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Deformation-induced martensitic transformation in Fe-Co-Ni-Cr-Mn high entropy alloy (HEA) thin film with nanocolumnar growth feature are revealed to readily occur at intermediate deposition power rather than low and high deposition power ranges. The high probability of deformation-induced martensitic transformation from face-centered cubic (FCC) to hexagonal close-packed (HCP) phase in 150 W-film results in low nanoindentation hardness and compressive yield strength, in comparison with 60 W- and 210 W-films. Dependence of the martensitic transformation probability has been explained in terms of the competition between grain size effect and nanocolumn cohesion effect on the phase metastability. The increased grain size with deposition power favors the mechanical instability of FCC parent phase caused by the weakened slip obstruction, while the enhanced nanocolumn cohesion with deposition power hinders the formation of HCP martensite due to the increased activation energy for martensitic transformation. The grain size effect is dominated over the cohesion between nanocolumn at low deposition power range, while column cohesion effect is dominant at high deposition power range, which gives rise to the crossover of FCC-to-HCP with deposition power. This work might provide a deeper understanding in phase metastability of sputtered films, for instance, the effect of deposition power on deformation-induced martensitic transformation. • The deformation-induced martensitic transformation is observerd in Fe-Co-Ni-Cr-Mn high entropy alloy (HEA) thin film. • The crossover of FCC-to-HCP with deposition power is discovered, in which the high probability exists in 150 W-film.; • The elucidation of the underlying mechanisms for this unusual deformation-induced martensitic transformation behavior. [ABSTRACT FROM AUTHOR]

The corrosion behaviors of (CoNiV) 100−x Al x (x = 0, 3, 5 at.%) MEAs in NaCl and H 2 SO 4 solutions have been systematically investigated. The corrosion properties of CoNiV alloys with different average grain sizes in the Cl−1 ions containing solution seems to be related to the proportion of (100) orientation plane. The Al addition results in the enhanced corrosion resistance in NaCl solution and no obvious difference in H 2 SO 4 solution. Oxides of V are the main components of the passive films formed on CoNiV and (CoNiV) 97 Al 3 alloys. The enrichment of the V- and Al- oxides in the passive film on the (CoNiV) 95 Al 5 alloy improves corrosion resistance. • Al addition enhances corrosion resistance of CoNiV MEA in 3.5 wt.% NaCl solution. • The corrosion of CoNiV MEA is related to the proportion of (100) orientation plane. • The concentration of ions in the solution states selective dissolution did not occur. • The passive ability of CoNiV MEA is similar to the nature of V element. • The V and Al oxides enriched layer on (CoNiV) 95 Al 5 MEA improves corrosion resistance. [ABSTRACT FROM AUTHOR]

Via tuning deposition power, a series of Co-Ni-V medium entropy alloy thin films, growing in a nanocolumn manner, with different microstructures and morphologies were synthesized. With increasing fluence, both the crystallinity and nanocolumn size experienced a process of first increasing and then decreasing, controlled by the adatom surface diffusion vs. deposition rate competition. Meanwhile, continuous strengthening with fluence was ascribed to improved bonding and reduced fraction of boundary at low fluence and amorphization reinforcement effect in high fluence range. [Display omitted] [ABSTRACT FROM AUTHOR]

• Nanostructured Co-Ni-V thin films are prepared at various substrate temperature. • Amorphous structure for 473 K and nanocrystalline structure for 573 K and 673 K. • Better mechanical properties for films deposited at higher temperature. • Improved columnar interface bonding and nanocrystallization are the main reason. • Both nanograin boundary and high-density stacking faults strengthening at play. In this work, amorphous and nanocrystalline Co-Ni-V medium entropy alloy (MEA) thin films were prepared by magnetron sputtering via tuning substrate temperature. The nanocrystalline Co-Ni-V thin film deposited at 673 K containing ultrahigh-density stacking faults was found to be more superior to amorphous Co-Ni-V thin film deposited at 473 K and some other face-centered cubic (fcc)-structured materials by exhibiting higher hardness of ∼9.5 GPa and yield strength of ∼4.0 GPa. The strengthening mainly stems from various defects including nanograin boundaries and high-density stacking faults, which were found to possibly serve as strong impediments to dislocation motion. Moreover, the weak boundaries between adjacent nanocolumns with relatively weak bonding is eliminated with increasing substrate temperature, which also contributes to the enhanced strength/hardness for the nanocrystalline Co-Ni-V film as compared with amorphous Co-Ni-V film. The prepared ultra-strong nanostructured Co-Ni-V MEA thin film exhibits high yield strength and micro-compressive plasticity (over 50%), suggestive of the relatively strong material among some reported fcc-structured metals and alloys. These results on nanostructured Co-Ni-V MEA thin film demonstrate that besides refining grain, interface strengthening, i.e., improving nanocolumn interface bonding via substrate temperature and introducing high-density stacking faults via rapid cooling of vapor deposition, could be considered when designing high strength alloy thin films for potential micro-electron-mechanical system applications. [ABSTRACT FROM AUTHOR]