Synthesis and Comparative Characterization of Electroless Ni–P, Ni–P-nano-Al2O3 and Duplex Ni–P/ Ni–P-nano-Al2O3 Coatings on Aerospace-Graded AA2024 alloy

Abstract

AbstractThe essence of electroless coatings is realized by the scientists since last decade, which makes them a vital player in material coating industry. Incorporation of a second phase micro or nanoelement into the Ni–P matrix widens the area of applications for these types of coatings. Researchers are showing their interest to develop more innovative electroless coatings where they are deploying different types of second phase material to enhance their physical, mechanical and chemical properties. Duplex coatings have shown promising capabilities by providing excess hardness, wear and corrosion resistance, which can be attributed to the resultant effect of two consecutive layers of coating. In our research, three different types of electroless nickel phosphorous (EN) coatings were applied on the aerospace-graded AA2O24 alloy substrate. The first type was plain Ni–P coating, the second one was a composite coating where nanoalumina was incorporated into the electroless Ni–P matrix, and the third coating was a duplex coating with the inner layer having Ni–P and the outer layer consisting of a Ni–P layer incorporated with nanoalumina particles. Characterization of the deposits by scanning electron microscopy (SEM) along with energy dispersive X-ray spectroscopy (EDS) confirms the production of flawless, adherent coatings onto the substrate. Maintaining the surface roughness at an acceptable level, a great increase in nanohardness was observed that was further enhanced by incorporation of nano-Al2O3 particles and provision of one additional external layer in duplex coating. Excellent wear resistance was also evaluated by the nanoscratch test. On the basis of results obtained, this study suggested the superiority of the electroless duplex coating onto AA2024 substrates especially used in aerospace and defence industries.KeywordsDuplex coatingsNanohardnessNanoscratch testAerospace and defence industries