Invited Speakers

Abstract: (Ti5Si3+TiBw)/Ti6Al4V titanium alloy matrix composites with two-scale network architecture were designed and successfully fabricated by reaction hot pressing. TiB whiskers (TiBw) were synthesized in situ around the Ti6Al4V matrix particles and formed the first-scale network structure. Ti5Si3 needles (Ti5Si3) were precipitated in the β phase around the exquiaxed α phase and formed the secondary-scale network structure. The results showed that the two-scale network structured composites exhibited more superior performances, such as, strength and ductility at room and high temperatures, high temperature oxidation resistance, high temperature creep resistance, and so on. The tensile strength can be increased to 1050MPa and 900MPa at 550℃ and 600℃ for Ti6Al4V matrix composites. In addition, the creep rate of the composites remarkably reduced by an order of magnitude compared with Ti6Al4V alloys. Moreover, the rupture time of the composites increased by 20 times, compared with Ti6Al4V alloys at 550℃/300 MPa. The superior creep resistance is attributed to the two-level hierarchical structures and the two-scale reinforcements. The TiB whisker reinforcement distributed in the first network boundary around Ti6Al4V matrix contributed to creep resistance primarily by blocking grain boundary sliding, while the nano-Ti5Si3 particles in the secondary network boundary (β phase) around α phase mainly by hindering phase boundary sliding. Such a (Ti5Si3+TiBw)/Ti6Al4V titanium alloy matrix composite is a candidate for the applications with low weigh and high temperature requirements.

Keywords. Titanium alloys, titanium matrix composites, structure, high temperature, mechanical properties

Abstract: Biodegradable metallic materials such as magnesium (Mg)-based alloys have attracted extensive interest for use as bone implant materials. However, the high biodegradation rate of existing Mg alloys in the physiological environment of human body leads to losing mechanical integrity before adequate bone healing and producing a large volume of hydrogen gas. Therefore, slowing down the biodegradation rate of Mg alloys is a critical task in developing new biodegradable Mg alloy implant materials. One of the most effective approaches to achieve this is to strategically design new Mg alloys with low biodegradation rate, excellent biocompatibility, and enhanced mechanical properties. Our research selected biocompatible and biofunctional alloying elements such as zirconium (Zr), strontium (Sr), and rare earth elements (REEs) to alloy Mg and has developed a new series of Mg-Zr-Sr-REEs alloys for biodegradable implant applications. Research results indicated that Sr and Zr additions can refine the grain size, decrease the biodegradation rate, and enhance the biological behaviors of the Mg alloys. This study systematically investigates the microstructure, mechanical properties, corrosion behavior, and biocompatibility of Mg-based alloys with the addition of different concentrations of scandium (Sc), i.e., Mg-0.6Zr-0.5Sr-xSc (x=0.5, 1, 2, 3 wt.%). Results indicated that high concentration of Sc in strontium (Sr)-containing Mg alloys can alter their microstructures by suppressing the intermetallic phases along the grain boundaries and improve the corrosion resistance by forming chemically stable Sc oxide layers on the surfaces of the Mg alloys. Cytotoxicity assessment revealed that the Sc containing Mg alloys did not significantly alter the viability of human osteoblast-like SaOS2 cells. This study highlights the advantages of using Sc as an alloying element to simultaneously tune Mg alloys with higher strength and slower degradation.

Keywords: Biocompatibility, magnesium, mechanical and biodegrade properties, rare earth elements.

Acknowledgements: The authors acknowledge the financial support for this research by the Australian Research Council (ARC) through the Future Fellowship (FT160100252) and the Discovery Project (DP170102557).

Abstract: Bifilm defect in casting was proposed by the famous scholar Prof. John Campbell about thirty years ago and has attracted numerous investigations coming from the community because it is deemed as the precursor of various macroscopic metallurgical defects and is widely discovered in different metallic systems. However, many aspects of bifilm defects such as morphology, composition and control process have never been explored in a state that they are kept inner of the casting (in-situ) so far, this prohibits the understanding of formation and evolution behaviors and mechanisms of them. The present talk will discuss these points based on our recent works of using varied advanced characterization techniques and studying methods to investigate the bifilms discovered in varied specific alloy castings. These results aroused updated understanding of bifilm defects in casting.

Abstract: Aims: The work presents the obtained results of the selected physicochemical, corrosion and biological properties of Ti6Al7Nb, NiTi and PE substrate after surface modification. During the experiments the PE CVD (Plasma Enhanced Chemical Vapour Deposition) method, as well as deposition of biopolymers (based chitosan coatings (CS)) using the immersion method was applied.
Methods: In the experimental part the different type and multi-system, based on DLC structure, were investigated. Additionally, the selected substrates were chemically treated or functionalized by plasmochemical process before coatings deposition. Typical techniques for materials engineering such as scanning electron microscopy with EDS analysis, AFM, optics profilometry, IR spectroscopy, ICP-MS and nanoindentation method were applied. Moreover, biological activity was also studied.
Results: It can be concluded that the obtained biopolymeric coatings (CS with or without Me_NPs) provide an efficient barrier to impede the out-diffusion of titanium and nickel ions. In the case of PE substrate modified by DLC:N/DLC multi-layers we observed the positive influence on the mechanical properties and biological activity.
Conclusions: In the case of PE and Ti-based substrates, this is the main goal of current scientific research focused on surface modifications to increase its safe medical application.
Acknowledgements: This work has been supported by Polish National Center for Science, NCN, grant decision DEC-2017/01/X/ST8/00886.