Journal of Materials Processing Technology 142 (2003) 725–737 XRD and XPS studies on surface MMC layer of SiC reinforced Ti–6Al–4V alloy M.S. Selamat, L.M. Watson, T.N. Baker ∗ a Advanced Materials Research Centre (AMREC) SIRIM Berhad, 1 Persiaran Dato Menteri, P.O. Box 7035, Section, 40911 Shah Alam, Malaysia b Metallurgy and Engineering Materials Group, Department of Mechanical Engineering, University of Strathclyde, 75 Montrose Street, Glasgow G1 1XN, UK Received 7 January 2002; received in revised form 9 April 2003; accepted 5 June 2003 Abstract Overlapping tracks were produced by laser processing using a powder SiC (∼6 m) preplacement technique which has been developed to modify the surface structure of a Ti–6Al–4V alloy. A continuous-wave CO 2 laser was used for the processing which produced six overlapping tracks covering 14 mm across the surface of a 10 mm thick plate. Under spinning beam conditions, a surface alloyed/metal matrix composite (MMC) layer over 300 m in depth was produced on the alloy. The surface contained a complex microstructure, but with no cracks and only two pores at the melt/HAZ interface. Using XRD and XPS analysis, it was shown that the solidified melt consisted of  ′ -Ti, Ti 0.55 C 0.45 and Ti 5 Si 3 phases, which vary with melt depth and with the particular group of overlapping tracks examined. Therefore, no new phases to those previously identified in single track laser processing experiments were found in this work. © 2003 Elsevier B.V. All rights reserved. Keywords: Laser surface melting; XRD; XPS; Titanium alloy; Composite 1. Introduction One of the major obstacles to the widespread use of bulk titanium metal matrix composites (MMC) is the high cost. Major advances have been made in using creative processing techniques with alloys by introducing surface MMC layers. The use of SiC particles for producing bulk titanium and aluminium MMCs suggested that this approach could be applied for surface alloying by laser processing through the incorporation of the same or similar ceramic particles [1–4]. To obtain a good dispersion of particles a smaller size of 3–7 m SiC was added via a preplacement technique [3,4] compared with 150 m particles injected by Ayers [1] and Abboud and West [2]. In the former case the SiC dissolved in the Ti alloy and Ti 5 Si 3 and TiC precipitated [5–7]. An increase in the potential life of a component may be associated with an improvement in the wear resistance [1,4,5]. This is normally dependent on an increase in both the hardness and the depth of the surface region. Laser pro- cessing can develop a deeper melt pool than other surface modification techniques. On solidification after laser pro- ∗ Corresponding author. Tel.: +44-141-548-3101; fax: +44-141-552-5105. E-mail address: tnb@mecheng.strath.ac.uk (T.N. Baker). cessing a very different microstructure from the parent al- loy may be produced through retaining SiC particles in the melt pool. Earlier work at Strathclyde University used large SiC particles, between 60 and 150 m in size which were either preplaced or injected [3,8]. The injected case led to rough surfaces with cavities and a poor distribution of SiC p which had undergone partial dissolution [8]. The preplace- ment technique resulted in a better particle distribution [3,8]. Partially dissolved SiC p provides Si, which forms Ti 5 Si 3 , and C, which forms spherical TiC particles in the complex microstructure [5–8]. Under some conditions, both Si and C can combine with Ti to form Ti 3 SiC 2 during the laser pro- cessing [6,7]. In the present work, a smaller particle size was em- ployed with the aim of producing complete dissolution of the SiC particles and giving a high fraction of Si and C atoms available for new compound formation. A detailed microstructural characterisation of a Ti–6Al–4V alloy with SiC preplacement was undertaken. The main aims were to identify, after laser processing, the phases present as a function of the melt depth, due both to the production of overlapping tracks and in progressing from the first to the sixth track, in a sequence designed to cover an area of the specimen surface. This should develop a better under- standing of the influence of the laser processing parameters 0924-0136/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0924-0136(03)00814-8