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)
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