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 .||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 ,|
, the particles jump off the substrate surface .
If V p = V c , erosion occurs at the substrate surface without any evidence of deposition
|V c depends on the particle/ substrate combinations .||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
cr2 and V
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 .