Solid freeform fabrication of alumina using laser-assisted ESAVD Yiquan Wu a , Kwang-Leong Choy b, * a Department of Materials, Imperial College London, London SW7 2AZ, UK b School of Mechanical, Materials and Manufacturing Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK Received 3 May 2005; accepted 21 July 2005 Available online 28 October 2005 Abstract Electrostatic spray assisted vapour deposition (ESAVD) has been used successfully to produce films and coatings. A combination of laser- assisted (LA) deposition and ESAVD has been developed for the direct fabrication of alumina ceramics. This novel laser-assisted ESAVD technique involves spraying a liquid precursor onto a substrate whilst a laser beam is simultaneously used to heat the precursor and cause the decomposition and chemical reactions of the precursor in order to produce a solid deposit. A desired three-dimensional (3-D) object can be formed through layer-by-layer deposition using a computer-controlled platform. Dense or porous alumina ceramics can be deposited on the substrate by optimizing the processing parameters. This paper reports the fabrication of alumina parts by the laser-assisted ESAVD method. The effect of processing parameters including laser scanning speed, laser beam size and laser power on the microstructure will be presented. Scanning electron microscope (SEM) and X-ray diffraction (XRD) have been used to characterise the phase and structure of the deposited alumina parts. # 2005 Elsevier B.V. All rights reserved. Keywords: Solid freeform fabrication; ESAVD; Ceramics; Laser deposition 1. Introduction Recently, there has been an increasing interest in laser- assisted (LA) fabrication of materials. For example, laser- assisted chemical vapour deposition has been used to prepare films and coatings from a gaseous mixture, and the micro- structure can be controlled by the incident laser power [1–3]. In addition to a gaseous mixture as the starting materials, powders or liquids have also been used as the starting materials for the laser-assisted fabrication of materials [4,5]. In searching for a flexible and cost-effective laser-assisted fabrication of materials, a novel technique named direct laser-assisted electrostatic spray assisted vapour deposition (ESAVD) has been developed by combining a carbon dioxide laser system as the heat source and an ESAVD system for materials deposition [6]. ESAVD has been used successfully to deposit films and coatings [7–9]. In the LA- ESAVD method, a liquid precursor is atomised and directed onto cermets substrate under an electric field whilst a laser beam is simultaneously used to provide localised heating of the cermets substrate and cause the decomposition and chemical reactions to produce a solid deposit. By carefully controlling the movement of substrate using a computer-controlled XYZ table, a desired ceramic pattern with controllable microstructure could be formed through layer-by-layer deposition using the LA-ESAVD. This paper reports the fabrication of alumina ceramics using the LA-ESAVD process, which has potential applications in solid freeform fabrication. 2. Experimental Aluminium alkoxide was used as a precursor to fabricate alumina [10]. The LA-ESAVD has been described in detail in refs. [6,11]. The atomised aerosol droplets were directed towards the substrate under an electric field. The processing parameters of laser power, P , laser scanning speed, V , laser beam size, D, laser power density, E and laser energy density, J, are summarized in Table 1. E is defined as E =4P/(pD 2 ) and J is defined as J = P/(VD). The formulation shows that the laser energy density is reciprocal to the laser beam size. Carbon dioxide laser is focused by a ZnS lens and can deliver continuous wavelength with an output of as much as 70 W. The www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 4809–4813 * Corresponding author. 0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.07.144