“…In general, substitution of ternary elements away from the stoichiometric composition reduces the composition region in which the L1 2 structure is stable by reducing the average electron atom ratio or increasing the atomic radius ratio. 5,39–42 The effects of compositional deviations from stoichiometry 32,43 and ternary additions 44–46 also fit the predicted behaviour of this concept. 8 The crystal structure of L1 2 (left), and D0 22 (right)…”
Section: Anomalous Yield In Intermetallic L12 Alloyssupporting
Nickel superalloys exhibit a remarkable characteristic. Their yield stress that required to cause the onset of plastic deformation increases with temperature. This typically occurs up to a temperature of around 800°C. This effect is thought to originate from the precipitates of the microstructure, which have an L12-ordered crystal structure. A number of other L12-based alloys exhibit similar yield properties. It is generally accepted that this is caused by the exhaustion of dislocations by cross-slip from {111} glide planes to {010} planes on which they are sessile. However, the underlying mechanisms that control this cross-slipping process are yet to be fully understood, with little consistency between empirical results and theory. A critical review of the various theories surrounding nickel superalloys is offered.
“…In general, substitution of ternary elements away from the stoichiometric composition reduces the composition region in which the L1 2 structure is stable by reducing the average electron atom ratio or increasing the atomic radius ratio. 5,39–42 The effects of compositional deviations from stoichiometry 32,43 and ternary additions 44–46 also fit the predicted behaviour of this concept. 8 The crystal structure of L1 2 (left), and D0 22 (right)…”
Section: Anomalous Yield In Intermetallic L12 Alloyssupporting
Nickel superalloys exhibit a remarkable characteristic. Their yield stress that required to cause the onset of plastic deformation increases with temperature. This typically occurs up to a temperature of around 800°C. This effect is thought to originate from the precipitates of the microstructure, which have an L12-ordered crystal structure. A number of other L12-based alloys exhibit similar yield properties. It is generally accepted that this is caused by the exhaustion of dislocations by cross-slip from {111} glide planes to {010} planes on which they are sessile. However, the underlying mechanisms that control this cross-slipping process are yet to be fully understood, with little consistency between empirical results and theory. A critical review of the various theories surrounding nickel superalloys is offered.
“…The preparation of the alloy containing Zn, being a volatile element, was done by hot pressing and sintering, which details were described elsewhere (11 Then the total flow stress can be tion energy, R is the gas constant, T is temperature and A and B are constants. To be noted is that the constant B is defined as 1/ G(dG/dT), where G is the shear modulus, and can be estimated to be 0.0003 for Ni3Al(9)(7).…”
A systematic evaluation has been made on the magnitude of the positive temperature dependence of strength in Ni3Al as affected by ternary additions of B-subgroup elements. The rate of change in activation energy to provide the mechanical anomaly per one atomic per cent of the solute, dU/dc, is determined for a variety of the ternary additions. It is shown that the larger the valence difference between the parameter change in the compound per one atomic percent of the solute, da/dc, the larger the dU/dC. These are well interpreted in terms of the phase stability concept to determine the relative magnitude of the mechanical anomaly in the Ll2 compounds, in which e/a ratio of the compound and the atomic radius ratio of the components, Re/RA, are the key factors to alter the stability of the phase against other geometrically close packed phases and thereby control the occurrence and the magnitude of the mechanical anomaly. The effect of ternary additions of B-subgroup elements on the rate of solid solution An intermetallic compound Ni3Al is one of the L12 compounds which show an anomalous positive temperature dependence of strength. The compound based on Ni3Al is a major microstructural constituent in commercial nickel base superalloys as precipitates to provide dispersion strengthening, and its volume fraction often reaches 60% or more. In alloy designing the superalloys for an improved high temperature performance, the best utilization of this compound is anticipated, which mechanical properties are known to be strongly affected by ternary alloy substitutions for one of or both of the components.In considering the effect of ternary additions on the mechanical properties of the compound Ni3Al, two factors are important, and they are the solid solution hardening and the magnitude of the positive temperature dependence of strength. Historically a work by Guard and Westbrook(1) was the first attempt on this regard in which the temperature dependence of hardness in Ni3Al as affected by various ternary additions was investigated. Recently the temperature dependence of 0.2% flow stress in Ni3Al with additions of several ternary alloying elements has been investigated by Thornton et a1.(2), Rawlings and StatonBevan(3) and Aoki and Izumi(4). There have been several reports(5)-(8) on the crystallographic orientation dependence of flow stress in single crystalline Ni3Al with small additions of Ti, Nb or W, but in those cases the alloy additions were made in order to suppress the peritectic reaction in the Ni-Al binary
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