properties of welded joints of L-DED Ti-22Al-25Nb alloy was investigated ( Table 6 ). The highest strength and ductility of welded joints were achieved with a minimum fraction of TiB 2 of 3.1%.…”