MODIFICATION OF ELEMENTAL COMPOSITIONS IN THE NEAR-SURFACE REGION OF LOW-ALLOY STEELS BY A GLOW-DISCHARGE PLASMA

The redistribution of matrix and impurity elements in the near-surface region of the low-alloy steel (2.0% Ni, 1.25% Cr) before and after tr eatment by a dc- and rf-discharge plasma in atmospheres of He, N-2, O- 2, Ar and N-2 + 25% H-2 was studied using SIMS and AES. It has been sh own that the treatment changes considerably the concentration of matri x elements in the near-surface region compared to the volume concentra tion. The changes depend not only on the chemical composition of the a tmosphere but also on the initial physico-chemical state of the surfac e. It was found that the near-surface region of the sample treated in the dc-discharge N-2 + 25% H-2 plasma was depleted of Cr and Ni to a c onsiderable degree. At the same time a similar treatment of the sample preceded by an ion-plasma cleaning of its surface resulted in an enri chment of the near-surface region with Cr and Ni up to 37% and 9%, res pectively. An explanation of the effect is suggested.