Ivo Kraus

Residual stress measurement in alumina coatings

Abstract Residual stresses in plasma-sprayed Al 2 O 3 layers were investigated by means of X-ray diffraction with Cr and Cu radiation. No stress gradient was indicated in the surface layers of the alumina coatings within the range of penetration depth of the applied radiation. Different stress values were obtained by a high speed drilling method.

Residual Stresses in Plasma-Sprayed Coatings Al 2 O 3

Residual stresses affect significantly the quality and performance of thermally sprayed coatings. The residual stresses in alumina coatings were investigated by means of X-ray diffraction with Cr- and Cu-radiations. The sin2Ψ method could be applied to the evaluation of the stress fields. A very small stress gradient was indicated in surface layers of alumina coatings.

X-ray diffraction analysis of Zr-based alloys oxidized in water and lithiated water at 360°C

The results of X-ray diffraction analysis of three Zr-based alloys are presented in this contribution. The tubular samples of ZrlNb, Zry4 W and ZIRLO alloys were simultaneously oxidized for various exposures in both pressurized VVER 1000 imitating water and water with 70 ppm Li as LiOH at 360°C. The effect of Li-environment was observed for all the characteristics obtained by means of XRD, i.e. residual stresses σ, krystallite size D and microstrains ε of oxide layers. The change of all the characteristics correspond to changes of corrosion kinetics in Li-environment for two types of the alloys: Zry4 W and ZIRLO. The behavior of ZrlNb alloy was found to be different. No effect of Li-environment was observed on stresses σ in metal underlying of alloys investigated.

X-ray stress analysis of oxidized Zr-based alloys

The results of X-ray diffraction analysis of macroscopic stresses in oxide layers and substrate of zirconium alloys are presented in this contribution. Stresses were studied on the tubular specimens of three types of alloys:Zr1Nb, low tin Zircaloy-4 and Zr-Nb-Sn alloy (ZIRLO) which were simultaneously exposed for various time in four environments: 360 degree(s)C water, 360 degree(s)C water with 70 ppm Li as LiOH, steam at 400 degree(s)C and steam at 450 degree(s)C. The courses of compressive stresses (sigma) vs. oxide thickness are quantitatively different for two types of alloys in all of environments used. The courses for ZIRLO seem to be less dependent on corrosion conditions. In the range of the large oxide thicknesses (> 10 micrometers ) two cases were observed: (1) the value of stress falls down to zero, (2) the values stay on some levels which differ for different alloys and environments. Only tensile residual stresses were indicated within substrate of all samples investigated. Microstructure characteristics (crystallite size and lattice strains) were evaluated for oxide layers and the metal underlying.

X-Ray Diffraction Analysis of Oxide Layers of Zr-Based Alloys

The results of X-ray diffraction analysis of macroscopic stresses σ and crystallite size D in oxide layers are presented in this contribution. The oxide layers were formed on tubular specimens of Zircaloy 4 and Zr1Nb alloys which were simultaneously oxidized for various times under temperature transient conditions (oxidation in water at 360 °C with a short-time shock in steam at 500 °C). A qualitative relation was outlined between the residual stresses in oxide layers and corrosion kinetics of the alloys under investigation.

X-ray diffraction analysis of oxidized Zr-based alloys

In this contribution the comparative XRD study of ZrlNb and Zircaloy 4 is presented. The aim of the study is to determine residual stresses σ and to analyze the microstructure of oxide layers formed on tubular specimens oxidized under temperature transient conditions (oxidation in water at 360°C with a short-time shock in steam at 500°C). The specimens of the both alloys which had not undergone the temperature transition were also studied. A strongly quantitatively varied texture occurred in oxide layers of specimens oxidized under transient conditions. Thus, the average values of residual stresses σ and crystallite size D in oxide layers can be used as qualitative characteristic for the behavior of the two alloys.

Residual stresses in oxide layers and corrosion kinetics of Zr-based alloys

The results of x-ray diffraction analysis of macroscopic stresses in oxide layers and substrate of zirconium alloys are presented in this contribution. Stresses were studied on the tubular specimens of two types of alloys: low tin Zircaloy-4 (Zry-4W) and standard Zircaloy (Zry-4S) which were simultaneously exposed for various time in water with 43 pm O2 at 360°C. Microstructure characteristics (crystalline size and lattice strains) were evaluated for oxide layers and the metal underlying. Only compressive stresses (up to 1,1 GPz) were determiend in the oxide layers of samples investigated. Only tensile stresses (up to 250 MPa) were determined in metal underlying for all the specimens investigated. The relation between the stress development in oxide layers and kinetics of the alloys investigated was outlined.

X-ray residual stress analysis of free-standing ceramics

The contribution is intended to present some of the porosity and residual stress measurements of the plasma-sprayed sheets of free-standing ceramics (Al2O3 + 4%TiO2 + 1%Fe2O3). The following relationships have been studied: porosity vs. sheet thickness, porosity vs. spray distance, residual stresses vs. porosity and residual stresses vs. sheet thickness. The correlation between the residual stresses on the free surface of the sheets and on the surface that was in contact with the steel substrate has been investigated.

Laser-treated surfaces

The contribution deals with studies on residual stresses and microhardness of laser hardened carbon steel surfaces. Laser hardening can greatly improve the wear and fatigue properties by inducing a hardened and compressed surface layer. Residual stress distribution across the hardened tracks were measured by means of x-ray diffraction. It has been found that compressive stresses exist in the hardened zone of all the specimens studied. The microhardness increased by as much as 350%.