Influence of interlayer temperature on microstructure and mechanical properties of TiAl alloys in wire and arc additive manufacturing

TiAl intermetallics have attracted widespread attention in the aerospace and automotive fields. This study fo-cuses on the in-situ fabrication of TiAl alloys by auxiliary wire gas metal arc (GMA) additive manufacturing in which pure Ti and Al wires are melted to form a eutectic molten pool. The effects of interlayer temperature on forming characteristics, microstructure, and mechanical properties of TiAl alloys were studied, i.e., 30, 170, 330, and 500 degrees C. As the interlayer temperature increases, the macro-cracks gradually disappear, the layer width in-creases, and the layer height decreases. The center and lower parts of the homogeneous zone in the middle region present dendritic and interdendritic gamma phases. However, these parts exhibit equiaxed alpha 2/gamma nearly-lamellar col-onies and massive gamma m phase at an interlayer temperature of 500 degrees C. The thicknesses of alpha 2/gamma fully-lamellar colonies in the homogeneous zone increase as the interlayer temperature increases. With the increasing interlayer tem-perature, the total average microhardness first decreases and then increases, the compressive strength mainly presents a decreasing trend, and the compression rate increases first and then decreases. The maximal compressive strengths in the vertical and horizontal directions are 1802.5 and 1814.3 MPa, respectively. By changing the interlayer temperature from 30 to 330 degrees C, the compression rates in both directions increase by 11.8 % and 13.4 %, respectively.