Effects of gradient nanostructures on the tribological properties and projectile abrasion during high-speed penetration in AerMet100 steel

To reduce the mass abrasion of AerMet100 ultra-high strength steel projectiles at increasing velocities, surface mechanical grinding treatment (SMGT) was employed to prepare a gradient nanostructure (GNS) on the AerMet100 surface. The microstructure of the GNS were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and nanoindentation. It was found that the gradient nano-crystal structure was successfully prepared, and the martensite plate width was reduced to about 30 nm. As the distance from the surface depth increased, the plate size gradually increased, with the depth of the grain refinement layer measuring approximately 300 μm. The microhardness of the GNS AerMet100 was 870 Hv_0.025, which was approximately 40% higher than that of the AerMet100 substrate. Additionally, the hardness was observed to decrease with increasing GNS depth. The friction and wear behavior of coarse grained (CG) AerMet100 and GNS AerMet100 were investigated. The results showed that their friction coefficients were similar, but wear volumes of GNS AerMet100 were smaller than those of CG AerMet100, the wear mechanisms of two surfaces were predominantly abrasive and adhesive wear. Furthermore, the projectiles penetration test showed that the mass loss of GNS AerMet100 was significantly lower than that of CG AerMet100 under similar velocity condition. Within the velocity range of 1200–1750 m/s, the degree of erosion and wear loss of the CG AerMet100 and GNS AerMet100 projectile noses increased with increasing penetration velocity, and the wear mechanism was mainly abrasive wear.