Evolution of microstructure of instrumental AISI M2 steel after plasma immersion nitrogen and carbon implantation

Investigations of the elemental and phase composition, microstructure, microhardness and tribological properties of AISI M2 steel subjected to nitrogen and carbon plasma-immersion ion implantation (PIII) at different regimes are presented. Elemental composition was studied by Auger electron spectroscopy (AES) and X-ray microanalysis. Phase composition was identified by means of conversion electron Mössbauer spectroscopy (CEMS) and X-ray diffraction (XRD). Using these methods it was established that nitrogen PIII at a target temperature of 380°C resulted in phase transformations: from α′-Fe(C,M)+M6C+MC (M: Fe,Cr,W,Mo) to ε-(Fe,M)2+x(N,C)+M6(C). With increasing temperature up to 500°C in nitrogen PIII the retained martensite, in addition to ε-(Fe,M)2+x(N,C), was observed. Joint nitrogen and carbon PIII leads to the formation of ε-(Fe,M)2+xC and (Fe,M)7C3 (M:Cr,W,Mo) carbides. Theoretical analysis of the distribution of thermoelastic stresses during PIII demonstrated the essential increase in the mass transport process of implanted atoms into the target volume. On the basis of the estimations conducted, it has been shown that migration processes of nitrogen into steel during PIII have a complicated character and can be described with the help of mechanisms stimulated by the reaction of a crystal lattice under the impulse influence.