Materials Science and Engineering A 456 (2007) 114–119 Fatigue and deformation of HVOF sprayed WC–Co coatings and hard chrome plating A. Ibrahim a,∗ , C.C. Berndt b a State University of New York at Farmingdale, Farmingdale, Route 110, Lupton Hall, Room 182, Farmingdale, NY 11735, USA b James Cook University, School of Engineering, Townsville, Qld 4811, Australia Received 7 August 2006; received in revised form 18 November 2006; accepted 8 December 2006 Abstract A challenge facing the finishing industry is to replace chrome plating since this technology has negative environmental and health effects. In the case of tungsten carbide and chrome carbide coatings, HVOF and detonation spray technologies have proven to be cleaner and more effective. In this paper, the results of a comparative investigation involve a detailed analysis of fatigue and deformation of two groups of AISI 4340 steel specimens. One group sprayed with HVOF WC–Co coating and the other group was plated with hard chrome. Rotating beam fatigue tests were performed on the coated and uncoated specimens. Optical and SEM microscopy were used to evaluate the fracture morphology. The fatigue life distributions of coated AISI 4340 steel specimens demonstrated that the HVOF coated specimens exhibited higher fatigue lives compared to the uncoated specimens. © 2006 Elsevier B.V. All rights reserved. Keywords: Fatigue; Fatigue life; HVOF; WC–Co coating; Hard chromium plating; Compressive residual stress 1. Introduction Chromium coatings are found in applications that take advan- tage of the unique combination of adhesion, hardness, corrosion, and wear resistance. However, chromium is on the Environmen- tal Protection Agency’s (EPA) list of toxic materials [1]. Existing and planned environmental legislation restricts the use of process chemicals containing hexavalent chromium ions and substanti- ates a need to develop an environmental friendly process as an alternative coating [2]. There are many coating technologies that would not be viable alternatives; even though they may produce coatings with supe- rior properties; for example, chemical vapor deposition and the vacuum-based coating technologies such as ion plating and sput- tering [3]. Thermal spray technologies especially, high-velocity oxygen-fuel (HVOF) thermal spraying is viewed as being capa- ble of replacing hard chrome. The Department of Defense tri-service/industry Hard Chrome Alternatives Team (HCAT) and Joint Group on Pol- ∗ Corresponding author. Tel.: +1 631 420 2309; fax: +1 631 420 2194. E-mail addresses: ahmed.ibrahim@farmingdale.edu, ahmed ibrahim123@yahoo.com (A. Ibrahim). lution Prevention (JGPP) are collaborating on a program to qualify HVOF thermal spray coatings as a replacement for hard chrome plating in the manufacturing and repair of aircraft land- ing gear [4,5]. The project team has developed a comprehensive Joint Test Protocol (JTP), which involves extensive fatigue, wear, corrosion, and mechanical property measurements. Ini- tial testing has demonstrated that in fatigue testing, hard chrome plating causes a significant loss of properties; whereas there is virtually no effect associated with HVOF sprayed WC–Co coatings [4]. This paper presents a comparative study between the HVOF- sprayed WC–Co coatings and hard chrome plating. Since fatigue is an important property of the coated components, fatigue tests were carried out on coated and uncoated specimens. The speci- men was submitted to rotating beam fatigue tests in air to obtain the S–N plots. Results of fatigue testing indicated that HVOF sprayed WC–17Co coating enhanced the fatigue strength of AISI 4340 steel while the hard chrome imparted fatigue strength degradation to the steel. Several experimental and analytical methods were developed to determine the stiffness factor and the modulus of elasticity of the coatings. Results of these tests underlined the significant improvement in the mechanical prop- erties of the HVOF sprayed specimens compared to the hard chrome plating. 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.12.030