Wear resistance of nitrided and DLC coated PH stainless steel

Abstract

Precipitation hardening stainless steels are extensively used as a material for plastic injection dies because of their dimensional stability during hardening, impact strength and wear and corrosion resistance. Plasma surface engineering can enhance even more the working life of these components preserving them from wear and corrosion damage by means of surface modification or coatings. In this work PH stainless steel Corrax® was ion nitrided and coated with DLC in a modified PACVD duplex process. DLC films are known not only for their hardness but also for their low friction coefficient, features that improve the wear resistance of steel components. Adhesion tests were performed; wear resistance was tested in a pin on disk machine with different counterparts and in the abrasion ASTM G65 test. Nitrided samples were compared in all tests with DLC only coated samples and the duplex ones (nitriding+coating). The thickness of the nitrided layer was of 14μm, and the coating, 1.8μm. The duplex samples had the best abrasive wear resistance; their mass loss was almost negligible and within the error of the instrument. The only coated samples had a very low mass loss compared with the only aged steel, but the coating was detached.The coated samples presented a low friction coefficient, about 0.03 against alumina and the no wear loss was detected. On the other hand, only the duplex samples presented an acceptable adhesion in the Rockwell C indentation test with 600N and the critical load was 28N in the scratch test.