4. Finish

After the above operations, we can carry out the heat or surface treatments that are common in metallurgy.

Heat treatments such as quenching or precipitation hardening pose no problem, as long as they are carried out in a neutral or reducing atmosphere. Treatments in salt baths should be avoided as soon as porosity is open.

The TTT and TRC curves (articles in the Heat Treatments section of this treatise) for non-porous alloys can be used, as cooling rates are governed by thermal diffusivity, which is little influenced by porosity. Indeed, the thermal conductivity λ of the solid varies as 1 – 1.5 · ε and, taking into account the conductivity of air in the pores, the coefficient 1.5 approaches 1.3. On the other hand, the volumetric heat capacity obviously varies as 1 – ε and the ratio of the two λ /ρc as 1 – 0.2 · ε (ε is the volumetric porosity,...