ABSTRACT
High entropy amorphous alloys (HEAAs) are materials that have received much attention in recent years. They exhibit many unique properties; however, research on their composition design method has not been deep enough. In this paper, we summarized some effective composition design strategies for HEAAs. By adjusting the atomic ratio from quinary bulk metallic glasses, Ti20Zr20Cu20Ni20Be20 HEAA with a high fracture strength of 2315 MPa was designed. By similar element addition/substitution, a series of Ti-(Zr, Hf, Nb)-Cu-Ni-Be HEAAs was developed. They possess good glass-forming ability with a maximum critical diameter of 30 mm. Combining elements from those ternary/quaternary bulk metallic glasses has also proved to be an effective method for designing new HEAAs. The effect of high entropy on the property of the alloy, possible composition design methods, and potential applications were also discussed. This paper may provide helpful inspiration for future development of HEAAs.
ABSTRACT
It is well known that the annealing process plays a key role in tuning the properties of Fe-based amorphous soft magnetic alloys. However, the optimal annealing process for a particular amorphous alloy is often difficult to determine. Here, Fe81.4B13.2C2.8Si1.8P0.8 and Fe82.2B12.4C2.8Si1.8P0.8 amorphous alloys (denoted as Fe81.4 and Fe82.2) were prepared to systematically study the effects of the annealing temperature and time on the soft magnetic properties. The results show that the optimum annealing temperature ranges of the Fe81.4 and Fe82.2 amorphous alloys were 623 K to 653 K and 593 K to 623 K, and their coercivity (Hc) values were only 2.0-2.5 A/m and 1.3-2.7 A/m, respectively. Furthermore, a characteristic temperature Tai was obtained to guide the choosing of the annealing temperature at which the dBs/dT begins to decrease rapidly. Based on the theory of spontaneous magnetization, the relationship between Tai and the optimum annealing temperature ranges was analyzed. When the annealing temperature was higher than Tai, the effect of the internal magnetic field generated by spontaneous magnetization on the relaxation behavior was significantly reduced, and the alloys exhibited excellent soft magnetic properties. It is worth indicating that when annealed at 603 K (slightly higher than Tai), the Fe82.2 amorphous alloys exhibited excellent and stable soft magnetic properties even if annealed for a long time. The Hc of Fe82.2B12.4C2.8Si1.8P0.8 amorphous alloys was only 1.9 A/m when annealed at 603 K for 330 min. This value of Tai is expected to provide a suggestion for the proper annealing temperature of other amorphous soft magnetic alloys.
ABSTRACT
The effect of deep cryogenic cycle treatment (DCT) on Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit-1) bulk metallic glass (BMG) prepared from high-purity raw materials was investigated. After DCT, no obvious rejuvenation of the samples was detected. With an increasing number of cryogenic cycles, the hardness of the samples first decreased and then increased, the room-temperature compression plasticity first increased and then generally remained unchanged, and the impact toughness underwent almost no obvious change. The absence of rejuvenation was attributed to the high fragility index (47-50) and high glass forming ability (GFA) of the material. As lower purity of the raw materials is expected in practical applications, DCT of Vit-1 BMG prepared from low-purity raw materials was also performed. After DCT, the samples prepared with the lower-purity raw materials were clearly rejuvenated, and the room-temperature mechanical properties improved significantly.Both the compression plasticity and impact toughness reached peak values after 5 cryogenic cycles. The initial impurities (including Y and O) had a complex and comprehensive effect on the deformation mechanism of the BMG during DCT. Our findings indicate that the structural heterogeneity, fragility index, and GFA of the BMG alter the effect of DCT.