The Li–Co–O and Li–Ni–O systems, used as cathodes in lithium ion batteries, have been investigated by means of ab initio calculations and empirical methods. An approach based on ab initio ...calculations to obtain accurate enthalpies of formation for transition metal oxides is proposed. With the obtained enthalpies of formation and the empirical entropy data, the Gibbs energy functions of the binary and ternary oxides in the Li–Co–O and Li–Ni–O systems are determined. To prove the accuracy of this thermodynamic model, we calculate the cell voltages of lithium ion batteries. Compared to the previously calculated results, which underestimate the cell voltages of lithium ion batteries, our calculations are in good agreement with the experimental data. The present theoretical approaches are reliable to evaluate the thermodynamic and electrochemical properties of lithium-containing transition metal oxides.
Display omitted
•7 and 18 ternary compounds are evaluated in the Al/Ni-Si-Y systems.•RE with same reference states tend to form compounds with same structures.•Al/Ni-Si-Y phase diagrams are ...constructed based on related RE-containing systems.•This is an essential base for the design of novel NiSiAlY alloys.
MCrAlY (M=Ni, Co, NiCo) alloys have been widely used as a bond layer for thermal barrier coatings (TBCs). However, oxides form discontinuously on MCrAlY surface in the marine environment since Cr2O3 can react with NaCl and H2O at temperatures above 500 ℃. Replacing Cr with other alloying elements (such as Si) might prevent severe salt-spray corrosion effectively. To save time and efforts in materials design of the Ni-Si-Al-Y system, we obtained the thermodynamic descriptions of the ternary compounds by coupling the CALPHAD (CALculation of PHAse Diagrams) approach and first-principles calculations. Seven and eighteen ternary compounds were evaluated and calculated in the Al-Si-Y and Ni-Si-Y systems, respectively. Phase diagrams of the two systems were depicted after a series of experimental Al/Ni-Si-RE (RE denotes rare earth elements, including La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, and Er) systems being analyzed. It is found that the RE elements with the same reference states tend to form ternary compounds with the same crystal structures. The model-based descriptions are the basis for the research and development of novel NiSiAlY alloys in resisting high-temperature corrosion.
•Energy variations of the liquid-solid transition in rapid and slow solidification.•A new thermodynamic interpretation of T0 curves based on energy analysis.•A “phase diagrams + T0 curves” indicator ...for exploring novel MGs and their GFRs.
This study presents a new thermodynamic interpretation of T0 curves in eutectic phase diagrams. By analyzing the Gibbs energy variation of liquid-solid transition in energy-composition schematics, we illustrated the thermodynamic particularities of the T0 curves. They are experimentally observed to be boundaries between the partitionless crystallization and amorphous areas in phase diagrams. Our interpretation basically rationalizes the capability of T0 curves in predicting new glass forming systems and their glass forming regions. Good agreements between the thermodynamic indicator “phase diagram + T0 curves” for metallic glasses and the experimental information were obtained in typical systems.
FeCrAl-based materials have attracted ever-increasing attentions due to their excellent resistances against high-temperature oxidation and stress-corrosion cracking, while enhancement of their ...mechanical properties can expand their potential applications. In this work, the micro-alloying method by adding Nb was applied to enhance the mechanical property of FeCrAl. The FeCrAl thin films with different Nb contents (Fe-16Cr-5Al, Fe-14Cr-5Al-1Nb, Fe-12Cr-5Al-2Nb, Fe-13Cr-3Al-7Nb, in wt%) were synthesized using magnetron co-sputter deposition. Benefiting from the refined grain size, the as-deposited Fe-13Cr-3Al-7Nb thin film exhibited the highest hardness (3.3 GPa), followed by Fe-14Cr-5Al-1Nb (1.5 GPa) and Fe-12Cr-5Al-2Nb (1.2 GPa), whereas the hardness of Nb-free film was the lowest (0.8 GPa). The fracture resistance (which is related to the ratio of hardness and elastic modulus) also enhances with the addition of Nb. After annealing (873 K for 6 h), the hardness of the Fe-13Cr-3Al-7Nb thin film further increased to ~6.7 GPa, in contrast to the as-annealed Nb-free thin film with no obvious hardness change. The CALPHAD (CALculation of PHAse Diagram) results indicate that with adding Nb the original single BCC (body centered cubic) phase tended to decompose into the Fe-rich and Cr-rich BCC domains, which is consistent with the transmission electron microscopic (TEM) observations. The observed strengthening of the annealed Nb-containing samples is therefore attributed to the phase separation. The first-principles calculations also support this notion. Thus, the current work has delineated the effect of Nb addition on both deposited and annealed FeCrAl-based thin films, which shows the usefulness of combined experimental and computational methods in interpreting microstructure and mechanical property evolutions of engineering materials.
Display omitted
•Grain refinement strengthens the as-deposited FeCrAl thin films by adding Nb.•Phase separation strengthens the as-annealed FeCrAl thin films by adding Nb.•The microstructure and mechanical property evolutions were well interpreted by experimental and computational methods.
The Y3Si2C2 coating on the silicon carbide (SiC) powders is reported to improve the sintering process, but the relatively high sintering temperature (1600°C) restricts the engineering application. A ...series of thermodynamic descriptions for the SiC with light rare‐earth elements are desired to develop potential SiC‐RE3Si2C2 core‐shell structures as sintering aids with lower temperatures. Coupling the CALPHAD (CALculation of PHAse Diagram) approach and first‐principles calculations, we have investigated the RE‐Si‐C (RE = La, Ce and Pr) systems. In the SiC‐RE3Si2C2 core‐shell structures, the RE3Si2C2 phases can react with SiC via ternary eutectic reactions at 810°C, 747°C, and 1148°C respectively. The predicted thermal behaviors of the Pr3Si2C2 phase were further confirmed by our key experiments. Therefore, our database can be used to predict promising sintering aids and guide the subsequent processes.
Incorporation of additional carbides into the widely-used Ti(C, N)-based cermets constitutes an important aspect of materials optimization strategy to impart better service properties for mining and ...machining applications. In this work, Ti(C, N)-WC-Mo2C–TaC-(Ni, Co) cermets with the WC content varying from 5.77 wt% to 19.68 wt% were specifically designed based on thermodynamic calculations, and their mechanical and tribological properties were subsequently examined. The results show that the increase of WC content brought about a higher fraction of the white core phase, which also induced a rise in hardness (by ∼10%) but a decline in toughness (by ∼20%). In addition, decreased wear rates (by ∼80%) at both 25 °C and elevated temperatures (400 and 750 °C) were also noted on the cermets containing the highest WC concentration. The wear behavior was found to be controlled by the surface hardness at 25 °C whereas the extent of oxide tribolayer formation at high temperatures. Micro-Raman spectroscopic and transmission electron microscopic observations suggested that the favorable generation of oxide tribolayers consisting of TiO2 and WO3 nano-crystals contributed to the improved high-temperature tribological properties.
As interest in new generations of nuclear reactors is increasing worldwide, development of accident tolerant fuel (ATF) cladding materials is crucial but suffers from large amounts of time and ...experimental efforts. Here, we present a strategy of the theory-guided bottom-up design of ATF cladding materials using ab initio calculations and the CALPHAD (CALculation of PHAse Diagrams) approach in combination with key experiments, which has been utilized to investigate the FeCrAl system. The thermochemical, physical and elastic mechanical properties, as well as the phase diagrams of the FeCrAl alloys, are well described using both modeling and experiment. Apart from the reported high-temperature steam oxidation resistance as the initial criterion, the present selection and optimization of the FeCrAl alloys as accident tolerant fuel cladding materials is based on three constraints: (i) single phase at 320 °C, a service temperature in a light water reactor; (ii) high melting point; (iii) good elastic mechanical property. Further optimization takes into account of alloy performance in literature. Consequently, a compositional range has been proposed as a guidance for the fabrication of new FeCrAl alloys, i.e., 0 at.% < Cr content ≤15 at.% and 11 at.% ≤ Al content ≤21 at.%. The present scheme may enhance the efficiency in designing new ATF cladding materials by promoting the discovery of the composition-structure-property-performance relationships.
Crystalline-to-amorphous transitions induced by chemical modulation have been attracting great research interests and an in-depth understanding of such transitions is always demanding. Here we design ...the Nb-Ti-Zr-(Si) alloy systems employing the empirical criteria and the related phase diagrams for enhancing mechanical properties accompanied by Si-induced microstructure evolutions. (NbTiZr)100-xSix (x = 0, 3.0, 10.2, 22.2, and 25.0 at.%) refractory medium-entropy alloy (RMEA) coatings are synthesized by magnetron co-sputtering. With increasing Si content, the pristine body-centered cubic (bcc) single phase transforms into a nanocomposite structure consisting of bcc nanocrystals embedded in an amorphous matrix and eventually into an entirely amorphous structure. This is well rationalized with a thermodynamic database of the Nb-Ti-Zr-Si system constructed using the CALPHAD (CALculation of PHAse Diagrams) approach, which suggests the bcc structure to be thermodynamically stable at low Si contents and the formation of amorphous RMEA to be preferred at higher Si contents. The superior mechanical property of the amorphous (NbTiZr)75.0Si25.0 (at.%) coating compared to the Si-free counterpart is achieved, i.e., the hardness (H) increases by 115% and the elastic modulus (E) increases by 70%. The Si-induced crystalline-to-amorphous transition in RMEA which leads to a consistently impressive strengthening effect was rarely found in other alloys or coatings.
Display omitted
•The designing strategy of crystalline-to-amorphous transition is presented.•The composition, microstructure and mechanical property relationship is analyzed.•The superior mechanical property is achieved compared to the Si-free counterpart.•The Si-induced crystalline-to-amorphous transition is rarely found.
The V–Zn system was investigated by a combination of CALPHAD modeling with key experiments and first-principles calculations. Based on a critical literature review, one diffusion couple and nine ...alloys were designed to reinvestigate the stabilities of the phases reported in the literature. The samples were annealed and cooled under different conditions, followed by examination with X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray spectrometry. Four phases ((V), (Zn), V Zn
3 and V
4Zn
5) were confirmed to exist in the phase diagram, while V Zn
16 and V
3Zn were not observed. By means of first-principles calculations, the enthalpies of formation for V Zn
3 and V
4Zn
5 were computed to be −4.55 kJ mol-atoms
−1 and −4.58 kJ mol-atoms
−1, respectively. A set of self-consistent thermodynamic parameters for this system was obtained by considering the reliable experimental phase diagram data and the enthalpies of formation acquired from first-principles calculations. The calculated V–Zn phase diagram agrees well with the experimental data.
