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Titanium-based nanotubelayer was formed through the electrochemical anodization technique on coarse-grained and ultrafine-grained Ti-13Nb-13Zr (wt.%) alloy, in 1M H3PO4 + NaF electrolyte for 90 minutes. The nanotube layer morphology was analyzed using the scanning electron microscopy (SEM) and the X-ray diffraction (XRD). The electrochemical impedance spectroscopy (EIS) technique was used to determine the corrosion resistance of the alloy before and after electrochemical anodization. These materials were exposed to a solution simulating conditions in the human body (Ringer' s solution) with pH of 5.5 at a temperature of 37 ºC. In order to investigate the titanium-based nanotube layer adhesion on alloy surface a scratch test was done. The scratch test was performedon nanoindenter G200, Agilent Technologies, using an indenter Berkovichtype diamond tip with applying an increasing load up to 40 mN. It was established that electrochemical anodization led to the formation of the nanotube oxide layer on the surface of titaniumbased materials. Influence of the ultrafine-grained material structure on the homogeneity of the nanotube layer obtained by electrochemical anodization has been noticed. Both coarse-grained and ultrafine-grained alloy showed excellent corrosion resistance in Ringer’s solution. Moreover, electrochemical anodization led to a decrease or an increase of the corrosion resistance of these materials, depending on the nanotube layer morphology. The scratch test showed that plastic deformation was present in the nanotube layer. The scratch resistance for the nanotube layer failure was on the higher load, pointing to the good adhesion for the titanium-based nanotube layer formed using electrochemical anodization.

Titanium alloys are metal materials widely used in medicine owing to their suitable characteristics such as low density, good corrosion resistance and biocompatibillity. High biocompatibility of the titanium alloy results from the creation of a spontaneous oxide layer with good adhesion and homogeneous morphology. In order to improve characteristics of the metallic materials for application in medicine, electrochemical methods that enable surface nanostructured modification are extensively used, and one of these methods is electrochemical anodization which makes it possible to obtain a nanostructured oxide layer composed of nanotubes on the surface of the metal material. The tested material was ultrafine-grained Ti-13Nb-13Zr (UFG TNZ) alloy obtained by the severe plastic deformation (SPD) processing using the high pressure torsion (HPT) process. Nanostructured oxide layer on the titanium alloy was formed by electrochemical anodization during the time period from 30 to 120 minutes. Characterization of the surface morphology obtained during different times of electrochemical anodization was done using scanning electron microscopy (SEM), while the topography and surface roughness of the titanium alloy before and after electrochemical anodization was determined using atomic force microscopy (AFM). Scratch test was used to determine the cross profile of the surface topography and critical load during scratching. Electrochemical anodization led to the formation of a nanostructured oxide layer on the surface of the titanium alloy. The obtained results indicated strong influence of the electrochemical anodization time on the oxide layer morphology - with its increase the diameter of the nanotubes increases too, while the wall thickness of nanotubes decreases. Also, electrochemical anodization led to an increase in the surface roughness.

The influence of friction stir welding parameters on thermo-mechanical behavior of the material during welding is analyzed. An aluminum alloy is considered (Al 2024 T351), and different rotating and welding speeds are applied. The finite element model consists of the working plate (Al alloy), backing plate and welding tool. The influence of the welding conditions on material behavior is taken into account the application of the Johnson-Cook material model. The rotation speed of the tool affects the results. If increased, it contributes to an increase of friction-generated heat intensity. The other component of the generated heat, which stems from the plastic deformation of the material, is negligibly changed. When the welding speed, i.e. tool translation speed, is increased, the intensity of friction-generated heat decreases, while the heat generation due to plastic deforming is becoming more pronounced. Summed, this leads to rather small change of the total generation. The changes of the heat generation influence both the temperature field and reaction force. Also, the inadequate selection of welding parameters resulted in occurrence of the defects (pores) in the model.

Wear damage behavior of new orthopedic Ti-13Nb-13Zr (mass %) alloy with martensitic microstructures developed by different thermo-mechanical treatments were examined during sliding in simulated physiological solution. The results obtained for this alloy processed by cold and hot rolling were compared with that of the standard Ti-6Al-4 V (mass %) alloy heat-treated to produce martensitic microstructure. The block-on-disk sliding friction and wear tests were conducted in Ringer’s solution. The friction coefficient, wear rate, and wear damage mechanisms were determined over a range of normal loads (20–60 N) and linear sliding speeds (0.26–1.0 m/s). The surface damage morphology revealed the presence of corrosive, abrasive, and adhesive wear in all investigated materials. The friction and wear properties were found to be dependent on the predominant wear damage mechanism and applied load/sliding speed combination. In the case of a Ti-13Nb-13Zr alloy, the adhesive wear contributes to the higher wear rate and better friction behavior. This cold-rolled alloy, having a martensitic microstructure with the lowest hardness, shows the lowest friction coefficient values due to high material transfer from the alloy surface. The lowest friction resistance is observed for the Ti-6Al-4 V alloy with the highest hardness since the dominant wear damage mechanism is abrasion resulting in the low wear rate and material transfer.

effect of initial microstructure on the mechanical properties and fracture mode of the Ti-6Al-4V ELI alloy subjected to the high-pressure torsion (HPT) processing at room temperature and 500 °C was investigated. In this purpose, the four different microstructures (fully lamellar, martensitic, equiaxed and globular microstructures) were developed by the proper heat treatments. The results showed that the application of the HPT processing provided substantial microstructural refinement, independent on the alloy initial microstructure. As a consequence, the alloy hardness, tensile strength and ductility significantly increased. At the same time, the elastic modulus of the HPT-processed alloy is almost 2 times lower as compared to that of the alloy in the initial heat treated state. The obtained improvements strongly depend on the alloy initial microstructure and HPT processing temperature. It was found that the initial martensitic microstructure is beneficial to improve the hardness, tensile and fracture properties. The HPT processing at 500 °C enhanced them more effectively. After the warm HPT processing, alloy with the initial martensitic microstructure exhibited exceptional hardness (455 MPa), high ultimate tensile strength (1546 MPa), high elongation to failure (18.8%) and low elastic modulus (78.6 GPa). Although the alloy with initial fully lamellar microstructure displayed the lowest elastic modulus (68 GPa), the ultrafine and homogeneous (α + β) two-phase microstructure produced by the HPT processing of the alloy with initial martensitic microstructure offered the best combination of the strength-ductility balance and strength-to-elastic modulus ratio (19.8 × 10−3). The complex fracture process, involving transgranular quasi-cleavage and ductile dimple fracture mode, corresponded to the changes in ductility.

In order to optimize and enhance the implant material properties, metallic materials may be modified by severe plastic deformation (SPD) procedures. One of the most attracting SPD methods is high-pressure torsion (HPT), which is method where deformation is obtained mainly by simple shear. In the present study ultrafine-grained titanium (UFG cpTi) and ultrafine-grained Ti-13Nb-13Zr (UFG TNZ) alloy were obtained by high pressure torsion (HPT) under a pressure of 4.1 GPa with a rotational speed of 0.2 rpm up to 5 rotations at room temperature. In order to analyse microstructure of materials before and after HPT process, scanning electron microscope (SEM) was used. The aim of this study was to determine the corrosion resistance of titanium and its alloy after HPT process. Electrochemical measurements were performed in artificial saliva with a pH value of 5.5 at 37°C, in order to simulate the oral environment. The materials were analysed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. All examined materials showed good corrosion resistance, but results indicate that HPT process can improves corrosion resistance. © 2018 The Authors.

Deposits and scales formed on heat transfer surfaces in power plant water/steam circuits have a significant negative impact on plant reliability, availability and performance, causing tremendous economic consequences and subsequent increases in electricity cost. Consequently, the improvement of the understanding of deposition mechanisms on power generating surfaces is defined as a high priority in the power industry. The deposits consist principally of iron oxides, which are steel corrosion products and usually present in colloidal form. Magnetite (Fe3O4) is the predominant and most abundant compound found in water/steam cycles of all types of power plants. The crucial factor that governs the deposition process and influences the deposition rate of magnetite is the electrostatic interaction between the metal wall surfaces and the suspended colloidal particles. However, there is scarcity of data on magnetite surface properties at elevated temperatures due to difficulties in their experimental measurement. In this paper a generalized overview of existing experimental data on surface characteristics of magnetite at high temperatures is presented with particular emphasis on possible application in the power industry. A thorough analysis of experimental techniques, mathematical models and results has been performed and directions for future investigations have been considered. The state-of-the-art assessment showed that for the characterization of magnetite/aqueous electrolyte solution interface at high temperatures acid-base potentiometric titrations and electrophoresis were the most beneficial and dependable techniques which yielded results up to 290 and 200 degrees C, respectively. Mass titrations provided data on magnetite surface charge up to 320 degrees C, however, this technique is highly sensitive to the minor concentrations of impurities present on the surface of particle. Generally, fairly good correlation between the isoelectric point (pH(iep)) and point of ze

Integrity of pipes is typically assessed by testing fracture mechanics specimens, such as compact tensile (CT) or single-edge notched bending (SENB). However, for some pipe dimensions it is not easy or possible to fabricate a specimen conforming to the requirements of standard procedures. A new type of specimen is proposed recently, which can be advantageous for relatively small pipe diameters and axial defects - the pipe ring notch bend specimen - PRNB. In this work, criteria for failure by ductile fracture of PRNB specimens are determined experimentally and by application of micromechanical analysis. The influence of size of the specimen, as well as size and shape of the stress concentrator, is analysed. The results of this study, along with previous authors results, lead to the conclusion that the pipe ring specimens can be applied in integrity assessment of pipes with defects. Also, the benefits of their application include much simpler fabrication and the same material history as the pipe itself. (C) 2017 Elsevier Ltd. All rights reserved.

The enhancement of commercially pure titanium (cpTi) mechanical properties, which is required for its medical application, can be achieved by grain refinement obtained by severe plastic deformation. In addition to mechanical properties improvement, excellent corrosion resistance of ultrafine-grained (UFG) cpTi in contact with human body fluids is required. Therefore, the aim of this study was to estimate electrochemical behavior of UFG cpTi obtained by high pressure torsion (HPT) under a pressure of 7,8 GPa at room temperature and up to 5 rotations. Electrochemical measurements were performed in artificial saliva at 37 degrees C in order to simulate oral environment, since development of UFG cpTi is primarily aimed for dental implant applications. Electrochemical behavior of UFG cpTi was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The obtained results indicate that HPT process, through significant grain size reduction, increases corrosion resistance of cpTi.

Integrity of pipes is typically assessed by testing fracture mechanics specimens, such as compact tensile (CT) or single-edge notched bending (SENB). However, for some pipe dimensions it is not easy or possible to fabricate a specimen conforming to the requirements of standard procedures. A new type of specimen is proposed recently, which can be advantageous for relatively small pipe diameters and axial defects - the pipe ring notch bend specimen - PRNB. In this work, criteria for failure by ductile fracture of PRNB specimens are determined experimentally and by application of micromechanical analysis. The influence of size of the specimen, as well as size and shape of the stress concentrator, is analysed. The results of this study, along with previous authors results, lead to the conclusion that the pipe ring specimens can be applied in integrity assessment of pipes with defects. Also, the benefits of their application include much simpler fabrication and the same material history as the pipe itself. (C) 2017 Elsevier Ltd. All rights reserved.

Significant enhancement of mechanical properties of metallic biomaterials can be achieved by grain refinement obtained by severe plastic deformation. The purpose of this study was to determine metallic ion release from commercially pure titanium (CPTi) and Ti-13Nb-13Zr alloy processed by high pressure torsion (HPT). The materials microstructures, in the initial state and after HPT deformation, were examined by scanning and transmission electron microscopy. The microhardness was determined along the radius of the disc-shaped samples of ultrafine-grained (UFG) CPTi and Ti-13Nb-13Zr alloy in order to evaluate homogeneity of HPT-processed materials. The quantities of released ions were determined using inductively coupled plasma-mass spectrophotometer for samples immersed in artificial saliva at 37 degrees C for 7 days. Also, the effect of artificial saliva pH value on metallic ion release was estimated. Obtained results revealed that the quantities of released ions from UFG CPTi and Ti-13Nb-13Zr alloy obtained by HPT process were higher than the quantities of released ions from CPTi and Ti-13Nb-13Zr alloy produced by traditional casting. This behavior can be explained by the fact that metallic ions are easily released from microstructure with smaller grains achieved by HPT process. (C) 2015 Elsevier Ltd. All rights reserved.

Commercially pure titanium (cpTi) and titanium alloys are the most commonly used metallic biomaterials. Biomedical requirements for the successful usage of metallic implant materials include their high mechanical strength, low elastic modulus, excellent biocompatibility and high corrosion resistance. It is evident that the response of a biomaterial implanted into the human body depends entirely on its biocompatibility and surface properties. Therefore, in order to improve the performance of biomaterials in biological systems modification of their surface is necessary. One of most commonly used method of implant materials surface modification is electrochemical anodization and this method is reviewed in the present work. Aim of the presented review article is to explain the electrochemical anodization process and the way in which the nanotubes are formed by anodization on the metallic material surface. Influence of anodizing parameters on the nanotubes characteristics, such as nanotube diameter, length and nanotubular layer thickness, are described, as well as the anodized nanotubes influence on the material surface properties, corrosion resistance and biocompatibility.

Metallic materials, such as Co-Cr-Mo alloys, are exposed to aggressive conditions in the oral cavity that represents an ideal environment for metallic ion release and biodegradation. The metallic ions released from dental materials can cause local and/or systemic adverse effects in the human body. Therefore, dental materials are required to possess appropriate mechanical, physical, chemical and biological properties. The biocompatibility of metallic materials is very important for dental applications. Accordingly, the aim of this study was to examine metallic ion release and cytotoxicity of Co-30Cr-5Mo cast alloy as the initial phase of biocompatibility evaluation. Determination of the viability of human (MRC-5) and animal (L929) fibroblast cells were conducted using three in vitro test methods: the colorimetric methyl-thiazol-tetrazolium (MTT) test, the dye exclusion test (DET) and the agar diffusion test (ADT). Furthermore, the morphology and growth of the cells were analyzed using scanning electron microscopy (SEM). The obtained results indicated that Co-30Cr-5Mo alloy did not release harmful elements in concentrations high enough to have detrimental effects on human and animal fibroblasts under the given experimental conditions. Moreover, the fibroblast cells showed good adhesion on the surface of the Co-30Cr-5Mo alloy. Therefore, it could be concluded that Co-30Cr-5Mo alloy is a biocompatible material that could be safely used in dentistry.

Metallic biomaterials, which are mainly used for the damaged hard tissue replacements, are materials with high strength, excellent toughness and good wear resistance. The disadvantages of metals as implant materials are their susceptibility to corrosion, the elastic modulus mismatch between metals and human hard tissues, relatively high density and metallic ion release, which can cause serious health problems. The aim of this study was to examine metallic ion release from Co-Cr-Mo alloy in artificial saliva. In that purpose, alloy samples were immersed into artificial saliva with different pH values (4.0, 5.5 and 7.5). After a certain immersion period (1, 3 and 6 weeks) the concentrations of released ions were determined using inductively coupled plasma-mass spectrometry (ICP-MS). The research findings were used in order to define the dependence between the concentration of released metallic ions, artificial saliva pH values and immersion time. The determined released metallic ions concentrations were compared with literature data in order to describe and better understand the phenomenon of metallic ion release from the biocom-patible cobalt-based alloy.

The electrochemical behaviour of the Ti-13Nb-13Zr and Ti-6Al-4V ELI alloys with martensitic microstructures was investigated by polarization and electrochemical impedance spectroscopy (EIS) in Ringers solution. The impedance spectra were interpreted by a two time-constants equivalent circuit. Both investigated alloys showed high corrosion resistance, but the thin and uniform passive film on the Ti-6Al-4V ELI alloy surface was more protective. The inner barrier and outer porous layer were highly resistant and capacitive. However, thicker and more porous passive film on the Ti-13Nb-13Zr alloy surface may be beneficial for osteointegration. The suitable thermomechanical processing improved the corrosion resistance of Ti-13Nb-13Zr alloy. (c) 2014 Elsevier Ltd. All rights reserved.

The effects of microstructural morphology on the fracture behavior of Ti-6Al-4V ELI (extra-low impurity) alloy in two different heat treatment conditions were examined. Alloy was solution treated above (beta ST) and below (alpha + beta ST) beta transus temperature followed by furnace cooling (FC) in order to obtain the fully lamellar and equiaxed microstructures. Tensile and fracture toughness tests were conducted. The crack tip opening displacement (CTOD) and strain distribution near the crack tip were measured on the compact tension (CT) specimen surface by digital stereometric method. The crack propagation resistance (CTOD-R) curves were developed by applying the modified normalization method and critical CTOD values were determined. To identify the microstructural length scale controlling the fracture resistance of this alloy, the crack propagation path and fracture surface morphology were evaluated. It was found that the reduction in the characteristic microstructural dimension of an order of magnitude and significant change in the alpha phase aspect ratio contribute to drastic increase in the tensile properties and decrease in the crack initiation and propagation resistance. The fully lamellar microstructure displays slightly better biocompatibility because of the lower elastic modulus and superior fracture resistance. The enhanced crack propagation resistance of this microstructure is associated with the larger propensity for crack tip tortuousity, due to the coarser microstructural dimensions (lamellar colony size vs. primary alpha grain size). The difference in the crack propagation modes affects the shape and size of the actual crack tip strain distribution. These results were discussed correlating the complex multiple fracture mechanisms with the stress state in two microstructures. (C) 2013 Elsevier Ltd. All rights reserved.

Metallic biomaterials, which are mainly used for the damaged hard tissue replacements, are materials with high strength, excellent toughness and good wear resistance. The disadvantages of metals as implant materials are their susceptibility to corrosion, the elastic modulus mismatch between metals and human hard tissues, relatively high density and metallic ion release, which can cause serious health problems. The aim of this study was to examine metallic ion release from Co-Cr-Mo alloy in artificial saliva. In that purpose, alloy samples were immersed into artificial saliva with different pH values (4.0, 5.5 and 7.5). After a certain immersion period (1, 3 and 6 weeks) the concentrations of released ions were determined using inductively coupled plasma-mass spectrometry (ICP-MS). The research findings were used in order to define the dependence between the concentration of released metallic ions, artificial saliva pH values and immersion time. The determined released metallic ions concentrations were compared with literature data in order to describe and better understand the phenomenon of metallic ion release from the biocom-patible cobalt-based alloy.

Wear and corrosion behaviour of cold-rolled Ti-13Nb-13Zr alloy, with martensitic microstructure, and Ti-6Al-4V ELI alloy, in martensitic and two-phase (alpha + beta) microstructural conditions, was studied in a Ringers solution. The wear experiments were performed at room temperature with a normal load of 40 N and sliding speeds 0.26. 0.5 and 1.0 m/s. The corrosion behaviour was studied at 37 degrees C using open circuit potential-time measurements and potentiodynamic polarization. It was found that Ti-13Nb-13Zr alloy has a substantially lower wear resistance than Ti-6Al-4V ELI alloy in both microstructural conditions. Surface damage extent increases with sliding speed increase and is always smallest for martensitic Ti-6Al-4V ELI alloy with highest hardness. Both alloys exhibit spontaneous passivity in Ringers solution. Corrosion potential values are similar for all three materials. However, Ti-13Nb-13Zr and martensitic Ti-6Al-4V ELI alloys show improved corrosion resistance comparatively to Ti-6Al-4V ELI alloy with (alpha + beta) microstructure. Martensitic Ti-6Al-4V ELI alloy possesses the best combination of both corrosion and wear resistance, although its corrosion resistance is found to be slightly higher than that of the Ti-13Nb-13Zr alloy. (C) 2010 Elsevier Ltd. All rights reserved.

The effect of heat treatment on the microstructure and corrosion behaviour of Zn27Al1 5CuO 02Mg alloy was examined The alloy was prepared by melting and casting route and then thermally processed (T4 regime) Corrosion behaviour of the as-cast and heat treated alloy was studied in 3 5 wt % NaCl solution using immersion method and electrochemical polarization measurements The applied heat treatment affected the alloy microstructure and resulted in increased ductility and higher corrosion resistance of the heat treated alloy Electrochemical measurements of the corrosion rate at the free corrosion potential are in agreement with the results obtained using the weight loss method 2010 Elsevier Ltd All rights reserved

The aim of this study is to compare the tribological behaviour of novel orthopaedic implant alloy Ti-13Nb-13Zr with that of the standard Ti-6Al-4V ELI alloy, available in four different microstructural conditions produced by variations in the heat treatments. The friction and wear tests were performed by using a block-on-disc tribometer in Ringers solution at ambient temperature with a normal load of 20-60 N and sliding speed of 0.26-1.0 m/s. It was found that variations in microstructures produced significant variations in the wear resistance of Ti-6Al-4V ELI alloy. The wear losses of materials solution treated (ST) above the beta transus temperature are significantly lower compared with those of materials ST in the (alpha + beta) phase field and are almost insensitive to applied load and sliding speed. Wear loss of the (alpha + beta) ST Ti-6Al-4V ELI alloy continuously increased as applied load was increased and was highest at the highest sliding speed. The Ti-6Al-4V ELI alloy in all microstructural conditions possesses a much better wear resistance than cold-rolled Ti-13Nb-13Zr alloy. Friction results and morphology of worn surfaces showed that the observed behaviour is attributed to the predominant wear damage mechanism.

An attempt has been made to model the plane-strain fracture toughness, KIc, in Al-Zn-Mg-Cu alloy forgings subjected to overageing. The proposed model, based on the multiple micromechanisms, reveals the quantitative relations between fracture toughness, fraction of all fracture modes and microstructural parameters associated with multiscale-sized second-phase particles and precipitate-free zones. The new model is validated by the present quantitative data of microstructural and fractographic analysis performed along with mechanical tests on hot-forged plates in T73 condition. The relevant parameters changed by the compositional variations were determined in two orientations. It was found that the predicted KIc values represent the tendency of fracture toughness change well. The new model provides better agreement for the case of dominant transgranular fracture mode.

The effects of microstructural parameters associated with the coarse intermetallic phases particles and precipitates on the fracture toughness of the overaged 7000 alloy forgings are investigated. Detailed microstructural and fractographic analysis together with fracture toughness tests are carried out using three alloys with different (Fe + Si) contents. The fracture mechanisms are identified and area fractions of different fracture modes are assessed. The data are then quantitatively correlated to plane-strain fracture toughness, K-Ic, and the bulk microstructural attributes estimated via image analysis. A multiple micromechanism-based model is developed, which accurately describes the dependence of K-Ic on individual microstructural parameters. (C) 2007 Published by Elsevier Ltd.

In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect on crack growth initiation in mismatched welded joints. The single-edged notched bend specimens (precrack length a(0)/W=0.32) were experimentally and numerically analyzed. The coupled micromechanical model proposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18mm). High-strength low-alloyed (HSLA) steel was used as the base metal in a quenched and tempered condition. The flux-cored are-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smooth specimen. The difference in fracture behavior between over- and undermatched welded joints obtained in experimental results was followed by numerical computations of void volume fraction in front of the crack tip.