Advanced Powder Technology, Vol.29, No.5, 1306-1316, 2018
Hardness, wear resistance and bonding strength of nano structured functionally graded Ni-Al2O3 composite coatings fabricated by ball milling method
Using initial powder mixtures with different Ni:Al2O3 weight ratios ranging from 1:1 to 16:1, nano structured Ni-Al2O3 composite coatings were deposited onto an aluminum plate by means of a planetary ball mill. It was shown that initial charges with Ni:Al2O3 weight ratios of 4:1 and greater, yielded wellcompact coatings. Coating deposited from the powder charge with Ni:Al2O3 weight ratio of 4:1, contained 20 vol% of alumina particles in the Ni matrix and submitted the highest hardness value (657 +/- 28 Hv) and wear resistance. Nevertheless, composite coating containing smallest amount of alumina particles showed the highest cohesive strength of 9.8 +/- 0.3 MPa. In the next step, nano structured functionally graded composite coatings were produced by the deposition of two separate layers containing different amounts of alumina particles. Although the graded coating showed superior hardness and wear resistance compared with the non-graded coatings, it suffers from low cohesive strength attributed to the presence of alumina particles at the interface region between the two layers. To overcome the poor adhesion between two layers, a thin intermediate plain Ni one was deposited between two layers leading to 80% and 30% improvement in the adhesion strength and wear resistance, respectively. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.