Manufacturing and cold spraying of hybrid composites - A path for metallizing thermoset matrix composites

This study aims to realize and metallize the hybrid thermoset-thermoplastic fiber reinforced composites for aerospace applications. Two variations in the manufacturing route including cocuring and hybrid interlayer were adopted for realizing the RTM6-PEI-CF composite. Low pressure cold spray metallization technique is applied by varying the processing parameters stand-off distance and traverse speed. Microstructural analysis and mechanical tests (roughness check, nanoindentation tests) were performed on sprayed composites. Overall, manufacturing routes affected the inherent structure of the composite and subsequent coating quality. Mechanical interlocking induced close contact of PEI-aluminum (Al) particles characterized into uniform coating with surface morphology variation shown in cocured composites. Coating adhesion strength increment up to 18 MPa was noted by using the PEI-carbon fiber (CF) semi-preg in manufacturing. The tomography scan highlighted the structural integrity of the manufactured and coated composites, revealing coating-thermoplastic contact, interphase, and porosity in the inter-tow fiber region. An increase in the traverse speed to 2 mm/s reduced the electrical conductivity and adhesion strength of the coating with the hybrid composite. Within the limits of this investigation, opting for lower stand-off distance and traverse speed (here, 10 mm and 1 mm/s) reflected in improved adhesion and approximately 1.5 mm coating thickness.