Microstructure evolution and tensile properties tailoring of graphene nanoplatelets/nickel composites fabricated by two-step 3D vibration milling

Uniformly dispersing graphene nanoplatelets (GNPs) with well-preserved structure into matrix is essential for pursuing high-performance nickel (Ni) based composites reinforced by GNPs. In this study, a two-step 3D vibration milling strategy was proposed to prepare GNPs/Ni composites with evenly-dispersed and slightly damaged GNPs. During step I milling, GNPs were exfoliated by Ni powders from graphite balls and initially distributed on powder surfaces synchronously. Followed by step II milling with zirconia balls, the uniform dispersion and thinner thickness of exfoliated GNPs were promoted, while the increased damage to GNPs was induced at higher vibration frequencies. The improved milling frequency boosted deformation of Ni powders and resulted in fine-grained matrix. The GNPs/Ni composites milled at 15 Hz in step II demonstrated a combination between homogeneously distributed GNPs with less defects and refined grains, thus actualizing the superior tensile strength (592 MPa) and ductility (30.6%). Therefore, it is feasible to tailor the microstructure and achieve exceptional mechanical properties for GNPs reinforced metal matrix composites by adjusting proper frequency in the two-step 3D vibration milling strategy.