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The ordered γ′-(Ni, Cu)3Al is a crucial strengthening phase that improves the high-temperature resistance of Cu-based alloys, so it is important to predict the kinetic evolution of the composition and microstructure of the phase for high-temperature applications. Herein, this paper discusses the temporal evolution of the composition and coarsening of the γ′ phase in a model ternary Cu50Ni37.5Al12.5 (at%) alloy during isothermal aging at 600, 700, 800, and 900 °C for 1–36 h. It is found that the γ′ phase composition evolves linearly toward a binary γ′ phase as the aging time increases during the process of aging at 800 and 900 °C, which cannot be predicted by the ternary phase diagrams alone. Meanwhile, through the utilization of the aforementioned linear law, the γ phase composition can be predicted at a given temperature within the alloy by determining the volume fraction of the γ′ phase. Additionally, the activation energy for coarsening decreases, and the coarsening rate of the γ′ phase increases owing to the higher diffusion rate of Cu at high temperatures. The addition of microalloying elements with strong enthalpic interactions is beneficial for reinforcing the structural stability of the γ′ phase. This work provides a simple method for the compositional analysis and performance prediction of Cu–Ni–Al alloys at elevated temperatures and sheds light on the subsequent compositional design and optimization of Cu-based high-temperature alloys. [ABSTRACT FROM AUTHOR]

The alloy composition and sensitization behavior are crucial factors that cannot be overlooked in Al–Mg alloys. The effect of Zn addition on mechanical properties and sensitization behavior of 5083 alloy was investigated by tensile tests, weight loss experiments, and first-principles calculation in this paper. The results show that Zn can significantly improve the strength and sensitization behavior of the alloy. The tensile strength of the cold-rolled alloy increased from 459 to 498 MPa with the addition of 1.5%Zn. Furthermore, by incorporating 2.0% Zn, the mass loss of the cold-rolled alloy after sensitization at 170℃/1 h decreased from 49.3 mg·cm−2 to 19.5 mg·cm−2. First-principles calculations indicate that Mg clusters can only exist stably near grain boundaries, while Mg–Zn clusters can exist stably both within and at grain boundaries. This reduces the number of corrosive media at grain boundaries and weakens their continuity. Moreover, the energy barrier that T-phase precipitation needs to overcome during precipitation is lower than β-phase, which transforms the stabilization schedule of the alloy from 240℃/12 h without Zn to that 210℃/4 h with 2.0% Zn-containing. The synergistic effects of Zn content and sensitization on the properties of the alloy were revealed, which sheds some light for the design of the composition and processing method according to application scenarios. [ABSTRACT FROM AUTHOR]

In this paper, the effect of deep cryogenic treatment (DCT) on the microstructure and properties of automotive 6063 aluminum alloy at different times was investigated with automotive 6063 aluminum alloy as the research object. The results show that under the conditions of deep cryogenic treatment, the lattice distortion occurs in the alloy matrix microstructure, and the resulting internal stress promotes the large proliferation of dislocations within the alloy and the increase of dislocation density; meanwhile, after the deep cryogenic treatment, the deformed grains are transformed into recrystallized and sub-crystals structural grains, the grains are refined, and the size of the grains is refined from the original 25.2 μm to 20.3 μm, with fine equiaxed crystals. Among them, the mechanical properties of the DCT36h specimen were the best, and its hardness, tensile strength, yield strength and elongation reached 142.44 HV, 328.32 MPa, 177.42 MPa, and 29.29%, which were 34.17%, 5.62%, 11.10%, and 32.77% higher than the original sample, respectively. We believe that the main mechanism for the increase in toughness is multiple reinforcement such as dislocation strengthening, grain refinement strengthening, precipitated phase strengthening and texture strengthening. [ABSTRACT FROM AUTHOR]

High frequency fatigue behavior of near surface of turbine disk are critical for its application and operation. High frequency indentation fatigue tests of GH4169 alloy under different load amplitudes, frequencies and mean loads at small length scale were conducted, and the dependence of load amplitude, load frequency and mean load on high frequency indentation fatigue property of GH4169 alloy are discussed in this paper. Depth amplitude (ha), mean depth (hm) and depth propagation rate (dh/dN) were employed as evaluation indicators of the indentation behavior. Results show that depth amplitude is only relevant with load amplitude, while mean depth is related to all the adopted influencing factors, ranked in an ascending order as load amplitude, mean load and frequency with a ranking relation of nm1=1.4 < nm2=1.71 < nm3=2.02. Furthermore, a modified Paris law was utilized to reveal the fatigue mechanism, and found the fatigue mechanism is dominated by intrinsic mechanism under the influence of mean load and load amplitude, while for the influence of frequency, the fatigue mechanism is governed by extrinsic mechanisms. Combined with SEM results and three-dimensional morphology analysis, it can be deduced that dislocation movement mode in high frequency indentation fatigue is dislocation slip. [ABSTRACT FROM AUTHOR]

Ductility dip cracking (DDC) is a solid-state failure occurring during multi-pass solidification processes (e.g., welding, additive manufacturing) for FCC alloys that exhibit a distinct dip in their ductility at intermediate temperatures. While the phenomenon has been studied for over a century, the majority of current research focuses on a subset of DDC-susceptible FCC alloys (Ni–Cr–Fe). The review paper herein presents an analysis of published data to evaluate the current state of understanding regarding the materials mechanisms at work. Recent advances in test methods have permitted highly controlled approaches for testing and quantifying DDC, but the wide range of unique tests often provide conflicting results regarding the fundamental materials behaviors and underlying mechanisms. At present, three mechanisms have been proposed for DDC: grain boundary sliding, precipitate-induced strain, and impurity element segregation. While the majority of published studies support grain boundary sliding as the primary mechanism of DDC, an examination of the aggregate data available across multiple studies suggests combinatorial impact of simultaneous (and competing) mechanisms for DDC. Further, the long-held assumptions regarding the negative impact of key alloying elements become less convincing when comparing results across studies. There are considerable future opportunities for research on DDC behaviors in other alloy systems, and there are a lacunae of data when considering the effect of welding process parameters on DDC and the use of modeling and simulation approaches to understand the DDC behavior in the highly susceptible FCC alloy systems. [ABSTRACT FROM AUTHOR]