Fatih Toptan

Influence of the processing route of porcelain/Ti-6Al-4V interfaces on shear bond strength

This study aims at evaluating the two-fold effect of initial surface conditions and dental porcelain-to-Ti-6Al-4V alloy joining processing route on the shear bond strength. Porcelain-to-Ti-6Al-4V samples were processed by conventional furnace firing (porcelain-fused-to-metal) and hot pressing. Prior to the processing, Ti-6Al-4V cylinders were prepared by three different surface treatments: polishing, alumina or silica blasting. Within the firing process, polished and alumina blasted samples were subjected to two different cooling rates: air cooling and a slower cooling rate (65°C/min). Metal/porcelain bond strength was evaluated by shear bond test. The data were analyzed using one-way ANOVA followed by Tuckeys test (p<0.05). Before and after shear bond tests, metallic surfaces and metal/ceramic interfaces were examined by Field Emission Gun Scanning Electron Microscope (FEG-SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS). Shear bond strength values of the porcelain-to-Ti-6Al-4V alloy interfaces ranged from 27.1±8.9MPa for porcelain fused to polished samples up to 134.0±43.4MPa for porcelain fused to alumina blasted samples. According to the statistical analysis, no significant difference were found on the shear bond strength values for different cooling rates. Processing method was statistically significant only for the polished samples, and airborne particle abrasion was statistically significant only for the fired samples. The type of the blasting material did not cause a statistically significant difference on the shear bond strength values. Shear bond strength of dental porcelain to Ti-6Al-4V alloys can be significantly improved from controlled conditions of surface treatments and processing methods.

Corrosion and tribocorrosion behavior of Ti-B4C composite intended for orthopaedic implants.

Poor wear resistance of titanium is a major concern since relative movements due to the cyclic loads in body environment cause wear between the bone and the implant material leading to detachment of the wear debris and release of metal ions due to the simultaneous action of corrosion and wear, defined as tribocorrosion. In order to increase the tribocorrosion resistance, Grade 2 Ti matrix 24vol% B4C particle reinforced composites were processed by hot pressing. Corrosion behaviour was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization in 9g/L NaCl solution at body temperature. Tribocorrosion tests were performed under open circuit potential, as well as under potentiodynamic polarization using a reciprocating ball-on-plate tribometer. Results suggested that the addition of B4C particles provided lower tendency to corrosion and lower corrosion kinetics under sliding, along with significantly reduced wear loss, mainly due to the load carrying effect given by the reinforcement particles.

Tribocorrosion behavior of bio-functionalized highly porous titanium

Titanium and its alloys are widely used in orthopedic and dental implants, however, some major clinical concerns such as poor wear resistance, lack of bioactivity, and bone resorption due to stress shielding are yet to be overcome. In order to improve these drawbacks, highly porous Ti samples having functionalized surfaces were developed by powder metallurgy with space holder technique followed by anodic treatment. Tribocorrosion tests were performed in 9g/L NaCl solution using a unidirectional pin-on-disc tribometer under 3N normal load, 1Hz frequency and 4mm track diameter. Open circuit potential (OCP) was measured before, during and after sliding. Worn surfaces investigated by field emission gun scanning electron microscope (FEG-SEM) equipped with energy dispersive X-ray spectroscopy (EDS). Results suggested bio-functionalized highly porous samples presented lower tendency to corrosion under sliding against zirconia pin, mainly due to the load carrying effect given by the hard protruded oxide surfaces formed by the anodic treatment.

Tribocorrosion behaviour of hot pressed CoCrMo−Al2O3 composites for biomedical applications

Abstract Alumina/alumina wear couple can lower the wear rates and thus metallic ion releasing on load bearing metallic implant materials. However, the low fracture toughness of ceramics is still a major concern. Therefore, the present study aims to process and to triboelectrochemically characterise the 5 and 10 vol.-%Al2O3 reinforced CoCrMo matrix composites. Corrosion and tribocorrosion behaviour of the composites were investigated in 8 g L−1 NaCl solution at body temperature. Corroded and worn surfaces were investigated by a field emission gun scanning electron microscope equipped with energy dispersive X-ray spectroscopy. After tribocorrosion experiments, wear rates were calculated using a profilometer. Results suggest that Al2O3 particle addition decreased the tendency of CoCrMo alloy to corrosion under both static and tribocorrosion conditions. However, no significant influence on the corrosion and wear rates was observed in composites mainly due to increased porosity and insufficient matrix/reinforcement bonding.

Glycerol/PEDOT:PSS coated woven fabric as a flexible heating element on textiles

A polyamide 6,6 (PA66) fabric pre-treated with a double barrier dielectric (DBD) atmospheric plasma in air was coated with 1 and 5 layers of an intrinsically conducting glycerol-doped PEDOT:PSS polymer (PEDOT:PSS + GLY) with the final objective of developing a cost-competitive and temperature controllable flexible-heating element to be used in clothing encapsulated between an outer and an inner separator layer in order to provide heat-reflecting properties and uniform temperature distribution, respectively. FTIR, DSC, TGA, SEM, EDS, XRD and DMA analyses show significant changes in morphology, chemistry, enthalpy, crystallinity and glass transition temperature confirming that PEDOT:PSS and glycerol are not only spread over the PA66 yarn surfaces but are dispersed in the bulk facilitating relaxation and increasing structure and chain flexibility. Electrochemical and electrical resistivity (ρ) measurements confirm that the plasma treated PA66 coated with 5 layers of PEDOT:PSS + GLY presents the highest stability, resistance and capacitive behaviour, and the best capability of storing electrical energy. This configuration needs only 7.5 V to induce a temperature change up to 38 °C at a current density of 0.3 A g−1. The desired temperature is easily adjustable as a function of the applied voltage and by the number of coated layers of PEDOT:PSS + GLY. Despite the need to improve the uniformity of the coating thickness on the fabric for uniform heat generation, the observed results are quite impressive since they can be compared to the temperature obtained in carbon nanotube composites using similar voltages. This cost-competitive, safe, highly flexible and stable thermoelectric fabric has potential for use in large area textiles as a heating element in a wide range of applications such as garments, carpets, blankets and automotive seats.

Improved tribocorrosion performance of bio-functionalized TiO₂ nanotubes under two-cycle sliding actions in artificial saliva

After insertion into bone, dental implants may be subjected to tribocorrosive conditions resulting in the release of metallic ions and solid wear debris, which can induce to peri-implant inflammatory reactions accompanied by bone loss, and ultimately implant loosening. Despite the promising ability of TiO2 nanotubes (NTs) to improve osseointegration and avoid infection-related failures, the understanding of their degradation under the simultaneous action of wear and corrosion (tribocorrosion) is still very limited. This study aims, for the first time, to study the tribocorrosion behavior of bio-functionalized TiO2 NTs submitted to two-cycle sliding actions, and compare it with conventional TiO2 NTs. TiO2 NTs grown by anodization were doped with bioactive elements, namely calcium (Ca), phosphorous (P), and zinc (Zn), through reverse polarization anodization treatments. Characterization techniques such as scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and scanning transmission electron microscopy (STEM), were used to characterize the films. Tribocorrosion tests were carried out in artificial saliva (AS) by applying two cycles of reciprocating sliding actions. The open circuit potential (OCP) was monitored before, during, and after both cycles of sliding, during which the coefficient of friction (COF) was calculated. The resulting wear scars were analyzed by SEM and EDS, and wear volume measurements were performed by 2D profilometry. Finally, the mechanical features of TiO2 NTs were accessed by nanoindentation. The results show that bio-functionalized TiO2 NTs display an enhanced tribocorrosion performance, ascribed to the growth of a nano-thick oxide film at Ti/TiO2 NTs interface, which significantly increased their adhesion strength to the substrate and consequently their hardness. Furthermore, it was discovered that during tribo-electrochemical solicitations, the formation of a P-rich tribofilm takes place, which grants both electrochemical protection and resistance to mechanical wear. This study provides fundamental and new insights for the development of multifunctional TiO2 NTs with long-term biomechanical stability and improved clinical outcomes.

Microstructural Characterization of Biofunctionalized Titanium Foams.

This study was supported by The Calouste Gulbenkian Foundation through “Programa de Mobilidade Academica para Professores”, “Acoes Integradas Luso-Francesas 2014 - ref.a: TC-12_14”, and the Portuguese Foundation for Science and Technology (FCT–Portugal), under the project EXCL/EMS-TEC/0460/2012.

Dry sliding wear behaviour of Ti-TiB-TiNx in-situ composite synthesised by reactive hot pressing

Ti and its alloys are attractive materials for a variety of fields; however, a major problem of Ti and its alloys is their poor wear resistance. It is known that reinforcing Ti with hard ceramic phases can substantially improve the wear resistance. Thus, Ti-TiB-TiNx in-situ metal matrix composites were synthesised by reactive hot pressing utilising Ti/BN powder blends with 23:1 Ti:BN weight ratio. Ball-on-plate reciprocating dry sliding wear tests were performed against a 10 mm of alumina ball under 10 N normal load, at a frequency of 1 Hz, and with the total stroke length of 3 mm during 1,800 s. Results showed that the total wear volume loss was significantly decreased on the composite (11.4 ± 2.0 × 10−3 mm3) as compared to the unreinforced Ti (40.9 ± 4.2 × 10−3 mm3) due to the strengthening effect of the in-situ reinforcing phases.

A comparative study on the dry sliding wear behaviour of nitrocarburised, gas nitrided, fluidised-bed nitrided, and plasma nitrided plastic mould steel

Plastic injection moulds suffer wear due to the relative movements of the mould parts and the polymeric material flow which is often reinforced by hard abrasive fibres or whiskers. Several studies were performed on the wear behaviour of diverse nitrided surfaces; however, comparative studies are needed. The present study aims to compare the dry sliding wear behaviour of nitrocarburised, gas-nitrided, fluidised-bed nitrided, and plasma-nitrided Impax Supreme (equivalent to AISI P20) pre-hardened plastic mould steel. The wear tests were performed against AISI 4140 pins under 100 N normal loads, with the total stroke length of 10 mm, the frequency of 1.5 Hz, and the total sliding distance of 400 m. After tests, worn surfaces and wear debris were microstructurally and chemically characterised and the wear rates were calculated. Results suggested that all samples presented mainly combination of adhesive and abrasive wear during the run-in period of sliding (severe wear), and mainly oxidative wear during the steady-state of (mild wear). Although no significant difference was observed between the treated samples, plasma-nitrided samples presented the lowest wear rate as mean values.

Corrosion and tribocorrosion behavior of Ti-TiB-TiNx in-situ hybrid composite synthesized by reactive hot pressing

Ti and its alloys are attractive materials for variety of fields, including biomedical implants, however, the wear behavior is yet to be improved. In the present work, Ti-TiB-TiNx in-situ metal matrix composites were synthesized by reactive hot pressing using a Ti-BN powder blend. Corrosion behavior was investigated in 9g/L NaCl solution at 37°C by performing potentiodynamic polarization and electrochemical impedance spectroscopy. Tribocorrosion behavior was investigated using reciprocating tribometer, against an alumina ball, under 1 and 10N normal load, 1 and 2Hz frequency, in 9g/L NaCl solution at 37°C. Results suggested that TiB and TiNx in-situ phases did not deteriorate the corrosion behavior of Ti but significantly improved the tribocorrosion behavior under 1N.