Electroless Nickel Deposit Procedures And Proton Irradiation Behaviors Of SiC/Al Composite With High SiC Content

In this paper, Due to its low density and expansion coefficient, high strength andconductivity, SiCp/Al composite with high SiC content becomes promising to apply ashigh-stable reflector and package materials for components in space applications.However, high ceramic content in the composite results in lower reflectivity andcorrosion resistivity, electroless nickel deposit on the materials is one of effective modeto improve the surface properties. Hence, pretreatment procedures and depositingprocess were systematically investigated and optimized. Afterward, structures,properties and irradiated stability of electroless deposits were studied using opticalmicrograph, scanning electron microscopy, x-ray diffraction patterns.According to the compositional characteristics of the studied SiCp/Al composite,the deposition processes were studied based on the pretreatment technologies forceramics and aluminum alloys. The results indicate that based on the sensitized andactivated procedures for ceramics, electroless nickel deposit on the composite presentsmycelium-like loose morphology. This is due to over-corrosion of surface aluminumregions in sensitized and activates solutions with hydrochloride acid. On the other hand,using zinced procedure for aluminum alloys, one can obtained dense and semi-brightelectroless nickel deposit on the composite and the electroless nickel layer could coverthe sample surface within5minutes. However, using this procedure, there may appearsome pits on the deposit due to side-growth to the SiC phase surface withoutself-catalysis from the initial preferential deposited layer on the metallic Al regions. Inthe meantime, electroless deposit shows more homogeneous ad bright on the chemicalpolished samples compared to those with mechanical polished surface.The analysis shows that electroless nickel deposit on the composite is amorphouswith cellulated morphology; the deposit hardness was detected as HV420. Theminimum critical load to peel the deposit from substrate was detected about3.5N usingscrape-off measurements. During the measurements, some intermittent sound singlescould be detected with loading. The reason for it is that the deposit has weaker bondwith the SiC phase on the composite substrate as compared with metallic surface. Afterelecrtoless nickel depositing, surface reflectivity increases drastically. It is also foundthat after irradiation with170keV proton up to a fluence of1E16cm-2, amorphous Ni-Pdeposit show crystallization, resulting in increasing its hardness.