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°C and 500°C) 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 (8×1018 ions/cm2, 380°C) 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 ε-(Fe,M)2+xN; 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 μm); the considerable increase of concentration of tiny (up to 0.2 μm) 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°C.