Effect of ball milling time on microstructure and mechanical properties of graphene nanoplates and TiBw reinforced Ti–6Al–4V alloy composites

Ti–6Al–4V (TC4) matrix composites with graphene nanoplatelets (GNPs) and TiB whiskers (TiBw) were synthesized by ball milling, Fast Hot-Press Sintering (FHPS), and hot rolling (HR) method. The microstructures of the ball-milled powders, the as-sintered and as-rolled composites were characterized by Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. It revealed that there was an optimal ball milling time existed for obtaining GNPs with uniform dispersion and an acceptable degree of defects. The Raman results indicated that the defects increased and the number of GNPs layers decreased with the increasing ball milling time. Tensile tests revealed that the ultimate tensile strength of the 8-h-ball-milling composites increased from 1098 MPa to 1182 MPa and the elongation only dropped slightly from 16.0% to 15.1% compared with that of TC4 alloy fabricated under the same procedure. The failure mechanism of composites was further discussed by analyzing the fracture surface morphologies. Overall, this study highlights the effect of ball milling time on the structure integrity and dispersion homogeneity of GNPs, which is crucial to make full use of the excellent properties of GNPs in TC4 matrix composites.