4.2.1 | Phase precipitations and transitions
Figure 12 shows the SEM morphology and EDS analyze results of the PSP
treated blades while the vibration stress is below the threshold value.
The major contents of different phases based on the EDS spot scanning
are listed in Figure 12(d). According to the elemental analysis results,
the phases labelled (a) and (b) are the γ’ phase and γ phase. The phase
labelled (c), which is rich in C, Ti, W and Co elements, is considered
to be the bulk MC carbides. Furthermore, the phase labelled (d) that
contains the insoluble W element and is short of Ti and Cr elements is
supposed to be the M6C carbides. Besides, the phase
labelled (e) should be the M23C6carbides which mainly consist of C and Cr elements [24].
In fact, the MC carbides may degenerate into the
M23C6 or M6C carbides
during the CCF tests in the form of the following equations:
MC+γ→M23C6+γ′ (1)
or
MC+γ→M6C+γ′ (2)
Especially, the formation of the M23C6carbides results in the depletion of the Cr element in the γ phase,
which further leads to the generation of cationic vacancies. These
cationic vacancies may enlarge, gather, connect with each other and
develop into the micro-holes [25].