SLIDING WEAR BEHAVIOR OF NI-P-W COMPOSITION-MODULATED COATINGS

We studied the unlubricated sliding wear behaviour of Ni-P-W compositi onally modulated coatings on mild steel pins, sliding against hardened steel discs in a pin-on-disc set-up. The multilayered coatings consis ted of high and low W-content layers. The linear velocity was constant for all tests, and the normal loads used were 200, 500, 800 and 1100 g. Coatings of various layer periodicities were studied. Friction coef ficients were recorded during the tests, and it was found that after a running-in period of about 30 m, friction coefficients reached a stea dy slate. An increase in the normal load caused a decrease in friction coefficients regardless of the layer periodicity of the coating. Coat ings with a smaller layer periodicity showed a better wear resistance than those with larger layer periodicities. Two major wear mechanisms were identified: brittle fracture of the individual layers accompanied by crack deflection at the interfaces between the layers and delamina tion of parts of the coating. The first mechanism was active for the w hole range of loads, whereas the second was operative only for loads o f 800 and 1100 g. (C) 1998 Elsevier Science S,A.