FABRICATION OF MICROLAMINATED AL/AL2O3 COMPOSITES BY MAGNETRON SPUTTERING FOR TRIBOLOGICAL APPLICATIONS

Microlaminated composites consisting of alternating layers of Al and Al2O3 have been produced using a radiofrequency triode magnetron sputtering unit equipped with metallic and oxide target sources. Composite films up to 25 mum thick with 100 Al/Al2O3 layers were fabricated in the form of square coupons 20 mm x 20 mm, which were suitable for wear testing using a miniature pin-on-disc tribometer. To measure the strength and the wear resistance as a function of the interlaminate spacing, composites with Al layers 100-500 nm thick were fabricated. The thicknesses of the Al2O3 layers were in the range 20-100 nm. Transmission electron microscopy and selected area electron diffraction studies showed that every Al layer consisted of polycrystallites with very fine grain size (20 nm on average), whereas the Al2O3 layers had an amorphous structure. Microhardness measurements showed that monolithic nanocrystalline Al produced using sputtering had a hardness of 1700 MPa (eight times higher than that of a pure Al target with a grain size of 5 mm) and the incorporation of Al2O3 layers increased the microhardness to 2300 MPa. Tribological tests revealed that the dry sliding wear resistance of Al/Al2O3 composites increased by a factor of two compared with that for monolithic nanocrystalline Al.