Developing L2₁-Co₂TiAl Precipitate-Strengthened Ferritic Medium Entropy Alloys with Excellent High-Temperature Strength

We designed new ferritic medium entropy alloys to improve the high-temperature strength by forming L21-Co2TiAl precipitates, known as having better high-temperature properties than the Ni2TiAl structure. Specifically, the Ni element has been replaced with the Co element. Moreover, the Ti element has been adjusted since the structural evolutions of precipitates, such as composition, lattice misfit and size rely on the Ti content. For instance, the addition of 2 wt% Ti forms a semi-coherent Co2TiAl precipitate with a relatively low density of misfit dislocations. More Ti addition up to 6 wt % leads to an increased lattice misfit, which results in a reduction of the elastic strain field around the precipitates. It was found that the semi-coherent interface with a high level of the elastic strain field (2 wt % Ti), as compared to the precipitates with a high amount of misfit dislocations (4 and 6 wt % Ti), plays an important role in enhancing the mechanical properties at 973 K.