Transcript

This video will show you how to make a single phase diffusion simulation using the graphical mode version of the diffusion module, also known as DICTRA. This example only uses two elements, so it can be run by anyone with a license for Thermo-Calc, even if you do not have a license for the diffusion module. It can also be run with the free educational package. This single phase example simulates the homogenization of a gradient composition of iron and nickel at an isothermal temperature of 1,400 Kelvin in a planar domain. At this temperature, the material is fully austenitic, meaning that the only phase present is the FCC, face-centered cubic phase. In Thermo-Calc, this phase is written as FCC_A1. The calculation is based on diffusion module, example one, which you can access from the example files icon on the home screen of Thermo-Calc, Diffusion Module. DICTRA. In this video, I'll walk you step-by-step through how to set up the calculation and explain what I'm doing. You can learn more about single phase simulations by going to our online help system through the icon on the home screen. Go to Add-on Modules & Property Model Libraries, Diffusion Module DICTRA, Quick Start Guide , Single Phase Simulations. Here, you can learn about the theory behind the calculation and more. To begin the calculation, click on the Diffusion or Diffusion Demo template from the home screen of Thermo-Calc. All the nodes we need to run the diffusion simulation will appear in the project pane. In the System Definer, select the Demo Steel and Fe Alloys database package. This will load both the thermodynamic and mobility databases. Select the elements iron and nickel. When you are making a diffusion simulation, you do not need to set the material composition because compositions in the diffusion module vary with distance. Click on the Diffusion Calculator node, which opens the Diffusion Module. Every diffusion simulation requires the user to define three items, the geometry, the region, and the thermal profile of the system. If you click on the Options tab, you will see that there are many other options you can define. This is also where you can change the default settings. These options are generally only required with more complex diffusion simulations, so they are placed on this separate tab to make the module easier to use. Let's go back to the Conditions tab. First, we will set the geometry. DICTRA is a 1D code, so it is suited for diffusion problems where composition varies along one spatial coordinate, represented in the image by the arrow. The geometry of your system can be planar, spherical, or cylindrical. A planar geometry corresponds to an infinitely wide plane of a certain thickness. A spherical geometry corresponds to a sphere with a certain radius. And a cylindrical geometry corresponds to an infinitely long cylinder of a certain radius. In this example, we will select Planar. Next, we will define the region. All diffusion simulations require at least one region to be defined. A region is a named container that designates a certain part of the domain. In this case, because we are doing a single phase simulation, one region makes up the whole domain. The name of the region is arbitrary and specified by the user. I will name this one Austenite. Notice that the tab is updated with the name. Next, we will set the width of the region to 1e to the negative four. Notice that when we enter a width, a visual representation of our region appears. Since this is a single phase simulation, there is only one color representing the one region. If we were to add another region, another color would appear. However, we only need one region, so I will delete the second. We will allow the program to automatically distribute the grid points. This is a feature added in Thermo-Calc 2025b to make it easier to set up diffusion simulations. If you have an earlier version of the software or you wanna set your own grid placement, select Linear with 50 points. Notice that when you do this, dots appear in the region representing the grid points. However, these do not appear when we select Automatic. They'll show up later. Set the phase to FCC_A1, which is how we write FCC or face-centered cubic in Thermo-Calc. Now if you hover your mouse over the region, you'll see information about it, such as the name, width, and smallest and largest grid spacing, which will be set by the program. Next, we need to set the composition profile, which will be given by a function. In newer versions of Thermo-Calc, the composition profile is set directly in the configuration window. If you have an older version of Thermo-Calc, click Edit next to Composition Profile.The initial composition profile must be specified for all regions. Since we only have one region, we only need to specify it once. Since our system only has two components, iron and nickel, we only need to set the initial composition profile for one of them because the other one will be dependent. We are looking for the composition profile of nickel, so we'll leave iron as the dependent component, which allows us to work with nickel. There are a few ways to specify the composition profile, and in this example, we'll accept the default, linear. You can hover your mouse over the dropdown menu to read about the different types. Set the profile from 10 to 50. These settings mean that the profile goes from 10 mass percent nickel at the left side to 50 mass percent nickel at the right side in a linear progression across the width of the region because we selected linear. Next, we need to define the thermal profile. We will leave Isothermal selected, meaning that it will have one temperature for the entire simulation time. The temperature is 1,400 kelvin and the simulation time is 30 hours. Notice that when we set the temperature, a visual representation of the composition profile appears in the Visualizations window. This shows that nickel will go from 10 mass percent on the lower left-hand side of the system to 50 mass percent on the upper right-hand side of the system, just as we said above. You can also click on the Thermal Profile tab to see a visual representation of the temperature. We can see that the temperature will remain at 1,400 kelvin for the entire simulation since we're running an isothermal simulation. Now click on the Plot Renderer node. All of the fields have been filled in with information we already set. We wanna see how the composition profile has changed from the beginning of the simulation, so we need to add a starting time in the Time field. Set your cursor before the 30 and add 0.0, then a space. Now click Perform at the bottom center of the program. Once the simulation is finished running, a plot will appear in the Visualizations window. The plot shows the composition profile of nickel with the initial time, zero hours represented in blue, and the final time, 30 hours or 108,000 seconds represented in red. If you hover your mouse over either of the lines at any point, you will see the distance followed by the mass percent nickel. We can see that the initial linear composition profile has started to level out. Running the simulation even further would eventually give the same composition in the entire region. We can see this if we add a calculation time of 300 hours. Set your cursor after the 30 and add 300. Then click on the Diffusion Calculator node and change the time to 300 hours. Click Continue at the bottom of the program. Once the calculation is done running, click on the Plot Renderer node to view the plot again. The plot now shows a third line representing 300 hours or 1,080,000 seconds. The line is nearly flat, showing that the composition is nearly the same in the entire region. 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