Surface durability of electroless Ni-P composite deposits

Different Ni-P composite coatings containing SiC particles, to improve wear resistance, and PTFE, MoS2 and BN particles, to reduce friction, were produced on a steel substrate by means of electroless deposition. A reference Ni-P deposit and a double Ni-P/SiC-PTFE co-deposit were also produced. The dry sliding behaviour against a steel counterface (made of AISI M2) was found to develop through two stages (indicated with stage I and II). Stage I was found to be connected with the initial wear damage of the co-deposit and is therefore representative of its surface durability. In this respect, the best performances were displayed by the Ni-P/PTFE and Ni-P/MoS2 co-deposits, since their wear rates were negligible during stage I. For the Ni-P/PTFE co-deposit, friction coefficient also remained very low (0.07) during this stage, whereas in the case of the Ni-P/MoS2 co-deposit, stage I, which also had a shorter duration, was characterized by a higher friction coefficient (0.18). The removal of the co-deposit (stage II) was, however, more difficult in the case of the Ni-P/MoS2 co-deposit than for the Ni-P/PTFE co-deposit. The Ni-P/SiC-PTFE co-deposit displayed better properties than the reference Ni-P deposit but worse than the Ni-P/MoS2 and Ni-P/PTFE co-deposits and, finally, the Ni-P/BN co-deposit showed the worst sliding behaviour, since its intense removal started from the beginning of the test. As far as the rolling-sliding behaviour of the co-deposits against the same steel counterface is concerned, the best properties were shown by the Ni-P/BN co-deposit and the worst performances were shown by the reference Ni-P deposit and the Ni-P/SiC co-deposit because of their brittleness. (C) 1999 Elsevier Science S.A. All rights reserved.