Effect of Manufacturing Conditions and Al Addition on Inclusion Characteristics in Co-Based Dual-Phase High Entropy Alloy

Abstract

Three Co-based dual-phase high-entropy alloys (HEAs) were produced by different manufacturing conditions: arc-melting with Ar protection (Ar-HEA), vacuum induction melting in Al2O3 crucible (Cr-HEA) and vacuum induction melting with 0.5 at. pct Al (Al-HEA), which resulted in different levels of impurity elements and inclusion characteristics. The inclusions that precipitated in different HEA samples were investigated through an electrolytic extraction process and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) characterization. The results showed that Mn(S,Se) inclusions were presented in all three alloys. MnCr2O4 inclusions were presented only in Ar-HEA, pure Al2O3 inclusions were presented in Cr-HEA and Al-HEA, and Mn–Cr–Al–O inclusions were also found in Al-HEA. Thermodynamic calculation software FactSage and Thermo-calc were used to predict the inclusion formations of the HEAs, which showed a good agreement with the experimental findings. The stable inclusions can transform from MnCr2O4 to Mn(Cr,Al)2O4 and then to pure Al2O3 with the increase of Al content. The inclusions in Al-containing HEA are spinel or Al2O3 depending on the content levels of Al and O. It is proposed that the formation of spinel and Al2O3 inclusions can be avoided in liquid HEA when the O content is controlled to be very low, which can result in smaller-sized inclusions. Moreover, the calculated coagulation coefficient of spinel inclusions is close but lower than that of Al2O3 inclusions. The collision growth of inclusions was affected by a combination of physical parameters of HEA and inclusions as well as the inclusion size and amount. Graphical Abstract

Strengthening and Toughening of the Co34Cr32Ni27Al3.5Ti3.5 Alloy Through Coherent L12 Nanoprecipitates

“…[29] Since reactive elements are present in most of the castings examined, excluding these inclusions in regular melting procedures is difficult. [30][31][32][33] The reactive element Al, which interacts with N 2 and O 2 more effectively, is believed to produce an inclusion defect in casting. Therefore, it is reasonable that the black precipitates were an inclusion defect.…”

Effect of hafnium and molybdenum addition on inclusion characteristics in Co-based dual-phase high-entropy alloys

“…MnCr 2 O 4 oxide inclusions are commonly found in CrMnFeCoNi alloys [14][15][16][17], and their influence on mechanical properties has been ignored because of their small volume fraction. Yu et al [18] reported that stable MnO-SiO 2 was formed in Si-added CoCrFeMnNi instead of the harmful MnCr 2 O 4 , which greatly enhanced the corrosion resistance of the alloy. Similarly, the stable inclusions can transform from MnCr 2 O 4 inclusions to Mn(Cr,Al) 2 O 4 inclusions and then to pure Al 2 O 3 inclusions with increasing Al content in HEA [19].…”