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— | tutorials:t9 [2019/05/16 18:39] – pwarczok | ||
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+ | ===== T9: Calculating pseudobinary phase diagrams ===== | ||
+ | //This tutorial was tested on\\ | ||
+ | MatCalc version 6.01 rel 1.003\\ | ||
+ | license: free\\ | ||
+ | database: mc_fe.tdb// | ||
+ | |||
+ | ==== Complimentary files ==== | ||
+ | |||
+ | Click {{: | ||
+ | |||
+ | A pseudobinary phase diagram is an equilibrium diagram calculated for a ternary or higher-order system, in which the phase boundaries resulting from the variation of two of the element contents are calculated, while the amounts of all the other elements are kept constant. | ||
+ | |||
+ | ==== Contents: ==== | ||
+ | |||
+ | * Further phase boundary calculations | ||
+ | * Coping with complex boundary shapes | ||
+ | * Diagrams with different reference elements | ||
+ | |||
+ | ===== Setting up the system ===== | ||
+ | |||
+ | Make a new workspace with the elements Fe, C and Nb and the phases FCC_A1, BCC_A2, LIQUID and CEMENTITE. Verify that Fe is selected as the reference element and enter the composition: | ||
+ | |||
+ | ===== Fe-C pseudobinary with constant Nb content ===== | ||
+ | |||
+ | This is similar in many respects to the Fe-Fe< | ||
+ | Add the liquid and austenite (FCC_A1) upper boundaries and the lower boundary of the delta-ferrite (BCC_A2) to the diagram. Suggested equilibrium temperatures for finding these lines are as follows: | ||
+ | * LIQUID: 1450°C | ||
+ | * FCC_A1: 1500°C (N.B. the correct value of Tsol ' | ||
+ | * BCC_A2: 1450°C | ||
+ | |||
+ | The high-temperature part of the diagram should look like this: | ||
+ | |||
+ | {{: | ||
+ | |||
+ | Next, calculate the boundary for niobium carbide (FCC_A1# | ||
+ | Increase the maximum T-step to 100 to cope with the steepness of the curve. The boundary may extend to very small temperature values; in this case, change the scale on the y-axis to **' | ||
+ | The final three lines can be calculated as follows: | ||
+ | * Upper boundary of alpha-ferrite (BCC_A2): 900°C. The maximum T-step can be reduced again to 20. | ||
+ | * Lower boundary of austenite (FCC_A1): 700°C. | ||
+ | *Upper boundary of cementite 850°C. In case of error message (because of the steep boundary), set the maximum T-step to 100. | ||
+ | |||
+ | The finished diagram, with titles and labels added, should look like this: | ||
+ | |||
+ | {{: | ||
+ | |||
+ | ===== Fe-Nb pseudobinary with constant C content ===== | ||
+ | |||
+ | In this case, the niobium content is to be varied from 0 to 1 wt.% for the stepped calculations. Proceed as before, by calculating an equilibrium at 1550°C and searching for the BCC_A2 phase boundary. For the stepped calculation, | ||
+ | The boundaries can be calculated with the same starting equilibrium temperatures as for the Fe-C diagram, because the basis composition used for calculating the equilibrium and finding a point on the boundary remains the same (0.1 wt.% C, 0.3 wt.% Nb). Search for and plot all the following boundaries: | ||
+ | * Upper boundary of delta-ferrite (BCC_A2) | ||
+ | * Lower boundary of liquid | ||
+ | * Upper boundary of austenite (FCC_A1) | ||
+ | * Lower boundary of delta-ferrite | ||
+ | * Upper boundary of alpha-ferrite (BCC_A2) | ||
+ | * Lower boundary of austenite | ||
+ | * Upper boundary of cementite (may need modification of maximum T-step to 100-200) | ||
+ | |||
+ | The NbC (FCC_A1#01) boundary is slightly more complex in this example, so it will be considered in more detail. Firstly, calculate an equilibrium at 1000°C and search for the FCC_A1#01 phase boundary varying temperature. This is at 1434.70°C. Make a stepped calculation from 0 to 1 wt.% Nb with 0,001 step and max. T-step value of 2. The calculation starts as usual at the niobium content used to calculate the equilibrium (0.3 wt.%), and this is first increased up to the **' | ||
+ | \\ | ||
+ | |||
+ | {{: | ||
+ | |||
+ | Just click on ' | ||
+ | |||
+ | {{: | ||
+ | |||
+ | ===== Nb-C pseudobinary with constant Fe content ===== | ||
+ | |||
+ | The final part of this tutorial considers the effect of both C and Nb contents on the stability of NbC. Previously, iron has been set as the **' | ||
+ | As usual, search for the upper boundary of the delta-ferrite phase. This should be found at 1531.43°C. In the stepped calculation dialogue box, enter 0, 0.004 and 1e-5 as the start, stop and interval values. Set the varying element to **' | ||
+ | Calculate the following lines. The solution temperatures are given as a guide, as well as notes on calculation settings (Accept any questions about changing the direction of calculation)). | ||
+ | * BCC_A2: 1531.43°C | ||
+ | * LIQUID: 1499.65°C. A warning message may appear; accept this with ' | ||
+ | * FCC_A1: 1466.53°C. The same warning may appear. | ||
+ | * BCC_A2: 1422.53°C | ||
+ | * BCC_A2: 891.37°C. Step from 0 to 0.00399 rather than 0.004 to avoid convergence problems. | ||
+ | * FCC_A1: 726.53°C. Calculation from 0 to 0.00399 with 1e-6 step. | ||
+ | * CEMENTITE: 726.53°C | ||
+ | |||
+ | Finally, the line for FCC_A1#01 can be calculated. Search for this line, which should be found at 1320.30°C. The temperature of this phase boundary decreases very steeply at both extremities of the x-axis, because the phase becomes less and less stable as either the niobium content or the carbon content tends to zero. To obtain an idea of the shape of the curve, set the start and stop-values as 0.00001 to 0.00399 (A maximum T-step of 50 is OK for this calculation.) Modifications can then be made to the calculation parameters, decreasing the start value, increasing the stop-value and increasing the maximum T-step to try to extend the curve further towards the edges.\\ | ||
+ | The finished diagram should look like this: | ||
+ | |||
+ | {{: | ||
+ | |||
+ | |||
+ | ===== Consecutive articles ===== | ||
+ | |||
+ | The tutorial is continued in article [[tutorials: | ||
+ | |||
+ | Go to [[: |