Chemical state depth distribution of boron in high-dose implanted iron surface

The resistance to wear and chemical corrosion of iron surfaces can be improved by surface boriding which is commonly achieved by the powder-pack boriding method, where the iron sample is embedded in a powder of high boron concentration and heat-treated in a furnace. The boron atoms from the powder diffuse into the iron by thermal excitation, resulting in a boron concentration gradient and a bilayer comprised of two distinct boride phases FeB and Fe 2 B. These phases possess different crystal structures and different thermal expansion coefficients, which leads to mechanical instability and spalling of the surface layer. In order to avoid the dual-phase structure, the boron was introduced into our samples by ion implantation, a non-diffusion-based method that can also be temperature-controlled. In this paper we report our new results of high-dose boron implantation of iron. Boron ions were implanted at a nominal fluence of 6.9⋅10 17 ion/cm 2 into the surface of polycrystalline iron sheets at 25 keV kinetic energy and at room temperature. After implantation, a thermal annealing was applied at the temperature of 400 °C for 1 h. The surface layer of samples was characterized by depth profile analyses of chemical constituents and of chemical states before and after annealing. We observed that when the implantation dose was high enough to produce an amorphous layer, the chemical bonds between Fe and B atoms were mainly FeB type. It was shown experimentally that these FeB chemical bonds were transformed into Fe 2 B bonds by high temperature annealing. The crystalline structure of the samples wase analysed by X-ray diffraction measurements which support our findings: freshly-implanted samples only contain FeB, annealed samples contain both Fe 2 B, and FeB. • Iron surface boriding by implantation. • High-dose boron implantation of iron. • Nanoscale depth profile analysis of iron-boride layers. • Depth distribution of chemical bonds in iron boride layers prepared by implantation.