Abstract

Very high temperature creep properties of twelve different Ni-based single crystal superalloys have been investigated at 1250 °C and under different initial applied stresses. The creep strength at this temperature is mainly controlled by the remaining γ′ volume fraction. Other parameters such as the γ′ precipitate after microstructure evolution and the γ/γ′ lattice parameter mismatch seem to affect the creep strength to a lesser degree in these conditions. The Norton Law creep exponent lies in the range 6–9 for most of the alloys studied, suggesting that dislocation glide and climb are the rate limiting deformation mechanisms. Damage mechanisms in these extreme conditions comprise creep strain accumulation leading to pronounced necking and to recrystallization in the most severely deformed sections of the specimens.

Highlights

  • Ni-based single crystal (SX) superalloys are key materials for the manufacture of blades and vanes used in the hottest parts of the most advanced aero-engines and industrial gas turbines [1,2,3]

  • Many previous research has focused on the creep strength, deformation mechanisms, and microstructure evolution at temperatures between 700 ◦C and 1150 ◦C [3,4,5,6,7,8,9,10,11,12,13,14,15], corresponding to regular service conditions

  • Ultra-high temperature creep performance data of Ni-based SX superalloys at temperatures above 1200 ◦C are limited to only a few studies [4,16,17,18,19,20]

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Summary

Introduction

Ni-based single crystal (SX) superalloys are key materials for the manufacture of blades and vanes used in the hottest parts of the most advanced aero-engines and industrial gas turbines [1,2,3] These alloys are currently used at temperatures of up to 1100 ◦C–1150 ◦C during operation of civil and military aero-engines owing to a combination of both good environmental resistance to corrosion and oxidation and excellent mechanical properties, especially under high temperature creep conditions. These properties are inherited from the specific microstructure of Ni-based superalloys consisting of a high volume fraction (>50%) of the γ phase (L12 structure) strengthening precipitates embedded coherently in an FCC disordered γ matrix with a high content of solid solution strengthening elements.

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