Abstract
Ir-based superalloys are irreplaceable in some specific harsh conditions regardless of their cost and high density. In order to develop a new class of Ir-based superalloy for future ultrahigh-temperature applications, the microstructure evolution, phase relationships, and mechanical properties of Ir–Al–W–Ta alloys with γ/γ′ two-phase structure were investigated. Room- and high-temperature compressions at 1300 °C, and room-temperature nanoindentation for the Ta-containing Ir–6Al–13W alloys were conducted. The results show that the addition of Ta can significantly improve the high-temperature mechanical properties, but does not change the fracture mode of the Ir-based two-phase superalloys. The compressive strength of quaternary alloys can be attributed to the precipitation of γ′-Ir3(Al, W) phase and solid solution strengthening. The microstructure and mechanical properties of Ir–Al–W–Ta quaternary alloys exhibit promising characteristics for the development of high-temperature materials.
Highlights
Structural materials need to be used at even higher operating temperatures than ever before.The temperature capability limit of Ni-based superalloys reaches about 1100 ◦ C, which is approximately85% of their melting points [1]
In order to promote the redissolution of the second phase in Ir matrix and obtain a homogenized solid solution, we consider that the homogenization temperatures in Ir–6Al–13W–xTa alloys should be performed at a higher temperature and the holding time needs to be extended
The results showed that Ir–6Al–13W γ/γ0 two-phase refractory superalloys alloyed with Ta are superior to the ternary Ir–6Al–13W alloy as an ultrahigh-temperature structural material in terms of strength, fracture behavior, and ductility
Summary
Structural materials need to be used at even higher operating temperatures than ever before.The temperature capability limit of Ni-based superalloys reaches about 1100 ◦ C, which is approximately85% of their melting points [1]. Structural materials need to be used at even higher operating temperatures than ever before. Many attempts have been made to develop intermetallic and refractory alloys which hold higher operating temperatures [2,3,4,5,6]. Platinum group metals are one of the candidates for the development of new refractory superalloys, due to their high melting temperature, exceptional mechanical properties and superior oxidation resistance. The melting point of Ir is 2447 ◦ C and it is the only metal that still possesses excellent high-temperature mechanical properties above 1600 ◦ C in an oxidizing atmosphere [7]. An intermetallic ternary γ0 -Ir3 (Al, W) phase with an L12 structure was discovered in the Ir–Al–W ternary system by Sato et al [8]. The coherent relationship between fcc-structure Ir and L12 -structure Ir3 (Al, W) in Ir–Al–W ternary systems is similar to the coexistence of γ/γ0 phases in
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