Microstructure and mechanical properties of nickel processed by accumulative roll bonding

Abstract

A detailed investigation of the microstructure and mechanical properties has been conducted in pure nickel deformed to high strains using accumulative roll bonding (ARB). Samples have been investigated after different numbers of ARB cycles and the results have been compared with data for nickel processed by other deformation techniques, with particular focus on conventional rolling. It is found that the structural evolution in ARB-processed nickel is rapid at low strains followed by a slower evolution as the strain approaches ultrahigh levels. Comparing samples processed by ARB and conventional rolling to an identical nominal strain, the microstructure after ARB is more refined and contains a greater fraction of high angle boundaries. This enhanced refinement is attributed to the geometric accumulation of shear-strain influenced volumes as a result of the ARB process and large-draught rolling conditions. Based on the observations, it is suggested that the key strengthening mechanisms in deformed nickel are grain boundary and dislocation boundary strengthening, and that the strength-microstructure relationship can be expressed by a single parameter equation, σ-σ0 = k2dav-0.5, where k2 is a constant and dav is the average boundary spacing in the deformed microstructure. Abstract: A detailed investigation of the microstructure and mechanical properties has been conducted in pure nickel deformed to high strains using accumulative roll bonding (ARB).Samples have been investigated after different numbers of ARB cycles and the results have been compared with data for nickel processed by other deformation techniques, with particular focus on conventional rolling. It is found that the structural evolution in ARB-processed nickel is rapid at low strains followed by a slower evolution as the strain approaches ultrahigh levels.Comparing samples processed by ARB and conventional rolling to an identical nominal strain, the microstructure after ARB is more refined and contains a greater fraction of high angle boundaries. This enhanced refinement is attributed to the geometric accumulation of shear-strain influenced volumes as a result of the ARB process and large-draught rolling conditions. Based on *Manuscript Click here to view linked References 2 the observations, it is suggested that the key strengthening mechanisms in deformed nickel are grain boundary and dislocation boundary strengthening, and that the strength-microstructure relationship can be expressed by a single parameter equation, σ-σ 0 = k 2 d av -0.5 , where k 2 is a constant and d av is the average boundary spacing in the deformed microstructure.

Analysis of through-thickness heterogeneities of microstructure and texture in nickel after accumulative roll bonding

“…Similar to the observations of heavily deformed materials produced by other deformation techniques [3][4][5][6], it has been found that the average boundary spacing in ARB-processed materials decreases with increasing strain, whereas the fraction of high angle boundaries (HABs) increases [7][8][9][10].…”

“…The observed variations in both texture and the heterogeneity in microstructural refinement highlight the fact that even though the average boundary spacing approaches a saturation value with increasing number of ARB cycles [10], the microstructure and texture experience significant changes as each successive surface layer is moved to the center and then deformed under PSC conditions.…”

“…A 2 mm thick strip of pure (99.967%) nickel with a fully recrystallized microstructure and a nearly random texture was used as an initial material [10]. The average grain size (including annealing twins) in this sample was measured to be ~20 µm.…”

Oxide dispersion-strengthened steel PM2000 after dynamic plastic deformation: nanostructure and annealing behaviour

“…The higher strength in the DPD-processed PM2000 is consistent with the finer microstructure in this material. The increase in strength of PM2000 during DPD is accompanied by a significant reduction in ductility-a phenomenon which has previously been observed in many cold-deformed materials due to their limited capacity of work hardening [8,27,28].…”

The influence of multiscale heterogeneity on recrystallization in nickel processed by accumulative roll bonding

“…It has been shown that ARB to high strains results in significant structural refinement and large fractions of high angle boundaries (HABs). For example, the average boundary spacing measured along the normal direction (ND) in ARB-processed nickel after a von Mises strain ε vM of 6.4 is ~0.1 µm and the fraction of HABs is ~60 % [3]. There are, however, significant through-thickness heterogeneities both in texture [4][5][6][7][8][9][10] and in the deformed microstructure [9][10][11][12][13][14] after ARB.…”