Materials Science Forum Vols. 618-619

Abstract: In the present study, surface melting of a magnesium alloy, ZE41 (4%-Zn, 1%-RE) is performed by an Nd:YAG laser (operating in a continuous wave mode). The degree of microstructural refinement and the depth of the laser melted zone is a strong function of laser processing parameters (laser power, beam diameter, scan rate). The corrosion properties of the laser treated and untreated zone is investigated by potentiodynamic polarization method. The microstructural changes on the surface due to laser surface melting were analysed by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy to understand their effect on the corrosion behaviour of ZE41.

Abstract: The corrosion resistance of phosphated Mg components is very low. A low cost and high corrosion resistant sealing technique is particularly desired. In this study, a new sealing technique was proposed and validated in laboratory trials. Phosphated AZ91D was simply dipped in an E-coating bath solution for a few seconds. After baking, the specimens were found to have considerably improved corrosion resistance.

Abstract: This paper is concerned with an investigation of the deformation behaviour of an Al-Cu alloy during tensile testing in the semi-solid state. It was carried out by fast in-situ X-Ray microtomography at ESRF, Grenoble. Deformation was performed at constant velocity, which was chosen to be small enough so as not to affect the acquisition of the images. It is observed that deformation is accompanied, initially, by some liquid flow from the adjacent regions towards the deformed zone. Then pores form in the liquid films and grow until they occupy a significant part of the cross section of the specimen. Quantification of this phenomenon was carried out thus leading to a better understanding of pore formation in semi-solid mixtures.

Abstract: Although the anodising process has been widely used in surface treatment of Al alloys, the well known sulphuric acid anodising process produces inhomogeneous and highly porous anodised coatings on Al alloys containing high Si due to the inertness of the silicon particles. The present work reports a novel micro-arc anodising process for such high-silicon aluminium alloys. Uniform and thick anodising coatings can be obtained through an anodising process in an alkaline electrolyte under high voltage and low current density conditions. The microstructure examination in SEM indicates that most pores in the coatings have been sealed during the anodising process, thus post-treatment that is normally needed for the currently used anodising process can be eliminated. The coating is very promising in the improvement of corrosion resistance for cast high-silicon aluminium alloys.

Abstract: Metallic biomaterials such as stainless steel and Co-based alloys are corrosion resistant and possess excellent mechanical properties and hence can be used in load-bearing implants for human tissue repair. However, these materials are bioinert and some of them can cause concerns over their long-term implantation as they release cytotoxic metal ions to surrounding body tissues. Forming a bioactive coating on implantable metals combats these problems and makes these materials very attractive for medical applications. This paper gives an overview of our research work over the past decade on using a number of surface modification techniques (plasma spraying, spraying-and-sintering, ion beam assisted deposition, biomimetic deposition, etc.) to improve the osteoconductivity of metallic biomaterials (Ti, Ti-6Al-4V and NiTi SMA).

Abstract: This paper outlines the current state of research into laser welding of titanium and its alloys for medical applications. The differences that exist between the medical and other industries are described and a direction for advancing research in this field is proposed.

Abstract: Interest in using titanium (Ti) alloys as load-bearing implant materials has increased due to their high strength to weight ratio, lower elastic modulus, and superior biocompatibility and enhanced corrosion resistance compared to conventional metals such as stainless steel and Co-Cr alloys. In the present study, the in vitro cytotoxicity of five binary titanium alloys, Ti15Ta, Ti15Nb, Ti15Zr, Ti15Sn and Ti15Mo, was assessed using human osteosarcoma cell line, SaOS-2 cells. The Cell proliferation and viability were determined, and cell adhesion and morphology on the surfaces of the binary Ti alloys after cell culture were observed by SEM. Results indicated that the Ti binary alloys of Ti15Ta, Ti15Nb and Ti15Zr exhibited the same level of excellent biocompatibility; Ti15Sn alloy exhibited a moderate biocompatibility while Ti15Mo alloy exhibited a moderate cytotoxicity. The SaOS-2 osteoblast-like cells had flattened and spread across the surfaces of the Ti15Ta, Ti15Nb, Ti15Zr and Ti15Sn groups; however, the cell shapes on the Ti15Mo alloy was shrinking and unhealthy. These results indicated that the Mo contents should be limited to a certain level in the design and development of new Ti alloys for implant material applications.

Abstract: Abstract Titanium and its alloys are widely used as dental implant materials due to their excellent biocompatibility, mechanical properties and erosion resistance. The b type titanium alloys are becoming more promising dental implant materials for their low elastic modulus and suitable mechanical properties. Because the titanium alloys are bioinert. The dental implant’s surfaces that contact with bone tissues need modification. To bioactivate the implants, hydroxyapatite/TiO2 composite material was coated onto dental implants by sol-gel and micro arc oxidation (MAO) methods. The HA (Hydroxyapatite) was employed to enhance the bioactivity of the Ti substrate. Owning to TiO2, the HA/TiO2 composite coatings adhered tightly to the dental implants and no longer existed cracks.

Abstract: The effects of alloy chemistry and heat treatment on the microstructure and mechanical properties of Ti-Nb-Zr-Mo-Sn near  type titanium alloys have been investigated. Near β titanium alloys consisting of non-toxic alloying elements Mo, Nb, Zr, Sn possess a low Young’s modulus, and moderate strength and plasticity. As the hot rolled TLM alloy (Ti-25Nb-3Zr-3Mo-2Sn) possesses high strength and low Young’s modulus a detailed investigation is performed for this alloy. Solution treatment of the hot rolled TLM alloy reduces strength and increases ductility without affecting the Young’s modulus. Ageing of the solution treated TLM alloy reduces elongation and increases the Young’s modulus with little change in strength. Both solution treated and aged conditions show features of two stage yielding associated with a strain induced martensitic transformation.

Abstract: With their very low density, excellent biocompatibility, and good mechanochemical properties, titanium alloys have been considered a high-end material for making biomedical devices and instruments. However, they still have some substantial challenges to be overcome. One major problem, which eventually leads to revision surgery, is the implant loosening- a result of tissue migration, formation of wear debris, insufficient interface bonding between bone and implant, and stress shielding. Nanosized features in the material have the potential to provide a solution to these problems. A nanostructured surface is able to not only promote tissue ingrowth, but also increase the surface hardness and therefore improving the wear resistance and enhancing fatigue strength. This paper reports our recent work on how surface treatment on titanium alloys changes their mechanical properties. The mechanism by which the surface nanostructuring alters mechanical properties has also been discussed.