Titanium alloys have grown in popularity owing to their high strength, low density and their excellent strength-to-weight ratio which enable them to be successfully employed in aerospace field, nuclear industries and in load-bearing implants. Specifically, the Ti-6Al-4V alloy has been the most attractive and most frequently used due to its excellent properties. Nonetheless, its applicability as an implant material has been on the decline owing to the poor surface properties it presents: such as low abrasive resistance in harsh environments which inhibit full realization of its working properties. In addition, tiny titanium particles have been found in the soft body tissues adjacent to the implants and are occasionally accompanied by inflammation due to the abrasion and corrosion in human bodies. Therefore, there is urgent need to improve the surface attributes of the Ti-6Al-4V alloy in order to ensure production and fabrication of safer and durable implants.
Recently, a team of researchers led by professor Liqiang Wang from the State Key Laboratory of Metal Matrix Composites at Shanghai Jiao Tong University in China proposed a study with the main objective to introduce titanium oxide particles to the Ti-6Al-4V alloy in order to improve its surface wear resistance properties as well as its biocompatibility when used as an implant material in human body. In order to achieve their objective, the authors of this paper opted to utilize the friction stir processing technique to introduce the titanium oxide particles and alter their biocompatibility. Their work is currently published in the research journal, Metallurgical and Materials Transactions A.
The research team commenced their research work by investigating the effects of the friction stir processing system, which was set up in an argon atmosphere so as to prevent oxidation, on the phase transformation and microstructure of TiO2-compounded Ti-6Al-4V systematically. Next, they cross-examined the grain refinement quality in the stirring zone and the phase transformation in the matrix of the material. Eventually, they employed transmission electron microscopy to elucidate on the grain refinement mechanism of the alloy.
The authors observed that the friction stir processing technique successfully introduced the titanium oxide particles into Ti-6Al-4V as second phase. Additionally, this placement technique was seen to promote the uniform distribution of the introduced titanium oxide particles and the grain refinement in the stirring zone. Furthermore, the researchers were keen to note that the friction stir processing also induced alterations in the microstructure of the three zones.
The study successfully presented the production of a composite layer containing titanium oxide nano-particles on the surface of Ti-6Al-4V using friction stir processing technique. It is pioneering to apply friction stir processing not only as a method of surface modification, but also to add second-phase particles into the material at the same time. Their results have shown that the microstructure reserves primary equiaxial dual phase of α and β but dislocation and twinning appear because of stress concentration. “Our idea of using friction stir processing to create nano-sized composite layer on the surface of material is insightful and it is really interesting to study its microstructure and performance.” Said Zihao Ding, first author of the paper. Altogether, the work provides a novel insight on how to enhance Ti-6Al-4V alloy so as to achieve the desired properties for biomedical applications, using the friction stir processing.
Zihao Ding, Chengjian Zhang, Lechun Xie, Lai-Chang Zhang, Liqiang Wang, Weijie Lu. Effects of Friction Stir Processing on the Phase Transformation and Microstructure of TiO2-Compounded Ti-6Al-4V Alloy . Metallurgical and Materials Transactions A, Volume 47A, December 2016—page 5675.Go To Metallurgical and Materials Transactions A