Graphene has attracted great attention as an ideal reinforcement in Al matrix composites. However, there are still challenges limiting the performance of the composites, such as the homogenous ...distribution of graphene in Al matrices. In this paper, graphene oxide/aluminum (GO/Al) composites with enhanced mechanical properties were fabricated by electrostatic interaction and subsequent powder metallurgy method. Firstly, GO was homogenously coated on the surface of micro-sized spherical aluminum powders by electrostatic interaction between GO and aluminum in water/ethyl alcohol solution with a little HCl acid. Then the mixture of GO/Al composite powders with different GO content (0.15 wt%, 0.3 wt%, 0.6 wt%) were cold compacted and sintered at 580°Cfor 3 h. Compared with unreinforced Al, the composite with only 0.3 wt% GO achieved 73.9% enhancement in ultimate tensile strength, which was up to 167 MPa with elongation of 11.5%. Three points bending test was also carried out for composite with 0.3 wt% GO, and the flexural strength reached 224 MPa. Fractured morphology displayed a ductile break and graphene oxide pull-out was detected at the edges of dimples. It was expected that this work could offer a simple method to prepare graphene reinforced metal matrix composites.
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•GO was simultaneously reduced and adsorbed on Al powders in liquid solution.•Bulk GO/Al composites were fabricated by subsequent powder metallurgy.•The microstructure and mechanical properties were compared and analyzed.•The presence of graphene enhanced its mechanical properties.
Copper–graphite composites which have low friction coefficient can be used as bearing materials in lieu of materials containing lead which cause environmental problems. So far, some methods such as ...powder metallurgy and centrifugal casting have been employed to produce these composites. In this study, friction stir processing (FSP) was used to produce copper–graphite surface composites. Five tools with different pin profile were employed in order to achieve a comprehensive dispersion. Results show that the tool with triangular pin gives rise to a better dispersion of graphite particles. Furthermore, four copper–graphite composites containing different graphite content were prepared using triangular tool through repeating the process passes. Friction and wear performance of the composites were studied using a pin-on-disc tribometer. It was indicated that the friction coefficients of composites were lower than pure annealed copper and decreased with increase in graphite content. The reduction in friction coefficient is due to decrease in metal–metal contact points, originated from the presence of graphite particles as a solid lubricant. Wear loss of the composites was also decreased with increase in graphite content. This is related to change in wear mechanism from adhesive to delamination wear and reduction of friction coefficient.
•Using FSP leads to particles homogenous distribution and prevents formation of clusters.•Friction coefficient is dramatically decreased with increase in graphite content.•Decrease in number of metal to metal contact point leads to drop in friction coefficient.•Wear loss of specimens is decreased with increase in graphite content.•Increase in graphite content increases delamination wear and decreases adhesive wear.
A bulk nanostructured alloy with the nominal composition Cu–30Zn–0.8Al wt.% (commercial designation brass 260) was fabricated by cryomilling of brass powders and subsequent spark plasma sintering ...(SPS) of the cryomilled powders, yielding a compressive yield strength of 950MPa, which is significantly higher than the yield strength of commercial brass 260 alloys (∼200–400MPa). Transmission electron microscopy investigations revealed that cryomilling results in an average grain diameter of 26nm and a high density of deformation twins. Nearly fully dense bulk samples were obtained after SPS of cryomilled powders, with average grain diameter 110nm. After SPS, 10vol.% of twins is retained with average twin thickness 30nm. Three-dimensional atom-probe tomography studies demonstrate that the distribution of Al is highly inhomogeneous in the sintered bulk samples, and Al-containing precipitates including Al(Cu,Zn)–O–N, Al–O–N and Al–N are distributed in the matrix. The precipitates have an average diameter of 1.7nm and a volume fraction of 0.39%. Quantitative calculations were performed for different strengthening contributions in the sintered bulk samples, including grain boundary, twin boundary, precipitate, dislocation and solid-solution strengthening. Results from the analyses demonstrate that precipitate and grain boundary strengthening are the dominant strengthening mechanisms, and the calculated overall yield strength is in reasonable agreement with the experimentally determined compressive yield strength.
In this study, Cu-based nanocomposites using nanographite, graphene nanosheet and carbon nanotubes have been fabricated by flake powder metallurgy. The objective of using different reinforcement ...contents is to assess their effect on the microstructure, density, electrical conductivity and hardness of Cu-based nanocomposites. The results show that the average particle size of the prepared Cu-based nanocomposite powders with reinforced 5 wt.% nanographite, graphene nanosheet and Cu-CNT nanocomposite are 97.8, 94.9 and 49.7 μm, respectively. The lowest final density 6.73 g/cm3 for sintered Cu-5 wt.% CNT nanocomposites, while the highest density value was 8.78 g/cm3 for sintered Cu-0.5 wt.% nanografit nanocomposites. For all nanocomposite groups, increasing the reinforcement content from 0.5 to 5 wt.% results in an decrease in hardness values. The electrical conductivity of the Cu-0.5 wt.% graphene nanosheet was approximately 79 IACs, and this value decreased slightly to 62 IACs with increasing graphene nanosheet content.
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•Cu-based nanocomposites were successfully fabricated by flake powder metallurgy.•Microstructure, density, electrical conductivity and hardness of the samples were studied.•The effects of content and ratio of reinforcement was investigated.
Refractory high-entropy alloys (RHEAs) are promising high-temperature structural materials due to their high melting point and extraordinarily high yield strength. However, their industrial ...application is greatly restricted due to their limited room-temperature ductility. In the present investigation, a ductile and strong single-phase NbTaTiV RHEA was synthesized by powder metallurgy method. Effects of the sintering temperature on the phase formation, microstructural evolution and the mechanical properties of the NbTaTiV RHEA were characterized. The results show that the NbTaTiV RHEA sintered at 1700 °C has an equiaxed single bcc phase microstructure, no obvious porosity and compositional segregation can be observed. The alloy exhibits a relatively high hardness of 510 HV, yield strength of 1.37 GPa, and compressive fracture strength of 2.19 GPa with a high fracture strain of 23% at room temperature. Typical strain softening and steady state flow occur during compressive deformation at high temperatures. During deformation at 1000 °C, the alloy still exhibits high yield strength of 437 MPa with a compression strain over than 40%. The outstanding mechanical properties is mainly attributed to the homogeneous and fine microstructures, and solid solution strengthening effect. It can be concluded that the powder metallurgy is a promising way for preparing ductile RHEAs with outstanding comprehensive mechanical properties.
•Fine and homogeneous microstructures were obtained in the NbTaTiV RHEAs through powder metallurgy.•The P/M NbTaTiV RHEA showed a combined high yield strength of 1.37 GPa and reasonable ductility over 20% at room temperature.•The P/M NbTaTiV RHEA still exhibited high yield strength of 437 MPa at 1000 °C with a compressive strain over than 40%.•The improvement of the compressive strength was caused by the solid solution strengthening and fine-grained strengthening.
•Pure aluminum was reinforced with graphene-platelets by using mechanical milling.•The composites were studied after sintering condition.•Milling time and graphene-platelet enhance the mechanical ...behavior of the composites.
Graphene can be considered as an ideal reinforcement for the production of composites due to its outstanding mechanical properties. These characteristics offer an increased opportunity for their study in the production of metal matrix composites (MMCs). In this research, the studied composites were produced by mechanical alloying (MA). The employed milling times were of 1, 3 and 5h. GNPs were added in 0.25, 0.50 and 1.0wt% into an aluminum powder matrix. Milled powders were cold consolidated and subsequently sintered. Composites were microstructurally characterized with Raman spectroscopy and electron microscopy and X-ray diffraction. The hardness behavior in composites was evaluated with a Vickers micro-hardness test. A homogeneous dispersion of graphene during MA and the proper selection of sintering conditions were considered to produce optimized composites. The obtained results with electron microscopy indicate a homogeneous dispersion of GNPs into the aluminum matrix. Analyses showed GNPs edges where the structure of the graphene layers conserved after MA is observed.
•Cu Ni Si alloy was prepared by hot-pressing sintering.•The sintered microstructure is mainly composed of Ni31Si12 phase and Ni2Si phase.•The Ni2Si phase precipitated after aging treatment was ...fibrous.•The comprehensive properties of the alloy were obviously improved.
In this work, Cu-Ni-Si alloy was prepared by hot-pressing sintering using Cu, Ni, and Si powders as raw material. The alloy was afterwards exposed to solution treatment at 900 °C for 2 h and aging at 450 °C for 4 h. The microstructural analysis revealed that the alloy was mainly composed of the granular Ni31Si12 phase at the grain boundaries and the fine δ-Ni2Si phase inside the grains after hot-pressing sintering. After solution treatment, the Ni2Si phase disappeared completely while a small quantity of Ni31Si12 was still observed. However, there was a large amount of fibrous δ-Ni2Si precipitates after aging. The mechanical properties and electrical conductivity of the alloy were tested as well. After aging, the alloy exhibited the best comprehensive characteristics with the hardness of 248.6 HV and the conductivity of 40% IACS. Therefore, the banded structure of Cu-Ni-Si alloys prepared by powder metallurgy and subjected to aging exerts a positive influence on their properties.
Natural Lignocellulosic Fibers as Engineering Materials—An Overview Monteiro, Sergio Neves; Lopes, Felipe Perissé Duarte; Barbosa, Anderson Paula ...
Metallurgical and materials transactions. A, Physical metallurgy and materials science,
10/2011, Letnik:
42, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Recent investigations on the tensile properties of natural cellulose-based fibers revealed an increasing potential as engineering materials. This is particularly the case of very thin fibers of some ...species such as sisal, ramie, and curaua. However, several other commonly used fibers such as flax, jute, hemp, coir, cotton, and bamboo as well as less known bagasse, piassava, sponge gourde, and buriti display tensile properties that could qualify them as engineering materials. An overview of the strength limits attained by these fibers is presented. Based on a tensile strength
vs
density chart, it is shown that natural fibers stand out as a relevant class of engineering materials.
► A network distribution of TiB whiskers has been successfully fabricated. ► Brittleness, drawback of DRTMCs is overcome by tailoring reinforcement network architecture. ► The composite exhibits a ...superior elongation of 11.8% allied with a strength increment of 74.6%.
As a success to challenge the brittleness of titanium matrix composites (TMCs) fabricated by powder metallurgy (PM), both the ductility and the strength have been significantly improved by tailoring a novel network reinforcement distribution. TiB whiskers are in situ synthesized along the “grain boundaries” of large titanium matrix particles and subsequently formed into a unique network architecture. The experimental results show that the as-sintered 8.5vol.% TiBw/Ti composite with a network microstructure exhibit a superior elongation of 11.8% allied with a strength increment of 74.6%. The significant improvement of ductility can be attributed to the network architecture, the retained large matrix particle and the interpenetrating matrix microstructure, while the superior strengthening effect can be attributed to the network architecture and the branched and dowel-like TiB whiskers.
Thermal aspects are becoming increasingly important for the reliability of the electronic components due to the continuous progress of the electronic industries. Therefore, the effective thermal ...management is a key issue for packaging of high performance semiconductors. The ideal material working as heat sink and heat spreader should have a CTE of (4–8)
×
10
−6
K
−1 and a high thermal conductivity. Metal matrix composites offer the possibility to tailor the properties of a metal by adding an appropriate reinforcement phase and to meet the demands in thermal management.
Copper/SiC and copper/diamond composites have been produced by powder metallurgy. The major challenge in development of Cu/SiC is the control of the interfacial interactions. Silicon carbide is not stable in copper at the temperature needed for the fabrication of Cu/SiC. It is known that the bonding between diamond and copper is very weak in the Cu/diamond composite. Improvements in bonding strength and thermo-physical properties of the composites have been achieved by
•
a vapour deposited molybdenum coating on SiC powders to control interface reactions,
•
using atomized Cu(X) alloys with minor additions of carbide formers, e.g. X
=
Cr, B, to improve the interfacial bonding in Cu-diamond composites.
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