The influence of lattice misfit on the occupation behavior and the ductility effect of Zr in Ni-Ni3Al alloys were explored. It is found in energy analysis that the preferable site of Zr between Ni sublattice and Al sublattice will change under different lattice misfit, however, the Zr prefers to segregate Ni phase rather than Ni3Al phase in all lattice misfit range, which makes it impossible for Zr to go into Ni3Al phase to occupy Al sublattice in Ni-Ni3Al system. Bond order （BO） analysis shows that the localized ductility effect of Zr differs in different region, and the comparison between Zr-free and Zr-doped BO analysis successfully explain the mechanism of the embrittlement of Ni-Ni3Al alloys and the ductility effect of Zr.
Two Ni/Ni3Al-interface-contained cluster models with/without lattice misfit are studied by first-principles method to clarify the debates about the segregation behaviors of Hafnium（Hf） and explore the influence of lattice misfit on the ductility effect of Hf.It is found that though Hf prefers to substitute Al rather than Ni in Ni3Al phase within most of the investigated misfit range,its stronger preferring to Ni phase than Ni3Al phase makes it impossible to go into Ni3Al phase to occupy Al site in Ni-Ni3Al alloys.Bond order analysis in Hf-free case shows that lattice misfit has different effects on the Griffith work of interfacial cleavage 2γint/E and the maximum theoretical shear stress τmaxof Ni and Ni3Al,contributing to the existence of anomalous strength-temperature phenomena in Ni3Al alloys.However,the addition of Hf will make the2γint/E(or τmax) of both Ni3Al and Ni decrease（or increase） with lattice misfit,indicating that the addition of Hf may make the anomalous strength-temperature relationship in Ni3Al region disappear locally.
Two Ni/Ni3Al-interface-contained cluster models with/without lattice misfit are studied by first-principles method to clarify the debates about the segregation behaviors of Hafnium （Hf） and explore the influence of lattice misfit on the ductility effect of Hr. It is found that though Hf prefers to substitute A1 rather than Ni in Ni3A1 phase within most of the investigated misfit range, its stronger preferring to Ni phase than NiaA1 phase makes it impossible to go into Ni3A1 phase to occupy A1 site in Ni-Ni3A1 alloys. Bond order analysis in Hf-free case shows that lattice misfit has different effects on the Griffith work of interfacial cleavage 27int/E and the maximum theoretical shear stress Zmax of Ni and Ni3A1, contributing to the existence of anomalous strength-temperature phenomena in NiaA1 alloys. However, the addition of Hf will make the 27int/E （or Zmax） of both Ni3A1 and Ni decrease （or increase） with lattice misfit, indicating that the addition of Hf may make the anomalous strength-temperature relationship in Ni3A1 region disappear locally.
Y. WuJ. GuoW. ZhangX. MaQ. ZhangJ. HouR. HuangX. Liu
