Synchrotron tomography of porosity in single-crystal nickel-base superalloys

Porosity in the single-crystal nickel-base superalloys CMSX-6, SRR99, CMSX-4 and CMSX-10 was investigated by synchrotron X-ray tomography, supplying information about the three dimensional distribution of pores and a statistical database of pore sizes and shapes. Tomography investigations were completed by scanning electron microscopy. In undeformed superalloys the porosity was found to increase with the content of refractory elements. In CMSX-4 creep tested at 1100 °C a deformation induced growth of porosity was observed. Shape and size of the pores was analysed quantitatively as a function of applied load and creep time. The growth was found to be based on the enlargement of pre-existing pores in the interdendritic areas and on the generation of new small pores. Growth processes at creep temperature result in polyhedral pores. Formation and shape transformation of the creep pores is discussed.