[en] The effects of Ta on microstructural stability and mechanical properties of hot corrosion resistant Ni-based single crystal superalloys during long-term thermal exposure at 900 °C were investigated in the present study by comparing two experimental alloys with different content of Ta (6Ta and 6.7Ta). The results indicated that the addition of extra 0.7Ta increased the volume fraction of the γ′ precipitates and accelerated the coarsening rate of γ′ precipitates, facilitated the formation of misfit dislocation and precipitation of σ phases. The 6.7Ta alloy exhibited higher hardness and better stress rupture properties than 6Ta and the variations of stress rupture properties during the exposure for 6Ta and 6.7Ta alloy are significantly different. The effects of γ′ coarsening, formation of σ phases and misfit dislocations were taken into consideration to identify the reasons of variations of mechanical properties during the thermal exposure.

[en] Highlights: • Te preferentially diffuses into the Ni-based alloy along grain boundaries at 800 °C. • Te can react with Cr to form cubic structure CrTe at both grain boundaries and intergranular carbide/matrix interfaces. • The CrTe is possible to induce intergranular cracking in the alloy. - Abstract: The corrosion behavior of a Ni–16Mo–7Cr–4Fe alloy was investigated in a tellurium (Te) vapor atmosphere at 800 °C. Te was identified via electron probe microanalysis at the grain boundary regions of the corroded alloy. The morphology, chemical composition, and crystalline structure of those areas were characterized in a transmission electron microscope. Chromium tellurides were observed at both grain boundaries and intergranular carbide–matrix interfaces. Based on the results, the mechanism of intergranular Te corrosion and its possible correlation with intergranular cracking is discussed

[en] Highlights: • Hot corrosion resistance of single crystal superalloys significantly depended on the ratio of Al/Ti in terms of the formation of a compact and protective NiTiO₃ layer. • Re significantly improved hot corrosion resistance of the experimental single crystal superalloy. • The influence mechanism that adding Re may facilitate diffusion of Cr in γ phase and diffusion of Ti in γ' phase had been explored in combined with first-principle calculation. • Potential design space for developing new type of hot corrosion resistant single-crystal superalloys was proposed. Hot corrosion behavior of three nickel-based single crystal superalloys with different key alloying elements (including Re, Cr, Al and Ti) contents in molten Na₂SO₄ salt at 900 °C was investigated. Comparative study of hot corrosion resistance was conducted on two Re-free superalloys with 12 wt% Cr and different content of Al and Ti. By further adding Re, the experimental alloy with moderate Cr content (8.5 wt%) and Al/Ti > 1 in the present research also exhibited excellent hot corrosion resistance. The influence mechanism of Re on promoting hot corrosion resistance was attempted to be explored in combined with first-principle calculation. In addition, the potential design space of new-developed single crystal superalloys was also proposed.