## 3 Results and Discussion
### Effect of RHT on the Creep Behavior of K465 Alloy  
To evaluate the effectiveness of RHT, all prereport samples after RHT were creep-tested again at the same creep condition. The creep strain vs. strain rate curves of different samples are shown in Figure 11. The creep rupture time and minimum creep rate of samples with different accumulated strain are summarized in Table 2. From this result, we can see that the creep strain rate of all samples firstly declines to a minimum value and then rises with the increase of creep strain. This phenomenon can be explained by the movement of dislocations, namely, the mobile dislocation density and velocity of dislocations. It is of interest to note that the minimum creep strain rate of RHT samples is strongly dependent on the prereport strain. For instance, the strain rate curve of the sample with prereport strain of 0.03 is analogous to the sample with an unaltered initial microstructure. The minimum creep strain of these two samples is also found to be similar. With the increase of prereport strain, there is an apparent increase in the minimum creep strain rate when the RHT samples are crept again. On the other hand, the minimum creep rate is reversely proportional to the creep rupture time, which can be rationalized by the Monkman-Grant empirical relationship [31]. The present results manifest that the creep property of prereport K465 alloy can be rejuvenated to a certain level by performing RHT. With low accumulated strain, the creep resistance of K465 alloy after performing RHT is almost equivalent to the sample after standard heat treatment. However, RHT cannot fully rejuvenate the creep property when the accumulated strain reaches a certain level, which roughly corresponds to minimum strain rate of samples with initial microstructure. In other words, the effectiveness of RHT is strongly dependent on the accumulated strain level, which can be interpreted by the microstructure observation after RHT. Through performing RHT on samples with low accumulated strain, the precipitation behavior of \(\gamma^{\prime}\) was almost similar to that after heat treatment, and dislocation networks were fully eliminated as is shown in Figures 6a and 10a. On the other hand, the homogeneous precipitation was not reproduced in the samples with high accumulated strain after RHT, as is evident in Figure 6b,c. Moreover, a number of dislocations still remained in matrix channels. Therefore, this degraded microstructure will deteriorate the creep property of K465 alloy. Similar results were also previously reported on a single crystal Ni-base superalloy [32]. However, it is still not \begin{table}
\begin{tabular}{c c c} \hline \hline
**Samples** & **Creep Rupture Time, h** & **Minimum Creep Rate,1/h** \\ \hline After heat treatment & 112 & \(1.01\times 10^{-4}\) \\ With 0.03 creep strain + RHT & 105 & \(1.31\times 10^{-4}\) \\ With 0.05 creep strain + RHT & 84 & \(2.73\times 10^{-4}\) \\ With 0.07 creep strain + RHT & 38 & \(5.24\times 10^{-4}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Creep property of samples after RHT. Figure 11: Creep rate curves of the samples after RHT. clear why the creep property of a sample with high accumulated strain cannot be fully rejuvenated by performing RHT. Perhaps some special measures should be taken during RHT--future work is needed to clarify this issue. It should be noted that there is a large amount of carbides formed in the matrix, which also contribute to the high temperature strength of K465 alloy. As mentioned above, The MC type carbides tended to transform continuously into M\({}_{6}\)C carbides during creep, and RHT cannot alter this transformation behavior of carbides. As a consequence, the area fraction of M\({}_{6}\)C carbides increases noticeably.