Nanocomposite Ni-P/Si3N4 and Ni-P layers were deposited on Al alloys by chem. redn. by using a polydisperse Si3N4 powder (grain size 20-25 nm) and studied for hardness, abrasion resistance (ball-on-disc method) and surface topogr. The addn. of Si3N4 nanoparticles resulted in improving tribol. properties of the surface layers.