Surface durability of electroless Ni–P composite deposits

Different Ni–P composite coatings containing SiC particles, to improve wear resistance, and PTFE, MoS 2 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/MoS 2 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/MoS 2 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/MoS 2 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/MoS 2 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.