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Micromachines
Special Issues
Shape Memory Alloys: Manufacturing and Micromachined Applications
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Shape Memory Alloys: Manufacturing and Micromachined Applications

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D：Materials and Processing".

Deadline for manuscript submissions: closed (10 October 2024) | Viewed by 4519

Special Issue Editor

Dr. Chanho Lee

E-Mail Website
Guest Editor
Department of Materials and Mechanical Engineering, Auburn University, Auburn, AL 36849, USA
Interests: deformation mechanisms; X-ray diffraction; solidification; material characteristics; high temperature materials; mechanical testing; advanced materials; in situ neutron diffraction; density functional theory; calculation of phase diagrams; alloy design
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue focuses on Shape Memory Alloys (SMAs), a unique class of materials with the ability to recover their original shape after deformation when subjected to certain temperature changes. This Special Issue explores the manufacturing techniques and micromachined applications of SMAs in various sectors, such as biomedical, aerospace, and robotics industries.

We aim for the publications in this Special Issue to cover a range of topics, including the development of advanced manufacturing processes for SMAs, such as additive manufacturing and powder metallurgy. Additionally, researchers are invited to discuss the design and optimization of microscale devices and components made from SMAs, highlighting their potential for use in minimally invasive medical procedures, actuation systems, and sensing applications.

Overall, we hope that this Special Issue will provide a comprehensive overview of the latest advancements in the field of Shape Memory Alloys, highlighting their unique properties and potential for innovative applications in a wide range of industries. Researchers and industry professionals interested in the manufacturing and micromachined applications of SMAs will hopefully find valuable insights and perspectives in this collection of publications.

Dr. Chanho Lee
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • shape memory alloys
  • alloy design
  • manufacturing
  • microstructural characterization
  • mechanical properties
  • deformation mechanism
  • shape memory alloy based micromachined devices

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Published Papers (2 papers)

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Research

13 pages, 7299 KiB  
Article
Thermal Cycling Behavior of Aged FeNiCoAlTiNb Cold-Rolled Shape Memory Alloys
by Li-Wei Tseng and Wei-Cheng Chen
Micromachines 2024, 15(11), 1338; https://doi.org/10.3390/mi15111338 - 31 Oct 2024
Viewed by 540
Abstract
Fe–Ni–Co–Al-based systems have attracted a lot of interest due to their large recoverable strain. In this study, the microstructure and thermal cycling behaviors of Fe41Ni28Co17Al11.5Ti1.25Nb1.25 (at.%) 98.5% cold-rolled alloys after annealing treatment [...] Read more.
Fe–Ni–Co–Al-based systems have attracted a lot of interest due to their large recoverable strain. In this study, the microstructure and thermal cycling behaviors of Fe41Ni28Co17Al11.5Ti1.25Nb1.25 (at.%) 98.5% cold-rolled alloys after annealing treatment at 1277 °C for 1 h, followed by aging for 48 h at 600 °C, were investigated. From the electron backscatter diffraction results, we see that the texture intensity increased from 9.4 to 16.5 mud and the average grain size increased from 300 to 400 μm as the annealing time increased from 0.5 h to 1 h. The hardness results for different aging heat treatment conditions show the maximum value was reached for samples aged at 600 °C for 48 h (peak aging condition). The orientation distribution functions (ODFs) displayed by Goss, brass, and copper were the main textural features in the FeNiCoAlTiNb cold-rolled alloy. After annealing, strong Goss and brass textures were formed. The transmission electron microscopy (TEM) results show that the precipitate size was ~10 nm. The X-ray diffraction (XRD) results show a strong peak in the (111) and (200) planes of the austenite (⁠⁠γ, FCC) structure for the annealed sample. After aging, a new peak in the (111) plane of the precipitate (⁠⁠γ′, L12) structure emerged, and the peak intensity of austenite (⁠⁠γ, FCC) decreased. The magnetization–temperature curves of the aged sample show that both the magnetization and transformation temperature increased with the increasing magnetic fields. The shape memory properties show a fully recoverable strain of up to 2% at 400 MPa stress produced in the three-point bending test. However, the experimental recoverable strain values were lower than the theoretical values, possibly due to the fact that the volume fraction of the low-angle grain boundary (LABs) was small compared to the reported values (60%), and it was insufficient to suppress the beta phases. The beta phases made the grain boundaries brittle and deteriorated the ductility. On the fracture surface of samples after the three-point bending test, the fracture spread along the grain boundary, and the cross-section microstructural results show that the faces of the grain boundary were smooth, indicating that the grain boundary was brittle with an intergranular fracture. Full article
(This article belongs to the Special Issue Shape Memory Alloys: Manufacturing and Micromachined Applications)
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12 pages, 3272 KiB  
Article
Structure and Properties of Bioactive Titanium Dioxide Surface Layers Produced on NiTi Shape Memory Alloy in Low-Temperature Plasma
by Justyna Witkowska, Tomasz Borowski, Krzysztof Kulikowski, Karol Wunsch, Jerzy Morgiel, Jerzy Sobiecki and Tadeusz Wierzchoń
Micromachines 2024, 15(7), 886; https://doi.org/10.3390/mi15070886 - 6 Jul 2024
Viewed by 3664
Abstract
Background: The NiTi alloy, known for its shape memory and superelasticity, is increasingly used in medicine. However, its high nickel content requires enhanced biocompatibility for long-term implants. Low-temperature plasma treatments under glow-discharge conditions can improve surface properties without compromising mechanical integrity. Methods: This [...] Read more.
Background: The NiTi alloy, known for its shape memory and superelasticity, is increasingly used in medicine. However, its high nickel content requires enhanced biocompatibility for long-term implants. Low-temperature plasma treatments under glow-discharge conditions can improve surface properties without compromising mechanical integrity. Methods: This study explores the surface modification of a NiTi alloy by oxidizing it in low-temperature plasma. We examine the impact of process temperatures and sample preparation (mechanical grinding and polishing) on the structure of the produced titanium oxide layers. Surface properties, including topography, morphology, chemical composition, and bioactivity, were analyzed using TEM, SEM, EDS, and an optical profilometer. Bioactivity was assessed through the deposition of calcium phosphate in simulated body fluid (SBF). Results: The low-temperature plasma oxidization produced titanium dioxide layers (29–55 nm thick) with a predominantly nanocrystalline rutile structure. Layer thickness increased with extended processing time and higher temperatures (up to 390 °C), though the relationship was not linear. Higher temperatures led to thicker layers with more precipitates and inhomogeneities. The oxidized layers showed increased bioactivity after 14 and 30 days in SBF. Conclusions: Low-temperature plasma oxidation produces bioactive titanium oxide layers on NiTi alloys, with a structure and properties that can be tuned through process parameters. This method could enhance the biocompatibility of NiTi alloys for medical implants. Full article
(This article belongs to the Special Issue Shape Memory Alloys: Manufacturing and Micromachined Applications)
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