3. Mechanical properties

Mechanical properties change with temperature. Whatever the material, it is common to find that below a certain temperature the material becomes brittle, as opposed to ductile (the property of a material to deform) when hot. The appearance of this brittleness leads to the selection of materials on the basis of their mechanical properties, and to the exclusion of materials that are brittle at low temperatures from the design of cryogenic equipment.

The cold behavior of metals and alloys depends on their crystal structure. Materials crystallizing in the face-centered cubic system (Cu, Ni and alloys, aluminum and its alloys, austenitic stainless steels, Ag, Pb, brass, Au, Pt) remain ductile up to very low temperatures thanks to their numerous possible slip systems.

Materials with compact hexagonal structures (Zn, Be, Zr, Mg, Co, Ti alloys,...