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Improving the mechanical properties of high-entropy alloys (HEAs) with a face-centered cubic (fcc) structure is critical for their potential applications. In this work, a Fe-Co-Ni-Cr-Mn thin film was prepared and deposited with a power of 360 W. This alloy thin film exhibits a dual-phase microstructure consisting of a fcc matrix and sigma phase (σ phase) precipitates. The 360 W-film shows ultra-high strength-ductility synergy, with a hardness of 10.4 GPa, yield strength of 6.2 GPa, and a fracture strain of ∼25 % (micro-pillar compression tests). The excellent mechanical properties can be mainly attributed to the grain size effect, the hardening effect of the σ precipitates, and deformation twinning. Moreover, this alloy thin film exhibits excellent tribological performances and corrosion resistance. Our results demonstrate high potential of the dual-phase HEA thin film for industrial applications as high-performance protective coating materials. • Fe-Co-Ni-Cr-Mn thin film exhibited a dual phase microstructure consisting of a fcc matrix and σ phase precipitates. • Ultra-high strength-ductility synergy with hardness of 10.4 GPa, yield strength of 6.2 GPa, and fracture strain of ~25 %. • Mechanical properties are attributed to grain size effect, σ precipitate hardening effect, and deformation twinning. • This alloy thin-film exhibits excellent tribological performances and corrosion resistance. [ABSTRACT FROM AUTHOR]

Films with a combination of high strength, large ductility, and high thermodynamic stability are always pursued for industrial applications. Here, we prepared the amorphous-crystalline Ti-Zr-Hf-Nb-Ta/Co-Ni-V nanolaminate with hardness and yield strength of 7.4 GPa and 3.8 GPa, and large deformability of ∼70%. The ductility is attributed to two aspects. One is the Ti-Zr-Hf-Nb-Ta/Co-Ni-V layer interfaces acted as barriers to obstruct the propagation of nanocracks at the heavily deformed stage. Another is that amorphous layers acted as dislocation sinks promoting the dislocations to get annihilated when undergoing plastic flow, maintaining the plastic deformability of the crystalline layers. After annealing at 873 K for 1 h, the Co-Ni-V layer changes to a V-rich amorphous layer with minor nanocrystals, while the Ti-Zr-Hf-Nb-Ta layer transforms to a Ni-rich amorphous layer, due to the diffusion of Co and Ni. This chemical partitioning and consequent amorphization lead to the enhanced hardness and yield strength of 9.4 GPa and 4.5 GPa, but low ductility. In addition, the microstructure and mechanical properties of the nanolaminate can be further optimized by adjusting substrate temperature, layer thickness, and annealing process. The findings provide a new avenue for improving the mechanical properties of nanolaminates in a controllable manner. ● Nanolaminate with excellent hardness and yield strength of 7.4 GPa and 3.8 GPa, and large deformability of ∼70% is prepared. ● Layer interfaces obstruct the propagation of nanocracks, and amorphous layers promote the dislocation annihilation. ● Mechanical properties of nanolaminate can be tuned by the layer thickness and deposition temperature. [ABSTRACT FROM AUTHOR]

Refractory Ti-Zr-Hf-Nb-Ta high entropy alloy (HEA) attracts numerous attention owing to its ductility at room temperature and biomedical application. Extensive work on mechanical properties of this alloy has been done in the bulk alloy, however, there is limited work dedicated to the investigation in thin film. In this work, a series of Ti-Zr-Hf-Nb-Ta thin films with the deposition power from 60 W to 360 W and film thickness of ∼1.5–2.0 µm are prepared. The film morphology, microstructure and nano-mechanical properties can be controlled by the deposition power and film thickness. With increasing deposition power, the amorphous fraction experiences a process of first decreasing and then increasing, and finally decreasing for 2.0 µm-thick film (saturation for 1.5 µm-thick film). The competition between adatom diffusion, available time and elevated temperature during deposition decides the phase selection in various deposition power range. At low deposition power range, adatom diffusivity is dominant, leading to the increased crystallinity with power. At intermediate power range, available time for atomic rearrangement controls phase selection, causing the regaining of amorphous phase. The elevated temperature effect is responsible for re-devitrification at high deposition power range. Furthermore, thicker film possesses higher crystallinity than thinner counterpart, and the crystallinity difference between ∼1.5 µm- and ∼2 µm-thick films at the same deposition power depends on atomic fluence. Also, continuous strengthening from 60 W- to 360 W-thin film are observed, which can be attributed to improved adhesion between nanocolumns at low deposition power range and bombardment effect at high deposition power range. This work sheds a comprehensive and profound light on deposition power-structure and film thickness-structure correlations. • The temperature during deposition gradually increases and saturates, and maximum temperature rises with deposition power. • The competition between adatom diffusion, available time and elevated temperature determines the phase selection. • Crystallinity difference between ∼1.5 µm- and ∼2 µm-thick films depends on deposition power. [ABSTRACT FROM AUTHOR]

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]

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]