- Award ID(s):
- 1810343
- NSF-PAR ID:
- 10378087
- Date Published:
- Journal Name:
- Nanomaterials
- Volume:
- 12
- Issue:
- 19
- ISSN:
- 2079-4991
- Page Range / eLocation ID:
- 3371
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
The microstructure, Vickers hardness, and compressive properties of novel low-activation VCrFeTaxWx (x = 0.1, 0.2, 0.3, 0.4, and 1) high-entropy alloys (HEAs) were studied. The alloys were fabricated by vacuum-arc melting and the characteristics of these alloys were explored. The microstructures of all the alloys exhibited a typical morphology of dendritic and eutectic structures. The VCrFeTa0.1W0.1 and VCrFeTa0.2W0.2 alloys are essentially single phase, consisting of a disordered body-centered-cubic (BCC) phase, whereas the VCrFeTa0.2W0.2 alloy contains fine, nanoscale precipitates distributed in the BCC matrix. The lattice parameters and compositions of the identified phases were investigated. The alloys have Vickers hardness values ranging from 546 HV0.2 to 1135 HV0.2 with the x ranging from 0.1 to 1, respectively. The VCrFeTa0.1W0.1 and VCrFeTa0.2W0.2 alloys exhibit compressive yield strengths of 1341 MPa and 1742 MPa, with compressive plastic strains of 42.2% and 35.7%, respectively. VCrFeTa0.1W0.1 and VCrFeTa0.2W0.2 alloys have excellent hardness after annealing for 25 h at 600–1000 °C, and presented compressive yield strength exceeding 1000 MPa with excellent heat-softening resistance at 600–800 °C. By applying the HEA criteria, Ta and W additions into the VCrFeTaW are proposed as a family of candidate materials for fusion reactors and high-temperature structural applications.more » « less
-
Zinc (Zn) alloys, particularly those incorporating magnesium (Mg), have been explored as potential bioabsorbable metals. However, there is a continued need to enhance the corrosion characteristics of Zn-Mg alloys to fulfill the requirements for biodegradable implants. This work involves a corrosion behavior comparison between severe-plastic-deformation (SPD) processed cast Zn-Mg alloys and their hybrid counterparts, having equivalent nominal compositions. The SPD processing technique used was high-pressure torsion (HPT), and the corrosion behavior was studied as a function of the number of turns (1, 5, 15) for the Zn-3Mg (wt.%) alloy and hybrid and as a function of composition (Mg contents of 3, 10, 30 wt.%) for the hybrid after 15 turns. The results indicated that HPT led to multimodal grain size distributions of ultrafine Mg-rich grains containing MgZn2 and Mg2Zn11 nanoscale intermetallics in a matrix of coarser dislocation-free Zn-rich grains. A greater number of turns resulted in greater corrosion resistance because of the formation of the intermetallic phases. The HPT hybrid was more corrosion resistant than its alloy counterpart because it tended to form the intermetallics more readily than the alloy due to the inhomogeneous conditions of the materials before the HPT processing as well as the non-equilibrium conditions imposed during the HPT processing. The HPT hybrids with greater Mg contents were less corrosion resistant because the addition of Mg led to less noble behavior.
-
A new type of high-entropy alloy, a nitride-based (AlCrTiZrMo)N/ZrO2 nano-multilayered film, was designed to investigate the effect of ZrO2 layer thickness on the microstructure, mechanical properties, and thermal stability. The results show that when the thickness of the ZrO2 layer is less than 0.6 nm, it can be transformed into cubic-phase growth under the template effect of the (AlCrTiZrMo)N layer, resulting in an increased hardness. The (AlCrTiZrMo)N/ZrO2 film with a ZrO2 layer thickness of 0.6 nm has the highest hardness and elastic modulus of 35.1 GPa and 376.4 GPa, respectively. As the thickness of the ZrO2 layer further increases, ZrO2 cannot maintain the cubic structure, and the epitaxial growth interface is destroyed, resulting in a decrease in hardness. High-temperature annealing treatments indicate that the mechanical properties of the film decrease slightly after annealing at less than 900 °C for 30 min, while the mechanical properties decrease significantly after annealing for 30 min at 1000–1100 °C. The hardness and elastic modulus after annealing at 900 °C are still 24.5 GPa and 262.3 GPa, showing excellent thermal stability. This conclusion verifies the “template” effect of the nano-multilayered film, which improves the hardness and thermal stability of the high-entropy alloy.more » « less
-
Al x CoCrFeNi High Entropy Alloys (HEAs), also referred to as multiprincipal element alloys, have attracted significant interest due to their promising mechanical and structural properties. Despite these attributes, Al x CoCrFeNi HEAs are susceptible to phase separation, forming a wide range of secondary phases upon aging, including NiAl–B2 and Cr-rich phases. Controlling the formation of these phases will enable the design of age-hardenable alloys with optimized corrosion resistance. In this study, we examine the critical role of Al additions and their concentration on the stability of the CoCrFeNi base alloy, uncovering the connections between Al composition and the resulting microstructure. Addition of 0.1 mol fraction of Al destabilizes the single-phase microstructure and results in the formation of Cr-rich body-centered-cubic (bcc) phases. Increasing the composition of Al (0.3–0.5 mol fraction) results in the formation of more complex coprecipitates, NiAl–B2 and Cr-rich bcc. Interestingly, we find that the increase of the Al content stimulates the formation of NiAl–B2 phases, increases the overall density of secondary phases, and influences the content of Cr in Cr-rich bcc phases. Density functional theory calculations of simple decomposition reactions of Al x CoCrFeNi HEAs corroborate the tendency for precipitate formation of these phases upon increased Al composition. Additionally, these calculations support previous results, indicating the base CoCrFeNi alloy to be unstable at low temperature. This work provides a foundation for predictive understanding of phase evolution, opening the window toward designing innovative alloys for targeted applications.more » « less
-
The mechanical bonding of dissimilar metals though the application of high‐pressure torsion (HPT) processing is developed recently for introducing unique ultrafine‐grained alloy systems involving microstructural heterogeneity leading to excellent mechanical properties. Considering further developments of the processing approach and the produced hybrid materials, the size effect on microstructural evolution and micromechanical responses of the mechanically bonded Al–Mg systems is evaluated. In practice, processing by HPT is conducted at room temperature on the separate Al and Mg disks having 25 mm diameter under 1.0 GPa at 0.4 rpm, and the results are compared with the mechanically bonded Al–Mg system having 10 mm diameter. The Al–Mg disks having 25 mm diameter show a general hardness distribution where low hardness appears around the disk centers, and it increases at the disk peripheries. Nanoindentation measurements demonstrate that there is excellent plasticity at the edges of the Al–Mg system with 25 mm diameter. The Al–Mg system with both 10 and 25 mm diameters show a consistent trend of hardness evolution outlining an exponential increase of hardness with increasing equivalent strain. The results are anticipated to provide a conceptual framework for the development and scale‐up of the HPT‐induced mechanical bonding technique.