Ir-base refractory superalloys for ultra-high temperatures

Abstract

The microstructure and compression strengths of Ir-15 at. pct X (X ϭ Ti, Ta, Nb, Hf, Zr, or V) binary alloys at temperatures between room temperature and 1800 ЊC were investigated to evaluate the potential of these alloys for ultra-high-temperature use. The fcc and L1 2 two-phase structures of these alloys were examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The strengths of the Ir-Ta, -Nb, -Hf, and -Zr alloys were above 800 MPa at temperatures up to 1200 ЊC and about 200 MPa at 1800 ЊC. The strengths of these alloys under 1000 ЊC are equivalent to or higher than those of the commercially used Ni-base superalloys, MAR-M247 and CMSX-10. The Nb concentration dependence of strength was investigated using a series of Ir-Nb alloys with Nb concentrations from 0 to 25 at. pct. It was found that the Ir-base alloys were strengthened by L1 2 precipitation hardening. The potential of the Ir-base alloys for ultra-high temperature use is discussed.

Development of a Refractory High Entropy Superalloy

“…Current high-temperature ceramics and intermetallics are incapable of meeting these requirements due to low toughness, while advanced Ni-based superalloys are approaching possible extreme property combinations with respect to their evolution and development; i.e., they still suffer from high density and their maximum temperature use is limited by melting at~1250-1300˝C. New metallic materials with higher melting points, such as W-based alloys hardened with HfC precipitates [2], Co-Re-or Co-Al-W-based alloys [3] or two-phase (FCC + L1 2 ) refractory superalloys based on platinum group metals (Os, Ru, Ir, Rh or Pt) [4,5], have been examined for use beyond Ni-based superalloys. The extremely high density and/or the cost of these new alloys are, however, the main obstacles.…”

Thermophysical Property Measurements of Liquid and Supercooled Iridium by Containerless Methods

“…In particular, it was used to make the standard meter bar of Paris (90% platinum-10% iridium alloy). Research on new iridium-based superalloys has recently been conducted to allow operation of gas turbines (jet engine, power plant generator) at higher temperatures [2]. However, because of its high melting point (2719 K) [1] and its reactivity at high temperatures, it is challenging to perform the measurement of thermophysical properties in its liquid state using conventional methods.…”

Interdiffusion in the Ir-Rich Solid Solutions of Ir-Pt, Ir-Rh, and Ir-Re Binary Alloys

“…Previous studies have demonstrated that Ir can exhibit substantially enhanced high temperature strength through optimal alloying strategies. [2][3][4] Although pure Ir possesses inadequate oxidation resistance (for volatile oxides IrO 3 forms upon air exposure at above 1293 K [5][6][7] ), this can be improved by the addition of Pt or Rh. [8] Another prospective field of Ir application is as the coating for high temperature materials.…”