Shot peening and deep cold rolling of a single crystal nickel superalloy

Author:  I. Bogachev1, K.M. Knowles1, G. Gibson2 1 University of Cambridge, Department of Materials Science and Metallurgy, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK – ib358@cam.ac.uk, kmk10@cam.ac.uk 2 Rolls-Royce plc, PO Box 31, Derby, DE24 8BJ, UK – grant
Source:  ICSP14 Milan
Doc ID:  2022059
Year of Publication:  2022
Abstract:  
The present research aims to further the understanding of the effects of mechanical shot peening (MSP) and deep cold rolling (DCR) on the single crystal nickel-based superalloy CMSX-4, used in the manufacture of jet engine turbine blades. Under the thermomechanical conditions of a turbine, the main resistance to fatigue crack growth is thought to come from the surface cold work generated by these procedures. Cold work in samples treated by MSP or DCR was characterised by scanning electron microscopy, both in the as-hardened state and following heat treatment at 900 and 1100 °C. Centre hole drilling was used to find the depths of residual stress also induced by the procedures. DCR was found to produce a deeper layer of relatively low cold work in comparison with MSP. Slip bands were induced by both procedures and were especially dense following MSP. After heat treatment at 900 °C for 500 h, topologically close-packed precipitates formed on slip bands, and discrete recrystallisation occurred in the cold worked layer, with little or no recovery. At 1100 °C for 100 h, complete surface recrystallisation was observed in both samples. DCR resulted in shallower recrystallisation in both cases. The microstructures of both samples underwent rafting at 1100 °C, with the depth levels of the rafting below the surface correlating with the depth levels of compressive residual stress, both being significantly greater than cold work depths. Keywords: nickel-based superalloys, single crystal, mechanical shot peening (MSP), deep cold rolling (DCR)