A New Single Crystal Superalloy for Power Generation Applications :

• A newly developed single crystal superalloy (known as STAL15) is described which is suitable for use in first stage blades of highly efficient industrial gas turbines (IGTs). With 15 wt% Cr and 4.55 wt% Al, the alloy combines good corrosion and oxidation resistance with sufficient creep and fatigue performance. Thus a novel and useful balance of environmental and mechanical properties is displayed. In this paper, the details of the development project are described. The new alloy is shown to be an alumina (Al2O3) former; the mechanisms behind the Al2O3-formation process are studied and the effects arising from changes in the chemical composition have been modelled. In addition, the mechanical properties in terms of creep and fatigue resistance are evaluated together with the alloy stability during long term (up to 10,000 hours) exposure. For such applications, the new alloy is superior to existing nickel-based single crystal superalloys designed for aero engine applications and which are optimized for very high creep resistance; experience has shown that they are not ideal for use in IGTs of the type used for power generation or mechanical drive, due to their low corrosion resistance. The main reason for this is that IGTs are exposed to more harsh conditions in terms of air quality through the turbine and significantly longer time between overhaul/inspection. Traditionally this has been handled by use of polycrystalline alloys such as IN792 and IN738LC or the single crystal alloy PWA1484; unfortunately these do not form a protective Al2O3 layer and hence display limited resistance to environmental degradation. The new alloy does not display this weakness and is therefore highly optimised for IGT applications.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Teknisk mekanik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Applied Mechanics (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Metallurgi och metalliska material (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Metallurgy and Metallic Materials (hsv//eng)

Nyckelord

Alloy development

single crystal superalloy

STAL15

oxidation

corrosion

creep deformation

thermomechanical fatigue

Si-additions

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