Effect of Temperature and Time on the Development of Hafnium Diboride (HfB₂) Coatings by Chemical Vapor Deposition (CVD)

Refractory metal borides possess an array of impressive properties which has led to their categorization as advanced technology boron products. These properties include high refractoriness, wear resistance, corrosion resistance, high hardness, and high fracture toughness. HfB₂ is a remarkably high temperature ceramic material with features like its immunity to high temperatures and its power to remain steadfast in extreme conditions. This component is essential to various systems in the advanced technology and defense industries, and it plays a crucial role in them. HfB₂ has a wide range of applications, including aerospace, aviation, and metallurgy. (Kauffman, 1965). HfB₂ is an ideal material for high-temperature ceramics because of its elevated melting temperature, remarkable thermal conductivity, outstanding resistance to thermal shock, a low thermal expansion coefficient, high-temperature resistance, and the ability to remain stable in extreme environments. HfB₂ has many impressive characteristics that make it a practical solution to be used as a thermal protection system for mission-critical applications, which include hypersonic flights, atmospheric entry systems, and rocket thrusters (Sonber, 2011).<br/>This research implemented a CVD-based gas phase coating technique, designed for the purpose, to produce HfB2 coatings on copper (Cu) substrates at various temperatures and time. CVD is a low-temperature process used for coating and powder production and can create pure products that other techniques cannot. Chlorides and hydrogen gases are among the most preferred reducing agents in CVD systems. The gas phase reactants were selected as in Reaction 1 (Pierson, 1999).<br/>HfCl₄+2 BCl₃+5 H₂→HfB₂+10 HCl (1)<br/>In the present study, HfB₂ refractory boride coatings were produced as a high purity coating from the gas phase using a specially developed reactor and process design (Bolluk, 2015).<br/><br/>We performed structural analysis methods in order to examine the coatings. According to the XRD results, high purity HfB₂ polycrystalline coatings were obtained. The SEM-EDS analysis was used to evaluate the impact of reduction temperature on crystallite size and to examine the effects of different reduction temperatures on nucleation, grain growth, and morphology. The X-ray photoelectron spectrometry (XPS) technique applies to examine the surface characterization, bond structure and elemental distribution of refractory boride coatings.<br/><br/>REFERENCES<br/>Kaufman, L. and Clougherty E. V. 1965. Investigation of Boride Compounds for Very High Temperature Applications-Part II, DTIC Document.<br/>Sonber, J.K., Murthy, T.S.R.C., Subramanian, C., Kumar, S., Fotedar, R.K., ve Suri, A.K. 2011. Investigations on Synthesis of ZrB₂ and Development of New Composites With HfB₂ and TiSi₂, International Journal of Refractory Metals and Hard Materials, 29(1): p. 21-30.<br/>Pierson, H.O. 1999. Handbook of Chemical Vapor Deposition (CVD) Principles, Technology, and Applications, Second Edition, Published in the United States of America by Noyes Publications / William Andrew Publishing, LLC, Norwich, New York, U.S.A.<br/>Bolluk, M. 2015. Synthesis of Group IVB Zirconium and Group VB Niobium Diborides via CVD Process as Free Particles and Evaluation of Sintering Properties (Thesis of Master), I.T.U., Istanbul, Turkey.