Development of graphene-reinforced aluminum and copper based innovative materials production by powder metallurgy

In this study, it is aimed that few-layered graphene (FLG) synthesized by electric arc discharge (EAD) was reinforced to Al-Cu, Al-Zn and Cu based matrix by powder metallurgy (P/M) and FLG reinforced Al-Zn and Cu based composites and Al-Cu and Al-Zn based functionally graded innovative materials, investigating the structural, mechanical and tribological properties of these materials. For this purpose, firstly, graphene was produced with few layers and high purity by EAD. The FLG, which is used as a reinforcement material, is added to Al-Cu and Al-Zn based matrix at various amounts (0-0.1-0.2-0.3-0.5-0.7 wt%) by mechanical alloying (MA). The produced FLG reinforced Al-Cu and Al-Zn based composite powders were designed to be as six layers according to the increasing FLG content, were compacted by stacking via an uniaxial press and, then subjected to sintering process. The relative density of the FLG reinforced Al-Cu and Al-Zn based functionally graded materials (FGM) changes from 96% to 98% and these FGMs showed an increase up to 50% in hardness values from the first layer to the last layer according to the increasing FLG content. Moreover, in regions with high FLG content, improvements in the coefficient of friction (COF) were determined due to the lubricating effect of graphene. The homogeneous distribution of the Al4C3 phase detected in the microstructural examinations performed by optical (OM), scanning (SEM) and transmission electron (TEM) microscopy and X-ray diffraction (XRD) analyzes in the matrix structure was considered to cause an improvement in mechanical properties by providing load transfer from the matrix. In addition, it was determined that increasing hardness values along each layer caused an increase in dislocation density and grain size reduction of the FLG reinforced to the ductile phase. FLG synthesized by EAD was reinforced to the Al-Zn based matrix via MA with different milling durations (0, 2, 4 and 8 h) performed at various amounts (0-0.5-1-2 wt%) Al-Zn based matrix and these composite powders were compacted by an uniaxial press and then exposed to the sintering process. In the microstructural examinations of FLG reinforced Al-Zn based composites, whose relative density vary between 88% and 99% according to the milling time and it was observed that FLG was homogeneously distributed in the matrix structure. Accordingly, the hardness value of 2 wt% FLG reinforced Al-Zn-Mg-Cu based composite produced with 4h-MA was reached 155 HV and the hardness value increased by 63.15% compared to the Al-Zn-Mg-Cu alloy. FLG synthesized by EAD was reinforced to the Cu-based matrix at various amount (0,0.1-0.3-0.5 wt%) via MA performed at different milling times (5 and 7 h), and these composite powders were compacted by an uniaxial press and then subjected to the sintering process. The porosity was determined due to pressureless sintering in the microstructural examinations which was performed by OM and SEM of FLG reinforced Cu based composites with relative density vary on 88% to 94%. Moreover, after 5h-MA, the deformation was observed in the matrix structure. It has been emphasized thas this deformation may be caused by the agglomeration of the FLG in the matrix structure. It was achieved the highest hardness value (101 HV) for the 0.1 wt% FLG reinforced Cu-based composite after 7h MA.