PVD NiAl intermetallic coatings: microstructure and mechanical properties

NiAl intermetallic coatings were fabricated using an rf magnetron sputtering system and a specially-designed composite target made from pure Ni and Al metals. The coatings which were similar to 10 mu m thick were deposited on a variety of substrates including 1100Al, commercial purity nickel, 316 type stainless steel and borosilicate glass. X-Ray diffraction (XRD) showed that the coatings produced for all substrates were the NiAl intermetallic compound with the ordered cubic B2 crystal structure. The coating deposited on a borosilicate glass substrate had a (111) preferred orientation. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) confirmed that the grain size of the NiAl was similar to 10 nm. The hardness and elastic modulus of the NiAl coatings were measured using an ultra-microhardness indentation system and found to be 11.52 GPa and 143.42 GPa, respectively. The NiAl intermetallic coating worn against a steel bearing pin exhibited a low wear rate (2.9 x 10(-4) mm(3)/m). The NiAl coating had a lower value of coefficient of friction (0.23) than the aluminum substrate (0.28) as measured using a scratch tester. (C) 1997 Elsevier Science S.A.