Oxidation of ductile particle reinforced Ti-48Al composite
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I.
INTRODUCTION
TITANIUM intermetallics are alloys that have shown promise for aerospace applications like hypersonic aircraft, advanced gas turbines, e t c . Their application has been limited due to problems of low ductility and toughness. In order to overcome these limitations, ductile particle reinforcements have been incorporated, t~,2~Current state of research indicates that a matrix of Ti-48A1 offers the best strengtht3j and toughness, and in this project, 20 vol pct TiNb particles were added as reinforcement. Oxidation behavior of TiAl-based monolithic materials has been studied extensively. I4-~2j However, an understanding of the oxidation behavior of ductile particle reinforced TiA1 matrix composites is lacking. Before these materials find application, a comprehensive understanding of their behavior under high-temperature oxidation environments needs to be developed. The oxidation of any metallic system proceeds because, at the temperature and environment of testing, the oxidation reaction results in a decrease in the surfacefree energy of the parent system. The oxidation then proceeds by a combination of two processes, oxygen dissolution and oxide scale formation. The formation of an oxide layer of finite thickness indicates that the kinetics of oxidation are higher than those of dissolution. The total oxidation rate (as measured by the rate of gain of weight) is governed by the transport characteristics of the oxide scale. Factors that control the transport characteristics of the oxide scale include the concentration of the diffusion species and the presence of high diffusion paths like cracks, pores, and grain boundaries within the oxide, t~3~The presence of a second phase like TiNb particles may also affect the oxidation rate. It is the aim of this study to examine the effect of temperature (704 ~ 815 ~ 898 ~ and 982 ~ on oxidation rate in an atmosphere of air, as well as the role S.A. KEKARE, formerly Graduate Student, Materials Science and Engineering Department, University of Texas, Arlington, TX 76019, is Student Assistant, Lawrence Berkeley Labs, Berkeley, CA 94720. J.B. TONEY, Scientific Technician, and P.B. ASWATH, Assistant Professor, are with the Department of Materials Science and Engineering, University of Texas, Arlington, TX 76019. Manuscript submitted April 12, 1994. METALLURGICAL AND MATERIALSTRANSACTIONS A
played by the environment at 982 ~ (air only, oxygen only, and oxygen followed by air) on the kinetics and characteristics of oxidation. Section II gives details of the experimental procedure, Section III provides details of a physical model of oxidation, Section IV details the experimental results and discussion, and Section V lists some key conclusions. II.
EXPERIMENTAL PROCEDURE
The Ti-48A1 + 20 vol pct TiNb composite was produced by phase blending of Ti-48A1 and TiNb powders. m The Ti-48AI was produced by Nuclear Metals, Inc. (Concord, MA) using the plasma rotating electrode process (PREP), and the TiNb was produced by Pratt and Whitney (West Palm Beach, FL) using a gas atom
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