COST 507 - Repositório Aberto da Universidade do Porto

satisfied the three requirements of an interfacial diffusion path. In the beginning of
reaction, A1N is decomposed and the nitrogen atoms are released to react with Ti to
form nitride TiN.. x between A1N and Ti layers. The TiN,. x layer serves as a trap for
nitrogen between A1N and Ti because nitrogen has a rather high solubility in it.
Hence, the formed (aTi) phase between TiN.. x and (ßTi) must be nitrogen­depleted.
Consequently, other diffusion paths which start from the Ti terminal but first go to
the nitrogen­enriched a(Ti,N) phase, such as βΤί/α(Τί,Ν)/τ./γ/τ 2 /δ/Α1Ν, are
impossible.
3.1.2 TiN/AI interface reaction
TiN as diffusion barrier between Al/Si [96Zen2]
ΤίΝ,.χ has been widely investigated as diffusion barrier between Al and Si. The
Al/TiN/Si system has been shown to be stable at temperatures between 500 and
600°C for around 30 min., but fail at longer annealing times. It has been suggested
that the barrier failure be initiated at the Al/TiNi_ x interface [82Wit]. The
thermodynamic description of the Ti-Al-N system in [97Zenl] has been used to
establish overall phase relationships of the Ti-Al-N system at 600°C and, then, in
conjunction with diffusion kinetics, provide a theoretical interpretation of
experimental results on the interfacial reaction between Al and TiN|. x films. It is
suggested that the observed stable TiAl 3 /TiN contact at 600 °C was in metastable
state due to extremely rapid growth of TiAl 3 , and hence the three-phase equilibrium
TiN-AlN-TiAl 3 proposed by [84Bey] is not a stable equilibrium.
Sintering of Al+TiNpowder mixture [97Zenl]
A promising Al-matrix composite, which is hardened by intermetallic compounds
TiAl 3 and A1N, have been synthesized from powder mixture of Al+TiN by means of
reaction sintering within temperature range of 550~650°C [92Koy]. From the
experimental results, it seems that there exists interdiffusion of Al and Ti but the
nitrogen atoms do not diffuse, and the reaction path is Al/TiAl 3 /AlN/TiN. This is
similar to the interfacial reaction between thin films Al and TiN mentioned above.
Therefore the thermodynamic description of the Ti-Al-N system in [97Zenl] can
also be applied to this case.
3.1.3 Metastable AIN-TiN films [97Zenl]
Discussion has been given on the thermodynamic description of the metastable
solutions in AIN-TiN thin films. It was concluded that fcc-(AI) and fcc-TiN x should
not be treated as the same phase. Using the current datasets a calculation of the
Gibbs energy surface of δ-(Τί,Α1)Νι. χ in the ternary system is possible. This provides
also data for the decomposition of N-deficient metastable films.
3.1.4 Nitridation of Ti-Al alloys [97Sch]
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