The formation of η-Ni3Ti phase microstructure in a cast nickel-based superalloy with high Ti/Al ratio
The formation of η-Ni3Ti phase microstructure in a cast nickel-based superalloy with high Ti/Al ratio
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DOI：
10.1016/j.jmrt.2024.01.156
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发表时间：
2024-01-23
影响因子：
6.4
通讯作者：
Ma，Yingche
中科院分区：
文献类型：
--
作者：
Hou，Kunlei;Ou，Meiqiong;Ma，Yingche
By over-aging at 900° C and 1000° C, a high volume-fraction of η-Ni 3 Ti phase was prepared in a cast nickel-based superalloy with high Ti/Al ratio. EBSD analysis shows that the η phase obeys a SN-type orientation relationship with γ matrix:< 11 2‾ 0> η//< 1 1‾ 0> γ,{0001} η//{111} γ. Four kinds of η phase variants with a 70.5° misorientation to each other are clarified. From the η/γ interface structure as detected by HRTEM, the thin plate-like morphology of η phase is attributed to the preferential growth of the incoherent {11 2‾ 0} η//{1 1‾ 0} γ interface. The formation of η phase at the grain boundary (GB) was by a discontinuous precipitation reaction, during which the original GB migrates from the η-nucleating side into the adjacent grain following the elongation of η phase to form a cellular structure. The detailed GB migration mechanism is investigated by EBSD and rationalized from the aspect of interface energy. For the formation of η phase in grain interior, three relative reactions are clarified:(i) MC+ γ→ M 23 C 6+ OA-γ′, OA-γ′→ η,(ii) γ→ M 23 C 6+ OA-γ′, OA-γ′→ η, and (iii) γ′→ OA-γ′, OA-γ′→ η, where OA-γ′ is the newly precipitated γ′ phase during over-aging which shares a similar elemental distribution with η. The intermediate phase OA-γ′ is formed due to the comparably low nucleation barrier from γ while its subsequent transformation to η is excited by the higher thermodynamic stability of η as revealed by the calculation results by using the VASP software. At last, as conformed by STEM-HAADF, the structure transformation of OA-γ′→ η is aided by the introduce of superlattice intrinsic stacking faults.
