Spinodal decomposition

Dr. Dmitri Kopeliovich

Spinodal decomposition is a spontaneous phase nanoscale separation (clustering) occurring in homogeneous supersaturated solutions (liquid or solid), which results in formation of two phases of different compositions but with identical crystal structure.
Spinodal phases form without nucleation and needs no incubation period.

Spinodal structure is extremely fine and continuous throughout the grains.

Some copper-nickel-tin alloys (Spinodal Bronzes) may perform spinodal decomposition resulting in formation of tin-reach phase homogeneously distributed throughout copper matrix and causing its hardening.
The hardening mechanism is different from that of conventional hardening processes such like strain hardening, grain size hardening, solid solution hardening, Precipitation hardening. Spinodal structure of Cu-Ni-Sn alloys is characterized by strains on the coherent boundaries between the copper-rich and tin-rich phases causing hardening of the alloy.

Spinodal heat treatment is similar to that of Precipitation hardening.

It consists of the following stages:

• Homogenization. At this stage the alloy is heated to a temperature above the miscibility gap in order to form mono-phase structure.
• Quenching. Rapid cooling resulting in formation of supersaturated solid solution at room temperature.
• Spinodal aging. The supersaturated mono-phase alloy is heated to a temperature within the range of spinodal decomposition followed by soaking for a time required for the decomposition process.

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• Solid solutions
• Grain structure
• Solidification
• Phase transformations and phase diagrams
• Basic principles of heat treatment
• Microsegregation
• Plastic deformation
• Heat treatment technologies
• Spinodal Bronzes

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