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

Abstract

Microscopic and sample-scale heterogeneities have been characterized in nickel processed by accumulative roll bonding to a von Mises strain of 4.8, and their influence on recrystallization has been analyzed. The microscopic heterogeneities in this material are mostly associated with regions near the bonding interface, which are more refined and thus possess a higher stored energy than other regions. These regions also contain characteristic particle deformation zones around fragments of the steel wire brush used to prepare the surface for bonding. The sample-scale heterogeneities are seen as variations in the distribution of different texture components and in the fractions of high misorientation regions between the subsurface, intermediate and center layers. Each of these heterogeneities affects the progress of recrystallization. Regions near bonding interfaces, particle deformation zones and shear bands are all found to act as preferential nucleation sites. On the sample scale, recrystallization proceeds faster in the intermediate layer than in the center and subsurface layers. Comparing the progress of recrystallization in ARB-processed nickel and conventionally rolled nickel, it is evident that * Corresponding author: e-mail: olmi@dtu.dk 1 additional deformation heterogeneities induced by ARB result in nucleation taking place over a more extended period of time.

Microstructural peculiarities and textural characteristics of Ni–W sheet alloy after accumulative roll-bonding and annealing

“…The presence of these particles (like S1, S2) originated from the fragments of the steel wire brush used during surface preparation. Similar observation was reported in ARB processed Ni alloy [16]. The presence of these steel particles allows the formation of new recrystallized grains with random orientation, which is ascribed to particle stimulated nucleation (PSN) mechanism [31].…”

“…Results showed that the homogeneity of the texture through the thickness was obtained after 8 ARB cycles (ε = 6.4), but the near surface and near center position was not clearly analyzed [11]. However, the recrystallization behavior along the multiscale heterogeneity of pure Ni was investigated after cold rolling [24] and only for sample processed by ARB to 6 cycles (ε = 4.8) and annealed at 200 °C for different time periods (up to 210 min) [16,17]. It was found that the fraction of {001}〈100〉 Cube texture was lower in the subsurface layers than in the center and intermediate layers of the sample due to the strong shear texture [17].…”

“…In practice, one ARB cycle consists of rolling two sheets together (50% thickness reduction), cutting, wire brushing of the surface and stacking them to achieve the initial thickness [12]. Such a complex plastic deformation (combination of plane strain deformation and shear deformation) in each ARB cycle introduces significant through-thickness heterogeneities in the microstructure and texture [7,[13][14][15][16][17][18]. Usually, the mid-thickness of the ARB processed material is characterized by elongated grains along the rolling direction and exhibits a typical rolling texture, while equiaxed grains with typical shear texture are observed in the external layers [7,10,14,18].…”

“…Up to now, little studies were devoted to investigate the variation of microstructure and texture through thickness during the annealing of ARB processed Ni-based alloys [11,16,17,23]. It was assumed that nearly 100% {001}〈100〉 Cube texture was obtained in pure Ni deformed by ARB processing and annealed at 800 °C for 1 h [11].…”

Strong pinning of triple junction migration for robust high strain nanostructures

“…The universality of the lamellar microstructure formed by GNBs and IDBs [6], and the agreement with respect to Y-junction migration between materials with very different material properties indicates the universality of this recovery mechanism. The strong connection between the characteristics of 1 It should be noted that the kinetics of recrystallization for 3N Ni at 220 °C shown in (c) is slightly different from that reported in a recent recrystallization study of the same deformed Ni [17]. This difference may have its cause in heterogeneities introduced during deformation and therefore a larger experimental error in the estimated activation energy is expected in the 3N Ni compared to that in the 2N Ni.…”