Thermally driven surface phase separation in intermetallic alloys

Intermetallic compounds are widely recognized for their high-temperature phase stability and resistance to composition and structural changes. However, we reveal athermally activated bulk-to-surface mass exchange mechanism that drives surface phase separation, resulting in the formation of surface precipitates with distinct composition andstructure from the bulk matrix. Using the archetypal β-NiAl system, we show that asymmetries in vacancy formation energies between Ni and Al atoms induce preferential Ni segregation to the surface, forming Ni-rich γ'-Ni₃Al precipitates. By integrating in-situ electron microscopy, synchrotron X-ray absorption spectroscopy and first-principles computational modeling, we establish a direct mechanistic connection between bulk thermal defect dynamics, surface compositional evolution, and phase segregation behavior. This bulk-surface coupling mechanism can be a driver of surface phase separation in multicomponent alloys under thermal stress. In conclusion, these results refine the thermodynamic boundaries of intermetallic stability and provide insights into managingthe performance and durability of intermetallic alloys for demanding high-temperature applications.. Authors: Patel, Shyam Bharatkumar [State Univ. of New York (SUNY), Binghamton, NY (United States)] (ORCID:0000000224497918); Chen, Xiaobo [State Univ. of New York (SUNY), Binghamton, NY (United States)] (ORCID:0000000329432926); Wu, Dongxiang [State Univ. of New York (SUNY), Binghamton, NY (United States)]; Zhou, Zhikang [State Univ. of New York (SUNY), Binghamton, NY (United States)] (ORCID:0009000613121495); Wu, Yupeng [State Univ. of New York (SUNY), Binghamton, NY (United States)]. DOE Contract: SC0001135; SC0012704. Subjects: 36 MATERIALS SCIENCE; Corrosion; Metals and alloys; Surface spectroscopy; Surfaces; interfaces and thin films