Duplex Surface Treatment due to Combined Plasma Nitriding and Ceramic or Cermet Thick Coatings of Cr-Ni-N System

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Austenitic type 304 stainless steel was duplex treated by ion-nitriding at about 803 K and subsequent ion-plating of Cr-N or CrNi-N.The nitride films of Cr-N or CrNi-N were deposited in the pure N_2 or N_2-H_2 mixed gas at about 2.5 Pa with a film thickness of 3-34mum. The following results are obtained.(1) As for the Cr-N system, the phase composition was a single phase of CrN or the mixed phases of Cr_2N and Cr. As for the CrNi-N system, it was the mixed phases of Cr^<**>N and Ni. Cr^<**>N was newly obserbed Cr nitride which may contain some Ni and identified as an f.c.c.structure (a=0.37 nm).(2) The film hardness was about Hv 1900 for Cr-N and about Hv 1000 for CrNi-N.The depositing rate of the CrNi-N film was faster than that of Cr-N,but the surface roughness was larger.(3) The ceramic flims of CrN coated onto the pre-nitrided steel showed the best wear resistance even under a heavy load. Among the CrN films of 3,10 and 19 mum, the CrN film with a thickness of 10 mum showed the minimum wear loss and the wear loss of CrN film with a thickness of above 10 mum coated onto the untreated steel decreased nearly to that of CrN film coated onto the prenitrided steel.(4) The cermet films of CrNi-N coated onto the untreated steels show the good wear resistance and these films coated onto the pre-nitrided steels exhibet the inferior wear resistance compared with ones coated onto the untreated steels, being contrary to the tendency of the common ceramic films like as CrN.