Alloying Behavior of Ni<SUB>3</SUB>M-Type Compounds with D0<SUB>a</SUB> Structure

Abstract

The atom substitution preference of ternary additions in Ni 3 M-type GCP (geometrically close-packed) compounds with D0 a structure was determined from the direction of single-phase region of the GCP phase on the reported ternary phase diagrams. In Ni 3 Nb, Co and Cu preferred the substitution for Ni-site, Hf, Ta, Ti, V and W the substitution for Nb-site, and Fe the substitution for both sites. In Ni 3 Ta, Co, Cu, Fe, Ir, Mn and Re preferred the substitution for Ni-site, Mo and Nb the substitution for Ta-site, and Al and Cr the substitution for both sites. In Ni 3 Mo, Pd and W preferred the substitution for Ni-site, and Al, Nb, Ta, Ti and Zr the substitution for Mo-site. The thermodynamic model, which was based on the change in heat of formation of the host compound by a small addition of ternary solute, was applied to predict the atom substitution preference of ternary additions. The heat of compound formation used in the thermodynamic calculation was derived from Miedema's formula. Good agreement was obtained between the thermodynamic model and the result of the literature search. For Ni 3 Mo, with a small negative heat of formation, a weak binding force between the constituent elements is often enhanced by the addition of the ternary elements that substitute for Mo-site.

On the Role of Superlattice Structures with Ni3X-type Composition in Selected Ni-Based Superalloys with Commercial Grades

“…9. Geometrically, the transformation involves a change in the cubic stacking sequence of close-packed planes in the L1 2 superlattice (ccc) into mixed hexagonal (h)-cubic (c) sequence (hchc) in the D0 24 superlattice [6]. Therefore, there is one-to-one correspondence between the close-packed planes and directions in the two superlattices expressed by the following orientation relationship: Transformation of the L1 2 superlattice into the D0 24 superlattice is promoted by the high Ti content of the alloy with respect to Al and the thermodynamic stability of Ni 3 Ti in the equilibrium Ni-Ti binary system [28].…”

“…Since the inception of the γ′-phase with Ni 3 Al-based composition as the primary source of strengthening turbine blade superalloys in the 1940s [1,2], Ni 3 X-type intermetallic compounds have emerged as potential candidate for developing new alloys for high-temperature structural applications [3][4][5][6][7][8]. Although in general, intermetallic compounds are characterized by potentially useful combination of properties, their widespread engineering applications are limited by relatively low ductility [4].…”

“…It is well known that Ni 3 X-type compounds such as Ni 3 Al, Ni 3 Ti, Ni 3 Nb, and Ni 3 Mo belong to a class of geometrically close-packed phases which are derivatives of the disordered face-centered cubic (fcc) structure [6,8]. Each phase is built from stacks of ordered close-packed layers of atoms where each atom has a coordination number of 12.…”

A nickel based superalloy reinforced by both Ni3Al and Ni3V ordered-fcc precipitates

“…L1 2 structure is adopted [11]. The only stable D0 22 Ni 3 X type intermetallic is Ni 3 V [11], and notably this has not been exploited in practical alloys.…”

“…L1 2 structure is adopted [11]. The only stable D0 22 Ni 3 X type intermetallic is Ni 3 V [11], and notably this has not been exploited in practical alloys. The D0 22 crystal structure is of particular interest as, unlike the D0 a and D0 24 structures, it is an fcc superlattice structure, being ordered across two fcc unit cells with 20 a 3:1 A to B site ratio (Figure 1c).…”