The Effect of Forging and Heat Treatment Variables on Microstructure and Mechanical Properties of a Re-Bearing Powder-Metallurgy Nickel Base Superalloy

In our previous works, the effects of forging and heat treatment variables on microstructure evolution and mechanical properties have been studied for an ingot-metallurgy Re-bearing nickel base superalloy. To overcome the issues associated with the production of large-scale ingots and fine-grained workpieces, in the present work, the effect of hot forging and heat treatment variables was studied in a Re-bearing nickel base superalloy prepared via powder metallurgy. The purpose of the study was to reach the properly balanced mechanical properties for the potential use of the superalloy as a disc material. The initial as-HIPed workpieces were subjected to different hot forging and post-forging heat treatment or only to heat treatment (no forging). For the processed workpieces, the recrystallization behavior, size, morphology and volume fraction of & gamma;& PRIME; precipitates were evaluated by scanning electron microscopy followed by a study of mechanical properties. The most properly balanced mechanical properties (strength, ductility, creep resistance and creep rupture lifetime) were reached for the & gamma; grain size of d(& gamma;) & AP; 13.6 & mu;m. A finer and coarser & gamma; grain size (down to d(& gamma;) & AP; 2.6 and up to d(& gamma;) & AP; 37.5 & mu;m) even when superimposed with a higher volume fraction of dispersed secondary & gamma;& PRIME; precipitates (in the case of d(& gamma;) = 27-37.5 & mu;m) was associated with worse mechanical properties.