Application of x-ray photoelectron spectroscopy in the investigation of wear of press tools strengthened with ion-vacuum coating

Abstract

UDC 543.42 Tungsten-containing high-speed steels and hard alloys are widely used in engineering for making press tools, but the scarcity of these materials makes it necessary to increase their wear resistance [i, 2]. One of the effective methods of strengthening the working surface of press tools is the application of a strengthening carbonitride coating. To reveal the mechanism by which the coating is formed and the mechanism of its wear, it is of interest to obtain information on the chemical and elemental composition of the surface of press tools after their coating. To solve this problem we used the method of x-ray photoelectron spectroscopy (XPS) which has been widely used lately for investigating the electron structure and the chemical composition of the surface of solids [3-6]. The method of XPS yields information on the chemical composition of atoms in the surface layers of a substance about 2.5 nm thick without destruction of the specimen. The high sensitivity of the method to all chemical elements (except hydrogen) makes it possible to carry out a quantitative analysis of the chemical composition of the surface. This means determining the overall concentrations of atoms of the elements under consideration as well as the concentration of atoms that are in certain chemical states. The study of the electron structure and composition of materials is important for the understanding of many of their physical properties, and also of the very process of obtaining these materials. Since the materials interact with each other and with the environment through the surface, the properties of the thinnest surface layers of the substance in particular determine in most cases the behavior of the entire bulk of the material and its operational characteristics. The investigations were carried out with an electron spectrometer JEE-15. The accuracy of determination of the position of the maximum of the photoelectron lines amounts to  eV. The vacuum in the spectrometer is equal to 5-i0 -s Pa. As source of photons we used MgK~ radiation (1253.6 eV). Information on the structure of the surface layer was obtained with an effective depth of electron detachment of about 2.5 nm. The sensitivity of the instrument is of the order of 1 atom of impurity for 10,000 atoms of the principal substance. The preliminary processing chamber is equipped with a system of electrodes for etching the surface with argon ions Ar~. Etching was carried out with continuous evacuation of residual gases and etching products at a pressure of about i0 Pa in the chamber. The investigated specimens were mounted on cylindrical aluminum bushes. To obtain information on the type of chemical compounds occurring on the surface of the specimens, we compared the obtained values of binding energy with the values of binding energy in pure elements or in compounds with known stoichiometry. The investigations showed that there are considerable changes in the quantitative content of individual elements across the depth of the zone of wear as well as in the qualitative nature of their compounds. By the method of x-ray photoelectron spectroscopy the present authors investigated for the first time the surface of piercing punches of steel R6M5, strengthened by a coating of