Gamma prime morphology and creep properties of nickel base superalloys with platinum group metal additions

The microstructure and creep properties of platinum group metal (PGM) modified nickel based superalloys have been investigated. Alloys containing Pt and/or Ir along with variations in Cr, Ta, Re, Ru, and W exhibited relatively high solidus and liquidus temperatures. Differential thermal analysis (DTA) showed a strong dependence of the gamma' solvus on the level of Ta. The morphology of the gamma' precipitates was influenced by the presence of Cr, Ta, Ru, and W and ranged from cuboidal to semi-spherical. Compression creep tests were conducted at 1000 degrees C at stresses ranging from 40-90 MPa. Alloys containing approximately 8 wt% Pt combined with Cr and Ta displayed the best resistance to creep deformation at stresses around 80 MPa. Post-creep analysis of the rafted structures indicated that all PGM modified alloys without Ru and W possessed positive misfit with magnitudes ranging from approximate to 0.3 to 1.5%. The partitioning of PGMs between the gamma and gamma' phases and their resultant influence on creep performance is discussed.