Microstructure evolution and superelasticity of layer-like NiTiNb porous metal

Significance 

Biomedical materials are vital in advancing medicine. They are widely used by medical practitioners and biomedical engineers to address various medical issues such as fixing broken limbs, artificial heart transplants, artificial veins among others. More research, however, is still being done on inventing more materials that will help address the challenges experienced in the medical and other related fields. NiTi alloys represent such widely used biomedical material. Such materials have distinct properties such as biocompatibility, superelasticity and good shape memory effect hence cannot affect the normal body function in any way.

However, more effort is still being put into manufacturing advanced structures with specialized properties for use as biomedical materials. An example of such is the porous NiTi alloy which is technically an improvement of the NiTi alloys. Various preparations methods can be used in the manufacturing of such structures to fit a specific use. For instance, it is possible to form laminated structured porous materials in various chemical compositions.

Although there is little information available on the microstructural features, superelasticity and preparation procedure of NiTi-Nb porous materials, there is still a belief that they are the crucial consideration in making such materials among new researchers. This has led to the development of various fabrication techniques for NiTi-Nb alloys such as the brazing process and metallurgic bonding for enhancing some properties like stiffness.

A group of researchers at Shanghai Jiao Tong University, School of Materials Science and Engineering in China: Professor Liqiang Wang, Professor Lechun Xie, Dr. Liangyu Chen, Zihao Ding, Yuting Lv, Wei Zhang, Professor Weijie Lu and Professor Di Zhang in collaboration with Professor Lai-Chang Zhang from Edith Cowan University in Australia developed a combination of several techniques to fabricate NiTi-Nb layer-like porous structures. They used 3-dimensional interconnected channels together with NiTi-Nb eutectic reactions. They further focused on analyzing the formation of the NiTi matrix and the solidified NiTi-Nb eutectic interface. Their research work is currently published in the journal, Acta Materialia.

From their experiments, the authors observed that the eutectic phase transformation process is highly dependent on the stacking faults and the dislocations taking place between the Nb-rich phase and the eutectic phase. On the other hand, the stress-induced martensite nucleation was aided by the reduction in the rate of the dislocation process due to the formation of the rod-like eutectic phase.

The interface between the brazed NiTi-Nb specimen experienced inhomogeneous chemical composition resulting to chemical instability in the region and thus the formation of the martensite phase. During the amorphous phase transformation, there is a reduction in the free energy due to various factors such as the presence of the stacking faults and dislocations, thereby leading to the amorphization of the crystalline NiTiNb. Much more superelastic recovery and elastic recovery for such a layer-like porous structure were attributed to formation of more martensites during deformation. It is the first demonstration that a strong, ductile layer-like NiTiNb porous metal can be easily created between NiTi wires to bond Nb foils, thus opening the door to producing shape-memory or superelastic NiTi scaffolds brazed from stacked, woven or braided wires. The researchers are optimistic that their combined techniques will advance manufacturing of more advanced biomedical materials.

Microstructure evolution and superelasticity of layer-like NiTiNb -Advances in Engineeringporous metal prepared by eutectic reaction

About the author

Liqiang Wang is an Associate Professor in the department of Materials Science and Engineering at Shanghai Jiao Tong University. He got his BS and MS degrees both in Xi’an University of Architecture and Technology in Materials Science in 2006. During 2004 to 2005, he joined as a researcher in Northwest Institute for Nonferrous Metal Research focus on beta titanium alloys. After receiving his PhD in Materials Science and Engineering at Shanghai Jiao Tong University in 2009, Dr Wang held position as Assiatant Professor at Shanghai Jiao Tong University and Visiting Professor at Northwestern University.

He focuses the research on the preparing, processing and analysing of biomedical titanium alloys and titanium matrix composites.

About the author

Dr. Lechun Xie is a Full Professor in School of Automotive Engineering at Wuhan University of Technology (Wuhan, China). He got his PhD degree at Materials Science in Shanghai Jiao Tong University in 2015. From 2011 to 2013, he worked in the Department of Mechanical Engineering at Northwestern University (IL, USA) as a visiting scholar. After receiving his PhD, Dr. Xie continued his postdoc research in Department of Chemical & Materials Engineering at University of Alberta (AB, Canada) from 2015 to 2016. After that, he got the Alfred Deakin Postdoc Research Fellowship and worked in Institute for Frontier Materials at Deakin University (VIC, Australia) as a research fellow from 2016 to 2018.

He joined Wuhan University of Technology on May of 2018, and his research focuses on additive manufacturing (3D printing) on titanium alloys and titanium matrix composites.

About the author

Dr Lai-Chang Zhang is an Associate Professor and the Program Leader Mechanical (Materials) Engineering at Edith Cowan University. After receiving his PhD in Materials Science and Engineering at the Institute of Metal Research, Chinese Academy of Sciences in 2005, Dr Zhang held several positions at The University of Western Australian, University of Wollongong, IFW Dresden and Technische Universität Darmstadt.

He focuses the research on the metal additive manufacturing (by selective laser melting and electron beam melting), titanium alloys and composites, and processing-microstructure-properties in high-performance materials (such as nanomaterials, ultrafine-grained materials and metallic glasses).

About the author

Zihao Ding received his BSc in Shanghai Jiao Tong University, and MSc in Carnegie Mellon University. During undergraduate, his research involved improvement of biomedical titanium alloys, including characterization of microstructure, corrosion resistance and biocompatibility. At present, he is pursuing his Ph.D. degree in Materials Science at CMU. His currently research is the assembly of anti-corrosion poly-dopamine composite coating on the surface of metal matrix.

Reference

Wang, L., Xie, L., Zhang, L., Chen, L., Ding, Z., & Lv, Y. et al. (2018). Microstructure evolution and superelasticity of layer-like NiTiNb porous metal prepared by eutectic reactionActa Materialia143, 214-226.

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