First phase formation at interfaces: Comparison between Walser-Bené and effective heat of formation model

• Published in: Materials chemistry and physics 1996-11, Vol.46 (2), p.238-247
• Main Authors: Theron, C.C., Ndwandwe, O.M., Lombaard, J.C., Pretorius, R.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Diffusion; interface formation; Effective heat of formation; Exact sciences and technology; Interfaces; Phase formation; Physics; Solid surfaces and solid-solid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Walser-Bené model
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/S0254-0584(96)01805-6

The only two models which make definite and unambiguous predictions regarding first phase formation during solid-state interaction are the Walser-Bené and effective heat of formation (EHF) models. Although these models appear to have certain features in common, such as models appear to have certain features in common, such as the choice of the liquidus minimum composition as a measure of atomic mixing at the interface, a careful analysis and comparison reveals fundamental differences between them, mainly owing to the fact that the EHF model also makes use of heats of formation. The EHF model in effect gives a quantitative reason for the relatively large margin of success of the Walser-Bené rules. A major feature of the EHF model is that it often predicts that there is not much to choose thermodynamically between the formation of several phases, whereas the Walser-Bené rules can only predict a single phase. In 53 out of 84 binary systems investigated it has been found that there is complete agreement between the predictions of the two models, whereas for 14 systems the Walser-Bené and EHF model predict the same first phase, the EHF model also predicts other phases, which usually are confirmed by experimental measurements. In seven binary systems, namely Al-Au, Al-Fe, Al-Gd, Au-Cd, Au-V, Au-Zn and Pt-Ti, the EHF model correctly predicts the first phase while Walser-Bené does not. There are also 10 systems where both models fail to predict the correct phase mainly because the liquidus minimum of the binary system is not well defined or the thermodynamically favoured phase has problems in nucleating.