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Micro-grain K447A superalloy with grain refined to 54 μm and yield strength up to 1022 MPa has been successfully fabricated in this work, whose strength is 200 MPa higher than that of conventional casting K447A. Owing to the bimodal distribution of γ′, two dislocation mechanisms act simultaneously at the initial stage of plastic deformation. That is, dislocations cut γ′ with radius less than 100 nm but bypass γ′ over 100 nm. Based on the deformation mechanisms of γ′ with different sizes, a frequency-weighted precipitation strengthening calculation method has been proposed to predict the contribution of precipitation strengthening accurately. Yield strength predicted by this method is in good agreement with experimental results with maximum error of 4.0 pct. Strength calculation indicates that micro-grain casting process improves the yield strength mainly by increasing the volume fraction of γ′ from 34.2 to 51.6 pct and reducing the grain size from 5 mm to 54 μm, compared with the conventional one. [ABSTRACT FROM AUTHOR]

Creep deformation is one of the main failure forms for superalloys during service and predicting their creep life and curves is important to evaluate their safety. In this paper, we proposed a back propagation neural networks (BPNN) model to predict the creep curves of MarM247LC superalloy under different conditions. It was found that the prediction errors for the creep curves were within ±20% after using six creep curves for training. Compared with the θ projection model, the maximum error was reduced by 30%. In addition, it is validated that this method is applicable to the prediction of creep curves for other superalloys such as DZ125 and CMSX-4, indicating that the model has a wide range of applicability. [ABSTRACT FROM AUTHOR]

The study on the temperature-dependent kinetic behavior of intermetallic compounds (IMCs) in Mg–Al–Zn (AZ) series alloy system is important since its close interrelation with the microstructure evolution under various alloying conditions as well as the T-dependent performance. However, there is a very lack of experimental study on the diffusion kinetics of the ternary IMCs in the AZ series alloy systems. The current work combines the diffusion couple technique and numerical inverse method to investigate the T-dependent kinetic coefficients, i.e., the parabolic growth constant (PGC) and interdiffusion coefficients, for ϕ-Mg5Al2Zn2 ternary IMC in the Mg–Al–Zn alloy system. The Arrhenius formula of both PGC and main interdiffusivities is obtained, i.e., ϕ k p = 5.48 × 10 - 5 exp 120010 RT m2/s, ϕ D ~ MgMg Al = 3.48 × 10 - 10 exp 50420 RT m2/s and ϕ D ~ ZnZn Al = 2.87 × 10 - 7 exp 91440 RT m2/s, based on which a numerical reproduction of the experimentally determined IMC growth is performed for verification. By comparing the current experimental and calculation results, the rate-controlling factor of the temperature-dependent diffusion growth of ϕ ternary IMC in the Mg–Al–Zn system is further discussed. [ABSTRACT FROM AUTHOR]

This work aims to study the differences in the microstructure and mechanical properties of a new nickel-based alloy without γ′ phase during long-term aging at 675 °C. The test alloy C-HRA-2 for next-generation power plant applications was simulated for 5000 h at the service temperature. The formation of long needle-like M 23 C 6 carbides inside the grains is a unique phenomenon compared to conventional nickel-based alloys. After aging for 500 h, the microstructure, strength and hardness tend to be stable, while the toughness shows a slow downward trend. Even so, the toughness still exceeds 110 J after aging for 5000 h. Compared with the alloy 617/617B containing the γ′ phase, the strength of the alloy without γ′ phase (C-HRA-2) reduced by about 5–10%, and the hardness lowered by 5–15%, but the elongation also increased by about 10–50%, and the toughness increased by about two times. • The formation of long needle-like M 23 C 6 carbides in alloy C-HRA-2 was investigated. • The toughness reached above 110 J after aging at 675 °C for 5000 h. • Quantitative phase analysis was performed on all samples. • The effect of γ′ phase -free on nickel-based alloy was analyzed. [ABSTRACT FROM AUTHOR]

In this paper, 10 groups of ternary Ag–Sn–Zn diffusion couples were prepared under 873, 973 and 1073 K within the fcc single-phase region. The element distribution across the diffusional interface was measured by EPMA, and a high-throughput determination of atomic mobilities in Ag-rich fcc Ag–Sn–Zn alloys was performed by using HitDIC (High-Throughput Determination of Interdiffusion Coefficients, https://hitdic.com/) software in the framework of the numerical inverse method. A self-consistent set of atomic mobility parameters was obtained. Reliability of the evaluated atomic mobility parameters were further verified by reasonably reproducing the experimental composition profiles. Insight into the composition- and temperature-dependence of various diffusion properties in fcc Ag–Sn–Zn alloy were subsequently retrieved and discussed. Furthermore, through the related Arrhenius information, the diffusion frequency factors and diffusion activity energies within the corresponding temperature and the composition range were obtained. • Ten groups of fcc single-phase Ag–Sn–Zn diffusion couples were prepared. • Composition-dependent interdiffusivities in fcc Ag–Sn–Zn alloys were obtained. • With a numerical inverse method, the high-throughput determination was realized. • The reliability of the obtained interdiffusivities was comprehensively validated. [ABSTRACT FROM AUTHOR]

Heretofore, understandings about the effects of scandium on properties of magnesium alloys for biodegradable implant applications are extremely limited. In the present study, four Mg–1.5Zn–0.6Zr– x Sc (ZK21– x Sc, x  = 0, 0.2, 0.5, 1.0 wt%) alloys were fabricated and investigated with respect to the microstructure and mechanical properties. Microstructure characterization indicated that grain sizes were refined and more precipitated particles were observed with increasing Sc addition. Mechanical testing revealed that improved yield strength and decreased elongation were obtained after Sc being added. Compared with other developed Mg alloys, the ZK21–0.2Sc alloy demonstrates balanced combination of strength and elongation, which shows great potential in biodegradable materials application. [ABSTRACT FROM AUTHOR]

• Propose a simple way for studying certain features of ablation castings. • Eutectic silicon is modified in A356 ablation castings due to water cooling. • Ablation castings have a faster heat treatment response than metal mold castings. This study focused on using a simple quench method to study the effect of ablation water cooling on microstructural features and heat treatment response of A356 alloy. Molten alloy of a given quantity was solidified in water and the resultant microstructure was characterized and compared with that solidified in metal molds and that reported on ablation castings. It is found that the simple method is suitable in simulating certain features of eutectic solidification during ablation casting. The microstructural length scales obtained in this multicomponent alloy are comparable to that predicted by theories developed for binary alloys. The heat treatment response of the water cooled samples are much faster than that of conventional castings which can be translated into reduced energy consumptions and significant cost savings if the heat treating process is optimized for ablation casting. [ABSTRACT FROM AUTHOR]

A comparative study on the microstructures and mechanical properties of the extruded Mg-xCa/Mn/Ce (x = 0.25, 0.5, 1, 2.0 wt%) alloys and pure Mg has been carried out. It was found that when the addition of Ca, Mn and Ce was more than 0.25 wt%, 0.5 wt% and 0.5 wt% respectively, microstructures with fine grain sizes smaller than 5 μm can be achieved by extruding at 375 °C with a extrusion ratio of 30 and a ram speed of 0.8 mm/s. While the grain size of pure magnesium extruded under the same condition was 26.6 μm. The addition of Ca, Mn or Ce has significant effects on the textures of the extruded Mg-xCa/Mn/Ce alloys. The maximum intensity peaks in PF and IPF of Mg are all deviated by a certain degree with the addition of Ca, Mn or Ce. In the 12 extrusion alloys, Mg-0.5Ca、Mg–2Mn and Mg–1Ce exhibited better mechanical properties, whose ultimate tensile strength and elongation are 243.6 MPa, 233.7 MPa, 321.5 MPa and 25.6%, 20.7%, 7.6%. While the ultimate tensile strength and elongation of as-extruded pure Mg is 173.8 MPa and 16.0% respectively. Mg-xCa and Mg-0.25Ce alloys with weak texture showed weaker tension-compression asymmetry. The experimental results showed that it is feasible to prepare fine grained (<5 μm) Mg-xCa/Mn/Ce alloys with much improved mechanical properties using conventional extrusion. [ABSTRACT FROM AUTHOR]

In this paper, a new type of non-γ′ phase nickel-based heat-resistant alloy C-HRA-2 was studied by solution heat treatment. It was determined that after removing the γ′ phase, the carbide dissolution temperature was reduced and the grain growth process of nickel-based alloy was accelerated. It was also determined that the dissolution of M 23 C 6 carbides is attributable to a gradual decomposition and diffusion process. High-temperature confocal scanning laser microscopy (HT-CLSM) was utilized to simulate the grain growth of the alloy during the solid solution treatment. The results revealed that only a portion of the grain boundaries migrated simultaneously, while most of the migration directions and distances followed the classical migration theory. Some grain boundaries expanded into new grain boundaries via sub-crystal rotation during grain growth. Following solution heat treatment, the yield strength of the alloy was mainly attributed to solution strengthening and grain boundary strengthening. The solution strengthening was found to be approximately 230 MPa and the grain boundary strengthening was found to be approximately 37–118 MPa. Carbides increase the precipitation strengthening of the alloy during dissolution. • The dissolution behavior of M 23 C 6 carbides in alloy C-HRA-2 was investigated. • The grain growth behavior was observed in-situ at high temperature. • The yield strength composition of the alloy after solution was subdivided. • Effect of γ′ phase -free on solution treatment of the alloy was analyzed. [ABSTRACT FROM AUTHOR]