# Material Transitions

## Material to Material Calculator

Examine how materials transition from one composition to another using the Material to Material Calculator included in all Thermo-Calc installations.

## About the Material to Material Calculator

The Material to Material Calculator is a module included in all Thermo-Calc installations that allows you to examine how materials transition from one into the other. These calculations are only based on thermodynamic equilibrium and are thus much faster and easier than involving diffusion calculations. The Material to Material Calculator is included in all Thermo-Calc installations.

The example plot shows the gradual transition from a martensitic stainless steel on the left to Alloy 800 on the right at 650 °C. Neither material is expected to form any detrimental phase on its own at this temperature. We see, however, that within the transition zone of these two materials, the detrimental sigma phase can potentially occur (red line). This type of calculation is simple and fast, but neglects any non-linear diffusion effects. Consequently, the actual phases being present in a welding joint or diffusion couple of these two materials might differ.

## Typical Applications of the Material to Material Calculator

The Material to Material Calculator can be applied in any situation where different materials are in contact with each other and will react significantly (usually at high temperature) or gradually transition into each other by design. The calculator performs equilibrium calculations along linear composition gradients, which allows for simple, stable, and fast calculations — avoiding the complexity of diffusion calculations. It can, however, not take into account complex non-linear or non steady-state diffusion effects.

Typical fields of application are:

• Non-similar material joints - such as welds of titanium with nickel-based superalloys
• Reaction of two materials - for instance the influence of volcanic ash layers on a turbine component in a jet engine
• Diffusion couples

• What are the stable phases to be expected when two materials are in contact and transition into each other with linear gradients? Are detrimental phases formed?
• How are the thermophysical properties (coefficient of thermal expansion, and so on) changing along the transition between the two materials?
• What is the composition of the phases present in such a transition?
• How do the phases and their compositions change with temperature?
• How are the transformation temperatures and solubilities changing along the transition between the two materials?

## The Material to Material Calculator Allows You to Calculate:

• Single equilibrium calculations with fixed fraction of second material
• One-axis calculations varying fraction of second material or temperature
• Phase diagram calculations varying both fraction of second material and temperature
• Evaluation of all quantities available in Thermo-Calc equilibrium calculations, including:
• Volume fraction of phases
• Composition of phases
• Driving force of phase formation
• Specific heat
• Heat capacity
• Heat of formation
• Enthalpy
• Density
• Electric resistivity
• Thermal conductivity
• Coefficient of thermal expansion...

## How the Material to Material Calculator Works

The Material to Material Calculator uses linear composition profiles for each element or component (e.g., c1, c2, and c3 in the diagram) between the composition of the first and the second material. The calculator performs equilibrium calculations along the composition profiles. All possible configurations are identical to that of regular equilibrium calculations. This means that, for example, phases can be set to dormant or components can be chosen instead of elements.

## Graded Transition Joint for FeCrNi Alloy using the Material to Material Calculator

Learn how to set up a calculation in the Material to Material Calculator in our tutorial video, which shows how to calculate the transition of an Fe-Cr-C alloy from one composition to another.

## Databases

The  Material to Material Calculator can be used with any thermodynamic and properties database available for Thermo-Calc. No diffusion database is required. Both materials in the calculation need to be able to be modeled with the same database — or with multiple databases that are compatible. Information about our broad range of databases can be found in the database section.