APPLICATIONS OF THERMO-CALC

Welding and Joining

Thermo-Calc can be used to simulate non-equilibrium metallurgical reactions such as solidification and diffusion and provide thermophysical data as a function of composition and temperature to enhance finite element welding models.

Applications to Welding and Joining

Many weldability/joinability issues are linked to metallurgical reactions such as solidification, precipitation, and diffusion. Finite element codes for welding typically do not capture these reactions. Thermo-Calc can be used to simulate these highly non-equilibrium reactions and provide thermophysical data to enhance finite element modeling.

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

  • Fraction solid curves for equilibrium and non-equilibrium solidification path
  • Solidus and liquidus and incipient melt temperatures
  • Thermophysical properties to input into other codes, for example:
    • Specific heat, enthalpy, latent heat, viscosity, density as a function of temperature, and shrinkage/relative length change
    • Effects of cooling rate and multi-pass thermal cycles on precipitation behavior
    • Diffusion between dissimilar metal welds during welding and post weld heat treatment
    • Slag/metal reactions and inclusion formation
    • Dissolution of precipitates, grain boundary liquation, and phase transformations in the heat affected zone
    • Dilution effects between base metal and filler metal

Application Examples

Thermo-Calc has many applications to welding and joining. Below are two such examples.

Diffusion in Dissimilar Metal Welds

Dissimilar metal welds can experience localized failure at the interface due to carbon diffusion. This can be due to the welding process, post-weld heat treatment, or service conditions. Carbon diffuses from the steel to the nickel causing a loss of strength in the steel and a locally hard zone in the nickel. The extent of property degradation is related to the extent of carbon diffusion, which can be predicted using the Diffusion Module (DICTRA) in Thermo-Calc.

This figure shows the simulated carbon profiles across the joint resulting from welding and post weld heat treatment for an AISI 8630 steel welded with 3 different Ni-base filler metals. As can be seen, the choice in filler metal has a significant influence on the carbon diffusion behavior.

A plot showing a diffusion simulation of carbon migration in steel to nickel DMW post weld heat treat 650c for 10 hours.

Weld Cracking in Ni-base Alloys

Many Ni-based alloys are susceptible to different weld cracking phenomena that can be sensitive to alloy chemistry. During the solidification of weld metal, the alloying elements segregate to either the liquid or the solid and cause local composition differences. Segregation of aluminum (Al), titanium (Ti), and/or niobium (Nb) causes local variances in gamma prime (γ′) and gamma double prime (γ″) precipitation kinetics and volume fractions, leading to a loss of creep strength. Depending on alloy chemistry, this segregation can also cause formation of low melting point eutectics, which can then cause solidification cracking. The extent of segregation can be predicted using the Scheil Solidification Simulation Calculator included in Thermo-Calc.

This figure shows the segregation across a hypothetical dendrite for Alloy 718. Nb, Mo, and Ti segregate heavily to the dendrite boundary, which will have an impact on the local precipitation behavior.

A plot showing segregation across alloy 718 dendrite.

Learn More about Applications to Joining and Welding

The Application of CALPHAD-based tools to welding and joining

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Thermodynamic and Kinetic Simulation of the Brazing Process Applied to Ni-Base Superalloys

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Thermodynamic and kinetic models for describing microstructure evolution during joining of metals and alloys

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Optimizing the Diffusion Welding Process for Alloy 800H: Thermodynamic, Diffusion Modeling, and Experimental Work

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