Review Surface carburizing of Ti–6Al–4V alloy by laser melting A.F. Saleh a , J.H. Abboud b , K.Y. Benyounis c,n a Department of Mechanical Engineering, University of Omer Almukhtar, P. O. Box 390M Elbyada, Libya b Department of Mechanical Engineering, Garyounis University, P. O. Box 1308, Benghazi, Libya c Department of Industrial Engineering, Garyounis University, P. O. Box 1308, Benghazi, Libya article info Article history: Received 18 June 2008 Received in revised form 30 October 2009 Accepted 3 November 2009 Available online 4 December 2009 Keywords: Titanium Laser melting Carburizing Microstructure Solidification abstract Surface carburizing of a Ti–6Al–4V alloy using laser melting has been investigated experimentally, with the aim of increasing surface hardness and hence improving related properties such as wear and erosion resistance. The surface of the material was coated with graphite prior to laser irradiation. Carburizing was achieved by a laser alloying mechanism, which includes melting the substrate and dissolution of the graphite in the liquid state. Two different types of lasers were used: (i) a continuous wave CO 2 (CW CO 2 ) laser with a maximum power of 3 kW, and (ii) a pulsating Nd–YAG laser with a maximum power per pulse of 100 W. Optical microscopy, scanning electron microscopy, EDS-analysis, and X-ray diffraction were carried out to analyze the microstructure and identify phases of the carburized layers. The results show that the carburized layers produced by CW CO 2 and Nd–YAG lasers are macroscopically homogeneous and have gradient features. The microstructures consisted of TiC crystals in the matrix of a 0 -Ti. The TiC crystals are either in the form of particles or dendrites. The depths to which these layers extend ranged from about 0.2–0.5 mm, depending on the treatment parameters. The volume fraction of the dendrites was found to decrease with increasing laser power or increasing traverse speed. Microhardness has been found to be directly related to the volume fraction and the size of the TiC phase. It increased to a value ranging from 500 to 800 Hv as compared to 350 Hv for the as- received substrate. & 2009 Elsevier Ltd. All rights reserved. Contents 1. Introduction ...................................................................................................... 257 2. Materials and experimental methods .................................................................................. 258 2.1. Material and sample preparation ............................................................................... 258 2.2. Laser melting ............................................................................................... 258 2.3. Surface characterization method................................................................................ 259 3. Experimental results and discussion................................................................................... 259 3.1. Morphology and microhardness ................................................................................ 259 3.2. Microstructure and X-ray diffraction ............................................................................. 260 4. Conclusions ...................................................................................................... 266 Acknowledgements ................................................................................................ 266 References ....................................................................................................... 266 1. Introduction The high specific strength and good corrosion resistance of titanium alloys make them suitable for many engineering applications such as jet engine compressor components, aero- space components, high pressure heat exchangers, sea water desalination plants, and petrol-chemical plants [1]. However, the wear resistance of titanium alloys is inadequate in many of these applications. Various means have been suggested for alleviating these wear problems. For example, the tribological performance of titanium alloys is much improved with nitride, carbide or oxycarbonitride coatings. Thin coatings have been prepared by many different methods such as ion radiation, chemical vapour ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/optlaseng Optics and Lasers in Engineering 0143-8166/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlaseng.2009.11.001 n Corresponding author. E-mail addresses: elmhdi1772000@yahoo.com (A.F. Saleh), jhabboud@yahoo. com (J.H. Abboud), kybenyounis@yahoo.com (K.Y. Benyounis). Optics and Lasers in Engineering 48 (2010) 257–267