THE CHARACTERISATION OF THE SINGLE CRYSTAL SUPERALLOY CMSX-4 FOR INDUSTRIAL GAS TURBINE BLADING APPLICATIONS

Abstract

The use of single crystal (SC) superalloys in advanced blade designs of industrial gas turbines (IGT) is widely regarded as necessary in order to achieve the required increases in firing temperatures. However the inherent anisotropy in these materials, as well as the anisotropy occurring due to microstructural changes after high temperature exposure, pose significant difficulties in the design assessment of components. The comprehensive characterisation of a candidate SC superalloy is therefore an important first step in understanding its deformation and failure behaviour, including the microstructural aspects of relevance to lifing prediction, and hence to provide the information required in the development of advanced design assessment methodologies. Preliminary data for the commercially available SC superalloy CMSX-4 have shown that it offers up to a 70°C advantage over traditional conventionally cast alloys and can be used in IGT provided it is coated in order to withstand the aggressive operating environment. A major part of the work of the SC Subgroup, Work Package 14 of the COST 501 programme has therefore concerned the characterisation of CMSX-4 in accordance with the above objectives. Emphasis was placed in understanding the behaviour of CMSX-4 in loading and temperature regimes of relevance to IGT applications and also in examining pertinent aspects of its behaviour, such as the strain rate sensitivity of the monotonic/cyclic deformation and failure, the anisotropy of the creep behaviour, and the interaction of creep - LCF and creep - HCF loadings.