Influence of Pre-spinning Induced Plastic Strain on Microstructure and Mechanical Properties of Superalloy Disc Forgings

Residual stress is one of the major factors that reduces the dimension stability of superalloy disc components during either machining or in service. A pre-spinning operation has been proven to be an effective technique to modify the unfavorable residual stress in disc forgings. By spinning the semi-finished disc forgings up to a certain rotational speed, a small amount of plastic strain is generated and accordingly results in a redistribution of the internal stress. The spinning-generated plastic strain, though quite small, significantly affects the mechanical properties of the disc forgings. To ensure the efficiency and reliability of the application, a clear understanding of the effects of the pre-spinning-generated plastic strain needs to be obtained. The two widely employed disc alloys GH4065A and FGH4096 were evaluated using a specifically designed, full-scale spinning experiment, the microstructure and the mechanical properties prior to and after the spinning were analyzed in detail. The results show that the pre-spinning generated a higher dislocation density, which is heterogeneously distributed. The dislocations tend to accumulate at the various types of internal interfaces and within primary gamma' precipitates. The formation of heterogeneous dislocation structures significantly affects the mechanical properties, including, but not limited to, the tensile strength, creep, and fatigue crack growth rate. By optimizing the spinning parameters, the mechanical properties can be well controlled to meet the design requirements for disc forgings.