Thin-Film Reactive Interdiffusion in The TI-AL System
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THIN-FILM REACTIVE INTERDIFFUSION IN THE TI-AL SYSTEM
P. MAUGIS, G. BLAISE AND J. PHILIBERTA Laboratoire de Physique des Solides ALaboratoire de Metallurgie Structurale, Orsay, France
Universit6 Paris XI,
91405
ABSTRACT We have studied the thermodynamics and kinetics of growth of Al-Ti phases in thin-film interdiffusion couples. A 1O0nm thick aluminum layer is vapor-deposited on a poly- or single-crystal titanium substrate, previously etched by ion bombardment. The sample is then annealed during a time ranging from a few minutes to a few hours, at temperatures from 300 to 600°C. The Al atomic fraction vs depth is determined using a sputtering technique, associated with At low temperature (STIMS). thermo-ionization mass spectrometry titanium diffuses along the grain boundaries of the (300-4500C). micro-crystalline aluminum 0 layer, to form an Al-rich phase. At higher temperature (450-500 C), the TiAI 3 phase grows rapidly up to the surface. Above 460*C, an intermediate Ti-72atAl phase grows and Ti. At 600°C, the aluminum layer becomes between TiAl 3 morphologically unstable. INTRODUCTION Reactive interdiffusion between titanium and aluminum has been widely studied [14]. When bulk samples are used, it leads to the formation of various ordered intermetallic compounds [9]. In order to study the first stages of growth of these compounds, thin film couples are used. One can wonder whether the compounds will be part if so, what is their stoichiometry. of the equilibrium diagram and, In this work, we use a thermo-ionization mass spectrometry to determine the chemical composition vs depth in reacted thin films. We report experimental results of the interdiffusion of a thin film of Al on a Ti substrate, annealed at temperatures below 500°C. EXPERIMENTAL PROCEDURE Sample preparation Three types of titanium substrates have been used: cold rolled, polycrystalline and monocrystalline. They are first mechanically by argon are sputter-cleaned the substrates then polished, bombardment just before the vapor-deposition of aluminum. A layer typically 100nm thick is deposited at a rate of lnm/s, in a vacuum 7 better than 2xlO- Torr. Ji sj'tu, using an treatments are performed The thermal electrical resistor that heats the sustrate on its back side. The
Mat. Res. Soc. Symp. Proc. Vol. 237. 01992 Materials Research Society
680
samples are annealed at temperatures ranging from 300 to 500°C. for lOmn to a few hours, in a vacuum better than 10-7 Torr. A stable temperature is reached after lOmn and the cooling is about lmn long. Sample analysis The concentration profiles are determined by STIMS analysis. The sample is bombarded by a primary scanned beam of Ar+ ions. The sputtered material enters a high-temperature cell where it is thermal-ionized. The resulting secondary ions are then extracted from the cell and analysed in a mass spectrometer. Refering to a standard of well known composition, the Al atomic fraction is calculated as a function of depth; the procedure has been described in details in [1]. SEM is used to determine the
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