A. Ossowska

Biocompatibility and Bioactivity of Load-Bearing Metallic Implants

Biocompatibility and Bioactivity of Load-Bearing Metallic Implants The main objective of here presented research is to develop the titanium (Ti) alloy base composite materials possessing better biocompatibility, longer lifetime and bioactivity behaviour for load-bearing implants, e.g. hip joint and knee joint endoprosthesis. The development of such materials is performed through: modeling the material behaviour in biological environment in long time and developing of new procedures for such evaluation; obtaining of a Ti alloy with designed porosity; developing of an oxidation technology resulting in high corrosion resistance and bioactivity; developing of technologies for hydroxyapatite (HA) deposition aimed at composite bioactive coatings; developing of technologies of precipitation of the biodegradable core material placed within the pores. The examinations of degradation of Ti implants are carried out in order to recognize the sources of both early allergies and inflammation, and of long term degradation. The theoretical assessment of corrosion is made assuming three processes: electrochemical dissolution through imperfections of the anodic oxide layer, diffusion of metallic ions through the oxide layer, and dissolution of oxides themselves. In order to increase the biocompatibility, the toxic elements, aluminium (Al) and vanadium (V) are eliminated. The experiments have shown that titanium - zirconium - niobium (Ti-Zr-Nb) alloy may be a such a material which can also be prepared by both powder metallurgy (P/M) technique and selective laser melting. The porous (scaffold) Ti-Zr-Nb alloy is now obtained by powder metallurgy, classical and with space holders used before melting and decomposed, or remained during melting and removed by subsequent water dissolution. The oxidation of porous materials is performed either by electrochemical technique in special electrolytes or by chemical and/or hydrothermal method in order to obtain the optimal oxide layer well adjacent to an interface, preventing the base metal against corrosion and bioactive because of its nanotubular structure, permitting injection of some species into the pores. The Ca, O and N ion implantation or deposition of zirconia sublayers may be used to increase the biocompatibility, bioactivity and corrosion resistance. The HA coating obtained by either electrophoretic, biomimetic or by sol-gel deposition should result in gradient structure similar to bone structure, possessing high adhesion strength. The core material of the porous material should result in a biodegradable material, allowing slower dissolution followed by stepwise growth of bone tissue and angiogenesis, preventing local inflammation processes, sustaining the mechanical strength close to that of non-porous material.

Materials Design for the Titanium Scaffold Based Implant

The main objective of here presented research is a design the scaffold/porous titanium (Ti) alloy based composite material demonstrating better biocompatibility, longer lifetime and bioactivity behaviour for load-bearing implants. The development of such material is proposed by making a number of consecutive tasks. Modelling the mechanical, biomechanical and biological behavior of porous titanium structure and an elaboration of results is performed by mathematical methods, including FEM and fuzzy logic. The development of selected Ti-13Zr-Nb alloy with designed porosity and no harmful effects is made by powder metallurgy (PM) with and without space holders, and by rapid prototyping with an use of selective laser melting (SLM). The development of an oxidation technology resulting in high corrosion resistance and bioactivity is carried out by electrochemical oxidation, gaseous oxidation and chemical oxidation, and their combination. The HA depositon is made by electrochemical and chemical (alternate immersion) methods. The core material is designed as a combination of natural polymer and bioceramics in order to allow slow dissolution followed by stepwise growth of bone tissue and angiogenesis, preventing local inflammation processes, and sustaining the mechanical strength close to that of non-porous material.

Formation of High Corrosion Resistant Nanotubular Layers on Titanium Alloy Ti13Nb13Zr

This paper presents results of oxidation tests and corrosion investigations of titanium alloy Ti13Nb13Zr performed at different conditions. The oxide layers have been formed by electrochemical method in 2M H3PO4 + 0.3% HF solution for 30 min. and 1 h at 20 V constant voltage. The corrosion tests have been made by potentiodynamic method in Ringer`s solution at pH ranged between 3 and 7. It has been shown that the nanooxide films, which improve corrosion resistance of titanium alloy Ti13Nb13Zr even if acidic environment, have appeared.

M-7 Influence of Laser Melting on Surface Layer Properties of Titanium Alloy Ti6Al4V

In time of rapid technology and medicine progress, implants are becoming more widely used in the human body, ranging from dental implants, stabilizing plates, screws, orthopaedic prostheses. For example, there are many types of hip prostheses used for hip replacement as well as various types of materials used for these orthopaedic prostheses. Properties of titanium alloys used in hip prostheses combined with good strength properties, corrosion resistance and low modulus of elasticity, are the most compatible of all prosthetic materials such as cobalt alloys, corrosion resistance steel. However, their major drawback is the low wear resistance. In order to tackle this drawback the solution may be a hardening of the surface while maintaining the core characteristics. The laser melting process is the method that is utilized for precise and selective treatment of the surface layer. By concentrating a large portion of energy in a small area, laser technology allows to obtain better structures [1-3] than produced in traditional process [4]. This article presents the investigations results of titanium alloy Ti6Al4V surface layer after laser melting process. The process of laser melting was performed using Nd-YAG laser. Individual samples were laser melted using different scanning speeds and different shifts in the laser beam. The evaluation of structure of the alloy as well as hardness and chemical composition was performed. It was shown that laser melting changes the structure and properties of titanium alloy Ti6Al4V, process parameters as scanning speed affects the thickness of zones in upper layer of the material. Due to the laser melting process more wear resistive surface can be obtained that increases the wear and corrosion resistance of orthopeadic prosthesis.

Properties of composite oxide layers on the Ti13Nb13Zr alloy

ABSTRACT The development of composite oxide layers on the Ti13Nb13Zr alloy, their structure and properties, were demonstrated. Two subsequent methods were applied to prepare the composite layers. During the first stage, gas oxidation produced a dense compact oxide layer, and subsequent oxide nanotubes were formed applied an electrochemical oxidation. The scanning electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and Raman spectroscopy were used to examine the appearance, thickness, chemical and phase composition of the oxide layers. The results obtained revealed that the composite layers composed of two zones. The electrochemical formation of the outer nanotubular oxide zone occurred if the thickness of the first inner oxide zone was small enough because of resistance increasing with the inner zone thickness followed by a decrease in electrochemical reaction rate. The decreasing corrosion resistance of the Ti13Nb13Zr alloy was observed and explained by a model electric circuit.

Hydrogen degradation of pre-oxidized zirconium alloys.

Abstract The presence of the oxide layers on Zr alloys may retard or enhance the hydrogen entry and material degradation, depending on the layer features. This research has been aimed to determine the effects of pre-oxidation of the Zircaloy-2 alloy at a different temperature on hydrogen degradation. The specimens were oxidised in laboratory air at 350°C, 700°C, and 900°C. After, some samples were tensed at 10-5 strain rate and simultaneously charged with hydrogen under constant direct voltage in 1 N sulfuric acid at room temperature. Other specimens were charged without any tension, then annealed at 400°C for 4 h and finally tensed at above strain rate. The SEM examinations were performed on the cross-sections and fracture faces of specimens. The obtained results demonstrate the effects of the oxide layer on the cathodic current and hydrogen entry, mechanical properties and the appearance of hydrides and fracture behaviour.

Properties of Duplex Stainless Steel Surface Layers after Burnishing Process

This paper investigates stress corrosion cracking resistance of cold worked layers of 25 Cr duplex stainless steel grade UR52N+. The surface layers were processed through burnishing treatment. The residual stresses at surface layers were determined using grazing angle incidence X-ray diffraction method (g-sin2 Ψ). Corrosion tests were performed with the use of Slow Strain Rate Test technique in boiling 35% MgCl2 solution. It has been demonstrated that burnishing treatment increases corrosion resistance of the steel. Stress corrosion cracking resistance depends on the magnitude of cold work at surface layers. High level of cold work diminishes corrosion resistance.

Properties of Surface Layers of Titanium Alloy TI6AL4V After Laser Melting Processes

Properties of Surface Layers of Titanium Alloy TI6AL4V After Laser Melting Processes The article presents the investigation results of titanium alloy Ti6Al4V surface layer after laser melting process. The process of laser melting was performed using Nd-YAG laser. The evaluation of structure of the alloy as well as hardness and chemical composition was performed. It was shown that laser melting changes the structure and properties of titanium alloy Ti6Al4V and process parameters as scanning speed affects the thickness of zones in top layer of the material. Due to the laser melting process more wear resistive surface can be obtained that increases the wear and corrosion resistance of orthopeadic prosthesis.