On the comparison of graded microstructures developed through High Reduction (per pass) Cold Rolling (HRCR) and Ultrasonic Nanocrystal Surface Modification (UNSM) in nickel-base Alloy 602CA

Highlights: • Rolling is a well-established process and the novelty of the investigated HRCR process lies within the specific combination of the rolling parameters. Two essential parameters are identified to be crucial for graded microstructure development• Primarily, it is essential to employ the maximum reduction per pass or lower numbers of passes. • Secondly, a minimum total reduction should be chosen such that the bulk is not excessively deformed. • It is established from our investigation that high reduction cold rolling in 2 passes with 40 % total reduction accomplished a graded microstructure according to the above parameters. • The unidirectional UR40 and cross rolling CR40 in HRCR process led to graded microstructures that compares well with those produced by UNSM in terms of dislocation density, residual stress and microstructure. -- Abstract: The development of graded microstructure in Ni-base Alloy 602CA, processed through the new technique of high reduction (per pass) cold rolling (HRCR) and the severe surface plastic deformation technique of ultrasonic nanocrystal surface modification (UNSM) was investigated. Clear through-thickness gradients in residual stress, dislocation structure and boundary density with misorientation >2° were observed after the HRCR and UNSM. However, the gradient in HRCR did depend on the roll-pass schedule: relative reduction per pass, total reduction and direction of the roll pass. Applying maximum reduction per pass and minimum number of passes exhibited an improved graded microstructure for 40% total reduction in both unidirectional (UR) and cross rolling (CR) cases. The UR40 and CR40 in HRCR process led to graded microstructures that compared well with those produced by UNSM.