Heat treatment of superalloys

Heat treatment of superalloys takes place at every stage of the manufacturing process, from the production of semi-finished products to the delivery of finished parts. They clearly determine the quality of the finished product, the mechanical properties of the materials and, to a large extent, the homogeneity of the results obtained.

It is customary to consider that treatments carried out upstream of parts production, such as chemical composition homogenization, at high temperature and for long periods, or preheating prior to shaping, are not strictly speaking heat treatments. They do, however, condition the quality of the initial material for part production and, in particular, the local response of the material to the heat treatments themselves, contributing to the ability to meet property targets and the statistical distribution of these properties.

In addition, by carrying out deformation sequences at specific temperature levels, followed or not by controlled cooling, it is possible to obtain microstructures with very high characteristics, through successive recrystallizations. These methods, described as thermomechanical treatments, are not the subject of this article. They are particularly well studied in the case of fine-grained structures obtained or not by powder metallurgy, implemented by extrusion and isothermal forging. The heat treatments themselves are carried out without deformation and correspond, on the one hand, to solution treatment, stabilization or precipitation to adapt the initial microstructure and determine the properties in service and, on the other hand, to softening and stress relaxation treatments related to forging, welding, machining, etc.

A coherent set of these treatments will guarantee the behavior of the parts produced.