Surface modification of monel K-500 by the plasma source ion implantation process

The monel series of nickel base alloys (Ni-Cu type) are attractive for components like bearings and shafts operating in high magnetizing environments because of their non-magnetic characteristic coupled with superior corrosion and oxidation resistance at extreme service temperatures. Unfortunately, the current bearing technology is based on the use of two classes of materials, 5000 series alloy steels and 400 series stainless steels, both of which are magnetic. Thus, the successful operation of a magnetic device requires a new class of bearing materials. Some of the non-ferrous materials such as monels have not demonstrated superior wear characteristics as bearing materials. Plasma source ion implantation (PSII), a non-line-of-sight technology for implanting preferably gaseous species, is a new and innovative approach to surface modification of materials. The principal objective of the present investigation was to apply PSII technology to improve the wear characteristics of monels for developing a new class of bearing materials operating in highly magnetic environments. Monel K-500 alloy samples were nitrogen implanted by the PSII process and the modified layers were characterized by profilometry and optical metallography, low load microhardness testing, scanning Auger microscopy (SAM), pin-on-disk wear testing and scanning electron microscopy (SEM). The results of nitrogen implantation show a significant improvement in wear resistance of this alloy without any perceptible increase in surface hardness.