4.1 | Results of untreated blades
The longitudinal section diagrams of untreated blades are shown in
Figure 11. In Figure 11(a) and (c), it is found that the cracks initiate
near the bulk carbides on the top surface. And the cracks are easy to
propagate along the grain boundaries. In fact, the carbides precipitate
from the matrix, connect with each other and rupture due to the
interaction of the high temperature and CCF load. This may make the
grain boundaries become the weaken locations. And the maximum total
stress is on the top surface. Therefore, the cracks initiate from the
carbides on the top surface and propagate along the grain boundaries
(Figure 11 (b) and (d)).