Influence of Heat Treatment on Defect Structures in Single-Crystalline Blade Roots Studied by X-ray Topography and Positron Annihilation Lifetime Spectroscopy

Single-crystalline superalloy CMSX-4 is studied in the as-cast state and after heat treatment, with material being taken from turbine blade castings. The effect of the heat treatment on the defect structure of the root area near the selector/root connection is emphasized. Multiscale analysis is performed to correlate results obtained by X-ray topography and positron annihilation lifetime spectroscopy (PALS). Electron microscopy observations were also carried out to characterize the inhomogeneity in dendritic structure. The X-ray topography was used to compare defects of the misorientation nature, occurring in as-cast and treated states. The type and concentration of defects before and after heat treatment in different root areas were determined using the PALS method, which enables voids, mono-vacancies, and dislocations to be taken into account. In this way, differences in the concentration of defects caused by heat treatment are rationalized

Solution heat treatment of single crystal castings of CMSX-4 nickel-base superalloy

CITATION: Rzyankina, E., et al. 2016. Solution heat treatment of single crystal castings of CMSX-4 nickel-base superalloy. In Competitive Manufacturing, International Conference on Competitive Manufacturing (COMA '16), 27-29 January 2016, Stellenbosch, Stellenbosch University, South Africa.The original publication is available at http://conferences.sun.ac.za/index.php/doie/coma16An investigation of the microstructure and mechanical properties for heat treated directionally cast rods, produced from the nickel-based superalloy, CMSX-4, is presented. The rods were cast using the Bridgman method for manufacturing single crystal structures. The microstructure of the cast rods consists of γ and γ' precipitates. This microsegregation has a negative effect on the microstructure and, hence, the mechanical properties of the castings. The solution heat treatment of the second generation, single crystal Ni-base superalloy, CMSX-4, is known to dissolve the eutectic γ and γ' region. This requires temperatures up to 1316°C and approximately 45 hours total time. These high temperatures and long processing times result in high costs. The aim of this study is to investigate the effect of the heat treatment protocol on the extent of improvement of quality of single crystal castings, as a basis for determining cost feasibility in practice.Publisher's versio