Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat Formation of Fe-TiC composite clad layers on steel using the combustion synthesis process Abtin Rahimi-Vahedi, Mandana Adeli ⁎ , Hassan Saghafian School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Narmak, Tehran 1684613114, Iran ARTICLE INFO Keywords: Combustion synthesis Clad Adhesion Microstructure Fe-Ti-C composite Mechanism ABSTRACT The application of thermal explosion mode of the combustion synthesis process to form Fe-TiC composite layers on a steel substrate was investigated. Starting powder mixtures of Fe, Ti, and C with different percentages of iron were cold-pressed onto a steel hollow disk and exposed to high heating rates under an argon atmosphere. A self- sustaining, exothermic reaction took place in all samples. In samples with lower Fe amounts (higher amount of Ti + C) poor clad/interface adhesion was obtained due to too intensive reactions and high amount of interfacial pores, while clad layers with higher Fe contents demonstrated increasingly better adhesion as revealed by SEM analysis. Microstructural studies on samples with lower Fe amounts showed very fine, granular TiC particles which were dispersed in a Fe-rich matrix following a dissolution-precipitation mechanism. Samples with higher amounts of Fe showed partial reaction on Ti particles, resulting in a distribution of hard particles consisting of distinct layers with differing chemical compositions. Since the released reaction heat is mostly consumed for heating-up and sintering of iron particles, Fe particles act as heat sinks giving rise to a deficiency of exothermic heat for the completion of reaction. Even in case of incomplete reactions, the distribution of hard particles throughout the softer iron matrix can improve the overall hardness of the clad layer. 1. Introduction TiC is a well-known, highly stable ceramic material with low fric- tion coefficient, high hardness, very high melting temperature, and low density [1,2]. When dispersed in a metallic matrix, TiC particles can improve wear resistance by performing as bearings for sliding surfaces and reducing the friction coefficient. Therefore, it has been used as a reinforcement material in a wide variety of metal matrix composites (MMCs) [3–8]. Among these, Fe-based MMCs offer several advantages such as availability and lower cost in many applications [3]. Besides, they are chemically compatible with steels and can be used to provide the surface with improved wear resistance, hardness, and stiffness when applied as coatings. The production methods for Fe-TiC composites such as conventional melting and casting, powder metallurgy, thermite reduction, combus- tion synthesis, and carbothermic reduction of ilmenite have been re- viewed by Das et al. [9]. However, most of these methods are not suitable to form a Fe-TiC composite coating on a Fe-based substrate. Combustion synthesis is one of the methods which can be used to apply a composite layer on a substrate. The process which takes use of the exothermic reactions between starting elements, has proved to be a fast, simple, and energy saving method for producing various refractory compounds including composites and cermets [10,11]. The implementation of the combustion synthesis process to produce Fe-TiC MMCs as well as TiC-Fe cermets has been studied in several research works. Saidi et al. [12] investigated the production of TiC and Fe-TiC via the combustion synthesis process, and measured ignition and combustion temperatures exceeding 1500 °C and 2500 °C, respectively, in the reaction between Ti and C. They added different amounts of iron as diluent to Ti + C equimolar mixture and found out that the presence of even small amounts of Fe resulted in a significant decrease in the ignition temperature of the system. They concluded that in the presence of iron, the ignition temperature was dictated by the eutectic tem- perature of the Fe-Ti system, not solid state reaction between Ti and C. An increase in the amount of iron resulted in a decrease in the calcu- lated combustion temperatures because of the consumption of exo- thermic heat by iron. Fan et al. [13] investigated the formation of TiC- Fe cermets using the combustion synthesis reaction between Ti and C in the presence of 30% wt%Fe. They suggested that in the presence of high amounts of Ti + C, carbon diffuses into iron resulting in the formation of lower-melting Fe-C alloys. The melting accelerates the dissolution of Ti followed by the precipitation of TiC particles out of the saturated melt. Feng et al. [14] synthesized TiC-Fe cermets under the action of an electric field. They found out that in such conditions, both Ti + C = TiC https://doi.org/10.1016/j.surfcoat.2018.04.086 Received 14 December 2017; Received in revised form 27 April 2018; Accepted 28 April 2018 ⁎ Corresponding author. E-mail address: adelim@iust.ac.ir (M. Adeli). Surface & Coatings Technology 347 (2018) 217–224 Available online 01 May 2018 0257-8972/ © 2018 Elsevier B.V. All rights reserved. T