Microstructure and magnetic properties of CoCrCuFeNiTi high entropy alloy coatings based on plasma surface alloying technology

The present study explored the correlation between microstructure and magnetic properties of CoCrCuFeNiTi HEA coatings prepared on Si substrate using plasma surface alloying technology. The coatings exhibited a mixture of Fe2Ti, FeCr, FCC, BCC phase and the amorphous/crystalline structure. The mircrostructure changed with the deposition duration, resulting in different coercivity. The crystalline part of the coating deposited for 1.0 h contained up to 81.9 % of Fe2Ti and more amorphous structure, causing a coercivity of 53.1 Oe. Fe2Ti showed a preferred orientation along the (201) direction, leading to columnar structure in the coatings and the vertical growth of columnar structure caused an increase in coating thickness. As the deposition duration increased to 1.5 h, a reduction of Fe2Ti and amorphous structure, as well as an increase of defects such as grain boundaries allowed the coercivity to increase to 104.5 Oe. FCC, FeCr, and BCC phase increased as increase of deposition duration, and the relative content of BCC phase increased to a maximum of 8.3 % at a deposition duration of 2.0 h. An increase of grain size and nonuniform distribution of different phases in coating led to a reduction of coercivity to 82.9 Oe. However, the vertical growth of the columnar structure made the coating to exhibit obvious shape anisotropy and the coercivity increased to 118.3 Oe when deposition duration was 3.0 h. The coercivity of HEA coating prepared by plasma surface alloying technology were sensitive to microstructure, and the deposition duration needed to be controlled to obtain the desired coercivity.