Mechanical performance of cold isostatic pressed W-6Ni-4Cu alloy with graphene reinforcements

We have assessed the manufacturability and impact of adding graphene platelets in contents of x = 0, 0.01, 0.05, 0.1 wt.% to W-6Ni-4Cu as a model ‘ductile phase toughened’ tungsten heavy alloy (WHA). These alloys are potential candidates for future nuclear technologies and other structural applications in high-temperature radiation environments. Graphene additions were studied as potential reinforcement and to increase the interface density for mechanical and radiation tolerance of the alloy. The materials were produced successfully by cold isostatic pressing of the pre-mixed powders at a compaction pressure of 140 MPa, followed by liquid phase sintering at 1450-1500 °C under reducing 75% H₂/ 25% N₂ atmosphere. The graphene platelets are located at the Ni/Cu matrix-W grain and W-W grain interfaces. The material’s density and surface roughness degrade when increasing the graphene content beyond 0.05 wt.%. This is coupled with a sharp reduction in tensile strength and elongation for 0.10 wt.% graphene, whereas those properties undergo an overall increasing trend with graphene content for x ≤ 0.05 wt.%. During tensile deformation of W-6Ni-4Cu (i.e. x = 0), strain localizes primarily in the ductile Ni/Cu matrix and at the matrix-W and W-W interfaces, with crack formation observed at W-W interfaces. However, graphene platelets enhance the load transfer from the matrix to the W grains, and also from grain to grain, therefore promoting a higher degree of cleavage inside the W grains. Graphene additions and cold isostatic pressing offer an avenue to enhance the WHA performance for applications in structures under ever demanding service environments.