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Redalyc.DENSIFICATION and ELECTROPHORETIC DEPOSITION Scientia Et Technica ISSN: 0122-1701 [email protected] Universidad Tecnológica de Pereira Colombia ENCISO MANRIQUE, JORGE LUIS DENSIFICATION AND ELECTROPHORETIC DEPOSITION (EPD) ON TI6AL4V SUBSTRATE USING BIOGLASS® Scientia Et Technica, vol. XII, núm. 32, diciembre, 2006, pp. 243-248 Universidad Tecnológica de Pereira Pereira, Colombia Disponible en: http://www.redalyc.org/articulo.oa?id=84911652043 Cómo citar el artículo Número completo Sistema de Información Científica Más información del artículo Red de Revistas Científicas de América Latina, el Caribe, España y Portugal Página de la revista en redalyc.org Proyecto académico sin fines de lucro, desarrollado bajo la iniciativa de acceso abierto Scientia et Technica Año XII, No 32, Diciembre de 2006. UTP. ISSN 0122-1701 243 DENSIFICATION AND ELECTROPHORETIC DEPOSITION (EPD) ON TI6AL4V SUBSTRATE USING BIOGLASS® SUMMARY JORGE LUIS ENCISO The goal of this article is to show the possibility to coat Ti6Al4V substrates with MANRIQUE bioglass powder by means of electrophoretic deposition (EPD), subsequently Ingeniero Metalúrgico, M.Sc followed by a suitable heat treatment to densify the coating. ingeniería de Materiales. Smooth defect free thick (> 1 mm) coatings were obtained on anodised Ti6Al4V Director Grupo de investigación cylindrical substrates by means of EPD. The voltage, powder concentration and GIMAP. time during EPD are important to produce coatings with the wanted thickness. Profesor Universidad de Ibagué EPMA and XRD analysis were performed on the densified coating and revealed [email protected] that the bioglass phase was transformed to a crystalline phase. KEYWORDS: Titanio, vidrio Bioactivo, Deposición Electroforetica, Recubrimiento Sinterizado, Microondas. ABSTRACT El objetivo de este articulo es mostrar la posibilidad de recubrir titanio Ti6Al4V con polvos de vidrio bioactivo (45S5) por medio de deposición electroforetica (EPD) seguido de un tratamiento de densificación del recubrimiento. Superficies suaves y libres de defectos fueron obtenidas (> 1mm) sobre un cilindro anodinado de Ti6Al4V por medio de EPD. El voltaje, la concentración de polvos y el tiempo durante el EPD son importantes para producir recubrimientos con espesores deseados. Análisis de EPMA y XRD fueron realizados sobre el recubrimiento densificado y revelo la transformación de fase del vidrio bioactivo en una fase cristalina. KEYWORDS: Titanium, Bioglass, Electrophorectic Deposition, Sintering, Coating, Microwave. 1. INTRODUCTION After electrophoretic deposition the obtained coating, One of the limiting factors, affecting widespread which is in fact still a powder compact, has to be application of bioglass is the difficulty on producing densified by a heat treatment. In this work microwave well-adhering coating by and industrial feasible process. sintering will be investigated. In microwave sintering, Different processes are possible for the deposition of a electromagnetic waves interact with ceramic materials, bioactive glass layer on titanium substrates like plasma leading to volumetric heating by dielectric loss. Such a spraying, chemical vapour deposition, dip coating, volumetric heating can help to improve the problems electrophoretic deposition (EPD) and electrochemical given with conventional heat transfer and to generate a deposition. The coating process not only influences the more uniform microstructure [2]. cost of the processing, but will also the coating structure, the adhesion with the substrate, the porosity (shape, size 2. TITANIUM ALLOYS morphology), and in this way the bioactivity. Ti already exists as a biomaterial for more than 60 years. Due to strength properties, titanium was replaced by one The method, which will be investigated here to coat of its alloys: Ti6Al4V, which is today's most used Ti6Al4V substrates with bioglass, is electrophoretic implant material [3]. Due to the formation of a stable deposition. This is a process in which suspended charged oxide surface, Ti is one of the most biocompatible powder particles are deposited on an electrode under metals. It is mainly used for orthopaedic and oral influence of an electric field. Some advantages of this implants thanks to the high corrosion and fatigue technique are high reproductivity, low cost, and the high resistance, a relative low E-modulus compared to bone, a speed. EPD can produce coatings with a broad thickness high strength/weight-relationship and a relatively high from less than 1µm to more than 500µm [1], while hardness [4]. deposition rates vary from seconds to minutes offering an Titanium exists in two crystallographic phases: a low easy control over the thickness and morphology of the temperature alpha (α) phase, which has a close-packed coating. hexagonal (c.p.h.) crystal structure, and a high temperature beta (β) phase that has a b.c.c. structure. To provide a wide range of useful mechanical property Fecha de Recepción: 31 Agosto de 2006 Fecha de Aceptación: 24 Noviembre de 2006 244 Scientia et Technica Año XII, No 32, Diciembre de 2006. UTP combinations, the morphology of these two allotropic 4. ELECTROPHORETIC DEPOSITION (EPD) phases has to be manipulated through alloy elements and thermo-mechanical processing [5]. Different microstructures are possible: α-, α/β-, β-alloys, and the Electrophoretic deposition (EPD) is very promising intermetallics (TixAl, where x = 1 or 3). Alloying because it is a fairly rapid, low cost process for the elements can be divided into substitutional fabrication of ceramic coatings, monoliths, composites, (molybdenum, vanadium, manganese, etc) and interstitial laminates and functionally graded materials varying in (oxygen, nitrogen and hydrogen) solutes [6]. The ranges thickness from a few nanometers up to centimetres [10]. and effects of different alloying element used in titanium Nowadays, coatings are world-wide processed by are shown in table 1. A number of authors [7] agree about electrophoretic deposition for phosphor screens, oxygen two mayor divisions of stabilised systems: α and β, sensors, fuel cells, photo-chemical cells, solar cell Molchona [ASM handbook, 2000] has developed a applications, etc. Most papers report on the possibility to convenient categorisation of titanium phase diagram. deposit coatings between nm scale and 200 µm on porous Titanium alloys like Ti6Al4V present a α/β structure, or dense substrates [11]. However, the main problem retaining more β-phase, which affects the properties (i.e. associated with this process is often the difficulty to when Ti6Al4V is cooled from high temperatures it can densify the coatings without cracking. transform the β-phase in a coarse acicular structure or a fine acicular α structure through a diffusion-controlled Electrophoretic deposition consists of two processes, i.e. nucleation and growth mechanism depending on the the movement of charged particles in suspension in an cooling rate). electric field between two electrodes (electrophoresis) Generally, acicular α improves creep resistance, fracture and particle deposition on one of the electrodes (see toughness and crack growth resistance, but loosing figure 1) or onto a membrane (electro-coagulation). ductility and fatigue. When the transformed β structure is coarse, toughness and crack-growth resistance are ++ -- improved and ductility and fatigue strength are reduced V [5]. Alloying element Range Effet on structure - Wt% - Aluminium 3-8 α stabiliser -- Tin 2-4 α stabiliser Vanadium 2-15 β stabiliser Molybdenum 2-15 β stabiliser - Chromium 2-12 β stabiliser Copper ± 2 β stabiliser Figure 1. Schematic view of the EPD process Zirconium 2-5 α and βstabiliser Silicon 0.05-0.5 Improves creep resistance After EPD, a powder compact with a green density Table 1. Ranges and effects of some alloying elements used in between 40 and 60 % of the theoretical density is titanium. obtained, which needs to be fully densified by sintering or curing. EPD requires a stable suspension in which the 3. BIOGLASS (45S5) powder particles must carry a sufficient charge. A suspension is termed stable if the particles experience a repulsive force when they approach each other, so that Bioglass is characterised by its behaviour and special agglomeration is avoided. Hence, more defect-free composition that increases the bonding. The surface deposits can be formed from such suspensions as the forms a biologically active hydroxyapatite layer, which incorporation of aggregates is avoided. Four mechanisms gives a bonding interface, forming a phase that is have been identified by which the charge on the particles chemically and structurally equivalent to the bone phase. can develop [10]. Bioglass (45S5) has a general composition of 45% wt (i) Selective adsorption of ions from the liquid phase SiO2, 6% wt P2O5, 24.5% wt CaO, and 24.5% wt Na2O. onto the solid particle, Compositions with 45-55% of SiO2 will join to the (ii) Dissociation of ions from the solid particle into the collagen of smooth tissues with the bone, and bioglass liquid, containing about 55-60% of SiO2 will only join to the (iii) Adsorption of dipolar molecules on the particle bone. The compositional dependence (in wt %) of bone- surface, bonding and soft-tissue bonding for Na2O-CaO-P2O5- (iv) Electron transfer between the liquid phase and the SiO2 glasses. All glasses contain a constant 6wt% of P2O5 solid particle. [9]. Scientia et Technica Año XII, No 32, Diciembre de 2006. UTP 245 The exact mechanism of deposition at the electrode is 2 εξ µ = ⋅ ()()1 + f ⋅ G α (2) still not entirely clear. Up to now, different
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