Preparation and characterization of ion-assisted amorphous NiTi(N) coatings

Abstract

In previous work it has been shown that the N + implanted NiTi alloy surface consists of crystalline TiN precipitates embedded in an amorphous structure. This surface modification considerably reduces the friction coefficient and dramatically increases wear resistance. A coating of this type on stainless steel has been prepared using a high-energy ion beam assisted deposition (IBAD) technique. TEM, SIMS and XPS analyses show that sputtering of an Ni 49Ti 51 target with 1.5 keV N + ions leads to an amorphous N1 53Yi 47 film with a high content of nitrogen and containing small TiN precipitates (5 nm). When the growing film is simultaneously bombarded with a 160 keV Ar + beam the precipitates are bigger (10 nm) and the coating-substrate interface is mixed over a thickness of 200 nm. The wear resistance of these coatings deposited on stainless steel 304L is excellent: this is explained in terms of the amorphous structure, fine precipitates created during ion-beam assisted deposition and the diffuse interface.