## 3 Results and Discussion
### Deformation Mechanism-Based True Stress Creep Model  
The second stage of creep accounts for most of the creep life, and the minimum creep rate is a key indicator to characterize the creep characteristics of materials. Therefore, the second creep stage is also studied in practical engineering. When studying minimum creep rates over a wide range of stresses, both linear and power-law creep must be considered, and the secondary creep model must be extended by introducing appropriate Arrhenius-type temperature functions and internal state variables to account for temperature dependence and microstructural degradation processes, such as subgrain coarsening and creep cavitation [32]. Over a wide range of stress and temperatures, creep is usually caused by a variety of mechanisms, including intragranular dislocation glide (IDG), intragranular dislocation climb (IDC), and grain boundary sliding (GBS). Therefore, the creep-constitutive model of CGI should be established based on the creep deformation mechanism to facilitate the study of the effects of different physical mechanisms on its creep. To date, the DMTS creep model has been proposed, it has performed well over a wide range of stresses, and it has been well applied under the conditions of wide stress and temperature range of Waspaloy alloy, modified P91 steel, G115 steel, and SA508 Gr.3 alloy [33; 34; 35; 30]. The derivation process of the CGI creep-constitutive model based on the DMTS creep model is as follows:  
The relationship between the minimum creep rate and the stress is usually expressed by the Norton-Bailey power law equation, as shown in the following Equation (1):  
\[\dot{\epsilon}=K\sigma^{n} \tag{1}\] \begin{table}
\begin{tabular}{c c c} \hline \hline
**Temperature/\({}^{\circ}\)C** & **Stress/MPa** & **Minimum Creep Rate/h\({}^{-1}\)** \\ \hline  & 300 & 2.407 \(\times\) 10\({}^{-1}\) \\  & 275 & 7.855 \(\times\) 10\({}^{-3}\) \\
450 & 250 & 6.344 \(\times\) 10\({}^{-4}\) \\  & 225 & 2.135 \(\times\) 10\({}^{-4}\) \\  & 200 & 3.4729 \(\times\) 10\({}^{-5}\) \\ \hline  & 275 & 2.6643 \\  & 250 & 3.432 \(\times\) 10\({}^{-1}\) \\
500 & 225 & 2.097 \(\times\) 10\({}^{-2}\) \\  & 200 & 6.18 \(\times\) 10\({}^{-3}\) \\  & 150 & 9.0978 \(\times\) 10\({}^{-5}\) \\ \hline  & 225 & 3.569 \(\times\) 10\({}^{-1}\) \\  & 200 & 7.1102 \(\times\) 10\({}^{-2}\) \\
550 & 175 & 7.3234 \(\times\) 10\({}^{-3}\) \\  & 150 & 3.72 \(\times\) 10\({}^{-3}\) \\  & 100 & 1.8968 \(\times\) 10\({}^{-4}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Minimum creep rate under various test conditions. where \(\dot{\epsilon}\) is the minimum creep rate (h\({}^{-1}\)), \(\sigma\) is the stress level (MPa), and \(K\) and \(n\) are material-dependent constants. Therefore, according to Equation (1), the minimum creep rates under the action mechanisms of GBS, IDG, and IDC can be expressed as:  
\[\dot{\epsilon}_{s}=A_{0}\exp\left(-\frac{Q_{A}}{RT}\right)\sigma^{p} \tag{2}\]  
\[\dot{\epsilon}_{g}=B_{0}\exp\left(-\frac{Q_{B}}{RT}\right)\sigma^{n} \tag{3}\]  
\[\dot{\epsilon}_{c}=C_{0}\exp\left(-\frac{Q_{C}}{RT}\right)\sigma^{m} \tag{4}\]  
where \(\dot{\epsilon}_{s}\), \(\dot{\epsilon}_{g}\), and \(\dot{\epsilon}_{c}\) are the minimum creep rates of GBS, IDG, and IDC, respectively, \(Q_{A}\), \(Q_{B}\), and \(Q_{C}\) are the activation energies (J/Mol) of GBS, IDG, and IDC, respectively, \(p\), \(n\), and \(m\) are the stress exponents of GBS, IDG, and IDC mechanisms, respectively; \(A_{0}\), \(B_{0}\), and \(C_{0}\) are proportional constants, \(R\) is the gas constant with a value of 8.314 J\(\cdot\)mol\({}^{-1}\cdot\)K\({}^{-1}\), and \(T\) is the thermodynamic temperature (K). Therefore, the total creep rate caused by these mechanisms of action can be expressed by the following Equation (5):  
\[\dot{\epsilon}=\dot{\epsilon}_{s}+\dot{\epsilon}_{g}+\dot{\epsilon}_{c} \tag{5}\]  
Figure 6 shows the relationship between the minimum creep rate and stress of CGI at different temperatures in the double logarithmic coordinate system.