The subgrain structure in turbine blade roots of CMSX-4 superalloy

• X-ray topography was applied to study the subgrain structure of the samples.
• Samples were cut from root part of the blades parallel to the growth direction.
• Macroscopic low angle boundaries existence were shown in the samples.
• Scheme of boundaries formation were presented.

As-cast single-crystal turbine blade roots made of CMSX-4 were investigated. The Laue method, X-ray diffraction topography, novel X-ray diffractometer provided by EFG company and scanning electron microscopy were applied to study the subgrain structure. It was found that low angle boundaries of macro scale length were present in the roots of the blades. Additionally, linear distributions of angles describing inclination of [001]γ′ direction to the main blade axis and rotation of this direction were defined across the low angle boundaries by EFG diffractometer. With the use of this diffractometer, the lattice parameter linear distributions across the low angle boundaries were also defined. The dendrites arrangement were determined by scanning electron microscopy (SEM) macro images. The mechanism of the formation of subgrain boundaries and characteristics of the orientation interactions between dendrites inside subgrains were proposed.