Sliding Wear Characteristics of Pack Cyanided Ductile Iron E.K. Ampaw, E.K. Arthur, A.Y. Badmos, J.D. Obayemi, O.O. Adewoye, A.R. Adetunji, S.O.O. Olusunle, and W.O. Soboyejo (Submitted June 17, 2019; in revised form October 2, 2019) In this paper, ductile iron was produced using a rotary furnace. The microstructures of the ductile iron (with and without cyanided coatings) were then characterized using optical microscopy and scanning electron microscopy (SEM). The surfaces of the ductile iron were subjected to high temperature carbo- nitriding using a pack cementation process in which carbon and nitrogen were diffused into the ductile iron from powder mixtures consisting of ground cassava leaves and barium carbonate (BaCO 3 ) energizers. The wear behavior of the coated and uncoated ductile iron was studied using the pin-on-disk method. The wear mechanisms are also elucidated using SEM and nano-wear experiments. The resulting wear rates are then compared with those from micron-scale wear tracks obtained from pin-on-disk experiments. The impli- cations of the results are discussed for the design of wear-resistant ductile irons. Keywords carbo-nitriding, ductile irons, nano-wear, pack cementation, wear volume 1. Introduction Significant efforts have been made to improve the surface mechanical and tribological properties of steels and cast irons using thermo-chemical heat treatment processes such as carburizing, nitriding and carbo-nitriding (Ref 1-23). However, in recent years, there has been strong interest in the develop- ment of a fundamental understanding of the underlying mechanisms that precede the failure of engineered surfaces. In most cases, conventional heat treatment processes are carried out using expensive gas chambers or salt baths (Ref 23, 24). Also, the toxicity of most of the gases and salts that are used makes these processes more complex. This has stimulated the recent use of natural cyanogenic materials (cassava leaves) in the improvement of the tribological properties of cast irons and steels (via the diffusion of carbon and nitrogen from dried cassava leaves) (Ref 25-30). Ibironke et al. (Ref 25) have contributed to the existing body of knowledge on the carbo-nitriding of mild steel. Their work provided a combination of experimental measurement and mathematical predictions of case depths in mild steel. Subse- quently, other researchers (Ref 26-29) have used cassava pack cyaniding methods to improve the surface properties of low carbon steels. Most of these studies have focused on the dependence of hardness, strength and wear resistance on heat treatment temperature. However, there have been no prior studies of the hardness and wear (macro-and nano-scale) behavior of carbo-nitrided ductile irons (DI) produced using the rotary furnace. Hence, the objective of the current work is to study the effects of heat treatment on the surface hardness and wear behavior of ductile irons. This will be achieved using a novel carbo-nitriding process that involves the use of ground cassava leaves and barium carbonate energizers. These will be diffused into the surfaces of a ductile iron by intermediate temperature heat treatment. The sliding wear characteristics of the resulting carbo-nitrided surfaces will then be elucidated using a combi- nation of nano-wear and pin-on-disk experiments. The impli- cations of the results are discussed for the surface engineering and microstructural design of engine structure and components. 2. Experiments 2.1 Materials and Methods In this study, ductile iron was produced using a rotary furnace (manufactured by Engineering Materials Development Institute, Akure, Nigeria). A conventional cast iron (used typically for automotive applications) was melted and alloyed in a rotary furnace. Ferro-manganese (Si = 42-44%; Mg = 4.8- E.K. Ampaw, Materials Science and Engineering Department, African University of Science and Technology (AUST), Abuja, Federal Capital Territory, Nigeria; and Mechanical Engineering Department, Koforidua Technical University (KTU), Koforidua, Ghana; E.K. Arthur, Materials Engineering Department, Kwame Nkrumah University of Science and Technology (KNUST), Kumasi, Ghana; A.Y. Badmos and J.D. Obayemi, Department of Mechanical Engineering, Worcester Polytechnic Institute (WPI), Worcester, MA 01609; O.O. Adewoye, Materials Science and Engineering Department, African University of Science and Technology (AUST), Abuja, Federal Capital Territory, Nigeria; and A.R. Adetunji, Materials Science and Engineering Department, African University of Science and Technology (AUST), Abuja, Federal Capital Territory, Nigeria; and Materials Science and Engineering Department, Obafemi Awolowo University, Ile-Ife, Nigeria; S.O.O. Olusunle, Engineering Materials Development Institute, National Agency for Science and Engineering Infrastructure (NASENI), Akure, Nigeria; and W.O. Soboyejo, Materials Science and Engineering Department, African University of Science and Technology (AUST), Abuja, Federal Capital Territory, Nigeria; and Department of Mechanical Engineering, Worcester Polytechnic Institute (WPI), Worcester, MA 01609. Contact e-mail: wsoboyejo@wpi.edu. JMEPEG ÓASM International https://doi.org/10.1007/s11665-019-04471-8 1059-9495/$19.00 Journal of Materials Engineering and Performance