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The Primary Crystallization Nucleation Kinetics in Al-Based and Fe-Based Metallic Glasses.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	The Primary Crystallization Nucleation Kinetics in Al-Based and Fe-Based Metallic Glasses./
Author:	Duan, Tianrui.
Description:	1 online resource (167 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-11, Section: B.
Contained By:	Dissertations Abstracts International85-11B.
Subject:	Materials science. -
Online resource:	click for full text (PQDT)
ISBN:	9798382596563

The Primary Crystallization Nucleation Kinetics in Al-Based and Fe-Based Metallic Glasses.
Duan, Tianrui.

The Primary Crystallization Nucleation Kinetics in Al-Based and Fe-Based Metallic Glasses. - 1 online resource (167 pages)

Source: Dissertations Abstracts International, Volume: 85-11, Section: B.

Thesis (Ph.D.)--The University of Wisconsin - Madison, 2024.

Includes bibliographical references

Amorphous alloys provide a valuable platform for dissecting the impact of local heterogeneities on nucleation and growth mechanisms, all without the interference of excess vacancies or dislocations that can complicate the kinetics in crystalline materials. Thus, amorphous alloys serve as an excellent model system for the systematic exploration of how spatial heterogeneities influence the crystallization process. In this thesis, we delved into nucleation behavior in two main systems: Al-Y-Fe and Fe-B alloys.In amorphous Al alloys, particularly Al-Y-Fe alloys, the primary crystallization reaction results in ultrahigh densities of Al nanocrystals, ranging from 1021 to 1023 per cubic meter, typically measuring 10-20 nm in diameter. These nanocrystals are dispersed within an amorphous matrix, significantly enhancing the mechanical properties of the material. The presence of Al-like medium-range order (MRO) regions as a form of spatial heterogeneity in Al88Y7Fe5 metallic glass (MG) acts as a catalyst, promoting primary crystallization. By measuring delay times using Flash Differential Scanning Calorimetry (DSC) and tracking Al nanocrystal density during isothermal annealing treatments via Transmission Electron Microscopy (TEM), we established an MRO-seeded nucleation kinetics model. This research demonstrates the profound impact of minor solute Cu on the crystallization behavior, affecting nanocrystal densities and transient behavior related to local spatial heterogeneities. The new nucleation model effectively accounts for the effects of heterogeneities induced by solute additions on primary crystallization.In the case of Fe-based glasses such as Fe-B-Si and Fe-B-Nb, primary crystallization plays a pivotal role in optimizing magnetic properties. It has been observed that the precipitation of BCC-Fe nanocrystals smaller than the exchange length (30-40 nm) in Fe-based MGs can influence reduced coercivity and increased saturation magnetic flux density. In our study, we investigated the impact of varying heating rates, ranging from 0.17 K/s to 5000 K/s, on the crystallization behavior of BCC-Fe and explored the limitations on size reduction using Flash DSC and TEM. Our analysis revealed the compositional profile of B solute between adjacent nanocrystals, indicating that the limited size reduction and eutectic decomposition of BCC-Fe and Fe3B at high temperatures result from diffusion field impingement. Importantly, our findings demonstrate that extremely fast heating exceeding 104 K/s is unnecessary for optimizing the binary Fe-B MGs composite with the best magnetic properties and, in fact, can lead to eutectic crystallization of BCC-Fe and Fe3B, diminishing magnetic performance.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798382596563Subjects--Topical Terms:

557839
Materials science.
Subjects--Index Terms:

CrystallizationIndex Terms--Genre/Form:

554714
Electronic books.

The Primary Crystallization Nucleation Kinetics in Al-Based and Fe-Based Metallic Glasses.
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520 $a Amorphous alloys provide a valuable platform for dissecting the impact of local heterogeneities on nucleation and growth mechanisms, all without the interference of excess vacancies or dislocations that can complicate the kinetics in crystalline materials. Thus, amorphous alloys serve as an excellent model system for the systematic exploration of how spatial heterogeneities influence the crystallization process. In this thesis, we delved into nucleation behavior in two main systems: Al-Y-Fe and Fe-B alloys.In amorphous Al alloys, particularly Al-Y-Fe alloys, the primary crystallization reaction results in ultrahigh densities of Al nanocrystals, ranging from 1021 to 1023 per cubic meter, typically measuring 10-20 nm in diameter. These nanocrystals are dispersed within an amorphous matrix, significantly enhancing the mechanical properties of the material. The presence of Al-like medium-range order (MRO) regions as a form of spatial heterogeneity in Al88Y7Fe5 metallic glass (MG) acts as a catalyst, promoting primary crystallization. By measuring delay times using Flash Differential Scanning Calorimetry (DSC) and tracking Al nanocrystal density during isothermal annealing treatments via Transmission Electron Microscopy (TEM), we established an MRO-seeded nucleation kinetics model. This research demonstrates the profound impact of minor solute Cu on the crystallization behavior, affecting nanocrystal densities and transient behavior related to local spatial heterogeneities. The new nucleation model effectively accounts for the effects of heterogeneities induced by solute additions on primary crystallization.In the case of Fe-based glasses such as Fe-B-Si and Fe-B-Nb, primary crystallization plays a pivotal role in optimizing magnetic properties. It has been observed that the precipitation of BCC-Fe nanocrystals smaller than the exchange length (30-40 nm) in Fe-based MGs can influence reduced coercivity and increased saturation magnetic flux density. In our study, we investigated the impact of varying heating rates, ranging from 0.17 K/s to 5000 K/s, on the crystallization behavior of BCC-Fe and explored the limitations on size reduction using Flash DSC and TEM. Our analysis revealed the compositional profile of B solute between adjacent nanocrystals, indicating that the limited size reduction and eutectic decomposition of BCC-Fe and Fe3B at high temperatures result from diffusion field impingement. Importantly, our findings demonstrate that extremely fast heating exceeding 104 K/s is unnecessary for optimizing the binary Fe-B MGs composite with the best magnetic properties and, in fact, can lead to eutectic crystallization of BCC-Fe and Fe3B, diminishing magnetic performance.
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