L12-Strengthened Cobalt-Base Superalloys Suzuki, Akane; Inui, Haruyuki; Pollock, Tresa M
Annual review of materials research,
07/2015, Letnik:
45
Journal Article
Recenzirano
The discovery of the γ′-Co
3
(Al,W) phase with an L1
2
structure provided Co-base alloys with a new strengthening mechanism, enabling a new class of high-temperature material: Co-base superalloys. ...This review discusses the current understanding of the phase stability, deformation, and oxidation behaviors of γ′ single-phase and γ + γ′ two-phase alloys in comparison with Ni-base γ′-L1
2
phase and γ + γ′ superalloys. Relatively low stacking fault energies and phase stability of the γ′ phase compared with those in Ni-base alloys are responsible for the unique deformation behaviors observed in Co-base γ′ and γ + γ′ alloys. Controlling energies of planar defects, such as stacking faults and antiphase boundaries, by alloying is critical for alloy development. Experimental and density functional theory studies indicate that additions of Ta, Ti, Nb, Hf, and Ni are effective in simultaneously increasing the phase stability and stacking fault energy of γ′-Co
3
(Al,W), thus improving the high-temperature strength of Co-base γ′ phase and γ + γ′ two-phase superalloys.
In this work, different from the commonly explored strategy of incorporating a smaller cation, MA+ and Cs+ into FAPbI3 lattice to improve efficiency and stability, it is revealed that the ...introduction of phenylethylammonium iodide (PEAI) into FAPbI3 perovksite to form mixed cation FAxPEA1–xPbI3 can effectively enhance both phase and ambient stability of FAPbI3 as well as the resulting performance of the derived devices. From our experimental and theoretical calculation results, it is proposed that the larger PEA cation is capable of assembling on both the lattice surface and grain boundaries to form quais‐3D perovskite structures. The surrounding of PEA+ ions at the crystal grain boundaries not only can serve as molecular locks to tighten FAPbI3 domains but also passivate the surface defects to improve both phase and moisture stablity. Consequently, a high‐performance (PCE:17.7%) and ambient stable FAPbI3 solar cell could be developed.
The introduction of a bulkier phenylethylammonium cation into FAPbI3 is revealed to effectively enhance both phase and ambient stability of FAPbI3. The larger hydrophobic cation is proposed to assemble on lattice surface and grain boundaries to form quasi‐3D perovskite structures, which tightens FAPbI3 domains and passivates surface defects, leading to a efficient and stable FAPbI3 based solar cell.
Abstract
Although all‐inorganic perovskite solar cells (PSCs) demonstrate high thermal stability, cesium‐lead halide perovskites with high iodine content suffer from poor stability of the black phase ...(α‐phase). In this study, it is demonstrated that incorporating InCl
3
into the host perovskite lattice helps to inhibit the formation of yellow phase (δ‐phase) perovskite and thereby enhances the long‐term ambient stability. The enhanced stability is achieved by a strategy for the structural reconstruction of CsPbI
2
Br perovskite by means of In
3+
and Cl
−
codoping, which gives rise to a significant improvement in the overall spatial symmetry with a closely packed atom arrangement due to the crystal structure transformation from orthorhombic (Pnma) to cubic (Pm‐3m). In addition, a novel thermal radiation heating method that further improves the uniformity of the perovskite thin films is presented. This approach enables the construction of all‐inorganic InCl
3
:CsPbI
2
Br PSCs with a champion power conversion efficiency of 13.74% for a small‐area device (0.09 cm
2
) and 11.4% for a large‐area device (1.00 cm
2
).
Due to the restriction of CMAS corrosion, the YSZ TBCs are facing great challenges, which accelerates the development of the novel potential thermal barrier materials. This work has investigated the ...CMAS corrosion resistance of the novel thermal barrier material GdTaO4 and YbTaO4 to assess their potential in replacing the traditional YSZ. The results indicate that GdTaO4 and YbTaO4 possess excellent phase stability, and there is no phase transition after 150 h sintering at 1350 °C. The crystallization phenomenon has occurred in the residual CMAS when the reaction time is 0.5 h, and the main crystallization product is CaMgSi2O6. In comparison, when the reaction time increase to 10 h, the crystallization phenomenon has disappeared completely. The maximum reaction layer thickness of GdTaO4 and YbTaO4 are ∼10 μm and ∼6 μm after 10 h CMAS corrosion, respectively. The XRD patterns indicate that the main product after 10 h reaction is Ca2Ta2O7. Compared with the CaMgSi2O6, the Ca2Ta2O7 possesses lower formation enthalpy and cohesion energy. With the reaction time rising, the formation of Ca2Ta2O7 consumes lots of Ca elements and restrain the formation of CaMgSi2O6. Besides, the difference of GdTaO4 and YbTaO4 in CAMS corrosion resistance is also attributed to cohesion energy. These results indicate that GdTaO4 and YbTaO4 exhibit enormous potential to manufacture the novel TBCs in CMAS corrosion resistance compared with the YSZ.
A metastable beta -Ti alloy, Ti-10V-3Fe-3Al (wt.%), was subjected to thermomechanical processing (TMP), where the temperature of isothermal holding in the alpha + beta phase field was varied in order ...to change the volume fraction of the alpha phase and, correspondingly, the beta phase stability. Following TMP, compression tests were performed at room temperature to evaluate the deformation mode. Microstructural features induced by compression were identified using transmission electron microscopy. It was found that {332}113 beta deformation twinning along with stress-induced products ( alpha double prime martensite and omega lamellae) and slip were operational in the least stable beta . The co-existence of {332}113 beta and {112}111 beta twinning was found at intermediate beta stability along with other deformation products. With further increasing of beta phase stability, no {332}113 beta twinning was detected whereas other deformation modes remained unchanged. In stable beta phase, dislocation glide was the only deformation mode to be found. It was revealed that triggering stress required inducing the deformation products increases with the beta phase stability. Based on the findings, a modification of the lower portion of the - phase stability diagram is proposed.
The effect of Co on the phase stability of the CrMnFeCoxNi family of alloys, where the atomic ratio x = 0, 0.5, 1.5, has been experimentally established following 1000 h heat treatments at 900 and ...700 °C and up to 5000 h at 500 °C. All the alloys were single phase fcc in the homogenised condition, except for CrMnFeNi which also contained bcc precipitates that remained present following exposures at 900 °C and 700 °C. The exposures at 900 °C and 700 °C also resulted in the formation of σ phase precipitates in the CrMnFeNi and CrMnFeCo0.5Ni alloys but not in the CrMnFeCo1.5Ni alloy. These data, in conjunction with results previously published in the literature, conclusively establish that Co stabilises the fcc matrix at elevated temperatures. However, at 500 °C, further bulk decomposition in the CrMnFeNi alloy was observed, consisting of a fine-scale intergrowth of a NiMn L10 phase and CrFe σ phase. Grain boundary precipitates were also observed following exposure at 500 °C in the CrMnFeCo0.5Ni and CrMnFeCo1.5Ni alloys. Four different phases were observed on the grain boundaries of the CrMnFeCo0.5Ni alloy (Cr carbide, σ, FeCo B2 and NiMn L10), whilst only two phases were found on the grain boundaries of the CrMnFeCo1.5Ni alloy (Cr carbide and NiMn L10). The experimental observations facilitated an assessment of the fidelity of current thermodynamic predictions of phase equilibria. All the phases predicted were observed experimentally and the σ stability fitted the experimental observations well. However, at lower temperatures, thermodynamic predictions were less consistent with experimental observations, underpredicting the extent of the B2 phase field and failing to predict the formation of the L10 phase.
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•Co stabilises fcc solid solution relative to σ and bcc phases at 700 & 900 °C.•All alloys decompose into multiple intermetallic phases when exposed at 500 °C.•NiMn L10, FeCo B2, Cr carbide & σ all identified following 500 °C exposures.•Fidelity of TCHEA3 predictions questionable, particularly at lower temperatures.
In this paper, the structural, mechanical, electronic, and thermodynamic properties of Ir3TM (TM = Sc, Ti, and V) intermetallic compounds in the cubic (L12) and hexagonal (D019 and D024) phases are ...presented. The outcomes of the simulation rely on density functional theory (DFT) within the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) based on the full-potential linearized augmented plane wave (FP-LAPW) approach. The existing study was performed on the L12 cubic phase. in addition to hexagonal D024 and D019 phases, which may be relative but differ in the way that the atomic layers are stacked. The calculated total, cohesive energy, and heat formation suggest that the Ir3Sc compound can be stable in the D024 phase because of an overlap between the L12 and D024 phases with a total energy difference of around 0.026 eV/atom. Ir3Ti and Ir3V are more stable in L12 and D019, respectively. From elastic constants calculations, it reveals that the studied compounds are mechanically stable and harder in the cubic phase than hexagonal phase. However, Ir3Sc has the lowest hardness due to its relative ductility. Inversely, Ir3V has the maximum hardness with a lack of ductility. It was observed that these compounds have an elastic anisotropy based on the three-dimensional Young's modulus surface, and Ir3Sc has the strongest anisotropy, while Ir3V has the weakest in the L12 phase. The total density of state (TDOS) calculations shows that Ir3Ti and Ir3V are stable in the L12 and D019 phases, respectively, except for the Ir3Sc compound which might undergo a martensitic transition. Also, the pseudogap for Ir3V moves quite close to the Fermi level, indicating that the covalent bonding in this compound is sharper than the other compounds. Moreover, via the quasi-harmonic Debye model within the Gibbs computational code, thermodynamic properties are calculated and analyzed with temperature and pressure.
Understanding the intrinsic phase stability and inherent band gap of formamidinium lead triiodide (FAPbI3) perovskites is crucial to further improve the performance of perovskite solar cells (PSCs). ...Herein, we explored the α‐ to δ‐phase transition and band gap of FAPbI3 single crystals grown by an inverse temperature solubility method. We found that the residual γ‐butyrolactone solvents in the inner empty space of the FAPbI3 single crystal accelerate the phase transition at kinetics. By adopting 2‐methoxyethanol as the solvent, over 2000 h of stable α‐FAPbI3 crystals could be acquired. This proves that although FAPbI3 is regarded as unstable at thermodynamics, it could own excellent kinetic stability without any doping or additives because of the slow solid to solid phase transition instead of the fast phase transition assisted by the solvents. Furthermore, we revealed that the bulk FAPbI3 single crystal with a size above 100 μm can have an inherent band gap of 1.41 eV. Thus, our work provides key scientific guidance for high‐performance FAPbI3‐based PSCs.
The residual γ‐butyrolactone (GBL) solvent molecules inside the void of α‐FAPbI3 single crystals promote the phase transition kinetics (2). By adopting the 2‐methoxyethanol (2‐ME) as solvent, highly stable α‐FAPbI3 crystals could be acquired due to slow solid to solid phase transition (1). α‐FAPbI3 with crystal size above 100 μm has an inherent 1.41 eV band gap.
In this paper, NbC reinforced Fe50Mn30Co10Cr10 high entropy alloy coatings with different NbC content were fabricated by laser cladding. The formation mechanism of NbC particles with micro/nano-scale ...was analyzed. Based on the interaction between the solid-liquid interface and NbC particles, the distribution of micro/nano-scale NbC particles is clarified. The effects of NbC content on microstructure and mechanical properties of the coatings were investigated. It demonstrated that the nanoscale NbC particles restricted the dendritic growth whilst promoting grain nucleation and altering the grain morphology from columnar grain to equiaxed dendrite. Besides, the influence of NbC particles on FCC phase stability was studied based on the lattice mismatch theory, which indicates that the addition of ceramic particles is a new way to modify the phase volume fraction in the dual-phase high-entropy alloys (HEA). The micro-hardness and wear resistance of the coatings significantly improved with the increase of NbC content. For the Fe50Mn30Co10Cr10-30 wt%NbC high entropy composite coating, the average Vickers hardness and friction coefficient value separately is 525 HV and 0.45. In addition, the large fluctuations on the friction coefficient of the coatings for 10 wt% and 20 wt% NbC addition may be related to the uneven distribution of nanoscale NbC particles in the matrix.
•Fe50Mn30Co10Cr10-xNbC (x = 0, 10, 20 and 30 wt%) composite coatings have been fabricated by laser cladding technique.•The formation and distribution mechanism of nano/micronscale NbC particles has been clarified in Fe50Mn30Co10Cr10-xNbC (x = 0, 10, 20 and 30 wt%) HEAs.•The effect of nanoscale NbC particles on FCC phase stability has been explained.
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