COST 507 - Repositório Aberto da Universidade do Porto

AIN and TiNi_ x is also given. Various combinations of different versions of the Ti-Al
and Ti-N binary data have been tried. Finally, two versions of the present modeling
are offered, based on two versions of the Ti-Al system. The experimental phase
equilibria at 1300°C can be well reproduced. Inconsistencies are detected at lower
temperatures, which are also related to the observed melting behavior of the ternary
compounds. Additional key experiments have been performed by our COST partner
(Universität Wien) and the results confirm that previous data refer to insufficient
equilibration. These inconsistencies and the current approach to determine the Gibbs
energies of the ternary phases in such a complex situation are discussed in detail.
Applications of the developed thermodynamic modeling include: (1) the joining of
A1N with Ti-braze, where also our own thin film experiments on the Ti/AIN
interface reaction are reported, and an interpretation of the diffusion path is given;
(2) diffusion barriers in semiconductor contacts, where an interpretation of the
Al/TiN interface reaction is given; (3) the in-situ synthesis of Al-matrix composites,
strengthened with (TiAl 3 +AlN) reaction products during sintering of Al+TiN powder
mixtures; (4) the formation of mixed AIN-TiN hard coatings and their stabilities with
respect to the pure nitrides; and (5) the nitridation of Ti-Al alloys. Details are given
in a publication [97Zenl] (see appendix Ilia). Preliminary data were published in
[96Zen2] (see Appendix Illb).
2.4 Ti-V-N system [97Zen2]
Experimental Ti-V-N phase diagram data have been thermodynamically assessed and
a consistent set of thermodynamic functions has been developed. Calculations have
been performed to reveal some important features of the system. Problem areas in
experimental data are indicated. The thermodynamic calculation is linked with
limiting cases for solid state diffusion kinetics. This is applied to a numerical
simulation of ternary solidification processes of Ti-V-N alloys and to a discussion of
nitriding behavior of Ti-V alloys. Details are given in a publication manuscript
[97Zen2] (see appendix IV).
2.5 Al-V-N system [97Du2,3]
Thin film diffusion couples V/A1N have been used to investigate the phase
relationships in the Al-V-N system. The couples were prepared by electron beam
evaporation and annealed at 1000 and 1300°C for 144 and 69 hr., respectively. The
phases were identified by X-ray diffraction. The Al-N-V ternary phase diagram is
calculated from the thermodynamic parameters of the corresponding binary systems.
It is shown that the direct extrapolation from the binary edges can describe the
experimental isothermal section at 1300°C from the literature. For the isothermal
section at 1000°C, however, the extrapolation does not reproduce the reported
A1N+(V)+VN X phase equilibrium. The calculated Al-N-V phase diagram is also
compared with the phase assemblage data resulting from our own thin film diffusion
couples V/A1N. It is plausible that these assemblage data are associated with
intermediate states approaching true equilibrium states. Details are given in two
publications [97Du2, 97Du3] (see appendices Va and Vb)
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