Formation of Multiple Twinned Structural Units in Electrodeposited Nickel after Annealing

Abstract

Electrodeposition is an advanced synthesis technique which involves the creation of a coating or free-standing material through an electrolytic process. Organic additives such as saccharin have been frequently used in electroplating operations to moderate deposit growth rates and to control film quality. In the present study, plating of Nickel without additives has resulted in a sub-microcrystalline microstructure and a <110>-fibre texture in growth direction. Structural units in form of groups of grains possessing a common <110>-zone axis in growth direction and low-Σ relationships between them have been found in the microstructure by use of EBSD. Upon annealing, grain growth sets in. However, the structural units and the texture are preserved up to 550°C. This means that the structural units stabilize the microstructure; there is no orientation change when grain growth occurs (e.g. by twinning). The low-Σ boundaries of the structural units are described in detail and texture development upon annealing is discussed in connection with results from previous studies on Ni and Ni-alloys of different initial texture.

Optimal microstructural design for high thermal stability of pure FCC metals based on studying effect of twin boundaries character and network of grain boundaries

“…Twin boundaries that form a unit enclosed by g-HAGBs such as sample S1, Fig. 5, or five-fold twins shown in [33] are more thermally stable as the exterior of the unit (HAGBs) interacts with other HAGBs and protects the interior of the unit composed of twin boundaries, as experimentally observed [28], [33], [34]. This means that the fragmented network of g-HAGBs in a GBE microstructure cannot protect the high density of CTBs and CTBs can be annihilated easily without effective drag of g-HAGBs on the movement of mobile boundaries.…”

“…thermal stability. This was demonstrated for nickel deposits, where, among others, multi-twinned grains were observed to have the highest thermal stability [33], [34].…”

“…However, it has been shown that in FCC materials these junctions are relatively stable [61]. High thermal stability is reported, specifically for nickel electrodeposits with a <110> fiber texture and five-fold twin boundary junctions [33], [34] which are encompassed by g-HAGB forming isolated units (unlike sample S3 which has a connected helical struture of five-fold junctions). Therefore, to understand the poor thermal stability, the dynamics of grain boundary interaction and the effect of connectivity of the grain boundaries should be considered.…”

Characterization of multiple twinned structural units in pulse-electrodeposited nickel

“…Related to a high twin density, 5-fold twins have been observed for different materials [14][15][16]. However, also structural units including other low-Σ boundaries than twins have been reported [17,18]. Common to the grains in 5-fold twins and low-Σ structural units is a <110>-orientation parallel to GD.…”

“…Common to the grains in 5-fold twins and low-Σ structural units is a <110>-orientation parallel to GD. Moreover, investigations perpendicular to GD showed clearly the 3-dimensional character of structural units [17,18]. In this paper, these structural units are investigated in more detail both parallel and perpendicular to GD.…”