Additive manufacturing of micro/nano multiphase synergistically reinforced Ti-55Al-7.5Nb with a reticular boundary precipitate via direct laser deposition

Abstract

Additive manufacturing, with features of micro-area metallurgy and rapid solidification, has become an effective way to construct complex components with high efficiency and production flexibility. Hereby, this study presents a micro/nano multiphase synergistically reinforced Ti-55Al-7.5Nb/Ti 2 AlN-Ti 5 Si 3 metal–matrix composite (TiAl MMC) synthesized via direct laser deposition. The as-prepared TiAl MMCs exhibit homogeneously equiaxed grains and no cracks, compared with the coarse columnar microstructure and macro/micro cracks of Ti-55Al-7.5Nb alloy. The grain size of the TiAl MMCs increases in the form of a parabola with increase of the laser power, and also increases from the bottom to the top along the building direction with fixed laser power. Precipitates of Ti 2 AlN and Ti 5 Si 3 can alleviate the texture index, and thus facilitate an in situ production of isotropic MMCs. Meanwhile, TiAl MMCs feature excellent compressive and high-temperature (900 °C) tensile strength, resulting from the precipitates of rod-like Ti 2 AlN dispersed inside the grains, and the micro/nano-Ti 5 Si 3 reticularly distributed at the grain boundaries (GBs). The micro/nano multiphase reinforcement could help guide the additive manufacturing of preparing reticular-boundary-reinforced cracks-free TiAl MMCs, which feature controllable microstructures and enhanced mechanical properties. • Novel TiAl MMCs, prepared by in situ additive manufacturing, exhibit even equiaxed grains but no Al segregation or cracks. • Precipitates, the same orientation relationship with matrix, tune TiAl MMCs microstructures that show lower texture index. • The grain size of prepared TiAl MMCs varies with laser powers was revealed by a combination of experiment and simulation.