Lee Hsun Lecture Series

Topic: Stress Contributions in Nickel-Base Superalloys

Speaker: Prof. Dr.-Ing. Uwe Glatzel
        Metals and Alloys, University Bayreuth, Germany

Abstract:

Nickel-base superalloys are widely used as material for blades in flight engines or stationary gas turbines. These blades are manufactured in complex shapes as single crystals (SX). Due to centrifugal forces, a high constant stress of 100 MPa and more are present at the foot of the blade.

Several strengthening mechanisms are present in these two-phase materials. Internal stresses of most of these strengthening mechanisms can be estimated by simple considerations. Some of these internal stresses interact or transform into each other. Due to coarsening of precipitates, the Orowan stress needed to push a dislocation into a narrow matrix channel is drastically reduced during service.

A comparatively low and by theory difficult to estimate internal stress contribution is provided by solid solution strengthening of the matrix. This strengthening mechanism can be considered as the backbone and being steadily active. An intense research has been carried out within my group in order to estimate this strengthening mechanism experimentally and to quantify the influence of several important solid solution strengthening elements, such as W, Mo and Re. This research has opened the pathway for the development of a new SX Ni-base superalloy composition.

Taking these considerations as well as other demands on turbine blades into account, a somewhat speculative outlook will be presented toward materials which might replace SX Ni-base superalloys in future, summarized by the keywords "Beyond Nickel-Based Superalloys".