Surface Modification Of Metallic Materials Research Articles

Recent trends in laser cladding and alloying on magnesium alloys: A review

This paper discusses about the recent advancements in laser cladding and alloying processes used for surface property enhancement of magnesium and its alloys. Laser cladding and alloying is advanced manufacturing method used for surface modification of metallic materials in the modern industries. The cladding process is surface modification technique, which is used for deposition of thick layer of advanced materials on surface of conventional materials to improve the surface properties like, wear resistance, hardness, oxidation resistance, corrosion resistance, biocompatibility and heat resistance. The advanced materials generally used for cladding operations are transition metals, alloys, ceramics, composites, nanomaterials, rare earth oxide and some solid lubricant additives. The conventional substrate materials are steel, cast iron, titanium alloy, aluminium alloy, magnesium alloys and copper alloys. Laser cladding is most widely used coating technique because of its attractive properties such as low dilution rate, good metallurgical bonding between coating and substrate, less distortion, narrow heat affected zone, high solidification and cooling rate. In this article magnesium alloy is considered as substrate material and the various coating materials used for its surface modification are explained. Also, the effects of various laser process parameters on phase composition, microstructure, elemental composition, mechanical properties, tribological properties and corrosion resistance are discussed. The characterization techniques such as XRD, SEM, EDS, Vickers microhardness test, wear and friction test, corrosion test used for coating analysis are described. Furthermore, the problem arises in laser cladding and alloying on magnesium alloy and their possible remedies are discussed.

Microwave heating: Fundasmentals and application in surface modification of metallic materials – A review

Abstract Recently microwave assisted materials processing earningvoguedue to inherent gains in terms of time and energy efficiency, substantially reduced process cycle time, revamp mechanical properties, and beneath environmental hazards. During processing of materials through microwaves, equally electric and magnetic energy is linearly transferred within materials via interfacing interaction between molecules. Microwave processing is pertinent to vast variety of materials including metal matrix composites (MMC), fibre reinforced polymer (FRP), alloys, ceramics, metals, pulverize metallurgy, metal coating/ cladding etc. This paper presents several key fundamentals of microwaves and concisely depicts the studied microwave materials interaction mechanism. Microwave energy are extensively used, notably in the areas like coating, glazing and cladding on various metallic substrate materials like mild steel, and different grades of stainless steel (SS-316, SS-316L, SS-304, AISI-420) etc. Microwave applications in improving the surface properties of metallic materials are briefly reviewed in this paper.

Morphology of the DIN 100Cr6 Case Hardened Steel after Plasma Nitrocarburizing Process

Nitrocarburizing is considered one of the most important thermochemical treatments for surface modification of metallic materials and involves the simultaneous diffusion of nitrogen and carbon onto the surface. Understanding and controlling the formation of the nitrocarburized layer have considerable industrial interest due to the improvements regarding wear, fatigue, and corrosion resistances. DIN 100Cr6 steel samples were treated by plasma nitrocarburizing for two hours, with two treatment temperatures (550 and 600°C) and four methane concentrations in the gas mixture composition (0, 1.0, 1.5, and 2.0%). SEM and XRD analyses, and wear resistance tests were used to characterize the samples. Results showed that the treatment temperature and atmosphere composition had considerable influence on the compound layer morphology. For nitrided samples the compound layer consists of γ'-Fe4N phase, and the presence of carbon in the gas mixture helps stabilize the ɛ-Fe2-3N phase. Higher CH4 concentration in the treatment atmosphere improve the sample superficial wear resistance.

Thermal stresses computation under high–current pulsed radiation of AISI M2 tool steel

Surface modification of metallic materials and alloys with concentrated energy flows (powerful electron beams and ion plasma flow, laser beams) has been widely used in various fields of manufacturing. The aim of physical and mechanical properties modification is to improve the performance of the critical parts fabricated from modified materials. The mentioned energy impacts give rise to radiation, thermal and mechanical effects causing the changes in morphology, microstructure, elemental and phase composition of the surface layers, which in turn may lead to hardness, wear corrosion resistance and red hardness increasing of modified materials. However, as experimental investigations are shown, in some cases irradiation promotes the crystal defects’ occurrence and often non-uniform heating leads to the cracks’ formation in the surface layers. Thus, selection of incident electrons energy, its current density and pulse duration, taking into account the thermal stress state, is an actual problem of modern radiation technologies. This paper provides a numerical solution of differential equations in partial derivatives for the temperature fields’ computation as well as radial and axial thermal stresses distribution in R6M5 (AISI M2) high-speed steel exposed to medium-energy (up to 400 keV) high–current (up to 1 kA/cm2) pulsed (up to 1 μs) electron beam radiation. The obtained results can be useful in the optimal modes selection of tool steels and products at surface radiation treatment and evaluation of their service life.

Surface modification of metallic materials designed for a new generation of artificial heart valves.

The main goal of this work was to develop haemocompatibile thin film materials dedicated to novel flexible mechanical heart valves intended for pulsatile ventricle assist devices. The studies performed have led to the selection of a material for the surface modification of the metallic scaffold. Haemocompatible, biofunctional, ultra-elastic, thin carbon-based coatings were proposed. The surface was designed to eliminate thrombogenic and microbial construction by a reduction in turbulence and sufficient washing of the biofunctional-adapted surfaces, thus allowing for extended use for temporary heart support. The article presents the influence of the mechanical properties of coatings and their influence on the haemocompatibility. In this study, we investigated a simplified model of the whole blood shear stress based on a cone and plate rotational viscometer. Several indices of platelet activation were analysed, including platelet and granulocyte-platelet aggregates, platelet activation markers and platelet-derived microparticles. The shear stress induced a platelet aggregate count in the range from 2% to 30% of the CD61 positive cells. For polyurethane (PU), the average value of platelet aggregates was on the level of 7%. The analyses have demonstrated that the cytometric methods of the direct determination of platelet-derived microparticles in plasma are reproducible and reliable. Considering the generation of microparticles on the tested coatings under hydrodynamic conditions, the best properties were observed for the coating a-C:H,N. The results indicate that a-C:H-based coatings with the thickness of 110 nm do not induce an immune response and do not influence the origin of platelet microparticle formation; thus, these type of coatings are the most promising for the parts which are planned to withstand blood contact under the high value of shear stress.

Sol Gel Glass Coating on Magnesium Alloys to be Used As Temporary Implants: Electrochemical and Surface Study in Simulated Body Fluid

Surface modification of metallic materials is the approach for developing functional properties to assure good biocompatibility, enhance tissue acceptance, and/ or inhibit corrosion rate. It opens a wide spectrum of possibilities oriented to develop the functional properties needed for an implant acceptance when the bare material is not enough to assure good biocompatibility and tissue regeneration. Further, the interface between the implant and the physiological environment becomes the key factor which conditions the prosthesis success or failure. The aim of this work is to generate a chemically modified surface of two commercial magnesium alloys with a 58S and 68S sol-gel made glass coating, obtained from organic precursors such as silicon and phosphate alkoxides and calcium lactate. The produced bioactive layer is sintered at low temperatures in order to maintain the substrate integrity. The glassy coating composition belongs to the SiO2-P2O5-CaO system and has the double goal of promote bone healing and retard the hydrogen evolution coming from the anodic reaction. AZ31B (Al 3%, Zn 1%, Mn 0.2%) and AZ91D (Al 9%, Zn 1%, Fe 0.005%, Mn 0.33%, Ni 0.002%) were used as substrates. Plane samples were polished until 2500 grit SiC paper and cleaned prior to coat. 58S and 68S glasses (60/70 mol% SiO2, 36/26 mol% CaO, 4/4 mol% P2O5, respectively) was prepared by sol-gel method using tetramethyl orthosilicate, methyltriethoxysilane, triethyl phosphite and calcium L-lactate hydrate as precursors, HNO31N was used as catalyser, ethylene glycol to improve the alkoxide condensation degree and methanol dissolve the calcium lactate. Micro-Raman assays were performed to analyze deposits composition (Invia Reflex Confocal, Renishaw RM 2000, UK) with a 785 nm wavelength laser. X-ray photoelectron spectroscopy (XPS) was selected to perform an elemental analysis of surfaces prior and after immersion of 72 h in HBSS. Measurements were made using a commercial VG ESCA 3000 system, using Mg Kα (1253.6 eV) radiation and an overall energy resolution of 0.8 eV. High resolution scans with 0.1 eV steps were conducted over Mg 2p, Ca 2p, P 2p, Si 2p and O 1s. In the entire cases surface charging effects were compensated by referencing the binding energy (BE) to the C 1s line of residual carbon set at 284.5 eV. Coatings visual integrity and deposits produced during immersion tests were examined by scanning electronic microscopy (SEM, JEOL JSM-6460LV, Japan) prior to immersion and after 24 h. Electrochemical assays were performed in a GAMRY Ref 600 electrochemical unit (Gamry, USA) with a conventional three electrode cell, using a saturated calomel electrode (SCE, Radiometer Copenhagen) as reference electrode, a platinum wire as a counter electrode and the coated and bare magnesium alloys as working electrodes. Electrochemical impedance spectroscopy (EIS) tests were registered also at the Ecorr with amplitude of 0.01V rms sweeping frequencies from 20000 to 0.005 Hz. Polarization curves for each sample were also recorded with an initial and final voltage of -1.8V (vs. reference) and 1 mV/s of scan rate. Hank Buffered Salt Solution (HBSS) at 37 ºC was used as electrolyte. Electrochemical test show that the coatings are able to retard anodic reaction being more efficiently on AZ91 alloy. Regarding the compositions, the coating with less calcium content (68S) is able to form more continuous films that the 58S with higher corrosion resistance after immersion in HBSS (Figure 1). Both coatings show signs of deposit of hydroxyapatite related compounds after immersion, as a first sign of bioactivity in vitro. Figure 1

Fabrication of Chromium (III) Oxide (Cr2O3) Coating by Electrophoretic Deposition

Chromium (III) oxide has been widely used as a coating material for corrosion resistance. In this study, electrophoretic deposition (EPD) of nano chromium (III) oxide (Cr2O3) particle (60 nm) was investigated to develop coatings with potential applications of anticorrosive material. The stable suspension of Nano‐Cr2O3 particles were obtained in the mixture of acetylacetone and ethanol containing 0.00025 M nitric acid. The coating growth rate was studied with using different deposition times in the range of 1–30 min at voltages of 50–150 V with various concentrations of suspension. The electrophoretic Cr2O3 coating was sintered at 1000°C and 1200°C for 2 h. The micro‐morphology of coating was qualitatively characterized by focused ion beam scanning electron microscopy (FIB/SEM). The SEM micrographs obviously showed that the electrophoretic Cr2O3 coating has formed a uniform and dense ultrathin layer after sintering at 1200°C. We demonstrated that nano‐Cr2O3 coating could be easily obtained by EPD for the surface modification of metallic materials for potential interest in hard wear‐resistant and/or low‐friction coatings.

Numerical Simulation of Residual Stress Field Induced by Water-Jet Cavitation Peening

Water-jet cavitation peening is a new technology for surface modification of metallic materials. Compress residual stress layer is induced by impact wave pressure in the submerged cavitating jets processing. Based on ANSYS/LS-DYNA finite element analysis software, residual stress field in the SAE1070 spring steel material surface induced by cavitate-jet water peening process is simulated, the magnitude and variation rules of the residual stress along the layer depth under different conditions is obtained. In order to verify the correctness of the numerical simulation, the size and distribution of residual stress by the X-ray diffraction method. The results show that the numerical simulation and experimental results are well consistent.

Numerical and Experimental Studies of Cavitation Behavior in Water-Jet Cavitation Peening Processing

Water-jet cavitation peening (WCP) is a new technology for the surface modification of metallic materials. The cavitation behavior in this process involves complex and changeable physics phenomena, such as high speed, high pressure, multiple phases, phase transition, turbulence, and unstable features. Thus, the cavitation behavior and impact-pressure distribution in WCP have always been key problems in this field. Numerous factors affect the occurrence of cavitation. These factors include flow-boundary conditions, absolute pressure, flow velocity, flow viscosity, surface tension, and so on. Among these factors, pressure and vapor fraction are the most significant. Numerical simulations are performed to determine the flow-field characteristics of both inside and outside the cavitating nozzle of a submerged water jet. The factors that influence the cavitation intensity of pressure are simulated. Fujifilm pressure-sensitive paper is used to measure the distribution of impact pressure along the jet direction during the WCP process. The results show that submerged cavitation jets can induce cavitation both inside and outside a conical nozzle and a convergent-divergent nozzle when the inlet pressure is 32 MPa. Moreover, the shock wave pressure induced by the collapse of the bubble group reaches up to 300 MPa.

Numerical and Experimental Studies of Cavitation Behavior in Water-Jet Cavitation Peening Processing

Water-jet cavitation peening (WCP) is a new technology for the surface modification of metallic materials. The cavitation behavior in this process involves complex and changeable physics phenomena, such as high speed, high pressure, multiple phases, phase transition, turbulence, and unstable features. Thus, the cavitation behavior and impact-pressure distribution in WCP have always been key problems in this field. Numerous factors affect the occurrence of cavitation. These factors include flow-boundary conditions, absolute pressure, flow velocity, flow viscosity, surface tension, and so on. Among these factors, pressure and vapor fraction are the most significant. Numerical simulations are performed to determine the flow-field characteristics of both inside and outside the cavitating nozzle of a submerged water jet. The factors that influence the cavitation intensity of pressure are simulated. Fujifilm pressure-sensitive paper is used to measure the distribution of impact pressure along the jet direction during the WCP process. The results show that submerged cavitation jets can induce cavitation both inside and outside a conical nozzle and a convergent-divergent nozzle when the inlet pressure is 32 MPa. Moreover, the shock wave pressure induced by the collapse of the bubble group reaches up to 300 MPa.

Microstructure and microhardness of AA1050/TiC surface composite fabricated using friction stir processing

Friction stir processing (FSP) has been developed by several researchers to produce an upper surface modification of metallic materials. The fabrication of TiC particulate (~2 \(\upmu \)m) reinforced aluminum matrix composite (AMC) using FSP is studied in this paper. The measured content of TiC powders were compacted into a groove of 0.5 mm × 5.5 mm. A single pass FSP was carried out using a tool rotational speed of 1600 rpm, processing speed of 60 mm/min and axial force of 10 kN. A tool made of HCHCr steel, oil hardened to 62 HRC, having a cylindrical profile was used in this study. The microstructure and microhardness of the fabricated AMC were analysed. Scanning Electron Microscope (SEM) micrographs revealed a uniform distribution of TiC particles which were well-bonded to the matrix alloy. The hardness of the AMC increased by 45% higher than that of the matrix alloy.

Electrophoretic deposition of selenium

Selenium has been suggested for a number of applications in the biomedical field. In this study, electrophoretic deposition (EPD) of Se powder (100-mesh) was investigated to develop coatings with potential applications in orthopedic implants. Se powder was suspended in sulfuric acid and stable suspensions were obtained with addition of ethanol and distilled water. The film growth rate was varied by different deposition times in the range of 5 to 20min at voltages of 1.5–3V. The deposits were characterized qualitatively by bending strength tests, SEM observations and EDX analysis. Results of this study demonstrate that Se coatings can be readily obtained by EPD for the surface modification of metallic materials which is of potential interest in orthopedics and bone tissue engineering applications where Se can be useful as an anticancer agent.

자기조립단분자막을 위한 보편적이고 기능화된 긴 사슬 알킬티올 연결자의 제조

본 연구에서는 자기조립단분자막(SAM)의 연구에 유용한 일련의 <TEX>$\omega$</TEX>-mercapto alkyl amine 1 및 <TEX>$\omega$</TEX>-mercapto alkanoic acid 2를 만드는 제조공정을 서술하였다. 먼저 첫 번째 목표물질인 <TEX>$\omega$</TEX>-mercapto alkyl amine 1의 제조방법은 다음과 같다: 먼저 시중에서 시판되는 potassium phthalimide와 <TEX>$\omega$</TEX>-bromo alcohol을 <TEX>$80{^{\circ}C}$</TEX>, DMF 용매에서 치환반응으로 화합물 3을 합성하였다. 아민기와 알코올기를 포함하는 화합물 4을 합성하기 위하여 먼저 화합물 3를 hydrazine hydrate로 환류시킨 후, 이어서 c-HCl로 처리하여 부반응물 5를 수반하여 생성물 4를 76-98% 수율로 만들었다. <TEX>$\omega$</TEX>-aminoakanol 4의 hydroxyl기를 HBr로 브로민화반응을 하여 <TEX>$\omega$</TEX>-bromoamine 화합물 6을 34-97% 수율로 만들었다. 티올기를 도입하기 위하여 화합물 6을 95% 에탄올 속에서 thiourea와 치환 반응하여 <TEX>$\omega$</TEX>-aminoalkanthiuronium 7을 만든 다음, 이 화합물을 센 염기(KOH)와 센 산으로 처리하여 목표화합물, <TEX>$\omega$</TEX>-mercapto alkylamines 1을 총 5단계를 걸쳐서 제조하였다. 덧붙여 두 번째 목표물질인 <TEX>$\omega$</TEX>-mercapto alkanoic acid 2는 다음과 같이 2단계를 통하여 제조하였다: <TEX>$\omega$</TEX>-bromo alkanoic acid를 95% 에탄올 속에서 thiourea로 처리하여 화합물 7을 만든 다음, 센 염기(KOH)를 처리하여 thiuronium bromide 를 제거한 후, 다시 센 산(HCl) 수용액으로 처리하여 두 번째 목표화합물 <TEX>$\omega$</TEX>-mercapto alkanoic acid 2을 얻었다. 제조한 긴 사슬 알킬티올 1과 2 유도체들은 금속(Au, Pt, Ti)에 자기조립단분자 막을 형성함으로써 단백질, 효소 및 다양한 생체분자를 고정하는 연결자로 사용될 수 있으며, 그 밖에 금속의 표면개질을 이용하여 다양한 응용 연구를 위한 화학 도구로 사용될 수 있다. In this research, the preparation processes for making a series of <TEX>$\omega$</TEX>-mercapto alkylamine 1 and <TEX>$\omega$</TEX>-mercapto alkanoic acid 2 useful for studying of the self-assembled monolayer(SAM) are described. The preparation methods of the first goal materials, <TEX>$\omega$</TEX>-mercapto alkylamines 1 were carried out as follows: First, <TEX>$\omega$</TEX>-phthalimide alkanol 3 was synthesized from commercially available potassium phthalimide derivatives and <TEX>$\omega$</TEX>-bromoalkanol in DMF at <TEX>$80{^{\circ}C}$</TEX> via substitution reaction. After refluxing <TEX>$\omega$</TEX>-phthalimide alkanol 3 with hydrazine hydrate in ethanol followed by treating with c-HCl, <TEX>$\omega$</TEX>-aminoalkanol 4 was obtained in 76-98% yield, accompanied with side-product 5. Bromination of hydroxyl moiety of <TEX>$\omega$</TEX>-aminoalkanol 4 using aqueous hydrobromic acid furnished <TEX>$\omega$</TEX>-bromoamine 6 in 34-97% yields. Substitution reaction 6 with thiourea in 95% ethanol gave <TEX>$\omega$</TEX>-aminoalkanthiuronium 7, which was treated with aqueous strong base and aqueous strong sulfuric acid gave desired products, <TEX>$\omega$</TEX>-mercapto alkylamines 1 through overall 5 steps. The second target material, <TEX>$\omega$</TEX>-mercapto alkanoic acid 2 was prepared via 2 steps. <TEX>$\omega$</TEX>-bromo alkanoic acid was reacted with thiourea to give <TEX>$\omega$</TEX>-thiourea alkanoic acid 7 in 69-85%, which was treated with aqueous strong base and strong acid to furnish <TEX>$\omega$</TEX>-mercapto alkanoic acid 2 in 50-98%. The fabricated long-chain alkylthiol(LCAT) can be used as linkers to immobilize protein, enzyme and various kinds of biomolecules on the surface of metallic materials(Au, Pt, Ti) by SAM, and can be useful chemical tools for the application study on the surface modification of metallic materials.

SURFACE MODIFICATION OF METALLIC MATERIALS BY HIGH CURRENT PULSED ELECTRON BEAM

High current pulsed electron beam (HCPEB) has been developing as a useful tool for surface modification of materials. This paper presents our research work on surface modification of metallic materials, such as mold steel, stainless steel and magnesium alloy, with a HCPEB equipment of working parameters as electron energy 27keV, pulse duration ~1µs and energy density ~5J/cm2. Investigations performed have shown that the most pronounced changes of phase-structure state and properties occurring in the near-surface layer. The formation mechanism of surface craters and their evolution regularity are discussed based on the elucidation of non-equilibrium temperature filed and different kinds of stress formed during pulsed electron beam treatment. After the HCPEB treatments, samples show significant improvements in measurements of wear and corrosion resistance.

A novel way to produce bulk SiCp reinforced aluminum metal matrix composites by friction stir processing

Friction stir processing (FSP) has been developed to produce upper surface modification of metallic materials in recent studies. The feasibility to make bulk dispersal SiCp reinforced Al metal matrix composites (MMCs) were studied successfully in this paper. The distribution of well-dispersed SiCp got a range of 5 mm × 2 mm on the cross-section of joints. Excellent bonding between SiCp and base metal can be obtained by this process. The percentage of SiCp over 1.5% was found in the bulk reinforced region not only confined to 100 μm magnitude under the upper surface. The microhardness of MMCs can reach steady 10% higher than the one of the base metal (about HV88) at the depth of 1.0 mm under surface.

Characteristics of Biomedical Beta-Type Titanium Alloy Subjected to Coating

Beta-type titanium alloys used in biomedical applications have been developed all over the world. In particular, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) is one of beta-type titanium alloys for biomedical applications that has been developed by the authors in Japan. Although TNTZ is composed of non-toxic elements such as niobium, tantalum, and zirconium, it still lacks bioactivity, which is the ability to form chemical bonds with living bones. The stems that are parts of artificial hip joints, dental implants, etc., which are made of metallic materials, etc. are required to bond strongly with living bones. However, these stems, dental implants etc., cannot form chemical bond with living bones by themselves. The bioactive surface modification of metallic materials by the application of ceramics is effective in improving the biocompatibility of TNTZ. Calcium phosphate ceramics such as hydroxyapatite (Ca 10 (PO 4 ) 6 OH 2 ; HAP) and β-tricalcium phosphate (β-Ca 3 (PΟ 4 ) 2 ; β-TCP) possess bioactivity. In this study, the characteristics and morphology of TNTZ coated with a calcium phosphate invert-glass-ceramic (CPIG) layer by dip-coating treatment or with a sodium titanate layer by alkali solution treatment are investigated before and after soaking it in a simulated body fluid (SBF). The bonding strength between a CPIG layer with a thickness of around 5 μm and a specimen surface of TNTZ is around 25 MPa. No cracks or exfoliations are observed along the boundary between the CPIG layer and the specimen surface. This is the reason why the difference in the thermal expansion coefficients between CPIG layer and TNTZ reduced due to a compositional gradient zone with a thickness of around 3 μm in CPIG layer. HAP is formed on the entire surface of the TNTZ specimen after soaking it in the SBF for more than 1728 ks. The fatigue properties of TNTZ coated with a CPIG layer are similar to those of as-solutionized TNTZ. A reticulate structure with a thickness of 400 to 800 nm is formed on the TNTZ specimen surface after soaking it in 3 to 10 kmol/m 3 NaOH solution for 86.4 ks and 172.8 ks. HAP is completely formed on the entire surface of the TNTZ specimen when it is soaked in the SBF for 1209.6 ks after being soaked in 5 kmol/m 3 NaOH solution for 172.8ks.

Simulation of thermophysical and physico-chemical processes occurring at coating formation in electron-beam technologies of surface modification of metallic materials

The paper reviews our theoretical research aimed at studying the processes that accompany electron-beam surface treatment of materials. The major attention is given to the description of nonequilibrium physico-chemical processes occurring in the treatment area. We briefly analyze three types of models corresponding to different technological schemes. The ways of further development of the theoretical approaches used in our research work are discussed.

115 微粒子投射による金属材料の表面改質(OS02-4 歯車の強度IV/OS03 歯車の材料・熱処理・表面処理)

115 微粒子投射による金属材料の表面改質(OS02-4 歯車の強度IV/OS03 歯車の材料・熱処理・表面処理)

Development of an Electrophoretic Sol-Gel Coating Process for Porous Metals

An electrophoretic sol-gel coating process was developed for applying to surface modification of metallic materials with complicated shapes such as porous metals. In this process, sol-gel transformation is directly induced on the substrates. In the present work, the formation of TiO2 coating layer on SUS 304 substrates is discussed as a practical example of the coating process. The colloidal particles derived from hydrolysis of titanium tetraisopropoxide in ethanol can be deflocculated using a small amount of CaCl2 to form a transparent solution. When a dc voltage of 1–5 V was applied between the substrate (cathod) and counter electrode in this solution, the gel film was formed on the substrate. After subsequent water-soaking and annealing processes, the coating layers with no cracking were obtained successfully on the substrate. As the results of X-ray photoelectron spectroscopy, the coating layers were found to consist of TiO2 doped with Ca2+ ions.

Electrophoretic Deposition of Hydroxyapatite Coatings and Corrosion Aspects of Metallic Implants

Metallic materials such as stainless steels, cobalt-chromium alloys, titanium and its alloys, have been used extensively for centuries in restoration of anatomical structures due to their superior mechanical properties. The most important considerations for their selection in the human body are their biocompatibility, corrosion resistance, tissue reactions, surface conditions, and osseointegration (a bone bed formed through direct attachment to bone). Metallic implants are unique in that they are exposed to living cells, tissues and biological fluids, which are not only dynamic but also form a hostile environment for the implant. Clinical experience has shown that metallic implants are susceptible to localized corrosion in the human body, releasing metal ions into the surrounding tissues. Numerous failures of such implants have led to the application of biocompatible and corrosion resistant coatings, as well as to surface modification of the alloys. Ceramic materials that are based on hydroxyapatite (HAP), the principal constituent of dentine, bone and other hard tissues, are considered promising for osteo-implants and as a means of aiding the regeneration of bone. There are indications that chemical bonding may occur between HAP and bone. However, the poor mechanical properties of HAP limit its use in implantation. Bioceramic coatings have been intensively studied in order to obtain implant materials which have both biological affinity and high mechanical strength. This article reviews various aspects of corrosion resistance and biocompatibility of metallic implants. Surface modification of metallic materials by electrophoretic deposition (EPD) of HAP and the corrosion performance of these coatings in simulated body fluid conditions are also discussed.