Abstract In the present work, a new material design of Ti6Al4V-PEEK hybrid cellular structure with improved wear resistance is proposed. Samples with different dimensions of the open-cells (350, 400, 450, 500 μm) were fabricated by... more
Abstract In the present work, a new material design of Ti6Al4V-PEEK hybrid cellular structure with improved wear resistance is proposed. Samples with different dimensions of the open-cells (350, 400, 450, 500 μm) were fabricated by Selective laser melting (SLM) technology, while Hot pressing (HP) technology was employed to produce Ti6Al4V-PEEK hybrid cellular structures. The tribological tests were performed in Phosphate Buffered Saline solution at 37 ± 2 °C. Results demonstrated that the addition of the biomedical PEEK protected the Ti6Al4V cellular structures, thus improving these hybrid structures wear resistance when increasing the amount of PEEK. The obtained results indicated that the Ti6Al4V-PEEK hybrid cellular structure with the dimensions of the open-cells of 500 μm is a suitable structure for orthopedic implants, with improved properties.
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ABSTRACT Nickel particulate-reinforced aluminum-silicon composites, with 5, 12.5 and 20 wt%Nickel were produced by a hot pressing route. Microstructural characterization showed a uniform distribution of the Nickel particulates in the... more
ABSTRACT Nickel particulate-reinforced aluminum-silicon composites, with 5, 12.5 and 20 wt%Nickel were produced by a hot pressing route. Microstructural characterization showed a uniform distribution of the Nickel particulates in the aluminum-silicon matrix. Ultimate tensile strength and hardness of the composites were found higher than for the aluminum-silicon alloy, while ductility suffered a decrease. Fracture surface analysis showed evidences of load transfer from the matrix to the reinforcement indicating the development of an effective interfacial bonding between Nickel particulates and aluminum-silicon matrix. Energy dispersive spectrometer and X-ray diffraction analyses performed in the particle/matrix interface revealed that it was formed by Al3Ni intermetallic. It was found that the amount of Al3Ni intermetallic has a paramount influence in the composites properties.
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ABSTRACT The aim of this paper was to evaluate the effect of different dispersion methodologies on mechanical properties of the aluminum-silicon (AlSi) composites reinforced by multi-walled carbon nanotubes (MWCNTs) coated with Ni.... more
ABSTRACT The aim of this paper was to evaluate the effect of different dispersion methodologies on mechanical properties of the aluminum-silicon (AlSi) composites reinforced by multi-walled carbon nanotubes (MWCNTs) coated with Ni. Different mixing procedures of MWCNTs with AlSi powder were tested, and AlSi-CNT composites were produced by hot pressing—powder metallurgy technique. The shear tests were performed to get the mechanical properties. Scanning electron microscopy with x-ray energy dispersive spectroscopy analysis and thermal analysis was used to investigate the microstructure of AlSi-CNT composites, interface reactions, and fracture morphology after shear tests. The experimental results proved that an improvement of dispersion of CNTs was achieved by using a combination of different mixing processes.
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ABSTRACT This work is concerned with understanding the influence of reinforcement mechanisms of carbon nanotubes (CNTs) on mechanical, wear, and fatigue tests on an Aluminium-Silicon (AlSi) alloy. The reinforcement mechanism is presented... more
ABSTRACT This work is concerned with understanding the influence of reinforcement mechanisms of carbon nanotubes (CNTs) on mechanical, wear, and fatigue tests on an Aluminium-Silicon (AlSi) alloy. The reinforcement mechanism is presented through the observation of fracture morphology of the different tests. Results of mechanical properties, fatigue life performance and wear loss is presented and discussed. It is shown that the CNTs reinforcement effect is active simultaneously in all previous properties and the reinforcement physical mechanism seems to be essentially due to a reinforcement effect of the interface that seems to be similar in all mentioned mechanical solicitations.
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ABSTRACT The damage of piston rings is attributed first to wear, then to lubrication and fatigue. Their damage may be substantially mitigated by creating a FGM-Functionally Graded Material composite with optimized mechanical and wear... more
ABSTRACT The damage of piston rings is attributed first to wear, then to lubrication and fatigue. Their damage may be substantially mitigated by creating a FGM-Functionally Graded Material composite with optimized mechanical and wear behaviour. The aim of this paper was to produce an AlSi-CNTs functionally graded material (FGM) that can be considered for engine compression piston rings. The AlSi graded composites (reinforced with 0 to 2wt.%CNT FGM approach) was obtained with a new equipment that was designed to produce FGMs by powder metallurgy (PM) processing route. SEM analysis showed that the produced FGMs have a gradual change in %wt. of reinforcement and on mechanical properties. Results of mechanical properties, fatigue limit performance and wear loss are presented and discussed. It is expected that the obtained AlSi-CNTs functionally graded composite developed for piston rings may have a global equilibrium of properties (mechanical, wear, and fatigue) and cost.
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ABSTRACT The aim of this paper was to examine the wear behaviour of a hybrid AlSi-2wt. %CNTs-5wt.%SiCp composite. For comparison purposes the unreinforced AlSi alloy, AlSi-2%wt.CNTs and AlSi-5wt.%SiCp composites were used. A powder... more
ABSTRACT The aim of this paper was to examine the wear behaviour of a hybrid AlSi-2wt. %CNTs-5wt.%SiCp composite. For comparison purposes the unreinforced AlSi alloy, AlSi-2%wt.CNTs and AlSi-5wt.%SiCp composites were used. A powder metallurgy processing route was used to produce the unreinforced AlSi alloy and AlSi composites. Dry reciprocating pin-on-plate wear tests were performed and the results showed that the wear behaviour was improved for all produced composites when compared to the unreinforced AlSi alloy. However the best wear behaviour was achieved in the case of AlSi hybrid composite. This improvement is attributed to the combine effects of both constituent reinforcements. The dominant wear mechanisms were characterized by scanning electron microscopy with X-Ray Energy Dispersive Spectrometry analysis.
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The aim of this work was to study, using the finite element method (FEM), the distribution of thermal residual stresses arising in metal-ceramic dental restorations after cooling from the processing temperature. Three different interface... more
The aim of this work was to study, using the finite element method (FEM), the distribution of thermal residual stresses arising in metal-ceramic dental restorations after cooling from the processing temperature. Three different interface configurations were studied: with conventional sharp transition; one with a 50% metal-50% ceramic interlayer; and one with a compositionally functionally gradated material (FGM) interlayer. The FE analysis was performed based on experimental data obtained from Dynamic Mechanical Analysis (DMA) and Dilatometry (DIL) studies of the monolithic materials and metal/ceramic composites. Results have shown significant benefits of using the 50% metal-50% ceramic interlayer and the FGM interlayer over the conventional sharp transition interface configuration in reduction of the thermal residual stress and improvement of stress profiles. Maximum stresses magnitudes were reduced by 10% for the crowns with 50% metal-50% ceramic interlayer and by 20% with FGM int...
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Aluminum alloys reinforced with ceramics such as silicon carbide (SiC) and alumina (Al2O3) have been conventionally used in order to improve aluminum alloys wear resistance [1]. It has been shown that the wear rate of aluminum alloys... more
Aluminum alloys reinforced with ceramics such as silicon carbide (SiC) and alumina (Al2O3) have been conventionally used in order to improve aluminum alloys wear resistance [1]. It has been shown that the wear rate of aluminum alloys decreases with the addition of SiC [2, 3], mainly due to SiC particle protective effect, preventing the aluminum matrix from suffering wear [4, 5]. Regarding mechanical properties, aluminum alloys reinforced with ceramics are known to exhibit increased strength although presenting decreased elongation to failure [6 - 10]. On the other hand, metallic reinforcements can be interesting alternative reinforcements for aluminum alloys for attaining improved wear performance and at the same time display improved strength and higher ductility than ceramic reinforced composites [6 - 8, 11]. Hybrid metal matrix composites are an interesting class of materials that combine two or more different types of reinforcement in a metallic matrix [1]. In these composites, ...
The bulk Functionally Graded Materials (FGM’s) is becoming na interesting field of research. The use of the Incremental Melting and Solidification Process (IMSP) in order to produce FGM’s seems to have the potential to be used to produce... more
The bulk Functionally Graded Materials (FGM’s) is becoming na interesting field of research. The use of the Incremental Melting and Solidification Process (IMSP) in order to produce FGM’s seems to have the potential to be used to produce high performance components. In this process a controlled liquid bath is maintained at the top of the component where new materials are added changing the components composition. Thus, a functionally graded material sis obtained with a varying composition along one direction of the component. This paper deals with influence of the speed displacement rates between heating coil and mould on the microstructure of different Cu-Ag alloys. Hardness and phase distribution, along the main casting axis, were assessed. Interface formation and its characteristics were also analysed. Results demonstrate that the speed rate has an influence on chemical composition gradation and phase distribution along the component. Mechanical properties, as obtained by hardnes...
Hybrid aluminium composites can substantially improve matrix material properties by adding reinforcements with different natures (ceramics and metals). It is known that Silicon Carbide particles (SiCp) used as reinforcement in an... more
Hybrid aluminium composites can substantially improve matrix material properties by adding reinforcements with different natures (ceramics and metals). It is known that Silicon Carbide particles (SiCp) used as reinforcement in an aluminium alloy matrix improves mechanical properties and also wear resistance. This happens in expense of ductility, which substantially decreases. Combining ceramic and metallic reinforcements (metallic reinforcements such as steel, nickel and titanium alloys) it is possible to increase composites mechanical properties without loss of ductility - due to the different reinforcement mechanisms in the matrix. SiCp improves mechanical properties mainly due to mismatch in the coefficient of thermal expansion during cooling after processing (causing residual stresses in the aluminium matrix) and due to restriction of slipping of grains causing an additional deformation constraint. On the other hand metallic reinforcements can mainly increase mechanical (includi...
Carbon nanotubes (CNT’s) incorporation in metal matrix composites (MMC’s) is hampered by the development of attractive van der Waals forces, which lead to the formation of CNT agglomerates. Most of the existing processes used to fabricate... more
Carbon nanotubes (CNT’s) incorporation in metal matrix composites (MMC’s) is hampered by the development of attractive van der Waals forces, which lead to the formation of CNT agglomerates. Most of the existing processes used to fabricate these MMC lead to the formation of these agglomerates. Therefore, a detailed characterization of CNT agglomerates size and dispersion can enlighten their influence in the composite strength. This work presents a comprehensive statistical study, quantifying agglomerates by size, for different CNT contents in the composite, in order to relate these factors with the obtained tensile strength of the composite.
ABSTRACT CNT incorporation in metal matrix composites is hampered by the development of attractive van der Waals forces, which lead to the formation of CNT agglomerates.. Therefore, a detailed quantification and characterization of CNT... more
ABSTRACT CNT incorporation in metal matrix composites is hampered by the development of attractive van der Waals forces, which lead to the formation of CNT agglomerates.. Therefore, a detailed quantification and characterization of CNT agglomerates and consequently CNT dispersion can enlighten their influence in composites strength. This work presents a comprehensive study, quantifying agglomerates by size, for three different composites (2, 4 and 6 CNT vol. %), made with an aluminum-silicon matrix by a powder metallurgy route. From the obtained experimental data, an empirical model that attempts to predict the tensile strength of these composites from CNT agglomerates analysis is presented.
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ABSTRACT This study is concerned with the influence of Nickel, as reinforcement, in an aluminum–silicon (AlSi) alloy when regarding wear behavior. For these composites, the effect of Ni content, in the tribopair performance, was... more
ABSTRACT This study is concerned with the influence of Nickel, as reinforcement, in an aluminum–silicon (AlSi) alloy when regarding wear behavior. For these composites, the effect of Ni content, in the tribopair performance, was evaluated. For this purpose, the pin but also the counterface wear behavior was analyzed. Nickel particulate reinforced aluminum–silicon (AlSi) composites, with 5, 12.5 and 20 wt.% Ni were produced by a hot-pressing route. Microstructural characterization showed a uniform distribution of the Ni particulates in the AlSi matrix. EDS and XRD analyses revealed that the particle/matrix interface was formed by Al3Ni intermetallic. Reciprocating pin-on-plate wear tests were performed with AlSi and AlSi–Ni pins against a gray cast iron (GCI) counterface. It was observed that the wear behavior of the AlSi–Ni/GCI tribopair is improved when compared with the AlSi/GCI system.
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ABSTRACT The present work is concerned with the ability of the incremental melting and solidification process to be used in a controlled way to produce functionally graded materials in industrial environments. For this purpose, the... more
ABSTRACT The present work is concerned with the ability of the incremental melting and solidification process to be used in a controlled way to produce functionally graded materials in industrial environments. For this purpose, the influence of the main process parameters, namely relative mould/coil rate and melt temperature, is evaluated in relation to the obtained final component chemical composition gradient. Several graded components of Cu–Sn alloys were produced. The effect of the process parameters on the final component gradient was quantified. It was verified that both the melt temperature and the relative mould/coil rate play a similar role in final component chemical composition gradient. Predictive equations for the gradient, namely the extension of chemical composition gradient zones, are proposed based on the two studied variables.
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ABSTRACT Au-50%Cu (at. %) alloy presents the shape memory effect (SME), which is dependent of the solid state transformation that happens during heating, after the introduction of an internal stress in the quenched state. The solid state... more
ABSTRACT Au-50%Cu (at. %) alloy presents the shape memory effect (SME), which is dependent of the solid state transformation that happens during heating, after the introduction of an internal stress in the quenched state. The solid state phase transformation temperatures were determined by means of Differential Thermal Analysis (DTA), both in heating and cooling cycles. With the obtained DTA results, a sequence of high temperature X-ray diffraction (XRD) experiments were made, in order to confirm the presence of the solid state phase transformations and to determine their stable crystal structure and lattice parameters. These XRD results were compared with those obtained from the literature. The displacements of the lattice parameters were determined, for each equilibrium phase, for measurements at room temperature and at high temperature. The characteristics of the quenched samples were also studied in order to determine the phase transformations that are responsible for the shape memory effect in this alloy.
ABSTRACT Friction stir welding (FSW) has been widely used to metals with moderate melting temperatures, primarily Al alloys. Recently, tool materials that withstand high stresses and temperatures necessary for FSW of materials with high... more
ABSTRACT Friction stir welding (FSW) has been widely used to metals with moderate melting temperatures, primarily Al alloys. Recently, tool materials that withstand high stresses and temperatures necessary for FSW of materials with high melting temperatures have been developed. In the present Study tungsten carbide (WC) was used for FSW of dissimilar monel 400 alloy and 316 stainless steel, and a defect-free weld was successfully produced. Microstructural characteristics, and mechanical properties in the weld were examined. The work included microstructure examination, microhardness, tensile and fatigue tests of all joints. This study shows that the friction stir welded dissimilar joint present better mechanical properties when compared with each base material. Microhardness and tensile strength increased by more than 30% and 20%, respectively, as compared to base metal.
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Functionally graded nanocomposite thin films (2D-FGM), of sub-micrometric thickness, were co-deposited from austenitic stainless steel (316L (AISI)) and poly(tetrafluoroethylene) targets by r.f. magnetron sputtering. All the deposition... more
Functionally graded nanocomposite thin films (2D-FGM), of sub-micrometric thickness, were co-deposited from austenitic stainless steel (316L (AISI)) and poly(tetrafluoroethylene) targets by r.f. magnetron sputtering. All the deposition parameters were kept constant except for the electrical characteristics applied to polymeric target. XPS revealed in the films fluorine contents between 0 and 60 at%. The TEM analysis revealed the evolution towards a nanocomposite structure with an increase in fluorine content (from 0 to 20 at%). For the higher fluorine contents the formation of a ceramic phase, FeF2, is the main structural feature. The hardness is higher for the films with the lowest fluorine concentration due to higher chromium carbides content. The residual stresses of the 2D-FGM are essentially compressive with values up to 2.2 GPa. The values of the friction coefficient of the nanocomposite thin films are in the range of 0.66-0.71, an exception is for the highest fluorine content where the value is 0.31.
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ABSTRACT This study is concerned with the influence of sintering stage duration on the interface load transfer capacity between NiTi fibres and AlSi matrix alloy and thus in the final composite strength. Short-fibre-NiTi/AlSi composites... more
ABSTRACT This study is concerned with the influence of sintering stage duration on the interface load transfer capacity between NiTi fibres and AlSi matrix alloy and thus in the final composite strength. Short-fibre-NiTi/AlSi composites were produced by a pressure-assisted sintering process, under vacuum, for sintering stages of 20, 25 and 60min. All the obtained composites, with different sintering stages, have shown the occurrence of load transfer from the matrix to fibres, indicating the development of an effective interface between fibre and matrix. Performed shear tests have shown a decaying of shear strength with increasing sintering stage, in the selected range of sintering times, with the lowest sintering time leading to higher properties. It was also concluded that with increasing sintering stage, the interface volume around the fibres increases and the load transfer capacity decreases.