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Abstract
The microstructural variation of three single crystal Ni based superalloys with various Ru contents has been investigated. The as cast, solid solution and fully heat treated microstructures were quantitatively analysed. The size of γ′ phase was decreased both in dendrite core and interdendritic regions with Ru additions after a solid solution heat treatment. Appropriate heat treatment schemes of three alloys were determined in terms of quantitative and qualitative microstructural characterisation. It was found that the size and volume fraction of γ′ phase were decreased, and the width of γ matrix channels was reduced in the dendrite core regions of fully heat treated microstructure with the additions of Ru. Moreover, the well known reverse partitioning occurred with increasing Ru content. The γ/γ′ lattice misfits changed from positive to negative and became more negative with Ru additions. The variation of γ/γ′ lattice misfit was caused by the changes of partitioning ratios of alloying elements via Ru additions.