Crystallographic orientations and twinning of electrodeposited nickel—a study with complementary characterization methods Hossein Alimadadi a,b, ⁎, Alice Bastos Fanta b , Marcel A.J. Somers a , Karen Pantleon a a Technical University of Denmark, Department of Mechanical Engineering, Produktionstorvet, Building 425, DK-2800 Kongens Lyngby, Denmark b Technical University of Denmark, Center for Electron Nanoscopy, Fysikvej, Building 307, DK-2800 Kongens Lyngby, Denmark abstract article info Article history: Received 9 January 2014 Accepted in revised form 8 June 2014 Available online 19 June 2014 Keywords: Electrodeposition Twinning Electron microscopy Diffraction A series of nickel layers was electrodeposited at different current densities from a Watts type electrolyte contain- ing the additive 2-butyne-1,4-diol in various concentrations. The internal structure of the nickel electrodeposits was systematically investigated applying complementary microscopic and diffraction based characterization methods involving both surface and cross section investigations with different resolution and statistics. The com- plementary information gathered from combining the various techniques of microstructure characterization, in particular, supported the investigation of twins and the preferred crystallographic orientations of grains in the electrodeposits. Additive-free deposition results in relatively large columnar grains with numerous growth twins of nanoscale dimensions. The presence of the additive in the electrolyte yields considerable grain refine- ment already at low additive concentration, but the preferred crystallographic orientation of grains changes grad- ually with increasing additive concentration and twins with nanoscale dimensions are detected also in these samples. © 2014 Elsevier B.V. All rights reserved. 1. Introduction For nickel layers, electrodeposition from the Watts electrolyte [1] certainly is most popular and has been extensively used, both for deco- rative purposes and the synthesis of functional electrodeposits. The Watts electrolyte with the basic composition of nickel sulfate, nickel chloride and boric acid originally does not contain additives. Modifica- tions by the addition of various organic additives were developed for tailoring microstructure and properties of electrodeposited nickel dedi- cated to specific applications. One of the most common additives for the Watts electrolyte is 2-butyne-1,4-diol (hereafter BD). This relatively simple molecule, which neither contains nitrogen nor sulphur, is a pow- erful class(II) brightener with the ability of both brightening and level- ling during the electrodeposition of nickel [2–5]. The long standing experiences of applying BD in a Watts-type electrolyte are numerously reported in the literature comprising both its chemical nature and the effect on altering the internal structure of the nickel electrodeposits (e.g. [6–9]). One of the major results of previous studies, although this partly dates back some decades, is the collection of data on crystallo- graphic texture in diagrams showing the occurrence of a certain texture and the transition between different texture components as a function of typical parameters (like pH-value, current density or additive concentration) of the electrodeposition process [3,5]. As a function of the applied process parameters, various preferred grain orientations yielding fiber textures of b111N, b110N, b100N, b211N, b210N or combi- nations thereof are frequently observed for electrodeposited nickel [3,5, 7,10]. Recently, on the example of copper electrodeposits, the impor- tance of twin boundaries, i.e. special boundaries between grains com- prising a well-defined crystallographic orientation relation, has been documented [11,12]. The twin boundaries allow the unique combina- tion of strength and ductility for copper electrodeposits and, in addition, enhance the (thermal) stability of the as-deposited layers [11]. Thus, twins also are of interest for the mechanical properties of nickel layers. Consequently, for microstructure analysis of nickel electrodeposits, not only the main texture components representing the majority of grain orientations, but, in addition, possible (minor) twin orientations and the corresponding detection of twins in the microstructure become of interest. Material synthesis must be closely linked to advanced micro- structure analysis with particular focus on the crystallographic orienta- tion of grains, corresponding misorientations and the characteristics of the grain boundaries [13]. In this respect, not only layers obtained from dedicated electrochemical deposition applying novel electrolytes or refined operating conditions, but also rather conventional layers de- posited from well-established electrolytes are of interest for detailed microstructure characterization with advanced methodology. The present work reports about the internal structure of nickel elec- trodeposited from a Watts type electrolyte. Cross sections covering the whole layer thickness from the substrate to the surface were systemat- ically investigated by the complementary use of microscopy and Surface & Coatings Technology 254 (2014) 207–216 ⁎ Corresponding author at: Technical University of Denmark, Center for Electron Nanoscopy, Fysikvej, Building 307, DK-2800 Kongens Lyngby, Denmark. Tel.: +45 45256468. E-mail address: hoal@cen.dtu.dk (H. Alimadadi). http://dx.doi.org/10.1016/j.surfcoat.2014.06.013 0257-8972/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat