Surface alteration of aluminium alloy by an exfoliated graphitic tribolayer during friction surfacing using a consumable graphite rich tool

Abstract

In present study, a strategy for mechanical exfoliation of graphite to a few layered graphene (FLG) coupled with its mechanical infusion onto aluminium (Al6061) substrate through a solid-state friction surfacing (FS) methodology is developed and documented. Here, a graphite-rich and expendable FS tool fabricated through conventional powder metallurgy is used as a source of graphite. Later on, this expendable tool is utilized for impregnating graphite on the aluminium alloy surface through FS. The high frictional shear stress during FS results in the exfoliation of graphite to FLG which is confirmed by the characteristic wrinkled morphology through FE-SEM studies. Experimental results revealed successful impregnation of FLG flakes up to ∼165 μm depth on the surface of aluminium matrix. The effect of graphite flake size (60 mesh (max. 250 μm) and 325 mesh (max. 44 μm)) on specific wear rate and its ability to mechanically exfoliate into a FLG structure is also analysed. Dynamic recrystallization due to plastic deformation during FS results in ∼ 90% grain size reduction relative to the as-received aluminium alloy (reference Al). Excellent interfacial bonding with mechanical intercalation between graphite flake and aluminium matrix is also observed through TEM studies. Intermetallic phase such as Al4C3 is observed at the Al/graphite interface with larger flake size. The tribological properties are significantly improved with the graphite reinforcement leading to the decrease in coefficient of friction by ∼12.5 and 26.7% with graphite of 250 (FS250) and 44 μm (FS44) flake size respectively as compared to the reference Al. The least specific wear rate is observed for FS44 which is about ∼53.4 % and ∼ 28.57 % less than the wear rate of reference Al and FS250, respectively. The microhardness, nano-hardness and XRD studies further corroborate the results.