Abstract

The newly designed ingot-metallurgy nickel-based superalloy SDZhS-15 intended for disc applications at operating temperatures up to 800–850 °C was subjected to homogenization annealing and canned forging at subsolvus temperatures, followed by solid solution treatment and ageing. Mostly a fine-grained recrystallized microstructure was obtained in the forgings. It was revealed that post-forging solid solution treatment at T > (Ts-50), where Ts is the γ′ solvus temperature, led to a significant γ grain growth, which in turn led to a decrease in strength and ductility of the superalloy. The solution treatment at (Ts-60)–(Ts-50) allowed to save fine γ grains (dγ = 10–20 μm) and to provide the formation of secondary γ′ precipitates with a size of around 0.1 μm. In the forged and heat-treated conditions, the superalloy demonstrated superior mechanical properties, particularly excellent creep resistance at 650–850 °C in the stress range of 400–1200 MPa. Microstructure examination of the creep-tested samples showed that a decrease in the creep resistance at 850 °C can be associated with enhanced diffusivity along γ grain and γ/γ′ interphase boundaries leading to formation of cracks along the boundaries. In spite of the heavy alloying, the topologically close-packed phases were not detected in the superalloy, including in the creep tested samples.

Highlights

  • Improving the energy efficiency of gas turbine engines (GTE) and similar energy-conversion systems is dependent on the development of new advanced materials with enhanced strength, heat resistance, and/or reduced specific weight

  • The as-cast material was subjected to long-term homogenization annealing at near the γ0 solvus temperature and solid solution treatment at 1210 ◦ C, followed by air cooling and two-stage ageing at 860 ◦ C (6 h) and 750 ◦ C (32 h)

  • The secondary γ0 phase precipitated during air cooling after solution treatment and ageing

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Summary

Introduction

Improving the energy efficiency of gas turbine engines (GTE) and similar energy-conversion systems is dependent on the development of new advanced materials with enhanced strength, heat resistance, and/or reduced specific weight. Increasing demands are being placed on nickel-based superalloys, which are widely used for manufacturing of rotary engine parts such as high pressure discs in GTE [1]. For this purpose, novel heavily alloyed disc superalloys with a higher content of the γ0 (Ni3 Al) forming elements, such as Russian superalloy SDZhS-15, are being designed. Novel heavily alloyed disc superalloys with a higher content of the γ0 (Ni3 Al) forming elements, such as Russian superalloy SDZhS-15, are being designed In this superalloy, the content of (Al + Ti + Nb + Ta) is 14.8 at. The goals of alloying were to: (i) increase the γ0 solvus temperature

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