Surface composition and near-surface hardness studies on high dose boron-implanted 304 stainless steel

Abstract

The modification of boron-implanted near surface of 304 stainless steel having strained and strain-free surfaces was studied. The energy of the boron ion was 130 keV at a dose of 2·5×10¹⁷ ions cm⁻². Ion-implantation is known to modify the tribological properties of metals, however, it is not well-understood as to how such a shallow implanted layer can affect the microhardening. A full understanding of the process involved is yet to emerge. In the present work the ion implanted layer was characterized for boron depth profiles using AES and XPS. The implanted layer is observed to contain B₂O₃, Fe₂B, FeB and CrB₂ compounds with small fractions of chromium and iron oxides. The strain-free surface of 304 SS shows an increase in microhardness by ∼ 80% after boron ion implantation at 2 gf and the strained surface by ∼ 30% at the same load. The annealing effects on microhardness for mechanically polished and implanted samples were also investigated in the temperature range 100 to 400°C. The possible correlation of near-surface microhardness increase with boride formation is discussed.