Industrial Member company Kawasaki Heavy Industries Ltd (KHI) recently consulted TWI to assess the service life of newly developed turbine blades for the L20A gas turbine ( Fig. 1). This is a new 20 MW-Class gas turbine developed by KHI, for distributed generation, co-generation and combined cycle applications. Blades were made from directionally-solidified and polycrystalline Mar-M247 and IN713C alloys.
The development of advanced turbine blades has seen the introduction of a new range of directionally-solidified and single-crystal superalloys with compositions, microstructures and mechanical properties tailored to suit the demanding requirements of the high-pressure section. The project has provided considerable data on the long-term stability of the blade alloys and was able to demonstrate that the blades were fit for purpose.
Nickel superalloys are mainly strengthened by the precipitation of ?' phase ( Fig.2), which forms coherently with the matrix. Detrimental microstructural changes may occur during high temperature service, degrading blade performance. Long-term stability is an important aspect of blade design and TWI were able to successfully demonstrate that the microstructure of the blades had not suffered any detrimental effects during service.
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