Characterization of aluminides formed on superalloy 690 substrate

Ni-Cr-Fe based superalloy 690 substrate, pack aluminized at 1273 K, revealed formation of multilayer comprising (NiCr)Al + Cr₅Al₈, Ni₂Al₃ + Cr₅Al₈, NiAl and γ phases. Knoop hardness number varied from 225 to 1142 along the cross-section. Wear and friction tests on aluminized specimen were performed in dry medium using reciprocating sliding wear and friction machine with tungsten carbide ball at 15 N load with frequencies at 10, 15 and 20 Hz. The coefficient of friction, the static ones were obtained in the vicinity of 0.2, 0.3 and 0.5, while dynamic ones were 0.3, 0.4 and 0.4 respectively. For the ball, the wear rate was 1.9 × 10^?6, 1.2 × 10^?5 and 1.5 × 10^?5 mm³/Nm, whereas the wear rate was 5.8 × 10^?5, 3.8 × 10^?4 and 4.6 × 10^?4 mm³/Nm respectively for the aluminized specimen indicating good adherent surface coating.