Realizing high strength and toughness of gradient high-entropy alloy coating by in-situ interface reaction of FeCoCrNi/FeCoCrAl

In the pursuit of high performance development of alloy materials, it is a long-standing problem to enhance strength and toughness simultaneously. In this study, by selecting heterogeneous high-entropy alloy (HEA) materials and conducting structural design and laser process optimization, an external-hard internal-tough HEA composite coating with an in-situ dual-phase interface layer was successfully prepared. For the microstructure, the phase structures at the top, middle, and bottom of the coating are single-phase body-centered cubic (BCC), dual-phase BCC/face-centered cubic (FCC), and single-phase FCC, respectively. Among them, the dual-phase interface layer gives priority to the FCC phase (79.4 %), supplemented by the BCC phase (16.7 %). In terms of mechanical properties, the hardness of the coating from the top to the bottom is 9.85 GPa, 5.53 GPa, and 4.86 GPa, respectively. As demonstrated by employing the three methods of K, H/E, and H3/E2, the HEA composite coating has favorable integrated characteristics of strength and toughness. Meanwhile, due to the in-situ generated dual-phase interface layer, the structural and performance differences between the high-hardness layer and the high-toughness layer are effectively alleviated, and the stress concentration is reduced, thus stabilizing the overall structure of the coating. Hence, the HEA composite coating designed and prepared in this study possesses better erosion resistance (mass erosion rate = 0.141 × 10−3 g.cm−2 s−1), tribological properties (wear rate = 0.30 × 10−6 mm3/(N · m)), and impact resistance (AKU = 103.5 ± 2.8 J). The study results can provide new methods and new theories for new HEA composite coatings with integrated strength and toughness, and can be used in guiding the development and design of similar HEA composite coating structures.