Tribological properties of plasma nitrided and hard coated AISI 4140 steel

In the present study, samples made of AISI 4140 steel pre-treated with plas ma nitriding and coated with different PVD coatings (TiN, TiAlN and ta-C) w ere investigated in terms of their microhardness, surface roughness, scratc h adhesion and dry sliding wear resistance. Wear tests, in which duplex-tre ated pins were mated to hardened ball bearing steel discs, were performed w ith a pin-on-disc machine. To examine the influence of the nitrided zone on the performance of the coating-substrate composite, coatings were deposite d on hardened as well as on plasma nitrided samples, prepared under differe nt nitriding conditions. The results of the investigation showed improved mechanical and wear proper ties of the plasma nitrided hard-coated specimens compared to the uncoated and pre-hardened ones. Furthermore, the compound layer was found to act as an intermediate hard layer leading to superior sliding wear properties of t he composite. (C) 2001 Elsevier Science B.V. All rights reserved.