Surface modification of constructional steels by irradiation with high intensity pulsed nitrogen plasma beams

This paper presents the results of the modification of two types of constru ctional steels induced by irradiation with multiple pulses of nitrogen plas ma generated in two facilities: IBIS (at Swierk, Poland) and PROSVET (at Kh arkov, Ukraine). The duration of pulses is in the microsecond range and the energy density attains a value of up to 20 J/cm(2). The treatment leads to melting and solidification of a surface layer of a thickness of few microm etres, with simultaneous introduction of a significant concentration of nit rogen. Irradiation results in marked improvement of the wear properties. Se veral analytical techniques such as conversion electron Mossbauer spectrosc opy (CEMS), conversion X-ray Mossbauer spectroscopy (CXMS), nuclear reactio n analysis (NRA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to reveal the nature of this improvement. Possible mech anisms of modification are discussed. It is concluded that the improvement of the wear properties should be associated with the formation of austeniti c fee gamma(N) phase in which an Fe atom has an interstitial N atom as the nearest neighbour. (C) 2000 Elsevier Science S.A. All rights reserved.