Abstract:In this study the L1 2 gamma prime phase (based on Ni 3 Al) has been highly alloyed with Cr, Co, W, and Ta in order to examine the effects on strengthening and thermal stability. The order-disorder transition temperature of gamma prime is decreased with higher alloying content. Thermodynamic calculations show that the ordering enthalpy decreases as the entropy term increases. Conversely, the hardness can be 1.5 times higher comparing to that of a conventional Ni-based superalloy. This indicates that the streng… Show more
“…According to JMatPro calculations, the APB energies of γ′ phase in HESA and CMSX-2 are 0.22 and 0.19 J/m 2 , respectively. Consequently, higher APB energy of γ′ may contribute to some degree of strengthening in HESA 28 . Figure 3 ( a ) The strain-aged cellular microstructure of γ/γ′, and (b) plot of - C γ vs. C m - C γ of HESA.…”
This article presents the high temperature tensile and creep behaviors of a novel high entropy alloy (HEA). The microstructure of this HEA resembles that of advanced superalloys with a high entropy FCC matrix and L12 ordered precipitates, so it is also named as “high entropy superalloy (HESA)”. The tensile yield strengths of HESA surpass those of the reported HEAs from room temperature to elevated temperatures; furthermore, its creep resistance at 982 °C can be compared to those of some Ni-based superalloys. Analysis on experimental results indicate that HESA could be strengthened by the low stacking-fault energy of the matrix, high anti-phase boundary energy of the strengthening precipitate, and thermally stable microstructure. Positive misfit between FCC matrix and precipitate has yielded parallel raft microstructure during creep at 982 °C, and the creep curves of HESA were dominated by tertiary creep behavior. To the best of authors’ knowledge, this article is the first to present the elevated temperature tensile creep study on full scale specimens of a high entropy alloy, and the potential of HESA for high temperature structural application is discussed.
“…According to JMatPro calculations, the APB energies of γ′ phase in HESA and CMSX-2 are 0.22 and 0.19 J/m 2 , respectively. Consequently, higher APB energy of γ′ may contribute to some degree of strengthening in HESA 28 . Figure 3 ( a ) The strain-aged cellular microstructure of γ/γ′, and (b) plot of - C γ vs. C m - C γ of HESA.…”
This article presents the high temperature tensile and creep behaviors of a novel high entropy alloy (HEA). The microstructure of this HEA resembles that of advanced superalloys with a high entropy FCC matrix and L12 ordered precipitates, so it is also named as “high entropy superalloy (HESA)”. The tensile yield strengths of HESA surpass those of the reported HEAs from room temperature to elevated temperatures; furthermore, its creep resistance at 982 °C can be compared to those of some Ni-based superalloys. Analysis on experimental results indicate that HESA could be strengthened by the low stacking-fault energy of the matrix, high anti-phase boundary energy of the strengthening precipitate, and thermally stable microstructure. Positive misfit between FCC matrix and precipitate has yielded parallel raft microstructure during creep at 982 °C, and the creep curves of HESA were dominated by tertiary creep behavior. To the best of authors’ knowledge, this article is the first to present the elevated temperature tensile creep study on full scale specimens of a high entropy alloy, and the potential of HESA for high temperature structural application is discussed.
“…This distortion interacts with the dislocations preventing their movement and then strengthening the sample. Improvement in hardness can be achieved due to lattice distortion strengthening and higher anti-phase boundary energy of gamma prime [33].…”
Section: The Formation Energy and The System Stabilitymentioning
In this study, the copper doping effect on the NiAl structural stability, strength, and electronic structure was investigated. The samples were prepared using induction melting at 2073 K. This material presents good mechanical and physical properties such as hightemperature strength, fatigue or impact, and corrosion resistance which meet technical requirements of many applications. The microstructure of the Cu-doped nickel aluminide was studied using a metallurgical microscope and its lattice parameter was also studied and characterized using an X-ray diffractometer for different concentrations of Cu. The lattice constant of the existing phases was calculated, and it was found that the lattice distortion and gamma prime phase energy have high values allowing the increase of the entropy term of the alloy and subsequently increasing its hardness. From the ab-initio calculation, it was determined that the Cu atoms have the Al sites as a preferred site and prefer to bond with Ni atoms which leads to the improvement of the material hardness. Ab-initio density functional theory was applied to study the formation energy that revealed increasing with Cu amount.
“…From another perspective, HEA phase formation during fabrication via the melting and casting route is suggested to hinge on binary constituent pairs rather than individual constituent elements [ 75 , 76 ]. An HEA system such as the AlCoCrFeNi alloy forms a BCC structure after processing; although among the constituent elements, only Cr and Fe have BCC crystal structures.…”
Section: Microstructural Evolution Of Heas Synthesized Through the Melting And Casting Routementioning
Microstructural phase evolution during melting and casting depends on the rate of cooling, the collective mobility of constituent elements, and binary constituent pairs. Parameters used in mechanical alloying and spark plasma sintering, the initial structure of binary alloy pairs, are some of the factors that influence phase evolution in powder-metallurgy-produced HEAs. Factors such as powder flowability, laser power, powder thickness and shape, scan spacing, and volumetric energy density (VED) all play important roles in determining the resulting microstructure in additive manufacturing technology. Large lattice distortion could hinder dislocation motion in HEAs, and this could influence the microstructure, especially at high temperatures, leading to improved mechanical properties in some HEAs. Mechanical properties of some HEAs can be influenced through solid solution hardening, precipitation hardening, grain boundary strengthening, and dislocation hardening. Despite the HEA system showing reliable potential engineering properties if commercialized, there is a need to examine the effects that processing routes have on the microstructure in relation to mechanical properties. This review discusses these effects as well as other factors involved.
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