Effect of Mechanical Alloying Modes on the Microstructure, Phase Composition, and Mechanical Properties of Powder High-Entropy Co-Cr-Fe-Ni-Ti Alloys

The influence of the duration of mechanical alloying (15, 30, 45, and 60 min), the Ti content (4, 8, and 12 at %), and the method of its adding (in the form of Ti metal powder or TiH2 powder) on the microstructure, phase composition, and mechanical properties of Co-Cr-Fe-Ni-Ti high-entropy alloys (HEAs) manufactured by powder technology has been studied. It has been established that the structure of powder mixtures attains a high degree of homogeneity within 30 min of mechanical alloying and contains 43 and 57% of BCC and FCC phases, respectively. In the process of subsequent hot pressing, the structure is further homogenized, and the FCC phase content increases, reaching 99% in the alloys manufactured with TiH2. The optimal combination of mechanical properties is attained in the CoCrFeNiTi8(TiH2): the hardness is 74 HRA, and the ultimate tensile and bending strength are 690 and 1255 MPa, respectively. In the group of alloys made with Ti metal powder, the strength, hardness, density, and wear resistance grow, and brittleness decreases. To further improve the mechanical properties of Co-Cr-Fe-Ni-Ti HEAs manufactured using powder technology, it is necessary to optimize the sigma-phase content and decrease the oxynitride phase content, which can be achieved both by adjusting the composition and by improving the modes of mechanical alloying.