Abstract
High-entropy alloys (HEAs) are novel solid solution strengthening metallic materials, some of which show attractive mechanical properties. This paper aims to reveal the effect of adding small atomic boron on the interstitial solid solution strengthening ability in the laser cladded CoCrFeNiAlxCu0.7Si0.1By (x = 0.3, x = 2.3, and 0.3 ≤ y ≤ 0.6) HEA coatings. The results show that laser rapid solidification effectively prevents brittle boride precipitation in the designed coatings. The main phase is a simple face-centered cubic (FCC) matrix when the Al content is equal to 0.3. On the other hand, the matrix transforms to single bcc solid solution when x increases to 2.3. Increasing boron content improves the microhardness of the coatings, but leads to a high degree of segregation of Cr and Fe in the interdendritic microstructure. Furthermore, it is worth noting that CoCrFeNiAl0.3Cu0.7Si0.1B0.6 coatings with an FCC matrix and a modulated structure on the nanometer scale exhibit an ultrahigh hardness of 502 HV0.5.
Highlights
It is well known that interstitial solutes can greatly improve the solution-strengthening effect of alloys and have less influence on the fracture toughness in comparison with second phase reinforcement
It was found that all the prepared high entropy alloys (HEAs) coatings are mainly composed of single solid solution phase, while other complex precipitated phases may exist with very low content and cannot be detected by X-ray diffractometer (XRD)—a desirable result
It could be found that the deviation tendency is higher in the Al0.3 By component than that in the Al2.3 By component; this may be attributed to the higher space occupied by octahedral interstice in the face-centered cubic (FCC) lattice compared to the body-centered cubic (BCC) lattice
Summary
It is well known that interstitial solutes can greatly improve the solution-strengthening effect of alloys and have less influence on the fracture toughness in comparison with second phase reinforcement. Boride precipitation seems unavoidable in traditional alloys, owing to the strong binding energy between small atomic boron and metallic elements [1]. Newly designed high entropy alloys (HEAs) with multi-principal elements are a breakthrough to the conventional alloying concept [2,3]. Several studies have shown that some HEAs are composed of simple solid solution phases with face-centered cubic (FCC) or body-centered cubic (BCC) crystal structure after solidification due to their high mixing entropy values. It is reckoned that the solid solution strengthening effect plays a key role in the high strength, high hardness, and high wear resistance properties of the HEAs
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