FG Metallkunde und Werkstofftechnik
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Institute
Tribological Study of Metals
(2021)
Wear is mass loss of a surface by abrasive, rolling, beating, scratching, chemical, and/or thermal stress.
This usually undesirable change in the surface is one of the main causes of component damage and the associated failure of machinery and equipment. The reduction of wear is therefore an essential way to increase the lifetime of machines and equipment and thus save costs and raw materials. In addition to the immense economic importance, the safety aspect also plays a decisive role in wear research. The failure of components due to wear sometimes has serious consequences, for example in automotive, aviation or rail traffic applications.
Tribology is an interdisciplinary subject area for the optimization of mechanical technologies as well as materials and surfaces by reducing friction and wear-related energy and material losses. Therefore, it is important to identify and characterize the different wear mechanisms to find methods of resolution for increasing the wear resistance of materials and components.
In order to create alloys with exceptional properties for orthopedic uses, this study focuses on the impact of zirconium (Zr) content on the structural, electrochemical, and tribological qualities of nanostructured Ti–25Nb-xZr [x = 5, 10, 15, 20, 25, and 30 atomic (at.) %] alloys. The structural evolution was investigated using XRD and SEM techniques. The mechanical characteristics of the produced alloys, including Vickers hardness and Young's modulus, were measured. In addition, the corrosion tests were performed using the OCP, EIS, and PD methods in Ringer's solution within the independent pH range at 37 °C. A ball-on-disc tribometer was used to investigate the tribological behavior of the alloys under various loads and wet conditions using the Ringer solution. It has been verified that Zr content (at. %) in the alloys had an impact on their morphologies, structural evolution, and mechanical characteristics. According to the morphological analysis, the particle and crystallite size decreases with increasing Zr content. Young's modulus and Vickers hardness show the same tendency. The EIS data demonstrated that a single passive film formed on the alloy surfaces, and the addition of Zr enhanced the corrosion resistance of the passive films. The polarization curves demonstrate that the alloys had low corrosion current densities and large passive areas without the passive films disintegrating. Likewise, the inclusion of Zr resulted in a reduction in the corrosion and passive current densities values. All of these results suggested that the titanium alloys exhibit a more noble electrochemical activity caused by Zr. From the tribological perspective, it was found that the friction coefficient of the alloys reduced with increasing Zr content.
This study investigates the in vitro biocompatibility, corrosion resistance, and adhesion strength of a gas abrasive-treated Ti6Al4V alloy, alongside microplasma-sprayed titanium and tantalum coatings. Employing a novel approach in selecting microplasma spray parameters, this study successfully engineers coatings with tailored porosity, roughness, and over 20% porosity with pore sizes up to 200 μm, aiming to enhance bone in-growth and implant integration. This study introduces an innovative methodology for quantifying surface roughness using laser electron microscopy and scanning electron microscopy, facilitating detailed morphological analysis of both the substrate and coatings. Extensive evaluations, including tests for in vitro biocompatibility, corrosion resistance, and adhesive strength, revealed that all three materials are biocompatible, with tantalum coatings exhibiting superior cell proliferation and osteogenic differentiation, as well as the highest corrosion resistance. Titanium coatings followed closely, demonstrating favorable osteogenic properties and enhanced roughness, which is crucial for cell behavior and attachment. These coatings also displayed superior tensile adhesive strengths (27.6 ± 0.9 MPa for Ti and 28.0 ± 4.9 MPa for Ta), surpassing the ISO 13179-1 standard and indicating a robust bond with the substrate. Our findings offer significant advancements in biomaterials for medical implants, introducing microplasma spraying as a versatile tool for customizing implant coatings, particularly emphasizing the superior performance of tantalum coatings in terms of biocompatibility, osteogenic potential, and corrosion resistance. This suggests that tantalum coatings are a promising alternative for enhancing the performance of metal implants, especially in applications demanding high biocompatibility and corrosion resistance.
The aim of the current study is to evaluate the effect of iron content (0, 2, 4, 6 and 10 wt%) on the structural, tribological and photocatalytical properties of a nanostructured ternary alloy Ti-6Al-XFe, prepared by high energy milling. The alloys’ characteristics such as lattice parameters, powder morphologies, surface roughness, relative density/porosity, and microhardness, were evaluated using X-ray diffraction (XRD), scanning electron microscope (SEM), surface profilometry, porosimeter and micro durometer, respectively. The W-H method was utilized to determine the crystallite size. Micro strain was also calculated, which is produced in the lattice due to the diffusion of iron atoms. The photocatalytical characterization was conducted by measuring their absorbance as a function of time using spectrophotometer of visible and ultraviolet light in the wavelength range of 500–800 nm. The tribological characterization was performed using an oscillating tribometer under wet conditions, simulating the human body environment using Phosphate Buffered Saline (PBS) solution with neutral pH 7.4, under different applied loads of 2, 6 and 10 N, respectively. Results showed that the addition of Fe has a significant effect on the structural properties of the developed alloys. The lattice parameter (aα) decreased with increasing Fe content from 2.9493 Å (0 wt% Fe) to 2.9491 Å (10 wt% Fe), while the average grain size increased considerably from 6.965 nm (0 wt% Fe) to 44.42 nm (10 wt% Fe). The wear test results showed that, friction coefficient and wear rate considerably decreased due to the formation of protective films such as TiO2. The photocatalytical characterization showed that, the degradation of methylene blue (MB) increased with increasing Fe content. The Ti-6Al-4Fe -catalyst gave the best degree of degradation of 90.76% within 60 min, which meant that the decolorization process could be operated rapidly at a relatively low cost without UV irradiation.
For over two decades, vascular stents have been widely used to treat clogged vessels,serving as a scaffold to enlarge the narrowed lumen and recover the arterial flow area. High-purityoligocrystalline austenitic steel is usually applied for the production of stents. Despite the popularityand benefit of stenting, it still may cause serious clinical adverse issues, such as in-stent restenosisand stent fracture. Therefore, the study of the mechanical properties of stents and in particularthe prediction of their life cycles are in the focus of materials research. In our contribution, withinthe finite element method, a two-scale model of crack initiation in the microstructure of stents iselaborated. The approach is developed on the basis of the physically based Tanaka–Mura model(TMM), considering the evolution of shear bands during the crack initiation phase. The model allowsfor the analysis of the microstructure with respect to the life cycles of real materials. The effects ofdifferent loading conditions, grain orientation, and thickness of the specimen on Wöhler curves wereanalysed. It was found that the microstructural features of oligocrystals are very sensitive to differentloading conditions with respect to their fatigue behaviour and play a major role in fatigue crackinitiation. Different grain-orientation distributions result in qualitative and quantitative differencesin stress distribution and in the number of cycles for crack initiation. It was found that presence ofa neutral zone in the cut-out of the microstructure under three-point-bending loading conditionschanges the qualitative and quantitative patterns of stress distribution and affects the number ofcycles for crack initiation. It was found that under both tensile and bending loading conditions,thicker specimens require more cycles for crack initiation. The Wöhler curves for crack initiation inoligocrystalline microstructures of stents could be compared with the ones in the experiment, takinginto account that for high cyclic fatigue (HCF), typically, more than 70% of the cycles refer to crackinitiation. The developed numerical tools could be used for the material design of stents
A necklace structure composed of fine grains formed by dynamic recrystallization was uncommonly observed at the pre-existing grain boundaries during the hot compression of a BCC Fe-25Al-1.5Ta alloy containing C14 - (Fe, Al)2Ta Laves phase precipitates. Two possible mechanisms for necklace formation were proposed; particle-stimulated nucleation and grain boundary bulging, depending on whether the original grain boundaries are occupied by C14 particles, or they are free of them. Recrystallization was initiated preferentially around the clusters of large particles at the boundaries containing particles. In contrast, the bulging of the original grain boundaries by strain-induced boundary migration was observed as a preliminary stage for necklace formation at the particle-free boundaries. The necklace structure expanded into the deformed volume in such a way that low-angle subgrain boundaries decorating the necklace layers transformed into grains with increasing deformation strain.
Titanium (Ti)-based alloys with only a β-phase have attracted academic and industrial interest for orthopedic application, due to their close properties to those of tissues. The current study aims to investigate the effect of milling time (2 h, 6 h, 12 h and 18 h) on the nanostructured ternary alloy Ti-25Nb-25Zr prepared by high energy milling, on its structural, physical and tribological behaviors. The alloys’ characteristics such as relative density/porosity, surface roughness, were evaluated using XRD, SEM, surface profilometry, and microdurometer, respectively. The tribological characterization was done using an oscillating tribometer under wet conditions, simulating the human body environment. Results showed that the crystallite and mean pore size reduced with increasing milling time, with the smallest values of 26 nm and 40 µm, respectively after 18 h. Structural characterization shows that the amount of the β-Ti phase increased with increasing milling time, resulting in spherical morphology and texturing of the synthesized alloys. The milled alloys' structural evolution and morphological changes were sensitive to their milling times. Also, the relative density, Young’s modulus and hardness, increased due to grain size decreased with increasing milling time. Tribological results showed that the effect of milling has a significant effect on both nanomaterial formation and friction-wear behavior of the alloys. The results showed that, friction coefficient and wear rate significantly decreased due to the increased formation of protective films such as TiO2, Nb2O5 and ZrO2 phases. The wear mechanism of the Ti-25Zr-25Nb system was dominated by abrasion wear accompanied by adhesion wear.
In this work was prepared α-Al2O3 alloys from laboratory aluminum oxide powder that was milled for different periods of time and sintered at a temperature of 1450 °C. The difference between the prepared samples was studied using several experimental measurement techniques, including X-ray diffraction, scanning electron microscopy and measurement of physical and mechanical properties. Moreover, the effect of milling time on the formation and sintering of alpha-alumina, by milling the mixture at different times using high energy crushing technique was studied. An influence of milling time on density, open spaces and microstructure of the samples was analyzed. The obtained results showed that longer milling duration led to alloys with higher hardness (H) and modulus of elasticity (E). This improvement is due to lower porosity and corresponding higher density at high temperatures. A noticeable decrease in the size of the particles with the increase of the milling time led to an increase in the lattice parameter accompanied by a decrease in defects and ionic voids. The percentage of pores reached 0.04 % within 24 h of grinding after it was approximately 0.20 %, while the density reached 96 % after the same highest grinding time. Tests showed that the value of friction coefficient decreases, while it increases with the increase in the applied pressure force and this was confirmed by SEM images of the samples. the main factor to reduce friction is the increase in grinding time, regardless of the value of the applied load. The results showed that the Al2O3 alloy applied to it with a load of 2 N and milled for 24 h had a minimum value of 1.94 µm3 wear volumes and a wear rate of 1.33 (µm3∙N−1∙µm−1). The sample milled for 24 h showed the best result, characterized by the lowest wear size, specific wear rate and the highest hardness with extraordinary density of 96 %, which is important in the field of biomaterials applications.
The main focus of this work is to investigate the impact of varying milling times (2 to 18 h) on the structural and mechanical properties of the developed Ti-Nb-Mo alloy. The morphology, phase composition, microstructure, and mechanical behavior of milled and sintered Ti-25Nb-25Mo alloy samples were characterized systematically using x-ray diffraction, scanning electron microscope, optical microscope, and Vicker microhardness. It was noted that the quantity of the β-Ti phase increased as the milling time increased. After 12 h of milling, the synthesized alloys exhibited a spherical morphology and texture with homogeneous distribution. The milled alloys' structural evolution and morphological changes were found to be dependent on their milling duration. Morphological analysis revealed that the crystallite size and mean pore size decreased when the milling duration increased, reaching minimum values of 51 nm and < 1 μm, after 12 and 18 h respectively. As the milling time increased, the grain size decreased, resulting in an increase in density, microhardness, and elastic modulus. Ti-25Nb-25Mo will presents good anti-wear ability and higher resistance to plastic deformation due to enhanced mechanical characteristics (H/E, and H3/E2). Hence, the developed Ti-25Nb-25Mo alloys with reduced elastic modulus and desirable mechanical properties were found to be a promising option for biomedical applications.