Microstructure and Texture of Electrodeposited Nanocrystalline Nickel in the As-Deposited State and After In - Situ and
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GRAIN size refinement is a classical way to increase the strength, fatigue life, and wear resistance of the materials. This has been realized in nanostructured metallic materials (grain size d < 100 nm) by a number of researchers.[1–5] Techniques like pulsed electrodeposition and pulsed laser deposition provide control over grain size and to some extent over texture of the as-deposited material.[6–9] Several studies have revealed the formation of nodule-like mesostructures during electrodeposition with a size several orders of magnitude greater than the grain size.[7,10–12] These mesoscale structures could influence properties such as corrosion resistance, toughness, ductility, coefficient of friction, and wear resistance which cannot be explained by grain size alone.[10,12] The nanocrystalline materials generally display a rather limited thermal stability, as the presence of an P. CIZEK, Senior Researcher, and M.R. BARNETT, Professor, are with the Institute for Frontier Materials, Deakin University, Geelong, VIC 3216, Australia. Contact e-mail: pavel.cizek@deakin. edu.au A. SANKARAN, formerly Researcher with the Institute for Frontier Materials, is now Researcher with the Ford Motor Company, Dunton Technical Centre, Basildon, Essex SS15 6EE, U.K. E.F. RAUCH, Professor, is with the SIMAP Laboratory, CNRS-Grenoble INP, BP 46 101, rue de la Physique, 38402 Saint Martin d’He`res, France. Manuscript submitted November 10, 2015. Article published online October 14, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
extremely large number of grain boundaries provides a large driving force for grain growth at elevated temperatures. The grain growth starts at a temperature as low as ~523 K (250 C) in pure nanocrystalline nickel and is characterized by the formation of abnormally grown grains.[12–18] It has been suggested that such grain growth starts with abnormal grain growth followed by normal grain growth.[13–15] Klement et al. have proposed that the abnormally grown grains might nucleate, through the coalescence mechanism, from (sub)grain clusters.[13–16,19] The presence of such clusters has frequently been revealed in the electrodeposited nanocrystalline materials by transmission electron microscopy (TEM) dark-field and moire´ fringe observations.[1,12,14–16] However, it has recently been argued that the above tentative suggestion might not be valid.[20] Thus, detailed characteristics of the (sub)grain clusters and their potential role in the abnormal grain growth in nickel electrodeposits need to be further elucidated. It has been revealed using X-ray diffraction that the as-deposited nanocrystalline nickel-based materials typically display bulk crystallographic texture characterized by a dominant fiber component with the h001i fiber axis parallel to the deposition direction (DD).[9,12,21] This texture component is occasionally accompanied by a comparatively weaker h111i//DD fiber component. It has been demonstrated that the grain growth occurring during annealing of these electrodeposits is accompanied by a texture change.[12,1
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