APPLICATIONS OF THERMO-CALC

Corrosion

Thermo-Calc can be used to study the susceptibility of alloys to different types of corrosion and aid the development of new alloys or environmental barrier coatings to reduce susceptibility.

Applications to Corrosion

Corrosion is often a life limiting process that affects almost all materials. Globally, it is estimated to cost over two trillion dollars annually.

Thermo-Calc can be used to study the susceptibility of alloys to different types of corrosion such as aqueous corrosion, high temperature gas corrosion, metal dusting, internal oxidation, degradation of coatings through inter-diffusion, and molten salt corrosion. It can also be used in the development of new alloy compositions or environmental barrier and thermal barrier coatings (TBCs) that mitigate corrosion.

Calculate the following as a function of material chemistry and temperature:

  • Pourbaix (Eh vs pH) diagrams for alloys to determine phase stability at different temperatures and aqueous conditions
  • Stability of oxide phases as a function of oxygen partial pressure
  • Degradation of coatings through interdiffusion between coatings and substrates
  • Extent of internal oxidation based on oxygen content and temperature

Application Examples

Thermo-Calc has many applications to corrosion. Below are three such examples.

Pourbaix Diagram Calculations for Pure Substances

Pourbaix diagrams are typically found in the literature for pure elements or only the most common alloys. As such, they often need to be determined experimentally, which can be costly and time consuming and still does not capture the composition variation that may be associated with an alloy. Using the Pourbaix Diagram Module, included in Thermo-Calc, it is possible to make such predictions specifying both the alloy composition and also the solution chemistry.

In this example, the calculation for a 2.25Cr-1Mo steel readily maps the regions associated with immunity (H2 Gas Reducing Area), passivity (Fe2O3 and Fe3O4), as well as the region where corrosion readily occurs. The results correspond well with the data found in traditional handbooks.

A Pourbaix diagram for pure iron in pure water.

Pourbaix Diagram Calculations for Alloys

The Pourbaix Diagram Module in Thermo-Calc can also create Pourbaix diagrams for multicomponent alloys in aqueous solutions that contain other solutes (such as chlorides or sulfides). The example plots show the effect of alloy additions on the stability of the passive regions relative to the pure Fe example shown previously.  The left plot is the Cr-Mo steel and the right plot is a 304SS (18Cr-8Ni) alloy. Additional Cr content can further stabilize this passive region in chloride containing environments, such as seawater. The module can be used to calculate thermodynamic stability from ambient temperature and pressure up to 350°C and 100 bar. To see the plot larger, right click and select “Open image in new tab.”

A Pourbaix diagram for 2-¼ Cr 1 Mo steel in pure water on the left and a Pourbaix diagram of 304 stainless steel (Fe-18Cr-8Ni) in seawater environment (3mol.% NaCl) on the right.

High Temperature Oxidation in Supercritical Water Reactor Service

Some high efficiency nuclear reactors rely on operating at conditions above the thermodynamic critical point of water, termed supercritical water reactors. Supercritical water is more corrosive than traditional reactor water solutions, which places challenges on design by requiring materials that maintain strength at high temperatures and are resistant to both corrosion and irradiation. This figure shows a calculation of oxide formation and stability as a function of the partial pressure of oxygen. This calculation reveals that 12Cr steels can form a complex layered oxide under normal reactor operating conditions.

A plot showing calculation of oxide formation of 12Cr steels used in high temperature supercritical water reactor service.

Learn more about Applications to Corrosion

Integrated computational materials engineering of corrosion resistant alloys

Read now

Materials Corrosion Applications with Thermo-Calc

Read now

A module within Thermo-Calc that allows you to predict materials corrosion resistance.

Learn more

Let Us Help You

Find the Right Products