Effect of mixing entropy on nano-scratching behavior in FCC polycrystalline MPEAs: A comprehensive study by molecular dynamics simulation and experiment integration

Investigations into the microstructure of polycrystalline multi-principal alloys (MPEAs) during nano-scratching play a crucial role in enhancing the material properties of MPEAs and gaining insights into the intricate behavior of complex material systems. As a critical factor affecting the structural stability of MPEAs, mixing entropy has been the focus of research. In this work, the nano-scratching process of FCC polycrystalline MPEAs with different mixing entropies (FeNiCr: 9.145 (J/(mol & sdot;K), FeNiCrCo: 11.556 (J/(mol & sdot;K), FeNiCrCoCu: (13.386 (J/(mol & sdot;K)) were simulated through molecular dynamics (MD) simulations. The tribological behavior of FCC polycrystalline MPEAs was comprehensively analysed from the perspective of mixing entropy's effect on grain boundary structure (GBs). In addition, nano-scratching tests were performed on the MPEAs (FeNiCr, FeNiCrCo, FeNiCrCoCu) to observe the tribological properties of the FCC polycrystalline MPEAs in a macroscopic perspective. The results show that as the mixing entropy increases, the GBs roughness increases, and there is a clear correlation between the GBs roughness and the tribological behavior of FCC polycrystalline MPEAs. It can be found that during the nano-scratching process, as the GBs roughness increases from 0.828 to 1.360, the deformation of the matrix surface becomes more severe, the abrasive debris increases, the normal friction from and tangential friction from 62.1nN and 57.3 nN to 68.8 nN and 63.9 nN, respectively, and the coefficient of friction increases from 0.932 to 0.963. The number of dislocations inside the matrix increases, the structural deformation of GBs is weakened, and the number of vacancies decreases. This work is scientifically crucial for providing theoretical support for further optimization of the friction and wear properties of MPEAs, understanding the role of mixing entropy in material nanoscale nano-scratching and elucidating the related behaviors.