Abstract:The notable effect of atomic radius ratio of the components of L12-0rdered alloys on the temperature dependence of their strength has been demonstrated using suitable alloys and alloying elements. Pt3 In and Pt3Sn were chosen and partial substitutions were made of the minor components with Ga and TI, and with Ge and Pb, respectively, keeping the electron concentration of the system constant. The positive temperature dependence was generally found to be strengthened by the smaller substituting atoms and to be w… Show more
“…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.
“…It was shown that among nickel base A3B compounds with B as one of transition elements, the structures of Ni3Ti, Ni3Zr and Ni3Hf themselves can not be L12(cT) but are the D024(chT) and that as the minority component of each compound changes from (Ti, Zr, Hf) to (V, Nb, Ta), the structures involving R component such as D022(cR) or D019(hR) appear (30) This would by itself predict that in Ni3Al, the addition of these transition metal elements results in reducing the stability of its cT structure and thereby enhancing the mechanical anomaly. With platinum based A3B compounds, a better illustration is possible.…”
Section: The Magnitude Of the Positive Temperature Dependence Of Strementioning
A systematic investigation is carried out on the temperature dependence of strength in ternary Ni3Al compounds with additions of transition metal elements. The rate of solid solution hardening per one with the rate of lattice parameter change, da/dc, although a linear correlation has been found for the addition of B-subgroup elements. The rate of change in activation energy to provide the anomalous positive temperature dependence of strength per one atomic percent of the solute, du/dc, is then evaluated. Together with the results for the addition of B-subgroup elements, the apparent valence is assigned for each transition metal element by an analogy utilizing equi-valence contour determined for B-subgroup elements. Then it becomes possible to discuss the relative magnitude of the mechanical anomaly in Ni3Al in terms of the phase stability concept of L12 phase, in which e/a ratio as well as the atomic radius ratio of the compound, RB/RA, as affected by ternary addition is an important parameter to alter the stability of the phase against other geometrically close packed phases. (Received August 9, 1985) Keywords shown that the characteristic mechanical anomaly of the compound is enhanced by such additions as to increase the electron-atom ratio and/or the atomic radius ratio of the compound. Then the rate of change in activation energy for the thermally activated process to provide the mechanical anomaly per one atomic percent of solute, dU/dc, has been evaluated for a variety of ternary alloying elements in relation to the valence difference between a ternary B-subgroup element andshown that the rate of solid solution hardening seems to be proportional to that of change in lattice parameter by additions of the Bsubgroup element, da/dc.In the present investigation, a similar strategy is extended toward evaluating the role of ternary additions of transition elements into the compound in its mechanical properties. Practically information on the effects of ter-
“…Oya et al [7] reported that the four L1 2 compounds, Ni 3 Al, Ni 3 Ga, Ni 3 Ge, and Ni 3 Si, form a tetrahedron of continuous solid solution in a temperature range of 900 -1000 8C, which means that these four L1 2 compounds are completely miscible. Suzuki et al [8,9] showed a continuous solid solution formation between Ni 3 Ge and Fe 3 Ge. The existence of the continuous solid solutions Cu 3 Au -Cu 3 Pd and Cu 3 Au -Cu 3 Pt was demonstrated by Nakahigashi et al [10].…”
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