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Review

Table 1

CGDS coating build-up stages and its V p and V c relationship.

Initial stage /first stage Second stage Third stage
Delay time or induction time. This is the time interval at the start of surface treatment when the particle flows and at the commencement of particle/substrate adhesion [17]. First thin layer coating occurs at this stage. Plastic deformation and adhesion of particles onto the substrate occur Surface interaction occurs at this stage. The deposition formed in the previous stage interact with the current particles. This stage is characterized by the build-up coating layers [17],
If V p  < V c , the particles jump off the substrate surface [69].
If V p  = V c , erosion occurs at the substrate surface without any evidence of deposition
V c depends on the particle/ substrate combinations [70]. V c at this stage involves the combination of particle/ substrate impact where both the powder materials and the substrate are of the same composition.
As shown in Figure 7, three velocity regions are evident: V cr1, V cr2 and V p [17].
If V p  < V cr1, multiple particles impact the substrate before adhesion can occur.
If V cr1 < V p  < V cr2, then adhesion occurs after some time. V p  > V cr2 (850 m/s), particles adhesion rapidly occurs. Higher erosion occurs due to up-limit velocity at this stage.
If up-limit velocity is greater than V p , build-up coating is achieved. The up-limit velocity of most powder particles is greater than 1000 m/s [70].