Metallurgical basis of heat treatments

Introductory articles and have shown that each type of post-treatment metallurgical structure can be associated with a set of characteristics that are more or less favorable to either shaping or end-use properties.

Examples of heat treatments, drawn in particular from the major families of alloys most commonly used and summarized in the article , are enough to convince us of the very wide variety of structures and properties they can be used for with relatively simple thermal cycles (a few hours, at a few hundred degrees Celsius, in neutral or reducing atmospheres that are fairly easy to industrialize).

As these are solid-state transformations sensitive to small additions (low precipitated volume fractions, very local crystallographic relationships, important role of segregations at grain boundaries, etc.), it is easy to see the need for thermodynamic data, to predict possible equilibrium phases, and kinetic data, to monitor the degrees of advancement of the various diffusions for critical elements in the alloy's nominal composition over reasonable cycles.

From a thermodynamic point of view, a number of concepts seem particularly important: chemical activity and potential, phase diagrams and corresponding crystallographic data, solubility products of essential precipitates...

In terms of kinetics, you obviously need diffusion data for the phases involved in the system under study, coalescence or redissolution rates of precipitates in favor of new phases, diagrams showing allotropic transformation or precipitation kinetics...

These metallurgical basics can of course be found in all general metallurgy books, but in this article we'll focus more specifically on the treatments envisaged.

Alongside the practical choice of processing conditions, there is also the question of the dispersion of expected results, due as much to operating dispersions as to inevitable alloy segregations.