Synthesis and coating of micro-metal-matrix composite by combined laser sol–gel processing Tamer Ezz a, ⁎ , Philip Crouse a , Lin Li a , Zhu Liu b a Laser Processing Research Centre, School of Mechanical, Aerospace, and Civil Engineering, University of Manchester, Sackville Street, Manchester, M60 1QD, United Kingdom b Corrosion and Protection Centre, School of Materials Science University of Manchester, The Mill, Manchester, M60 1QD, United Kingdom Received 6 February 2006; accepted in revised form 18 October 2006 Available online 28 November 2006 Abstract Of the many methods of laser treatment for improving materials surface properties that have been reported, very few have addressed laser-assisted chemical reaction. In this work laser deposition of metal-matrix composites is reported, using chromium oxide and silicon carbide powders mixed in silica sol–gel mixtures, on EN43 mild steel substrates. Very fine SiC particles ≤ 1 μm and M 7 C 3 carbides were synthesised in situ and dispersed in ferrite matrix by this process. A diode laser at different powers and scanning speeds was applied to specimens coated with slurries of different chemical compositions. The effect of solution composition and bath depths were examined in order to achieve optimum experimental parameters. Surface morphology and microstructure of the deposited coatings and substrate surface layers were examined using optical microscopy, scanning electron microscopy (SEM) and field emission gun scanning electron microscope (FEG-SEM). Chemical composition was determined by energy dispersive X-ray analysis (EDX). The different phases were identified by X-ray diffraction (XRD). Results of microhardness measurements and wear properties of the coatings are also reported. Thermodynamic analysis of the reactions taking place is also given. © 2006 Elsevier B.V. All rights reserved. Keywords: Laser-sol/gel-metal matrix composites 1. Introduction During the last few years, considerable research effort has been directed towards the production of metal-matrix compo- sites (MMCs) and/or surface alloying with fine ceramic particle coatings by laser cladding or laser alloying. These types of coatings provide exceptional physical and mechanical proper- ties, improving wear and corrosion resistance in many industrial applications. It combines metal alloy properties such as tough- ness and ductility with ceramic characteristics like high strength, hardness and thermal stability. Several types of ceramic phases including WC, TiC, TiN, Cr 3 C and SiC can be introduced into various compositions of metal matrix alloys by either laser alloying or laser cladding [1–8]. It was reported that laser surface alloying of H13 die steel with micro-size TiC particles increases the wear resistance by more than 100%, and that surface alloying with nanoparticle size TiC decreases the hardness by 25% [9,10]. This is explained by the dissolution of the very fine particles into Ti and C in the Fe matrix during laser processing, causing stabilization of the ferrite phase as Ti is a strong ferrite-former. Thus the microstructure produced in this case consists of ferrite instead of martensite and undissolved TiC. Molian and Jiang, [9] report that other coating techniques for producing ceramic coatings such as chemical and physical vapour deposition, thermal spraying and ion implantation are not capable of meeting all the requirements for effective coat- ings. These include: excellent bonding; adequate thickness; absence of flaws; suitable mechanical properties; thermal shock resistance; and high temperature stability. Tjong and Ma [11] state that in situ MMCs, where reinforce- ments are synthesised in a metallic matrix by chemical reaction between elements or between elements and compounds, exhibit advantages which include: thermodynamic stability of the rein- forcement particles in the metal matrix; strong interfacial Surface & Coatings Technology 201 (2007) 5809 – 5814 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. University of Manchester, School of Mechanical, Aerospace and Civil Engineering, Laser Processing Research Centre (LPRC), A26D, Sackville Street Building, PO Box 88, Manchester M60 1QD, United Kingdom. Tel.: +44 161 306 3828; fax: +44 161 306 3803. E-mail address: Tamer.Ezz@manchester.ac.uk (T. Ezz). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.10.030