Plasma immersion N and N+C implantation into high-speed tool steel: surface morphology, phase composition and mechanical properties

The effect of plasma immersion N and N + C implantation at elevated temperatures (380 degreesC and 500 degreesC) on microstructure, element and phase composition, microhardness and tribological properties of high-speed tool steel (HSS) has been studied. It has been established that under plasma immersion ion implantation (PIII) of nitrogen (8 x 10(18) ions/cm(2), 380 degreesC the microhardness of steel surface layers increases by a factor of 2.5 and the friction coefficient decreases by a factor of 2. By methods of Auger electron spectrometry (AES), energy dispersive X-ray analysis (EDX), glancing X-ray diffraction (GXRD) and scanning electron microscopy (SEM) it is shown that transformations of near-surface layers are associated with: the formation of strained epsilon-(Fe,M)(2+x)N; nitrogen doping of M6C carbide; the formation highly defective regions (channels and/or pores) predominantly localized near carbide precipitates in near-surface layers (up to 10 mum); the considerable increase of concentration of tiny (up to 0.2 mum) carbide phases doped with nitrogen; the formation of less modified deep layers in the case of N + C as compared to N PIII; the significant selective sputtering of martensite at 500 degreesC. (C) 2001 Elsevier Science B.V. All rights reserved.