Hao, Liangyan
(2023)
Physics-Based CALPHAD Modeling of the Ga-Mn-Ni System Using Third Generation Unary Data.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
The CALPHAD (CALculation of PHAse Diagrams) approach is an effective tool towards materials design and the foundation of the ICME (Integrated Computational Materials Engineering) framework. It is especially important for multicomponent and multiphase systems that are challenging and time-consuming to be investigated by experiments. However, the second generation CALPHAD merely relies on empirical polynomials and thus suffers from poor predictions of low-temperature thermodynamics and magnetic properties, as well as unphysical kinks of heat capacity curves. This study aims to apply the physics-based third generation models in thermodynamic descriptions of the Ga-Mn-Ni system.
Firstly, a model system Cr-Ni and the constituent elements were optimized to demonstrate the advantages of third generation models over second generation models. It was found the third generation models can reproduce experimental heat capacities for pure Cr and Ni down to 0 K. Infinitely positive or negative entropy at 0 K is avoided. Furthermore, the new magnetic model can successfully predict magnetic transition temperatures and magnetic moments within the entire composition range for fcc and bcc phases in which Cr and Ni exhibit different magnetism.
Secondly, the Ni-Ga system was reoptimized to validate the Equal Entropy Criterion (EEC) due to the low melting point of Ga. Although the bcc phase becomes stable at high temperatures, it can be removed by EEC. The unsatisfactory predictions of liquidus temperatures on the Ga-rich side and enthalpies of mixing suggest that refined descriptions for Ga and advanced models for liquid may be necessary.
Thirdly, the Mn-Ni system was reassessed to improve the descriptions of magnetic properties for the (γMn,Ni) phase. By employing the new magnetic model, experimental magnetic properties can be well reproduced and thus the anomaly on the phase diagram is removed. Besides, the four-sublattice model was successfully implemented to describe both bcc and fcc ordering.
Finally, the Mn-Ga system was optimized for the first time after extensive evaluation of available experimental data. An experimental phase diagram was proposed and supported by differential scanning calorimetry (DSC) and energy dispersive spectroscopy (EDS) measurements. Magnetic contribution to Gibbs energy was considered for stoichiometric compounds. The obtained parameters can reasonably reproduce the Mn-Ga phase diagram.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
14 September 2023 |
| Date Type: |
Publication |
| Defense Date: |
15 June 2023 |
| Approval Date: |
14 September 2023 |
| Submission Date: |
5 June 2023 |
| Access Restriction: |
2 year -- Restrict access to University of Pittsburgh for a period of 2 years. |
| Number of Pages: |
154 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Materials Science and Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Magnetic shape memory alloy |
| Date Deposited: |
14 Sep 2023 13:37 |
| Last Modified: |
14 Sep 2023 13:37 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/44938 |
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