Barbara Kucharska

Prediction of the Depletion Zone due to Selective Oxidation of P91 Steel

Experimental measurements do not allow for a unique determination of the concentration profiles, e.g., in case of multi-layer systems. The measured concentration of the elements at the alloy/scale interface is an average concentration in an alloy and in a scale near the spot of the beam [1]. The knowledge of the concentration of the elements at the boundary is necessary for the understanding corrosion of alloys. This essential obstacle of experimental techniques can be overcome by computer modelling. Namely, by combining the different methods (non-unique measurement with unique modelling). The Danielewski-Holly model of interdiffusion has a unique solution. This model enables to predict the evolution of component distributions in the reacting alloy. The model is valid for time dependent boundary conditions and consequently can be used for modelling the more complex reactions, eg., the formation of complex oxides. To avoid the nonphysical values of fluxes in reacting alloy the kinetic constraint on all fluxes was introduced, i.e., the flux limitation method. The results of the selective oxidation of the P91 steel (0,1 wt.% C, 8,6 wt.% Cr, 0,25 wt.% Ni) are presented. Calculated concentration profiles are compared with the experimental data. We show the evolution of chromium distribution in oxidizing steel up to 3 000 hours. The computations demonstrate that chromium depletion is the key factor determining the scale composition.

Diffractometric examination of the structure of heat-resisting steel-based coatings in different measurement geometries

Coatings of the composition of 310S heat-resisting steel dopped Al and Ir additions, deposited on a substrate of the same steel by the magnetron sputtering method, were examined. The measurements were made in the classical Bragg-Brentano geometry and by the GXRD method. With the fixed and different position of the coated sample by rotating the sample by angles ψ. The coating as deposited and after being soaked at 400°C for 15 minutes was subjected to examinations. The examination carried out have shown that coatings may have a unique, subtle structure which is metastable and undergoes irreversible changes in the temperatures up to 400°C. It has been found that in the outermost coating zones and zones closer to the substrate, areas occur in the coating structure, which have the different lattice parameter compared to the basic phase. Additionaly, the local period of the structure equal 5.9 nm was found.

A Comparative Study on the Cu/Ni Multilayer Period Using Two X-Ray Wavelengths

This paper presents the results of X-ray research on the structure of Cu/Ni multilayers magnetron-deposited on a Si (100) substrate. The multilayers, each consisting of a hundred Cu/Ni double-layers, but with a variable thickness of the Ni (1,2÷3nm) sublayer, were investigated. The thickness of the Cu sublayer was the same for all multilayers investigated and equalled 2nm. X-ray measurements were taken using filtered radiation with λCu=0.15405 nm and λCo=0.17902nm. The coatings were examined in respect of the angle at which the (111) reflection and satellite peaks appeared together. The obtained reflections were fitted using the Pseudo Voight curves. The thickness of the multilayer periods, resulting from the analysis of the diffraction pattern obtained for the above wavelengths of radiation, was compared. The thicknesses closest to those assumed in the deposition process were obtained for multilayers examined using radiation with Cu and utilizing the position of both satellite peaks, and multilayers examined using radiation with Co and utilizing the position of the main Cu/Ni(111) reflection and the S-1 satellite reflection.

The X-Ray Measurement of the Thermal Expansibility of Al-Si Alloy in the Form of a Cast and a Protective Coating on Steel

The paper presents the investigation of the expansibility of an Al-Si alloy in the form of a protective coating applied on a steel substrate and as a conventional cast, respectively. Examinations were carried out in the temperature range of troom÷220°C using the diffractometric technique based on reflections (311), (222), (400), and (331) from the Al solid solution. It was demonstrated that the coating exhibited better thermal expansibility compared to the cast, and its thermal expansion coefficient was close to the standard values for alloys of the same chemical composition. For the cast, the thermal expansion coefficient was lower by approx. 25% in relation to the standard value. It was also found that the soaking of alloys during X-ray examination reduced their texturing and caused changes in the microstructure of both the coating and the cast by thinning the silicon crystals and rounding their edges.

Research into the relationship between the surface topography, texture and mechanical properties of PVD-Cu/Ni multilayers

The paper presents the results of structural examinations and mechanical tests of Cu/Ni multilayers fabricated by the magnetron sputtering method. The investigated multilayers were differentiated by Ni sublayer thickness (1, 3 and 6 nm), while the retaining Cu sublayer thickness was unchanged (2 nm). Measurements demonstrated that the multilayers were strongly textured in the direction of their growth [111], with the thinnest multilayer (Cu/Ni = 2/1) showing a stronger texture. Stronger texturing was associated with greater surface roughness. Multilayers with the largest thickness had higher hardness and Young’s modulus. The properties of Cu/Ni multilayers depended both on the thickness of their sublayers, as well as on their total thickness.

Characterization of the surface topography and nano-hardness of Cu/Ni multilayer structures

This article describes the results of a study of Cu/Ni multilayer coatings applied on a monocrystalline Si(100) silicon substrate by the deposition magnetron sputtering technique. Composed of 100 bilayers each, the multilayers were differentiated by the Ni sublayer thickness (1.2 to 3 nm), while maintaining the constant Cu sublayer thickness (2 nm). The multilayer coatings were characterized by assessing their surface topography using atomic force microscopy and their mechanical properties with nano-hardness measurements by the Berkovich method. The tests showed that the hardness of multilayers was substantially influenced by the thickness ratio of Cu and Ni sublayers and by surface roughness. The highest hardness and, at the same time, the lowest roughness was exhibited by a multilayer structure with a Cu-to-Ni sublayer thickness ratio of 2:1.5.

Degradation of coatings based on 310S steel doped with Al and Ir additives by the scratch test

Mechanical tests of PVD coatings made on steel 310S were carried out within this study by the scratch test method. It was found that the additions of Al and Ir caused lower critical load values compared to the coating without additions. Despite the reduction of the critical load of the coating by the aluminium addition, the effect of aluminium was considered advantageous owing to the refinement of the structure causing the coating to become more plastic and reducing the number and sizes of micro-cracks. The addition of iridium results in an embrittlement of the coating structure and its poorer adhesion to the substrate. Comparison of the findings from the scratch test with the observations from an optical and a scanning microscopes was also made.

Thermal Expansibility of 310S Steel-Based PVD Coating in Presence of Metastable Phase

The paper discusses the examination of the thermal expansibility of a coating composed of the austenitic steel 310S using the X-ray diffraction technique. Temperature measurements were made in the temperature interval of Tamb200°C, in which the transition of the metastable bcc phase forming the as-applied coating into an fcc-type phase occurred in the coating. The values of the coefficients of thermal expansion of both phases were determined by using the weighted average of the intensities of diffraction reflections recorded. The values of the coefficients of thermal expansion of both phases within the entire examination range (Tamb200°C), determined as the weighed averages with the weight allowing for the intensities of individual reflections, were found to be, respectively, 0.910-5 K-1 for the bcc phase and 1.510-5 K-1 for the fcc phase, and by approx. 0.110-5 K-1 lower than the values typical of the phases of austenite and ferrite in conventional steels.

The Effect of Al and Si Additions on the Resistance Properties of Magnetron-Deposited FeCrNi Coatings

The PVD magnetron sputtering method is one of the most efficient methods enabling the spraying of the multi-component materials and almost unlimited setting of the chemical composition of coatings. The micro-and nanocrystalline coating structure favours the selective diffusion of chromium and other alloy additions that form compact oxide layers. The paper presents the study of coatings made in the process of magnetron sputtering of AISI310S grade chromium-nickel steel. The study covered coatings of the steels composition with additions of 2-5% Si and of 2-5% Al. The resistance of the coatings at temperatures induced by electric current flow was assessed. The coatings provided a resistance element in the electric circuit, and the measurementof their temperature was made by the voltage drop indirect method. It was found that the steel coatings had a resistance of 0.176 Ω within the entire range of testing temperature, and their failure occurred at a temperature of 350°C due to cracking and delamination from the substrate. Introducing the Si or Al addition to the coatings resulted in an increase in coating resistance and temperature stability, respectively, to 450 and 400°C. Changes of coating’s phase composition and texture were not found. The resistance of the coatings with the Al and Si additions decreased with temperature due to their oxidation.

Stresses in a Cr-Ni Superficial Steel Layer Based on X-Ray Measurements and Electropolishing

Research of residual stresses in steel at different depths from its surface is presented in this paper. The material used for research was AISI 310S heat resistant steel (containing approx. 0.2%C, 25%Cr and 20%Ni) in form of a rolled steel sheet with a thickness of 2mm. Stress measurements were conducted with the use of KαCo radiation by the sin2ψ method in three directions, including the direction of the sheets rolling (φ = 0°). For the purpose of measuring stresses at different depths from the surface, the steel underwent the process of electropolishing in electrolyte based on perchloric acid at 32 V for various durations (every 1-5 s) to the maximum depth of 35 μm. The set residual stress distributions vary depending on the direction of the test. The strongest stresses are on the steels surface, and stresses have the widest range (from compressing to streching ones) in the area under the surface, which occurred in the rolling direction, and the narrowest range in its transverse direction. A correlation was discovered in the distribution of compression stresses and microhardness in the outer layer of the steel to a depth of 10 μm, where the role of plastic deformation in shaping the qualities of the steel outweighs the influence of structure content. This was proven using polar figures.