Comparison of sliding wear behaviour of pulse electrodeposited Ni-Cu nanocrystalline alloys and Ni-Cu/Cu multilayers

This study presents a comparison of tribological properties of electrodeposited nanolayered Ni-Cu/Cu multilayers and nanocrystalline Ni-Cu alloys. In this work, nanocrystalline Ni-Cu alloys containing 35.8 and 26.0 wt-% Cu with grain sizes of 12.8 and 6.6 nm respectively were chosen for wear tests in which the tribological performances of these alloys were compared with Ni-Cu/Cu multilayers: [Ni-Cu (4.5 nm)/Cu (1.97 nm)](n) (30.4 wt-% Cu) and [Ni-Cu (7.8 nm)/Cu (1.97 nm)](n) (20.2 wt-% Cu) respectively. All the test samples were electrodeposited under pulsed current conditions on polished stainless steel substrates keeping total thickness fixed at similar to 10 mu m. Reciprocating dry sliding experiments of these samples at a constant normal load in the range 3-11 N were performed in ball on plate geometry keeping the amplitude fixed at 0.001 m. The obtained average coefficient of friction of nanocrystalline alloys was found to be slightly inferior compared to that of multilayers. On the other hand, the wear rate of nanocrystalline alloys was lower than that of multilayers under identical conditions. Higher hardness and lower elastic modulus of nanocrystalline alloys compared to that of multilayers was found to be responsible for the observed wear rate variation.