Extraordinarily high strength Ti-Zr-Ta alloys through nanoscaled, dual-cubic spinodal reinforcement

Significance Statement

Titanium alloys find vast applications as orthopedic implant materials. This is as a result of their excellent mechanical properties and biocompatibility. However, with the recent development in alloys with superior fatigue, strength, corrosion resistance and biochemical impact, there is still an issue to do with high elastic modulus that leads to a mismatch in stiffness between the bone and the implant. The mismatch is known to initiate stress shielding.

A porous structure can be used to reduce the implant’s stiffness, but will reduce its yield strength. It therefore becomes necessary to consider the material’s elastic admissible strain, which is the ratio of the yield strength to elastic modulus. A material with high elastic admissible strain is desirable because it can maintain sufficient strengths even when stiffness is reduced. Thermomechanical methods proposed for improving titanium mechanical properties, are not desirable and therefore it is important to focus on mechanical improvement with minimal processing in the as-cast state.

Spinodal decomposition is one alternative that does not require particle nucleation, thus, allowing uniform nanostructures to be realized without long aging and granting fine control over the microstructure via aging. Researchers led by Professor Cuie Wen investigated the potential value of spinodally strengthened structure in the biomaterial field. They needed to know whether the spinodal effect could be reliably induced in a straightforward approach and whether this would contribute to material strength without increasing the modulus. Their work is now published in Acta Biomaterialia.

The authors developed a novel β-type Titanium-Zirconium-Tantalum (Ti-Zr-Ta) alloy system with varying concentrations of zirconium and tantalum and characterized it both microstructurally and mechanically. As-cast ingots were then cut into rods of 10 mm length and 5mm diameter for compression tests and 2mm thick discs with 10 mm diameter for microstructural analysis and biocompatibility assessment.

The authors cut transmission electron microscopy specimens using a diamond-tipped saw and ground them to about 60nm thickness. They performed uniaxial compression testing on a small rod specimen with a constant compression rate. They measured the strain through a combination of inbuilt strain gauge and a video monitoring system. The researchers used human osteoblast-like sarcoma cells in assessing the biological response of the alloys.

The authors observed that the spinodal decomposition initiated by enthalpy of mixing of the tantalum and zirconium species yielded a uniform nano-scaled dispersion of the tantalum β2 phase in the zirconium β1 matrix. This was however characterized by a cuboidal modulation arranged in the (1 0 0) body centered cubic directions of the lattice. The cuboid volume fraction increased with tantalum content.

Titanium served an important role in moderating the amount of spinodal decomposition, but ensuring that enough β-stabilization remained in the zirconium β1 phase in a bid to retard undue α-precipitation regardless of the low timescales related to cooling in the as-cast state.

The spinodal decomposition contributed to the alloys’ exceptional strength. Compressive yield strengths of 1220MPa and 1400 MPa were achieved in the alloy with the highest tantalum content, with these strengths allowing elastic admissible strains of 1.25-1.48% to be  realized in the as-cast state. The strength was realized without sacrificing biocompatibility.

Extraordinary high strength Ti-Zr-Ta alloys through nanoscaled, dual-cubic spinodal reinforcement - advances in engineering

Extraordinary high strength Ti-Zr-Ta alloys through nanoscaled, dual-cubic spinodal reinforcement - advances in engineering

About The Author

Dr Arne Biesiekierski is currently employed as a Research Assistant at RMIT University under supervision of Dist. Prof. Cuie Wen, following his recent graduation from Swinburne University with a PhD focusing on novel biocompatible Ti-based alloys. His current research remains focused in this field, with a particular interest in studying the nanostructure of novel Ti alloys. Still beginning his academic career, Arne has been first author of 6 peer-reviewed articles with 129 citations to date.

About The Author

Dr Dehai Ping is a principle researcher at National Institute for Materials Science (NIMS), Japan. His research interest currently focuses on the phase transition in metals and alloys, particularly ancient carbon steels. He has uncovered the metastable ω-Fe phase in the twinned martensite structure in steels, and co-authored in more than 200 scientific articles.

About The Author

Dr Yuncang Li is an ARC (Australian Research Conceal) Future Fellow employed at RMIT University. His research focuses on developing of metallic biomaterials for biomedical applications. He specializes in microstructure-mechanical property relationships, corrosion, and biocompatibility of metallic biomaterials. He also has expertise in surface modification, nanostructured metals and alloys, and metal foams. He has published 7 refereed book chapters, 122 peer-reviewed journal articles, and 33 refereed conference papers (162 in total). His h-index is 25 and citations count 2010 (GS, May 2017).

About The Author

Mr Jixing Lin is currently a PhD candidate under supervision of Professor Guanyu Li at Jilin University and Professor Cuie Wen at RMIT University. He will graduate with a PhD degree in June 2017. During his PhD study, he has been the first author of 3 Journal articles and co-authored in more than 10 journal articles. His research interests include biocompatible titanium alloys, biodegradable magnesium alloys, corrosion and surface modification for metals and alloys.

About The Author

Dr Khurram Shahzad Munir is currently working as a Research Assistant at RMIT University and carrying out research in the areas of biomaterials engineering. Khurram’s research is focusing on relationships between processing parameters, microstructures, mechanical/biological/functional properties, and also identification of key strengthening mechanisms in the fabricated alloys and composites. He has published 14 original peer reviewed articles with an h-index of 5 and citation count of 56 (GS, May 2017).

About The Author

Dr Yoko Yamabe-Mitarai is Deputy Director of Research Center for Structural Materials in National Institute for Materials Science, Japan. Her specialty is a phase transformation and mechanical properties for high temperature metallic materials. Recent interest is high temperature shape memory alloys using compounds of titanium – platinum metals, and high temperature titanium alloys for jet engine.

About The Author

Dr Cuie Wen is Distinguished Professor of Biomaterials Engineering at RMIT University and leads the biomaterials research team. Cuie has won a number of industrial and national competitive grants. She has mentored 10 postdoctoral research fellows, 21 PhD students and 4 Masters students to completion. She is an editorial board member for the journals Acta Biomaterialia and Bioactive Materials. Cuie’s research focuses on new biocompatible titanium alloys and scaffolds; biodegradable metals including magnesium, iron, and zinc based metals, alloy and composites; surface modification; nanomaterials; metal foams; nanolaminates, etc. She has published 337 original peer reviewed articles with an h-index of 39 and citation count of 5632 (GS, May 2017).

Reference

Arne Biesiekierski1,2, Dehai Ping3, Yuncang Li1, Jixing Lin4, Khurram S. Munir1, Yoko Yamabe-Mitarai3, Cuie Wen1,2. Extraordinary high strength Ti-Zr-Ta alloys through nanoscaled, dual-cubic spinodal reinforcement. Acta Biomaterialia, volume 53 (2017), pages 549–558.

Show Affiliations
  1. School of Engineering, RMIT University, Melbourne, Victoria 3001, Australia
  2. Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
  3. National Institute for Materials Science, Tsukuba 305-0047, Japan
  4. College of Materials Science and Engineering, Jilin University, Changchun, Jilin 130025, China

 

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