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

A surface of a high-speed tool steel has been modified by an intense pulsed ion beam (IPIB) that has the ion energy of 180 keV, the ion current density of 460 A/cm/sup 2/, and the pulse duration of 65 ns. The transformation of the crystalline structure in a sample surface layer by IPIB-irradiation was observed by a glancing angle X-ray diffraction and a transmission electron microscopy. The second-phase carbides, V/sub 4/C/sub 3/, Cr/sub 6/C, and Fe/sub 6/C, were dispersed from the irradiated surface layer. A ferritic or martensitic matrix in the surface layer was converted into an austenitic matrix by 10-pulses-irradiation of the IPIB. After repeated IPIB-irradiation of 100 pulses, a mixed phase of the austenite containing 2.0 wt.% carbon and the cementite was formed in the surface layer. The grain size of the sample was reduced from 7 /spl mu/m for the untreated to 40 nm after 100-pulses-irradiation. The Vickers hardness of the treated surface was approximately H/spl nu/=1000 corresponding to 1.2 times of the untreated one. In addition, the friction coefficient of the treated surface was reduced to from 1.2 to 0.9 and the durability of the surface was significantly improved.