High temperature corrosion and corrosion protection of porous Ni22Cr alloys J. Karczewski a, ⁎, K.J. Dunst b , P. Jasinski b , S. Molin b a Faculty of Applied Physics and Mathematics, Gdansk University of Technology, Gdansk, Poland b Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Poland abstract article info Article history: Received 7 July 2014 Accepted in revised form 22 October 2014 Available online 31 October 2014 Keywords: Porous metallic support Corrosion resistance Solid oxide fuel cell Infiltration Yttria In this work corrosion kinetics of the porous IN625 alloy is studied in the temperature range of 700 °C–800 °C in air and humidified hydrogen for up to 1000 h. Moreover, an effective and simple method of reducing corrosion rates of porous alloys by the infiltration of the rare earth elements is shown. Modification by the yttrium contain- ing precursor reduces the corrosion rate by a factor of 50 in air at 700 °C so that the lifetime of the infiltrated alloy is greatly extended. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Although metallic alloys are very common engineering materials, their use in the porous form has been very restricted so far. Only in the last few years a considerable attention was restored to this group of materials [1,2]. In many applications there is a need to replace expen- sive ceramic materials with more cost effective counterparts. This has driven their research and thus is opening new possibilities for their applications. One of the rapidly growing fields of applications of porous metals is high temperature fuel cells. Solid Oxide Fuel Cells are gaining a considerable attention as a possible efficient energy converting devices [3,4]. First commercial systems are already on the market demonstrat- ing large potential of this technology in the distributed energy systems. One of the largest driving forces in the development of fuel cells is low- ering their price. Current generation of solid oxide fuel cells (SOFC) is based on a supporting structure (on a cell level) being made of a porous ceramics, usually a nickel oxide–yttria stabilized zirconia (YSZ) compos- ite. In order to lower the price of SOFCs, there is a tendency to substitute ceramic materials with the metallic ones. This happened in the case of the interconnectors, where expensive and hard to produce ceramic interconnectors were replaced with more cost effective stainless steels [5–7]. It is expected that the next generation of SOFCs will use porous metals as the supporting structures [1]. These, so called 3rd generation cells, are currently developed at several laboratories in the world [2]. Besides lowering the cost, the use of metallic alloys can also have a ben- eficial effect by allowing higher heating and cooling rates and therefore can result in a faster start up of the system. High thermal conductivity of the alloys offers a possibility to expand these fuel cells for example to an auxiliary power units for trucks to reduce their idling pollution. One of the challenges of using the porous alloys at high temperatures is their large surface area, meaning that the ratio of the surface to vol- ume is high. During high temperature corrosion an oxide layer is formed from the metal, typically and preferentially chromium, and grows con- tinuously over time. This oxide growth, after long enough time, can cause depletion of the protective element and lead to a breakaway oxi- dation. In comparison to studies of corrosion of dense interconnectors [8,9], corrosion evaluation of porous alloys is a relatively new topic with not too many publications available [10–16]. So far only a few com- positions were tested: 316 L, 430 L, and IN600. Due to relatively high thermal expansion coefficient of the austenitic alloys, higher than of the ceramic materials, mostly ferritic steels were tested as possible supports. However, austenitic Hastelloy X alloy has been successfully used as a support for SOFCs and therefore, showing possibility of using materials with the austenitic structure. The commercial availability of the alloy materials in the porous form is very limited. Although they find some niche applications in filters, their high temperature use is very limited with one of the possibilities being supports for SOFCs [14,17–19]. In order to extend the lifetime of the dense interconnectors, studies of the protective coatings are broadly performed [20–23]. Positive ef- fects of thin layers of rare earth elements on lowering corrosion have been reported for dense alloys [24–26]. So far Molin et al. [10] have directly shown that in the case of the porous alloys, the corrosion rate can be considerably reduced by adding a protective coating. In this case an yttria precursor was impregnated into the IN600 alloy and Surface & Coatings Technology 261 (2015) 385–390 ⁎ Corresponding author. E-mail address: jkarczew@mif.pg.gda.pl (J. Karczewski). http://dx.doi.org/10.1016/j.surfcoat.2014.10.051 0257-8972/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat