Fatigue properties of Fe–Al intermetallic coatings prepared by plasma spraying R. Mus ˇa ´ lek a, b, * , O. Kova ´r ˇı ´k a , T. Skiba a, b , P. Haus ˇild a , M. Karlı ´k a , J. Colmenares-Angulo c a Department of Materials, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Trojanova 13,120 00 Prague 2, Czech Republic b Department of Materials Engineering, Institute of Plasma Physics AS CR, v. v. i., Za Slovankou 3,182 00 Prague 8, Czech Republic c Center for Thermal Spray Research, Department of Materials Science and Engineering, Stony Brook University,11794-2275, Stony Brook, NY, USA article info Article history: Received 29 September 2009 Received in revised form 15 December 2009 Accepted 1 February 2010 Available online 26 February 2010 Keywords: A. Iron aluminides B. Fatigue resistance and crack growth C. Plasma spraying F. Electron microscopy, scanning abstract In this research, FeAl based coatings were deposited on low carbon steel using two different plasma spraying technologies – gas stabilized plasma gun (GSP) and water stabilized plasma gun (WSP) – resulting in different deposition conditions. Significant changes in local chemical composition compared to feedstock material were observed due to uneven evaporation of Fe and Al from the molten material during the interaction of feedstock with plasma. Influence of coatings on substrate fatigue properties was characterized at room temperature using special testing device ‘‘SF-Test’’. Fatigue lifetimes of specimens with different coatings were compared with those of uncoated specimens. Fractographic analysis of failed specimens revealed that substrate fatigue cracks initiated at coating–substrate interface and grew by striation mechanism. The coatings failed due to intrasplat cracking and intersplat decohesion. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The most critical area of both structural and non-structural components is usually their surface where the maximum loading is achieved (e.g. mechanical and thermal load, corrosion, wear, and their combinations). One possibility to achieve a better service durability of such parts is to protect them by thermal sprayed coatings. One of the promising materials for thermal spraying could be FeAl intermetallics because of its low density, relatively low cost, and excellent resistance to oxidation and corrosion, carburization, sulfidation, or wear even at elevated temperatures [1–4]. FeAl applications for harsh environments were proposed (e.g. heating elements, heat-exchangers pipings, porous metal filters, or deflec- tors for burning high sulfur coal). Some of the FeAl disadvantages (such as brittleness and low ductility or fabrication difficulties [2,5]) can be solved by the deposition of FeAl layer on ductile and machinable substrate by thermal spraying. Microstructure of the thermally sprayed coatings consists of flattened particles (so called splats), pores, microcracks, or impu- rities and therefore significantly differs from the microstructure of bulk material. Differences in the microstructure of thermally sprayed material can result in more favorable properties of FeAl for some applications (e.g. strain or thermal shock resistance [6]). Thermal spraying is suitable for deposition of thick renewable protective coatings on parts with complex shape without need of welding or other joining. Thermally sprayed FeAl based coatings were previously successfully prepared by several authors mostly using high velocity oxygen fuel (HVOF) technique, e.g. [7,8], which can be characterized by high impact speed and relatively low particle temperature. Fewer reports were published on gas stabi- lized plasma (GSP) spraying [9,10] or water stabilized plasma (WSP) spraying [11] of FeAl. It is known from the previous studies [12–15] that thermally sprayed coatings can significantly influence (both improve or deteriorate) fatigue life of the coated bodies. Knowledge of the coating effect on the fatigue life of the substrate is crucial for the considered coating application. Aim of this study was to deposit FeAl using two different plasma spraying technologies (GSP and WSP), compare their microstruc- ture, and characterize the coating influence on the fatigue pro- perties of the low carbon steel substrate. 2. Materials and methods Two plasma spraying technologies were used to deposit FeAl powders (see Tables 1 and 2) delivered by LERMPS (Belfort, F) on both faces of low carbon steel (eq. to ASTM A283) substrates. Flat dog-bone shaped substrates (thickness 4 mm) were degreased and grit-blasted prior to the coating deposition. Gas stabilized plasma (GSP) torch F4 (Sulzer Metco, Westburry, NY) was used to spray atomized Fe-43 at%Al (Fe-29 wt%Al) and Fe-56 at%Al * Corresponding author. Department of Materials Engineering, Institute of Plasma Physics AS CR, v. v. i., Za Slovankou 3,182 00 Prague 8, Czech Republic. Tel.: þ420 266053077; fax: þ420 286586389. E-mail address: musalek@ipp.cas.cz (R. Mus ˇa ´ lek). Contents lists available at ScienceDirect Intermetallics journal homepage: www.elsevier.com/locate/intermet 0966-9795/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2010.02.001 Intermetallics 18 (2010) 1415–1418