Microstructure and Mechanical Properties of Low-Density, B2-Ordered AlNbZrTix Multi-Principal Element Alloys
Abstract
:1. Introduction
2. Materials and Methods
3. Results and Discussion
3.1. Phase Formation
3.2. Microstructural Characterization
3.3. Mechanical Property: Compressive Stress–Strain Analysis
4. Conclusions
- (1)
- As Ti content increases, the microstructure of the MPEAs transforms, from a mixture of B2 matrix and Zr5Al3-type phase (x = 1, 1.5) to a single-phase B2 structure (x = 2, 3). When x = 1, the Zr5Al3-type phase exhibits polygonal and rod-like shapes. When x = 1.5, the polygonal particles become irregular and the rod-like phase evolves into a continuous net along the B2 grain boundaries.
- (2)
- The Ti element in these alloys can stabilize a single-phase B2 structure, rather than a nanoscale BCC/B2 mixture, which can also be predicted by three previously-proposed parameters (Ω ≥ 1.1, δ ≤ 6.6%, and VEC < 6.87). These MPEAs exhibited a steady decrease in B2 lattice parameters, from ~0.3336 nm (x = 1) to ~0.3309 nm (x = 3), which is attributed to weaken lattice distortion caused by a reduced δ value.
- (3)
- The actual densities of the AlNbZrTix (x = 1, 1.5, 2, 3) MPEAs reduced by ~8.7%, from ~5.85 g·cm−3 (x = 1) to ~5.34 g·cm−3 (x = 3), and were lower than that of most reported MPEAs (≥6 g·cm−3). Thus, the specific yield strengths (SYS) of the AlNbZrTix (x = 1, 1.5, 2, 3) MPEAs were calculated to be ~270 kPa·m3·kg−1, ~238 kPa·m3·kg−1, ~221 kPa·m3·kg−1, >208 kPa·m3·kg−1, respectively.
- (4)
- The excellent fracture strain of AlNbZrTix (x = 1, 2, 3) alloys were ~17.8%, 21.8%, and >50%, respectively. This Ti-addition-induced ductility improvement was attributed to the reduced δ and gradual disappearance of the Zr5Al3-type phase. An exception was AlNbZrTi1.5 with a limited ductility of ~7.8%, which was explained through the distinct morphology and distribution of hard Zr5Al3-type phase.
- (5)
- The combined compressive properties (SYS and fracture strain) of AlNbZrTix (x = 1, 2, 3) were superior to the reported data of most BCC/B2-dominant MPEAs. The deformation mechanism of the B2 structure is closely related to a dislocation-based ductility mechanism, accompanied by antiphase domains. Our results provide an explanation for the high strength and exceptional room-temperature ductility of low-density B2 MPEAs.
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
Appendix A
Abbreviations | Nomenclature | Definition |
MPEA | Multi-principal element alloy | |
FCC | Face-centered cubic | |
BCC | Body-centered cubic | |
HCP | Hexagonal-close-packed | |
B2 | Ordered body-centered cubic | |
SYS | Specific yield strength (strength-to-density ratio) | |
XRD | X-ray diffraction | |
TEM | Transmission electron microscopy | |
STEM | Scanning transmission electron microscopy | |
SEM | Scanning electron microscopy | |
BSE | Backscatter electron | |
EDS | Energy-dispersive spectrometer | |
EBSD | Electron backscatter diffraction | |
HAADF | High-angle annular dark-field | |
FFT | Fourier transformation | |
IPF | Inverse pole figure | |
KAM | Kernel average misorientation | |
SAED | Selected area electron diffraction | |
∆Gmix | Gibbs free energy | |
∆Hmix | Mixing enthalpy | |
∆Smix | Mixing entropy | |
δ | Atomic misfit | |
Ω | Multi-component solid solution rule | |
VEC | Valence electron concentration | |
Tm | Average calculated melting point | |
Ti | Melting point of ith pure metal | |
ci | Atomic fraction of the ith constituent | |
cj | Atomic fraction of the jth constituent | |
ith-jth-constituent mixing enthalpy | ||
R | Gas constant | |
ri | ith-constituent radius | |
(VEC)i | Valence electron concentration of the ith constituent |
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Al | Nb | Zr | Ti | |
---|---|---|---|---|
Al | - | −18.2 | −43.7 | −29.5 |
Nb | - | - | 3.9 | 2 |
Zr | - | - | - | −0.2 |
Ti | - | - | - | - |
Alloys | Tm (K) | ∆Hmix (kJ·mol−1) | ∆Smix (J·K−1·mol−1) | δ (%) | Ω | VEC |
---|---|---|---|---|---|---|
AlNbZrTi | 1935.74 | −21.4250 | 11.53 | 3.85 | 1.04 | 4 |
AlNbZrTi1.5 | 1936.56 | −19.6642 | 11.38 | 3.70 | 1.12 | 4 |
AlNbZrTi2 | 1937.22 | −18.1440 | 11.08 | 3.57 | 1.18 | 4 |
AlNbZrTi3 | 1938.21 | −15.6778 | 10.33 | 3.34 | 1.28 | 4 |
Alloys | Region | Chemical Compositions (at.%) | |||
---|---|---|---|---|---|
Al | Nb | Zr | Ti | ||
AlNbZrTi | Nominal | 25 | 25 | 25 | 25 |
I | 23.1 | 24.7 | 25.2 | 27 | |
II | 34.2 | 12.9 | 41.1 | 11.8 | |
III | 35.1 | 12.8 | 41.2 | 10.9 | |
AlNbZrTi1.5 | Nominal | 22.2 | 22.2 | 22.2 | 33.4 |
I | 21.9 | 21.5 | 22.7 | 33.9 | |
II | 33.5 | 12.9 | 38.3 | 15.3 | |
III | 28.7 | 12.9 | 40.9 | 17.5 | |
AlNbZrTi2 | Nominal | 20 | 20 | 20 | 40 |
I | 19.9 | 19.3 | 20.5 | 40.3 | |
AlNbZrTi3 | Nominal | 16.7 | 16.7 | 16.7 | 49.9 |
I | 16.3 | 17.0 | 16.9 | 49.8 |
Alloys | Actual Density (g·cm−3) | Yield Strength (MPa) | Fracture Strain (%) | Strength-to-Density Ratio (SYS, kPa·m3·kg−1) |
---|---|---|---|---|
AlNbTiZr | 5.85 | 1579 | 17.8 | 270 |
AlNbTiZr1.5 | 5.72 | 1364 | 7.8 | 238 |
AlNbTiZr2 | 5.56 | 1227 | 21.8 | 221 |
AlNbTiZr3 | 5.34 | 1111 | >50 | >208 |
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Tang, Q.; Su, H.; Peng, S.; Chen, W.; Dai, P. Microstructure and Mechanical Properties of Low-Density, B2-Ordered AlNbZrTix Multi-Principal Element Alloys. Metals 2022, 12, 932. https://doi.org/10.3390/met12060932
Tang Q, Su H, Peng S, Chen W, Dai P. Microstructure and Mechanical Properties of Low-Density, B2-Ordered AlNbZrTix Multi-Principal Element Alloys. Metals. 2022; 12(6):932. https://doi.org/10.3390/met12060932
Chicago/Turabian StyleTang, Qunhua, Honghong Su, Shilong Peng, Wei Chen, and Pinqiang Dai. 2022. "Microstructure and Mechanical Properties of Low-Density, B2-Ordered AlNbZrTix Multi-Principal Element Alloys" Metals 12, no. 6: 932. https://doi.org/10.3390/met12060932