The characterization of corrosion resistance in the Ti-6Al-4V alloy fusion zone using a gas tungsten arc welding process
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Huang-Chih Lin Graduate School of Defense Science, Chung Cheng Institute of Technology, National Defense University, Tao-Yuan 33509, Taiwan, Republic of China (Received 2 June 2009; accepted 1 September 2009)
The Ti-6Al-4V sheet alloys were welded by using a common gas tungsten arc welding process. In this work, we study the correlation of corrosion resistance and oxide layer structure produced after commonly used industrial heat treatments. We also study the oxide scales that were formed as a result of the heat-related treatment/aging process. The results indicate that better corrosion resistance of the Ti-6Al-4V alloy weldment can be obtained and significantly improved by a solution treatment plus an artificial aging (ST+AA) treatment, owing to the enhanced intensity of TiO2, V2O5, and Al2O3 oxides that compacted and grew on the surface of fusion zone. The newly found g-TiAl and a2-Ti3Al particles that nucleated in the fusion zone due to different heat treatments do affect the composition of the oxide layer. The possible mechanism for this oxide layer formation in the fusion zone is discussed.
I. INTRODUCTION
Titanium and titanium alloys have many applications, notably as aerospace, cryogenic, or biomedical materials,1,2 in which the alloys show such attractive properties as high strength, good strength-to-mass ratios, and excellent biocompatibility. Ti-6Al-4V alloy is the most widely used a+b-type alloy among the wide variety of titanium alloys. Successful joining of these materials can be achieved by using gas tungsten arc welding (GTAW), which will further increase their utility in engineering applications. However, due to the remaining residual stress produced from the welding process, corresponding heat treatments are necessary to eliminate the retained stress. Therefore, the mechanical property of the weldment may be significantly improved. Ti-6Al-4V alloys are heat treatable to optimize their special mechanical properties and are chemically active at elevated temperatures and readily oxidize when exposed to air. Thus, the corrosion resistance of a Ti-6-4 weldment is critical to increase their safety as well as utility in engineering applications. However, the corrosion problem (e.g., oxidation) is not of primary concern in the heat treatment of titanium in the commonly used ASM standard,3 although in weldments it has a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0444
3680
http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 12, Dec 2009 Downloaded: 17 Mar 2015
always been an inescapable problem due to the fact that premature failure may occur from the produced oxide layer resulting from the complex precipitation or segregation of solute atoms in the fusion zone during the welding process, in which a significant amount of variable heat input may also lead to local readable change in material composition and microstructure. This process would result in further competitiveness of the solute atom in precipitation as well as possible segregati
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