ABSTRACT
The development to commercial application of a range of nickel-based superalloys, specifically for the production of complex castings in the form of single crystals, has contributed significantly to the progressive improvement in gas turbine efficiency by allowing significant increases in operating temperature. Until now, single crystal superalloys have been predominantly used to produce relatively small rotating turbine blades for aeroengines. However, there is a growing trend to apply this technology to a wider range of aero components which experience more complex loading conditions involving multiaxial stresses and varying stresses and temperatures. In addition, their application is being extended to industrial gas turbines for power generation, where components are expected to have much longer lives and to experience different loading histories from those in aeroengines. Solidification of such large industrial components involves lower temperature gradients and solidification rates than have been previously used, and this leads to difficulties in controlling the crystal orientation and to a propensity for the generation of solidification defects.
