Metallurgical stability refers to the physical and
chemical behavioral conditions of metallic elements, their intermetallic
compounds and their mixtures such as alloys. It is the tendency of a material to resist change or decomposition due to an internal reaction, or due to the action of air, heat, light or pressure.
Physical stability refers to the
structural stability, elastic strength and metal hardness. Chemical
stability refers to the thermodynamic stability of the metal in corrosive environments.
Ideally, in harsh corrosive conditions metal structures and their associated equipment will be metallurgical stable (i.e., the metal’s physical and chemical stability should remain intact).
The physical stability of a material is relatively unaffected in a corrosive environment compared to its chemical stability. In materials science, a chemical substance is said to be stable if it is not particularly reactive in the environment or during normal use, and retains its useful properties on the timescale of its expected usefulness. In particular, the usefulness is retained even in the presence of air, moisture, heat and under the expected conditions of application. In this meaning, the material is said to be unstable if it can corrode, decompose, polymerize, burn or explode under the conditions of anticipated use or normal environmental conditions.
For example, advanced ceramics are highly resistant to chemical corrosion due to their high levels of chemical stability. Corrosion-resistant ceramics possess low chemical solubility and therefore have a particularly high resistance to chemical corrosion.
Chemical substances can persist indefinitely even though they are not in their lowest energy state if they experience metastability, a state that is stable only if it is not disturbed too much. A substance (or state) might also be called kinetically persistent if it is changing relatively slowly. Metastable and kinetically persistent species or systems are not considered truly stable in chemistry.
Chemically stable materials are less reactive and therefore more corrosion resistant.