Structural characterisation of hardening of Ti-Al-V alloys after nitridation by plasma immersion ion implantation

The surface hardness of the titanium alloy Ti-6Al-4V, widely used as constr uction material, can be improved by nitrogen implantation. The paper report s on a complex study of the structural mechanisms of hardening and its loss at higher temperatures with different methods (grazing incidence X-ray dif fraction (GIXRD), in situ high- temperature diffraction with synchrotron ra diation, elastic recoil detection analysis (ERDA), hardness measurements an d surface inspection by scanning electron microscopy (SEM)). Plasma immersi on ion implantation (PIII) produces a nitrogen profile directly below the s urface. The formation of small TiN crystallites is detected, but the hardne ss increase is only about 40%. Annealing leads to the reduction of the TiN phase and the formation of Ti2N deeper in the material. The in situ X-ray d iffraction (XRD) study of the phase formation gives information about the t emperature dependence of these changes. The hardness increases after anneal ing by a factor of 2.5 compared to the unimplanted state. It is explained b y precipitation hardening due to the formation of titanium nitrides in diff erent depths of the material. (C) 2001 Elsevier Science B.V. All rights res erved.