Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Mechanical Engineering | en_US |
| dc.contributor.advisor | Zheng, Guangping (ME) | en_US |
| dc.creator | Ma, Siyao | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/14607 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Investigation on magneto-structural transition and caloric effects in Ni-Mn-Sn-based magnetic alloys | en_US |
| dcterms.abstract | Ni-Mn-Sn-based magnetic alloys, which exhibit both magnetocaloric and elastocaloric effects, hold significant application potential in solid-state refrigeration. However, their intrinsic brittleness leads to structural fatigue issues. This study focuses on Ni-Mn-Sn magnetic alloys, employing first-principles calculations to investigate the effects of Fe and Cu doping on the crystal structure, magneto-structural phase transitions, and magnetic properties of Ni-Mn-Sn alloys, as well as the influence of B doping on their mechanical properties. Building on the computational results, the research systematically explores the magneto-structural phase transitions, magnetocaloric and elastocaloric effects, their stability, and the multi-field regulation and optimization of caloric effects in Fe-, Cu-, and B-doped Ni-Mn-Sn-based magnetic alloys. The study reveals the mechanism by which reversible components during martensitic phase transitions influence caloric effects, providing a theoretical foundation for the development of low-cost, high-performance Ni-Mn-Sn alloy refrigeration materials. | en_US |
| dcterms.abstract | First-principles calculations reveal that Fe atoms preferentially occupy Ni sublattice sites in the Ni43.75Mn37.5Sn12.5Fe6.25 alloy. The energy difference between the austenite and non-modulated martensite phases gradually decreases with Fe doping, resulting in a decrease in the martensitic transformations temperature. Phase transitions become difficult when the Fe doping exceeds 6 at.%. Fe doping also enhances alloy stability and magnetic properties. In Ni43.75Mn37.5Sn12.5Cu6.25 and Ni37.5Mn37.5Sn12.5Cu12.5 alloys, Cu atoms preferentially occupy Ni lattice sites. The Curie temperature of Ni43.75Mn37.5Sn12.5Cu6.25 alloy decreases with increasing Cu content. Cu doping also gradually lowers the martensitic transformations temperature, although its effect on enhancing the alloy's magnetic moment is slightly lower than that of Fe. | en_US |
| dcterms.abstract | Research on Ni50-yMn38Sn12Fey (y=0, 1, 2, 3, 4, 5) alloys shows that there are no second phase precipitates when the Fe doping level is low, and the microstructure at room temperature consists of 10M martensite. In alloys with Fe doping reaching 3 at.%, there exists an extremely small amount of the second phase precipitates. Fe doping enables the magnetic-structural coupling regulation of the alloy. The Ni47Mn38Sn12Fe3 alloy undergoes two-step reverse martensitic transformations: 10M→L2₁ and 10M→4O, followed by 4O→L2₁. These two-step transformations lead to two entropy change (ΔSm) peaks of 15.2 J/kg∙K and 9 J/kg·K at 259 K and 267 K, respectively, with a working temperature range of 255–268 K and a refrigeration capacity (RC) of 142.5 J/kg. | en_US |
| dcterms.abstract | Studies on Ni50-xMn38Sn12Cux (x=0, 2, 3, 4, 5, 6) alloys indicate that Cu doping significantly improves the mechanical properties of the alloys through solid solution strengthening, with both compressive strength and strain increased by more than 1.8 times. Cu doping also enhances the cyclic stability of the alloys. During rapid adiabatic loading-unloading cycles, the elastocaloric effect remains stable after about 30 cycles for the 3 at.% Cu-doped alloy. The Ni48Mn38Sn12Cu2 alloy achieves partial magneto-structural coupling, with ΔSm reaching 10.3 J/kg·K under a 5 T magnetic field. The Ni47Mn38Sn12Cu3 alloy achieves complete magneto-structural coupling, with ΔSm reaching 21.2 J/kg·K under 5 T, an average hysteresis loss of only 45 J/kg, and a relative cooling power of 108 J/kg. | en_US |
| dcterms.abstract | Modulated Differential Scanning Calorimetry (MDSC), which superimposes a small sinusoidal temperature variation on a constant heating rate, allows for the separation of reversible and nonreversible components during martensitic transformations, establishing a direct link between thermal hysteresis and frictional dissipation during the transition. Additionally, an accurate method for characterizing adiabatic temperature changes based on MDSC is developed. Calculations reveal that when Cu doping is x=3, the alloy exhibits a high reversible latent heat, low frictional dissipation, and a high ΔTad, closely approaching the directly measured ΔTad result of 10.3 K. | en_US |
| dcterms.abstract | Research shows that B doping in (Ni47Mn38Sn12Cu3)100-zBz (z=0, 0.2, 0.4, 0.6) alloys gradually refines the grains and leads to the precipitation of a small amount of second phases. When the B doping level increases to 0.6 at.%, the martensitic transformation temperature decreases by approximately 1 K. The B element effectively inhibits alloy fracture along grain boundaries, with the strengthening mechanism mainly originating from grain refinement and grain boundary strengthening due to microalloying. The (Ni47Mn38Sn12Cu3)99.4B0.6 alloy exhibits excellent cyclic stability during 500 heating-cooling cycles, 10⁵ magnetic cycles, and 200 rapid adiabatic loading-unloading cycles. | en_US |
| dcterms.abstract | Research demonstrates that stress assistance can broaden the working temperature range for caloric effects. The (Ni47Mn38Sn12Cu3)99.4B0.6 alloy achieves a large and reversible caloric effect within the temperature range of 260−336 K. With hydrostatic pressure coupling, the magnetic entropy change of the alloy remains constant, while the working temperature window for refrigeration expands. At H=3 T and 10 kbar, the RC value reaches 100.2 J/kg, representing a 20.8% increase in refrigeration capacity compared to 0 kbar. | en_US |
| dcterms.abstract | The optimal preparation parameters for (Ni47Mn38Sn12Cu3)99.4B0.6 ribbons are a heating power of 8 kW and a copper roller speed of 1800 rpm. The as-spun ribbons have an average thickness of 20 μm. After heat treatment, the ribbons can reach saturation in a low magnetic field (0.02 T) parallel to the grain growth direction. Under a 2 T magnetic field, ΔSm reaches 7.6 J/kg·K, and the maximum ΔSm value is 15.2 J/kg·K under a 5 T magnetic field. The ribbons achieve RC values of 143 J/kg and 119 J/kg for parallel and perpendicular magnetic fields, respectively, and corresponding RCP values of 187 J/kg and 156 J/kg. | en_US |
| dcterms.extent | x, 212 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2026 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/14607