Kovove Mater. 51 2013 351–356 DOI: 10.4149/km 2013 6 351 351 Evaluation of an electroless nickel-boron (Ni-B) coating on corrosion fatigue performance of ball burnished AISI 1045 steel R. Sadeler*, S. C ¸orak, S. Atasoy, F. B¨ ulb¨ ul Department of Mechanical Engineering, Faculty of Engineering, Atat¨ urk University, 25240 Erzurum, Turkey Received 5 October 2012, received in revised form 24 May 2013, accepted 24 May 2013 Abstract The aim of this research is to analyze the corrosion fatigue behaviour of the AISI 1045 steel for two different surface treatments (i.e., single ball burnishing and a duplex treatment combining ball burnishing with an electroless Ni-B coating). The tests were carried out in order to study the fatigue performance both in air and in a 5 % NaCl solution under rotating bending condition (R = –1). Corrosion fatigue tests were conducted at alternating stress levels ranging between 240 and 450 MPa. The results indicated that the 5 % NaCl environment reduced the fatigue life drastically, but the ball burnishing was found to increase the corrosion fatigue life. Also, the duplex treatment improved the corrosion fatigue resistance compared to the case of the ball burnishing alone. The surface morphologies after corrosion fatigue tests were studied by using a scanning electron microscopy (SEM). K e y w o r d s: corrosion fatigue, electroless nickel-boron (Ni-B) coating, ball burnishing treatment 1. Introduction Corrosion fatigue occurs by the combined syner- gistic actions of cyclic loading and corrosive environ- ment leading to premature failure of metals by crack- ing [1]. Corrosion fatigue behaviour of a given mater- ial/environment system refers to the characteristics of the material under fluctuating loads in the presence of a particular environment. Many mechanical, me- tallurgical and electrochemical variables have an ef- fect on corrosion fatigue behaviour [2]. Many small pits occur in corrosion fatigue because of interaction of aggressive environment and surface of a metal un- der applied stress [3]. Many studies have shown that corrosion fatigue cracks start from corrosion pits [4–6], which can support early cracks development by acting as a high stress concentrator. Therefore, pitting can be considered as one of the most important deterioration mechanisms reducing the life of a component under corrosive environments. Damage of a material caused by corrosion fatigue is much more severe and faster than a simple sum of damages caused separately by fatigue and corrosion, so that corrosion fatigue can cause unexpected dam- *Corresponding author: tel.: +90442 2314841; fax: +90442 2360957; e-mail address: receps@atauni.edu.tr ages in industrial sites or engineering fields [5]. Corrosion fatigue life of a metal is known to be greatly affected by the surface state of the metal [6]. A number of methods such as metallic or non-metallic coatings, the formation of surface compressive resid- ual stresses and the elimination of stress concentrators by careful design are available for minimizing corro- sion fatigue damage. The protection against corrosive attack under applied stresses can be achieved through mechanical surface enhancement methods. All cur- rently available methods of surface enhancement de- velop a layer of compressive residual stress following mechanical deformation. The most commonly used treatment is shot peening [7]. Shot peening usually increases hardness and induces compressive residual stress in the material’s surface. When repeated load of sufficient magnitude is applied to a material, slip bands are formed. If the material is shot-peened, a pro- tective layer is formed on the material’s surface and the resistance to corrosion fatigue increases [8, 9]. New surface enhancement technologies have recently been developed, which are superior to shot peening regard- ing compressive residual stress magnitudes and depths to which compression can be achieved. Ball burnish-