Surface modification of superalloys and heat resistant steels by irradiation of low and high energy ion beams

Abstract

The effect of ion beam treatment (IBT) using low and high energy ion beams, on surface topography, chemical composition and structure of surface layer and service properties of nickel based superalloys, heat resistant steels and pure Ni was studied. It was shown that low energy high current IBT ( E ≈ 10 −1 to 10 ° keV, j ≈ 10 −1 to 10 mA cm −2) enabled: (1) to form a surface of irradiated samples with a roughness varying over a wide range; (2) to carry out radiation-enhanced relaxation of residual stress, formed during pretreatment; (3) to clean the surface layers of the sample from contamination by C, O and S; (4) to detect the cast superalloy macrostructure. The results of gas and metal ion implantation investigation indicate that at the traditional regimes of implantation ( E ≈ 10 keV, < j> ≈ 10 μA cm −2, D ≈ 10 17 ions cm −2), the depth of ion penetration is 10 −2 to 10 −1 μm and the thickness of the modified structure layer is h M ≈ 10 −1 μm. One can increase the h m considerably by high current ion implantation (j≥10 3 μA cm −2) and high power pulse IBT ( N p≥10 7 W cm −2, τ p ≈ 10 1 to 10 2 ns). The irradiation by high energy ion beams allows to change the service properties of the materials (wear resistance, oxidation resistance, fatigue strength) over a wide temperature range. Plausible reasons of these changes are discussed.