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Nozzle of RKX l00 rocket contributes 30 % to the total weight of the structure, so that allowing furtherresearch on weight reduction. An alternatiye for this is by substitution of massive graphite, which iscurrently used' as thermal protector in the nozzle, with thin layer of HVOF (High Velocity Oxy-Fuel)thermal spray layer. A series of study on the characteristics of various type of HVOF coating materialhave been conducted This paper presents the investigation on the HVOF Cr,C3-NiCr thermal spraycoating, particularly, the optimization of bonding strength by varying surface roughness of substrates.Characterization includes bonding strength test, microhardness measurement and microstructuralanalysis by both optical and scanning electron microscopes (SEM). The results showed that grit blastingpressure increases the surface roughness from 4.54 ,urn to 5.72 _um at the pressure of 6 bar. Averagemicrohardness of the coating is 631 VHN_;m.Coating applied to the Surface with roughness of 5.42 ,annpossessed the highest bonding strength of 4 4 MPa. Microstructural observation by using opticalmicroscope and scanning electron microscope (SEM) confirmed dense lamellae structure with variablecomposition. High coating adherence was found to be due to mechanical interlocking. |
