Understanding the part geometry is important to fixturing and tooling in order to maintain the proper spray angle. The following acceptable practices and design considerations should be considered for compliance with coating requirements (Fig. 4).
When the substrate target area is undercut to accept a coating (Fig. 4a), always chamfer or radius the corners before spraying. One rule of thumb is that the radius should equal or exceed the sprayed coating thickness.
Likewise, the substrate edges as shown in Fig. 4(b) should be chamfered or radiused. Again, a 45° chamfer or radius equal to the coating thickness is suggested or recommended. Edge effects common to all coating techniques cause unacceptable stresses at the edges, which in turn will lead to cracking and coating separation.
Figure 4(c) shows the acceptable practices for depositing a coating onto a substrate and against a shoulder or boss. Using procedures similar to undercutting, corners must be radiused or chamfered. Sharp corners against a shoulder are likely to result in porosity and voids.
Image – Fig. 4 – Design of substrate geometry for thermal spray coating processes
This information is from ASM Handbooks Online, Vol. 5A: Thermal Spray Technology, Coating Structures, Properties, and Materials. To find this information (subscription required), click on the link below and scroll down to Figure 4.
https://dl.asminternational.org/handbooks/book/12/chapter/134972/Introduction-to-Coating-Design-and-Processing
