Graphene has a high fracture strength, good ductility and low coefficient of thermal expansion, making it an ideal reinforcement for composite materials. This paper reports on an aluminum-matrix composite reinforced with graphene (graphene/Al) using ball milling and hot-press sintering. The effect of the graphene content on the microstructures, mechanical properties and fracture mechanisms of the composites were investigated. It is shown that 0.25 w/% and 0.5 w/% graphene contents modified with copper are homogeneously dispersed into the aluminum matrix. The composite with the 0.5 w/% graphene content exhibits the highest tensile strength and elongation; its improvement over the unreinforced aluminum matrix is 31.0 % and 30.6 %, respectively. With the increasing graphene content up to 1.0 w/%, the aggregation of graphene in the composite is apparent, seriously reducing the tensile properties. The fracture mechanism of the composites changes from ductile to brittle.
Magnesium-matrix composites reinforced with graphene nanosheets (Mg-Gr) were fabricated using a combination of powder metallurgy and hot rolling. The effects of the graphene-nanosheet content on the microstructures and density of the composites were investigated. It was found that the graphene nanosheets were gradually dispersed in the magnesium matrix with an increasing ball-milling time and a uniform dispersion was achieved after 72 h for the composite with a graphene content of 1.0 % of mass fraction. In addition, no obvious agglomeration of graphene was observed in the as-sintered and as-rolled composites with the graphene contents of up to 1.0 % of mass fraction. A coordinated deformation of multilayer graphene nanosheets occurs with a deformation of the surface grains during the rolling, which may cause a significant reduction in the number of layers of the graphene nanosheets. When increasing the graphene content, the density of the Mg-Gr composites shows an increase. Keywords: magnesium-matrix composites, graphene nanosheets, powder metallurgy Kompoziti s kovinsko osnovo, ki so bili oja~ani z grafitnimi nanoplastmi (Mg-Gr), so izdelani s kombinacijo postopkov metalurgije prahov in metodami vro~ega valjanja. Raziskani so bili vpliv vsebnosti grafitnih nanosov na mikrostrukturo in gostoto kompozitov. Ugotovljeno je bilo, da se grafenske nanoplasti postopoma razpr{ijo v magnezijevo matriko, s pove~anjem~asa krogli~nega mletja. Pri kompozitu z 1,0 % ute`nih odstotkov vsebnosti grafena so dobili enakomerno disperzijo po 72 h mletja. Pri obeh, sintranih in valjanih kompozitih niso opazili nobene o~itne aglomeracije grafena do vsebnosti 1,0 % ute`nih odstotkov grafena. Med valjanjem je isto~asno z deformacijo povr{inskih zrnpotekala usklajena deformacija grafesnkih nanoplasti, kar lahko povzro~i znatno zmanj{anje {tevila grafenskih nanoplasti. Z zvi{evanjem vsebnosti grafena se je pove~evala gostota Mg-Gr kompozitov. Klju~ne besede: kovinski kompoziti, oja~ani z grafenom; grafitne nanoplasti, metalurgija prahov
The microstructure, hardness and tribological properties of hot-pressed Al 7075 matrix composites containing the same SiC nanoparticles and different amounts of graphene were investigated. The results show that the Al-SiC-graphene composites exhibit higher hardness and wear resistance compared with Al-SiC composite and Al 7075 alloy.The friction coefficients decrease significantly with the increase of graphene content in the composites, whereas the limited impact on reducing friction is found on SiC nanoparticles. The dominant wear mechanism of Al-SiC-graphene composites transfers from abrasive wear to delamination wear with the increase of graphene content in the composites. It is believed that the hardness and wear-resistance improvements of the Al-SiC-graphene composites are attributed to the unique strengthening effect as well as the good lubricating efficiency of graphene, which demonstrates that graphene is an ideal filler for aluminum-matrix composites, acting as not only a favorable reinforcement but also an impactful lubricant.
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