In this study, the effect of gas pressure on the shape and size of the AZ91 alloy powder produced by using the gas atomization method was investigated experimentally. Experiments were carried out at 820°C constant temperature in 2-mm nozzle diameter and by applying 4 different gas pressures (0.5, 1.5, 2.5 and 3.5 MPa). Argon gas was used to atomize the melt. Scanning electron microscope (SEM) to determine the shape of produced AZ91 powders, XRD, XRF and SEM-EDX analysis to determine the phases forming in the internal structures of the produced powders and the percentages of these phases and a laser measuring device for powder size analysis were used. Hardness tests were carried out to determine the mechanical properties of the produced powders. The general appearances of AZ91 alloy powders produced had general appearances of ligament, acicular, droplet, flake and spherical shape, but depending on the increase in gas pressure, the shape of the powders is seen to change mostly towards flake and spherical. It is determined that the finest powder was obtained at 820°C with 2 mm nozzle diameter at 3.5 MPa gas pressure and the powders had complex shapes in general.

To clarify the effect of copper powder morphology on the microstructure and properties of copper matrix bulk composites reinforced with Ni-doped graphene, spherical and dendritic copper powders were selected to fabricate the Ni-doped graphene reinforced copper matrix bulk composites. The Ni-doped graphene were synthesized by hydrothermal reduction method, followed by mixing with copper powders, and then consolidated by spark plasma sintering. It is found that the Ni-doped graphene are well bonded with the dendritic copper powder, whereas Ni-doped graphene are relatively independent on the spherical copper powder. The copper base bulk composite prepared by the dendritic copper powder has better properties than that prepared by spherical copper powder. At 0.5wt.% Ni-doped graphene, the dendritic copper base bulk composite has a good combination of hardness, electrical conductivity and yield strength, which are 81.62 HV, 87.93% IACS and 164 MPa, respectively.