Local chemical ordering (LCO) in the CrCoNi medium-entropy alloy was investigated by transmission electron microscopy (TEM) after different annealing treatments and their corresponding mechanical ...properties by bulk tensile tests and nanoindentation. A cold-rolled alloy was annealed at 1000°C for 0.5 h followed by ice water quenching and then aged at a number of different temperatures (600°C, 700°C, 800°C, 900°C, and 1000°C) under vacuum for 240 h to generate different degrees of chemical ordering. A splat-quenched sample rapidly cooled from the liquid phase was also examined. While bulk mechanical properties did not vary among samples with equivalent grain sizes, nanoindentation tests revealed notable differences. As indicated by the load at first pop-in using a Berkovich tip or the indentation yield strength via continuous stiffness measurements using a 10 μm spherical tip, the nanoindentation tests revealed that the stress for onset of plasticity during indentation varied with heat treatment and peaked in the 900°C aged sample. Energy-filtered TEM characterization indicated the presence of ordering in all specimens, with a higher degree of LCO in the aged samples relative to the splat-quenched and 1000°C-quenched samples. The evolution of LCO during aging was determined to occur on the time scale similar to those of bulk diffusion. The difference in nanoindentation strength was attributed to the difference in dislocation nucleation barriers imposed by different degrees of LCO.
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Refractory alloys can be difficult to fabricate by laser-based manufacturing methods due to their high melting temperatures, high interstitial solubility, and propensity for low temperature ...brittleness. Laser-based processes, such as welding and additive manufacturing (AM), yield similar populations of defects, including microsegregation and solidification and solid-state cracking. Given the extreme challenges and cost associated with the production of refractory powders, this research aimed to develop a rapid screening methodology that combines predictive defect formation metrics with single track melting experiments. A flexible single laser track melting platform was designed to perform screening experiments on conventional and multi-principal element refractory alloys across a wide range of laser energy inputs. The platform was employed to investigate laser melting on solid substrates, or on a substrate with a single layer of powder feedstock, and is demonstrated with the highly fabricable Nb-base alloy C103. Preliminary investigations are performed on refractory multi-principal element alloys in the Hf-Mo-Nb-Ta-Ti family, and significant differences in cracking resistance and solidification morphology are observed. Implications for future alloy design and processing strategies for defect-resistant refractory alloys for AM are discussed.
•A single track laser set-up was developed for rapid screening of refractory multi-principal element alloys.•Similarities in solidification morphology and defects observed in laser melted C103 wrought and powder feedstock substrates.•Significant changes in crack resistance, solidification morphology observed with Ta substitution in the Hf-Nb-Mo-Ti family.•Predictive ductility and cracking criteria in tandem with single track experiments can assist refractory alloy design for AM.
This data article presents a compilation of mechanical properties of 630 multi-principal element alloys (MPEAs). Built upon recently published MPEA databases, this article includes updated records ...from previous reviews (with minor error corrections) along with new data from articles that were published since 2019. The extracted properties include reported composition, processing method, microstructure, density, hardness, yield strength, ultimate tensile strength (or maximum compression strength), elongation (or maximum compression strain), and Young's modulus. Additionally, descriptors (e.g. grain size) not included in previous reviews were also extracted for articles that reported them. The database is hosted and continually updated on an open data platform, Citrination. To promote interpretation, some data are graphically presented.
An equiatomic HfNbTaRuZr refractory multi-principal alloy was cast via arc melting and characterized in both as-cast and vacuum annealed conditions. (Nb, Ta)-rich body-centered cubic (BCC), (Hf, ...Ru)-rich B2, and (Hf, Zr)-rich hexagonal close-packed (HCP) phases in annealed materials were identified by both x-ray diffraction and transmission electron microscopy, with all phases stable from 1350 to 1575 °C. At 1575 °C the alloy contained 35.9 % of a morphologically stable B2 phase. Preferential segregation of oxygen and nitrogen to the HCP phase was observed. The volume fractions of the HCP and B2 phases increased and decreased, respectively, with increasing annealing temperature. Lamellar microstructures present along grain boundaries were determined to result from a discontinuous transformation from a disordered BCC phase to B2 and BCC. Refinement of the grain size and microstructure was achieved by splat quenching, resulting in exceptional hardness due to nano-scale precipitates.
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HfNbTaTiZr is a refractory multi-principal element alloy (RMPEA) that exhibits high strength combined with good ductility at room temperature. An insufficient understanding of RMPEA tensile behavior, ...however, limits their ability to be thermo-mechanically processed and optimized for engineering applications. In this investigation, uniaxial tensile tests were conducted at room temperature, 800 °C, and 1200 °C under vacuum on sheet materials fabricated by hot and cold rolling combined with annealing treatments. At testing temperatures of 25 °C and 1200 °C, the HfNbTaTiZr alloy exhibited high tensile ductility (16.0% and 121.0%, respectively). At 800 °C, the HfNbTaTiZr alloy exhibited significantly decreased ductility (2.0%) compared to room temperature, and coincided with a transition from ductile to intergranular fracture. SEM and TEM studies revealed precipitation reactions at grain boundaries following thermal exposure and during tensile testing at 800 °C, resulting in tantalum and niobium-rich BCC precipitates, and finer-scale hafnium and zirconium-rich precipitates. After annealing at 800 °C for 100 h, nanoindentation revealed soft and stiff tantalum and niobium-rich BCC precipitates located at grain boundaries. Thermodynamic calculations corroborated the existence of two BCC phases and predicted an HCP phase to be stable between 703–804 °C, which was consistent with TEM observations. At 1200 °C, high tensile ductility resulted from the combined effects of dynamic recovery and partial dynamic recrystallization. These experimental and computational results underscore a need to understand the high temperature phase equilibria and complex deformation behaviors of refractory MPEs so that their microstructure and mechanical performance can be better controlled across the elevated temperature ranges of interest.
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Bayesian inference with sequential Monte Carlo is used to quantify the orientation distribution function coefficients and to calculate the fully anisotropic elastic constants of ...additively manufactured specimens from only the experimentally-measured resonant frequencies. The parallelizable and open-source SMCPy Python package enabled Bayesian inference within this new modeling framework, resulting in an order of magnitude reduction of the computation time for an 8-core machine. Residual stress-induced shifts on the resonant frequencies were explicitly accounted for during the Bayesian inference, enabling the estimation of their effect on the resonant frequencies without a stress-relief heat treatment. Additively manufactured cobalt-nickel-base superalloy (SB-CoNi-10C) specimens were sectioned at multiple inclinations relative to the build direction and scanned with resonant ultrasound spectroscopy to demonstrate characterization of any arbitrarily textured cubic microstructure through the resonant frequencies. The orientation distribution function coefficients of the textured polycrystalline microstructure were estimated in tensorial form to calculate both the 2nd order Hashin-Shtrikman bounds and the self-consistent estimate of the elastic constants, enabling accurate determination of all 21 possible independent elastic constants through the convergence constraints of the texture. Pole figures generated directly from the calculated texture coefficients showed good agreement with experimentally measured textures.
Bayesian inference with Sequential Monte Carlo was used to determine the single crystal elastic constants of additively manufactured (AM) cobalt‑nickel-based superalloy specimens from only the ...resonant frequencies and texture data. This novel framework enables the quantification of the single crystal elastic constants for AM and polycrystalline specimens using only electron backscatter diffraction (EBSD) and Resonant Ultrasound Spectroscopy (RUS), avoiding the expense of bulk single crystal fabrication or synchrotron experiments. A parallelizable and open-source Python package (SMCPy) was used to perform Bayesian inference of the single crystal elastic constants from resonant frequencies of AM specimens. The single crystal elastic constants determined from AM cobalt‑nickel-base superalloy specimens were validated with measurements of the single crystal elastic constants on a bulk single crystal specimen. EBSD texture data was used to determine the single crystal elastic constants from the resonant frequencies of AM specimens, and validated with neutron diffraction data by considering the experimental uncertainty in both the EBSD and neutron diffraction data. The robustness of this framework for varied texture orientations relative to the build direction (BD) was demonstrated for AM specimens printed at 0° and 20° BD-inclinations.
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•Single crystal elastic constants are determinable with RUS/ EBSD of AM specimens.•Textures both aligned and misaligned to BD are demonstrated.•Single crystal constant variability driven by error in input texture coefficients.•Parallelized SMC enables 10× computation time reduction.
Ru-based B2 phases present an opportunity to design two-phase BCC + B2 refractory multi-principal element alloys (RMPEAs) with higher temperature stability compared to B2 phases observed in RMPEAs. ...In this investigation, seven equiatomic Ru-containing RMPEAs were characterized in the as-cast and annealed conditions. Of the two Hf-free alloys, Mo
25
Nb
25
Ta
25
Ru
25
was determined to be a single-phase B2 alloy and Mo
20
Nb
20
Ta
20
W
20
Ru
20
was single-phase BCC. Within all five Hf-containing alloys, phases formed during solidification included HfRu–B2, disordered BCC, and HfO
2
phases. The Hf-containing alloys also precipitated B2 nanoparticles within the BCC phases after further cooling in the solid. All phases were still present after annealing at 1500
∘
C to 1600
∘
C. The HfRu–B2 nanoparticles in as-cast Hf
20
Mo
20
Nb
20
Ta
20
Ru
20
were characterized by transmission electron microscopy (TEM), and a lattice misfit of < 1 pct between the BCC phase and B2 nanoparticles was calculated. Room-temperature micropillar compression tests were performed on BCC + B2 nanoparticle regions in annealed Hf
20
Mo
20
Nb
20
Ta
20
Ru
20
. Post-mortem TEM analysis revealed precipitate shearing by dislocations, resulting in paired dislocations, along with bowing of dislocations around precipitates. Utilizing the insights from this investigation, compositions for RMPEAs with solutionable B2 precipitates stable above 1200
∘
C are suggested.
Folate receptor (FR) overexpression in a wide range of solid tumors provides an opportunity to develop novel, targeted cancer therapeutics. In this study, we investigated whether prebinding the ...chemotherapeutic methotrexate (MTX) to folate-binding protein (FBP), the soluble form of FR, would enable the protein to serve as a targeted therapeutic vector, enhancing uptake into tumor cells and improving therapeutic efficacy. In an in vivo study, using an FR-overexpressing KB xenograft model in SCID mice, modest improvement in inhibiting tumor growth was observed for the MTX/FBP mixtures as compared to saline control and free MTX. Surprisingly, FBP alone inhibited tumor growth compared to saline control, free MTX, and FBP/MTX. In order to better understand this effect, we investigated the cytotoxicity of micromolar concentrations of FBP in vitro using the KB, HeLa, and A549 cancer cell lines. Our results revealed concentration-dependent apoptosis (24 h; 10–50 μM) in all three cell lines accompanied by a time- and concentration-dependent reduction (6, 12, and 24 h; 10–50 μM) in metabolic activity and compromised cell plasma membrane integrity. This study demonstrates an apoptosis pathway for cytotoxicity of FBP, an endogenous serum protein, in cancer cell lines with widely varying levels of FR expression. Furthermore, in vivo tumor growth suppression for xenograft KB tumors in SCID mice was observed. These studies suggest novel strategies for the elimination of cancer cells employing endogenous, serum transport proteins.
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