Quantcast


CURATOR
A pinboard by
this curator

I am a PhD Researcher that focuses on characterising the microstructural behaviour of superalloys.

PINBOARD SUMMARY

Follow this board to keep updated with all the exciting research in shape memory alloys

In 10 Seconds? Shape memory alloys are a relatively new development in the field of material science – and over the past few years, they have seen a significant amount research to develop its capabilities.

Therefore, in simple terms, a shape memory alloy is a metallic material that can revert to its original shape. However, it can only revert if a thermal load is applied. The main fields of applications lie in aerospace, structural and biomedical. The most commonly used shape memory alloy is NITINOL, which is a combination of nickel and titanium.

Don’t believe it? Review the selected pinned articles to observe just how big an impact SMA’s have had on biomedical applications in particular. They have been very successful in the biomedical field due to their super elastic material properties and being biocompatible.

The science behind the shape memory phenomenon

It is all to do with the alloys crystal structure i.e. the arrangement of atoms – more specifically, the phase change from martensite to austenite and vice versa. Therefore, when the alloy is in its martensite phase it can be easily deformed, note that this deformation only occurs at low temperatures (i.e. below the alloys transformation temperature). Consequntly, as you heat the alloy above its transformation temperature it will automatically revert to its original shape because the atoms within the crystal structure revert to their preferred positions.

What is the opportunity?

Medical – As stated earlier, the medical industry realised the potential of SMA’s. SMA’s have allowed certain surgical procedures to be less invasive. This is because the SMA can be inserted into the body then a particular stimuli will cause the SMA to change size or shape – for example self-expanding stents.

Problem – The drawback from SMA’s for medical applications within the body is that it they cannot be identified through x-rays. Therefore, research is ongoing to identify the most cost effective technique to allow x-rays to pick up SMA components within the body.

For all you entrepreneurial scientists out there, this could be an opportunity to make some $$$’s– do you have a big idea to solve the issue?

Non-technical factors that could hinder innovations within this field

• The main hurdle that would restrict the potential of SMA’s within the biomedical field would be government funding!

• Global political issues can cause the price of raw materials to rise

9 ITEMS PINNED

Mechanical behavior and microstructural analysis of NiTi-40Au shape memory alloys exhibiting work output above 400 °C

Abstract: Substituting Ni with Au in NiTi leads to dramatic increases in transformation temperatures, meeting one of the requirements for a viable high temperature actuator material. Consequently, four alloys containing between 49 and 51 at.% Ti, a fixed 40 at.% Au, and balance Ni, were prepared and investigated in detail using load-biased thermal cycling (LBTC), scanning electron microscopy (SEM), aberration corrected scanning transmission electron microscopy (STEM), and X-ray energy dispersive spectroscopy (XEDS). LBTC experiments demonstrated work output well above 400 °C, with full recovery up to 100 MPa. The alloys exhibit minimal variation in shape memory properties despite the relatively large composition range from Ti-lean to Ti-rich, in stark contrast to most other NiTi-based systems, which demonstrate extreme compositional sensitivity. Electron beam analysis revealed the presence of two types of secondary phases present in all compositions, which are subsequently characterized. Differences in secondary phase content as a function of alloy composition is shown to have a moderating effect on the transforming matrix composition - an important asset for this alloy system - potentially easing processing requirements and opening up shape memory alloys to new fabrication techniques. Unrecovered strain during cycling at higher loads is analyzed from a theoretical perspective to gain insight into the mechanisms of defect formation responsible for functional fatigue.

Pub.: 21 Mar '17, Pinned: 20 Apr '17

Microstructures and phase transformations of Ti-30Zr-xNb (x=5, 7, 9, 13at.%) shape memory alloys

Abstract: Publication date: December 2016 Source:Materials Characterization, Volume 122 Author(s): Wentao Qu, Xuguang Sun, Bifei Yuan, Chengyang Xiong, Fei Zhang, Yan Li, Baohui Sun The microstructures, phase transformations and shape memory properties of Ti-30Zr-xNb (x=5, 7, 9, 13at.%) alloys were investigated. The X-ray diffraction and transmission electron microscopy observations showed that the Ti-30Zr-5Nb, Ti-30Zr-7/9Nb and Ti-30Zr-13Nb alloys were composed of the hcp α′-martensite, orthorhombic α″-martensite and β phases, respectively. The results indicated the enhanced β-stabilizing effect of Nb in Ti-30Zr-xNb alloys than that in Ti-Nb alloys due to the high content of Zr. The differential scanning calorimetry test indicated that the Ti-30Zr-5Nb alloy displayed a reversible transformation with a high martensitic transformation start temperature of 776K and a reverse martensitic transformation start temperature (A s) of 790K. For the Ti-30Zr-7Nb and Ti-30Zr-9Nb alloys, the martensitic transformation temperatures decreased with the increasing Nb content. Moreover, an ω phase transformation occurred in the both alloys upon heating at a temperature lower than the corresponding A s , which is prompted by more addition of Nb. Although the critical stress in tension of the three martensitic alloys decreased with increasing Nb content, the Ti-30Zr-9Nb alloy showed a critical stress of as high as 300MPa. Among all the alloys, the Ti-30Zr-9Nb alloy exhibited the maximum shape memory effect of 1.61%, due to the lowest critical stress for the martensite reorientation.

Pub.: 23 Oct '16, Pinned: 20 Apr '17