Structural analysis of a high-speed tool steel irradiated by an intense pulsed ion beam

Summary form only given, as follows. Irradiation of an intense pulsed ion beam (IPIB) to a metal with a high power density and a short pulse duration leads to a rapid heating of the metal surface, which is followed by a rapid cooling with a cooling rate of 10/sup 7/ to 10/sup 10/ K/sec. The rapid heating and cooling produce nonequilibriurn microstructures such as amorphous, nanocrystalline, or metastable phases in a metal surface layer, resulting in enhancement of mechanical and chemical properties. In this paper, the surface modification of a high-speed tool steel (SKH51) with irradiation of a proton-IPIB has been demonstrated experimentally. The non-irradiated sample consisted of an /spl alpha/-Fe structure and some second phase carbides such as VC, Cr/sub 6/C and Fe/sub 6/C. After I-pulse-irradiation, in the surface layer of the IPIB-irradiated sample, a high-temperature phase, /spl gamma/-Fe, was formed partially. The second phase carbides were dispersed from the irradiated surface, and the alloyed elements, V, Cr, and C were solved into the matrix of the /spl gamma/-Fe structure. In addition, the average grain size was reduced from 8 /spl mu/m to 240 nm by IPIB-irradiation. The /spl gamma/-Fe was more dominant with an increase in number of IPIB-irradiation. After 10-pulses-irradiation, the single phase of the /spl gamma/-Fe was formed in the surface layer of the sample, and the average grain size was estimated to be 40 nm. The /spl gamma/-Fe structure, however, was converted into the /spl alpha/-Fe after 100-pulses-irradiation of the IPIB. The AES profile indicated that the alloyed elements were solved into the matrix of the /spl alpha/-Fe. This structure, martensite (/spl alpha/´-Fe), has excellent hardness and wear properties. The X-ray diffraction profile of the sample treated by 100-pulses-irradiation showed broadened diffraction peaks, indicating that the grain size of the sample was reduced to several nano-meters.