PROPERTIES OF SURFACE-LAYERS ON TITANIUM-ALLOY PRODUCED BY THERMOCHEMICAL TREATMENTS UNDER GLOW-DISCHARGE CONDITIONS

The recent rapid progress in surface treatment techniques dictates tha t the titanium alloys should have an improved resistance to frictional wear without any loss of their high corrosion resistance. These requi rements can be satisfied by producing surface layers of specified micr ostructure and phase composition. The present paper describes a modifi cation of the plasma discharge nitriding treatment of titanium alloys, i.e. the glow discharge-assisted oxycarbonitriding, which by introduc ing oxygen, nitrogen and carbon into the surface zone of the layer [a Ti(NCO) type layer] improves its useful properties, primarily the resi stance to frictional wear and the resistance to corrosion [1,2]. This is because titanium shows a good affinity to oxygen, carbon and nitrog en, whereas the chemical composition of the layer depends on the chemi cal composition of the low-temperature plasma that forms under the con ditions of glow discharge. The present paper also discusses the result s of the corrosion behaviour of the OT4-0 titanium alloy in simulated human body fluids before and after the sterilization process. The isot hermal and cyclic plasma nitriding and carboxynitriding processes on t itanium alloys can be carried out in a specially modified glow dischar ge chamber designed for the plasma nitriding process. (C) 1997 Elsevie r Science S.A.