Influence of Laser Treatment on the Creep of the Ti-6Al-4V Alloy
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THE development of alloys to increase creep strength, permitting the use in higher turbine entry temperatures, has resulted in a general reduction in chromium and an increase in the aluminum content of nickel superalloys. Such an environment is experienced by aircraft operating among airfields with low approach over the sea with relatively short sector times. Improvements in aero gas turbine performance in terms of power, efficiency, and weight have demanded the use of high-specific-strength and low-density materials.[1,2] One major factor limiting the life of titanium alloys in service is their degradation within a gaseous environment, in particular, the one containing oxygen at elevated temperatures during long-term use.[3] The sensitivity of titanium alloys to high-temperature exposure is a wellknown phenomenon. When titanium alloys are heated to temperatures above approximately 1073 K (800 °C), oxygen, hydrogen, and nitrogen can penetrate into them. The penetration of these elements increases hardness and brittleness while decreasing the toughness of the alloy.[4] The interaction of titanium alloys with oxygen not only causes losses in the material because of the formation of A.G. REIS, Master Degree Student, and D.A.P. REIS and C. MOURA NETO, Teachers and Researchers, are with the Instituto Tecnolo´gico de Aerona´utica (ITA/DCTA), Sa˜o Jose´ dos Campos 12.229-900, Brazil. Contact e-mail: [email protected] M.J.R. BARBOZA, Teacher and Researcher, is with Escola de Engenharia de Lorena (EEL/USP), Lorena 12.600-970, Brazil. C.R.M. SILVA, Teacher and Researcher, is with Universidade de Brası´ lia (UNB), Brası´ lia 70.910-900, Brazil. F. PIORINO NETO, Researcher, is with Instituto de Aerona´utica e Espac¸o (IAE/DCTA), Sa˜o Jose´ dos Campos 12.229-900, Brazil. J. ON˜ORO, Teacher and Researcher, is with Escola Polite´cnica de Madrid (EPM), Madrid 28006, Spain. Manuscript submitted February 8, 2011. Article published online July 16, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
oxides but also causes embrittlement in the subsurface zone of the component because of oxygen enrichment.[3] Titanium alloys are one of the most technologically important materials in the aeronautics and aerospace fields for their high strength and low density. However, this material does not possess satisfactory tribological properties. For this reason, surface strengthening of titanium alloys has attracted significant attention.[5] Laser oxidation or nitration of titanium surfaces is interesting for local hardening and improvement of wear resistance. It is known that melting the surface layer can enhance chemical reactions, avoiding significant vaporization and particulate removal, representing the main requirement in direct laser surface oxidation or nitration of metallic targets in controlled reactive atmospheres.[6] Titanium nitride thin films are of interest for applications in technological areas because of their excellent hardness, wear, and corrosion resistance; high melting point; chemical inertness; and high electrical conduct
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