Nanocomposite layers Ni-P/ Si3N4 produced on aluminium alloy AA 7075 by electroless nickel plating
Maria Trzaska, Beata Kucharska
Quarterly No. 2, 2010 pages 100-104
DOI:
keywords: nickel-phosphorus surface coatings, composite Ni-P/Si3N4 coatings, microhardness, scratch test, tribological properties
abstract One of the major drawback to using aluminum alloys in transport applications are not good their tribological properties. Produced on the same aluminum substrate AA 7075 some composite coatings with hard ceramic disperse phase have exhibited improved properties. The aim of the present research was to investigate the influence of disperse ceramic phase of silicon nitride on the structure and surface properties of composite layers Ni-P/Si3N4 deposited on the aluminum alloy substrate (AA 7075) by the chemical reduction method. Chemical nickel-phosphorus coatings (Ni-P) were also investigated to have a comparison with composite layers. The coatings were deposited from acid bath. Powder of silicon nitride was dispersed in the bath. The size of powder particle dimensions was in the range of 10÷30 nm. The electroless deposition processes were performed with constant contents of Si3N4 disperse phase in the bath (5 g/dm3). The topography and morphology of produced layers were identified by electron scanning microscope techniques. The phosphorus and silicon contents of the Ni-P/Si3N4 coatings were measured using energy dispersive spectroscopy (EDS) analysis. The microhardness of the produced materials has been measured by using the Vicker's method. It was observed that the hardness of the composite layers exhibited much more greater values when compared with nickel-phosphorus layers. The adhesion of produced layers was evaluated by the scratch test. The morphologies of nickel-phosphorus and composite layers after scratch tests and diagram of acoustic emission are presented. It was found that very thin zinc-plating on the aluminum alloy substrate before electroless plating layers reveals perfect adhesion to the aluminum alloy substrate. The course of wear tests as time functions of duration of attempt of the Ni-P and Ni-P/Si3N4 layers are presented. In conclusion, it has been checked that the silicon nitride disperse phase involved into amorphous Ni-P matrix importantly increases their abrasion wear.