Characterization of Spectral Emissions from Laser Irradiated Titanium
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1040-Q08-02
Characterization of Spectral Emissions from Laser Irradiated Titanium Ravindra Kumar Akarapu1, Puneit Dua2, Alan Campbell2, Dana Scott2, Abdalla Nassar2, Judith Todd2, and Stephen Copley2 1 Engineering Science and Mechanics, The Pennsylvania State University, 212 Earth and Engineering Sciences Building, University Park, PA, 16802 2 The Pennsylvania State University, University Park, PA, 16802 ABSTRACT Titanium nitride (TiN) is a candidate material for hard and wear resistant coatings on metallic substrates such as titanium (Ti), stainless steel and aluminum. Coating processes include chemical vapor deposition, ion implantation, plasma and thermal nitriding under vacuum and controlled environments. The motivation for the present research is to develop a laser plasma process for high rate formation of TiN coatings on Ti substrates at near-atmospheric pressures. Laser induced plasma generated by a pulsed CO2 laser was used to excite a Ti substrate. The species in the vapor plume were characterized by optical emission spectroscopy. Spatially and temporally resolved spectral characterization was performed as a function of laser power, position of the substrate relative to the focal plane, pulse parameters, and shielding gases. These experiments are a first step in understanding laser assisted plasma deposition of nitride/oxynitride coatings on titanium metal under atmospheric conditions. Results indicate a window of optimal process parameters for developing titanium nitride coatings. INTRODUCTION Plasmas have been extensively used in various manufacturing and material processes such as cutting, deposition, surface treatment etc. [1-4]. While thermal plasmas have been used for cutting and various heat treatment processes, non-thermal plasmas, with high electron densities and low gas temperatures are extensively employed for material processes. DC voltage, low and high frequency electromagnetic sources are used to initiate and sustain plasmas in a wide variety of gaseous mixtures. Plasma electron density and electron temperature depend upon power, frequency of the energy source and composition of the gaseous mixture. Both density and energy distribution of electrons dictate gas phase and surface reactions. In comparison to other electromagnetic sources, lasers are capable of producing localized plasmas with very high electron densities (ne = 1020 cm-3). In addition, lasers can sustain discharges in gas phase (laser sustained plasma) as well as generate plasma by irradiating solids. The main objective of the present work is to investigate the potential of laser generated plasmas for surface modifications. In this article we demonstrate plasma assisted surface nitriding of titanium using pulsed and continuous wave CO2 lasers. Nitridation with the aid of plasma generated near the surface of a Ti substrate in controlled atmospheres using high repetition rate (HRR) pulses of CO2 or excimer lasers has been studied by many authors [5-10]. Microsecond pulses of CO2 laser irradiation were used to breakdown nitrogen (N2
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