Effects of P segregation on deformation mechanism in Ni-P nanocrystalline by atomic simulations

Abstract

By using hybrid Monte Carlo-molecular dynamics (MC-MD) simulations, the segregation behavior of solute P atoms in the grain boundaries (GBs) of nanocrystalline (NC) Ni-P alloy was studied under different temperatures. The effects of P segregation on the mechanical properties and quantitative deformation mechanism of the Ni-P alloy were also investigated at high temperatures (800 K). The results show that the temperature strongly influences the segregation behavior of P atoms. Uniform P segregation occurs along GBs at 300 K, while at elevated temperatures (e.g., 1000 K), P atoms are concentrated at triple junctions (TJs), forming Ni-P precipitates. The uniform grain boundary segregation of P leads to Ni-P alloy with larger grain sizes and higher strength, while Ni-P precipitates at TJs result in alloy with smaller grain size, higher yield and flow stresses, which could be attributed to the Zener pinning effect. Moreover, quantitative analysis of the deformation mechanisms reveals that for NC Ni-P alloy with small grain size, Ni-P precipitates show significant effect on the competition between intracrystalline deformation and grain boundary deformation. A low percentage of elastic strain on the GBs was observed in the elastic deformation stage. The plastic deformation process of the non-segregated sample with grain size of 5 nm is dominated by grain boundary deformation, whereas for non-segregated samples of 10 and 15 nm, the strain is accommodated by both intragranular dislocation slip and grain boundary deformation. Importantly, Ni-P precipitates can reduce the degree of grain boundary deformation in alloys with small grains and thereby stabilize the GBs. The less grain boundary deformation caused by uniform grain boundary segregation of P and the more dislocation slip play a major role in improving the mechanical properties of the alloy with large grains. The results and findings of this study provide further insights into the segregation-induced strengthening mechanisms of NC Ni-P alloys.