## 4 Discussion  
A comprehensive analysis of the microstructure and tensile deformation behavior allowed us to examine the processes of decomposition of Cr- and Mo-enriched supersaturated \(\gamma\)-phases in the studied Ni-based alloys. Additionally, assessment of the contribution \begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**Spectrum** & **Al** & **Si** & **Cr** & **Mn** & **Fe** & **Ni** & **Mo** \\ \hline Spectrum 1 & 0.94 & 0.94 & 3.02 & 0.88 & 2.83 & 77.52 & 13.85 \\ Spectrum 2 & 0.72 & 0.13 & 2.50 & 0.72 & 1.71 & 73.24 & 20.96 \\ Spectrum 3 & 0.88 & 0.88 & 2.96 & 1.01 & 2.71 & 77.55 & 14.00 \\ Spectrum 4 & 1.32 & 0.69 & 2.88 & 1.00 & 3.07 & 77.88 & 13.16 \\ Spectrum 5 & 0.53 & 0.40 & 1.91 & 0.86 & 1.65 & 74.03 & 20.63 \\ Spectrum 6 & 0.94 & 0.94 & 3.02 & 0.88 & 2.83 & 77.52 & 13.85 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Chemical composition of phases in Hastelloy® B-3® aged at 650 \({}^{\circ}\)C for 5000 h (at.%). Figure 21: Secondary phases formed in Hastelloy® B-3® after 5000 h of aging at 650 \({}^{\circ}\)C.  
Figure 22: Typical engineering stress-strain curves of Hastelloy® B-3® specimens after long-term aging at 650 \({}^{\circ}\)C.  
of secondary-phase particle type and morphology to the evolution of mechanical properties during long-term aging (for up to 5000 h) was estimated. The observed property changes can be represented in a structural strengthening and embrittlement diagram (Figure 23), where the increase in yield strength (YS) due to aging is primarily associated with the dispersion-hardening mechanism, and this process is accompanied by embrittlement (expressed through the YS/TS ratio). Based on the impact on mechanical properties, the experimental data on the diagram can be divided into several regions. These regions reflect the influence of intra- and intergranular precipitates. In the \"as-received\" state, the investigated corrosion-resistant nickel alloys exhibited relatively low yield strength and the lowest degree of embrittlement, indicating high plasticity and strain-hardening capability. Analysis of the aged samples showed that material strengthening was directly related to the localization of particle nucleation and the Cr/Mo ratio. The predominance of secondary-phase precipitates at the grain boundaries in Hastelloy\({}^{\circledR}\) G-35\({}^{\circledR}\) alloy and partially in the C-group alloys under certain conditions provides a more balanced combination of mechanical properties--moderate strengthening while preserving ductility. In contrast, the formation of intragranular Ni-Mo intermetallic precipitates significantly reduces plasticity and enhances the material's tendency to embrittlement. Therefore, Hastelloy\({}^{\circledR}\) B-3\({}^{\circledR}\) (Ni-Mo system), during aging at 550-700 \({}^{\circ}\)C, undergoes significant strengthening accompanied by complete embrittlement (YS/TS = 1). Such behavior results from the intensive formation of intragranular precipitates and an increase in their volume fraction that leads to a gradual rise in yield strength and degradation of ductile properties. Loss of plasticity becomes more pronounced with increasing aging temperature. The embrittlement of the Hastelloy\({}^{\circledR}\) B-3\({}^{\circledR}\) alloy during prolonged aging is  
Figure 23: Correlation between strengthening and embrittlement of selected nickel alloys due to precipitate localization after 5000 h of long-term aging. unfavorable for applications within the working temperature range of molten salt reactors. Aging at a lower temperature (500 \({}^{\circ}\)C) also showed a tendency toward embrittlement, and the YS/TS ratio gradually increased to 0.77. Alloys of the C-family exhibit the most stable mechanical behavior during long-term aging and have an intermediate position among the studied materials. Their strength properties increase gradually up to 650 \({}^{\circ}\)C due to precipitation of ordered Ni\({}_{2}\)(Cr,Mo) particles but without a drastic drop in ductility, as seen in B-type alloys.