This book is an old classic and still relevant:

Kubaschewski, Oswald and Hopkins, Bernarr. 1962. Oxidation of Metal and Alloys. London, Butterworths.

Let's Sit & Discuss It

 

The book focuses on theory and production of systems where oxidation plays a significant role. Let's summarize.

In air we find that almost none of the pure metals and no alloys are entirely stable at room temperature; they form nitrides or oxides. The rates of reaction may be small, but these rates are not zero; they are not negligible. Especially if metals are being joined.

As temperature increases this rate of reaction also increases and at yet higher temperatures the oxides of some alloys tend to dissociate and form their own pure metals. Therefore most solid and liquid state metals are unstable in air at any temperature, because the dissociation temperatures are, in most cases, above the boiling points of the metals.

Reaction products will therefore almost certainly form at the gas and metal interface unless they are sufficiently volatile and this layer of product will form an intermediate layer mostly separating gas and metal surface.

The reaction products, their structure and form, and their location affect in turn the reaction process that created them and which contributes further reaction products material. Further reaction products may be different.

Such a feedback makes the system not simple to predict.

The reaction products formed at the interface with a specific composition as a result of reaction processes depending on the composition can change the composition and therefore future reaction processes occurring there and therefore future reaction products and where they are formed.

Pores or cracks in the case of a noncompact surface open up the possibility of diffusion and a more more complex system. Diffusion may be along grains or along their boundaries. Thermal expansion processes, which are not the same for different components of alloys, or parts of joints, can produces such defects along which diffusion will proceed.

And then all the component metals in an alloy, depending on their relative free energies, may preferentially for reaction products with gases. But the energies along surfaces are not similar to those inside the bulk of materials ...

Some oxides may form only temporarily because they are not stable and these may grow on surfaces despite the fact that the material forms only a few stable oxides. This is one reason why prediction of oxide formation is generally difficult.

At high pressures we find more complex structures such as whiskers and high pressures may result from thermal expansion or contraction and this can further affect growth of unstable oxides. This is another reason why prediction of oxide formation is generally difficult.

Alloys have eutectic compositions such that the alloy has a melting point lower than the melting points of all its pure components. Heating melts it, and it may react preferentially to some materials near, or diffuse, changing the composition, changing the melting point, and solidify at that temperatures, instead of reacting to other materials. This complex process might result in rapid oxidation, and requires we think about relative rates involved for all possible feedback processes and free energy and least energy states.

Thus begins our discussion of the book. We've covered the preliminaries here.

The book is particularly useful for material scientists and engineers who participate in industrial production of high strength metal or composite structures and we will therefore discuss it in a series of posts.

Let's share knowledge.

UPDATE

We may resume this blog. To start writing more about new materials joining technology. Not all materials are new but often new properties in less widely known materials are found when looking for different kinds of things. It is often worth reconsidering them in new contexts. That may be worth an essay. Examples may be "new" HEA filler metals, like the less well known Co_3 Ni_1 Si_1 Mo_1 Cr_1.3, Co_3 Ni_1 Si_1 Nb_1 Cr_1.3, and others with that pattern and near that pattern, where the coefficients are atomic ratios and the rest being impurities or additives, and the material Ti_4 Zr_1 Nb_1 Cu_1.5 Ni_1.5, which is more widely known but not as a HEA material. HEA filler metals for low temperature joining is a relatively new context. These are also examples where a complex system of more components gives a much more homogeneous result after everything interacts, and that is also something else worth discussing.

Images by Arbit (CC BY 4.0).

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