Hexagonal close-packed (HCP) magnesium alloys are widely used in automotive and aerospace industries due to their low density and high specific-strength. Their applicability is mainly restricted due to poor formability and pronounced plastic anisotropy. The formability is usually improved by altering the chemistry (adding rare-earth elements like Y) or modulating the microstructure (e.g., grain refinement). However, grain refinement alone cannot yield the desired ductility, and the scarcity of rare-earth elements also limits the extent to which the alloying strategy can be used. To overcome these issues, in this work, it is proposed that the formability of Mg alloys can be improved by combining the grain refinement and alloying approaches. To quantitively explore this possibility, a crystal-plasticity-based constitutive model, which is sensitive to both alloying concentration and grain sizes, is developed. To demonstrate, the model is applied to study the combined effect of Y content and grain size on the mechanical responses of Mg alloy. The calculations are used to build maps of plastic anisotropy measures, such as tension–compression asymmetry ratio and Lankford coefficients, for a wide range of Y content and grain sizes. From these maps, the grain size that would yield the desired performance of Mg alloy for a fixed Y content can be identified. This work provides an accelerated pathway to optimize both the microstructure and chemistry simultaneously to achieve formability and to reduce the dependence on alloying.
more »
« less
This content will become publicly available on March 1, 2025
Thermo-mechanical behavior of hypoeutectic Ni-Y-Zr alloys
Microstructure refinement and optimized alloying can improve metallic alloy performance: stable nanocrystalline (NC) alloys with immiscible second phases, e.g., Cu-Ta, are stronger than unstable NC alloys and their coarse-grained (CG) counterparts, but higher melting point matrices are needed. Hypoeutectic, CG Ni-Y-Zr alloys were produced via arc-melting to explore their potential as high-performance materials. Microstructures were studied to determine phases present, local composition and length scales, while heat treatments allowed investigating microstructural stability. Alloys had a stable, hierarchical microstructure with ~250 nm ultrafine eutectic, ~10 µm dendritic arm spacing and ~1 mm grain size. Hardness and uniaxial compression tests revealed that mechanical properties of Ni-0.5Y-1.8Zr (in wt%) were comparable to Inconel 617 despite the small alloying additions, due to its hierarchical microstructure. Uniaxial compression at 600 °C showed that ternary alloys outperformed Ni-Zr and Ni-Y binary alloys in flow stress and hardening rates, which indicates that the Ni17Y2 phase was an effective reinforcement for the eutectic, which supplemented the matrix hardening due to increased solubility of Zr. Results suggest that ternary Ni-Y-Zr alloys hold significant promise for high temperature applications.
more »
« less
- Award ID(s):
- 1810431
- NSF-PAR ID:
- 10495151
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Materials Today Communications
- Volume:
- 38
- Issue:
- C
- ISSN:
- 2352-4928
- Page Range / eLocation ID:
- 108410
- Subject(s) / Keyword(s):
- ["Nickel alloys","Thermomechanical processing","Mechanical properties","Mechanical properties (high-temperature deformation)","Intermetallic compounds (IMCs)","Solid solution","Ternary alloys","Zr."]
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Here we report a systematic research on effects of Fe and Cu upon properties relevant for the magnetic shape memory effect of Ni–Mn–Ga ferromagnetic shape memory alloys. Fe and Cu were identified as elements with potential synergism to increase the martensite transformation temperature of Ni–Mn–Ga magnetic shape memory (MSM) alloys. Eighteen Ni–Mn–Ga–Fe–Cu alloys with different systematic trends in substituting the ternary elements with Cu and Fe have been investigated. We found a method to describe the effectiveness of Ni, Mn, and Cu upon raising the martensitic transformation temperature, lowering the saturation magnetization, and varying the Curie temperature. We find the martensite transformation temperature most influenced by the Ni content, followed by Mn, with a smaller effect of Cu. The saturation magnetization decreases with similar coefficients for Mn and Cu alloying. The Curie temperature monotonously decreases with Mn, but not Cu. The 10M martensite structure is stable for the composition Ni46.5Mn25?XGa25-X-YFe3.5CuY with X and Y range of 0–5.7, and 0.8–3.0. Used in combination with the total e/a, the elemental e/a-ratio gives some insight into the complex behavior of quinary MSM alloys and is a useful method of analyzing MSM alloys for improved functional properties.more » « less
-
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
-
This paper describes the main findings from an experimental investigation into local and overall strength and fracture behavior of a microstructurally flexible, quadruplex, high entropy alloy (HEA), Fe42Mn28Co10Cr15Si5 (in at%). The alloy consists of metastable face-centered cubic austenite (g), stable hexagonal epsilon martensite (ε), stable body-centered cubic ferrite (a), and stable tetragonal sigma (σ) phases. The overall behavior of the alloy in compression features a great deal of plasticity and strain hardening before fracture. While the contents of diffusion created a and σ phases remain constant during deformation, the fraction of ε increases at the expanse of g due to the diffusionless strain induced γ→ε phase transformation. High-throughput nanoindentation mapping is used to assess the mechanical hardness of individual phases contributing to the plasticity and hardening of the alloy. Increasing the fraction of the dislocated ε phase during deformation due to the transformation is found to act as a secondary source of hardening because g and ε exhibit similar hardness at a given strain level. While these two phases exhibit moderate hardening during plasticity, significant softening is observed in σ owing to the phase fragmentation. While the phase transformation mechanism facilitates accommodation of the plasticity, the primary source of strain hardening in the alloy is the refinement of the structure during the transformation inducing a dynamic Hall-Petch-type barrier effect. Results pertaining to the evolution of microstructure and local behavior of the alloy under compression are presented and discussed clarifying the origins of strain hardening. While good under compression, the alloy poorly behaves under tension. Fracture surfaces after tension feature brittle micromechanisms of fracture. Such behavior is attributed to the presence of the brittle σ phase.more » « less
-
more » « less
Abstract A face-centered-cubic (fcc) oriented FeCoCrNiAl0.5dual-phase high entropy alloy (HEA) was plastically strained in uniaxial compression at 77K and 293K and the underlying deformation mechanisms were studied. The undeformed microstructure consists of a body-centered-cubic (bcc)/B2 interdendritic network and precipitates embedded in 〈001〉-oriented fcc dendrites. In contrast to other dual-phase HEAs, at both deformation temperatures a steep rise in the stress-strain curves occurs above 23% total axial strain. As a result, the hardening rate associated saturates at the unusual high value of ~6 GPa. Analysis of the strain partitioning between fcc and bcc/B2 by digital image correlation shows that the fcc component carries the larger part of the plastic strain. Further, electron backscatter diffraction and transmission electron microscopy evidence ample fcc deformation twinning both at 77K and 293K, while slip activity only is found in the bcc/B2. These results may guide future advancements in the design of novel alloys with superior toughening characteristics.
