Papers by Author: Martin Juliš

Abstract: Hard anodized layers were produced by two different manufacturers on the same type of aluminium alloy on a vacuum pump part of complex shape. The sulphuric acid/water solution was used to produce alumina layers, which were subsequently sealed in demineralized water. A comparative analysis based on metallographic methodology, with the aim to control the stability of alumina formation process and to identify its defects, was performed by means of light and scanning electron microscopy, surface profilometry and microhardness measurements. To determine the thickness of alumina layers, the image analysis was also used.

Abstract: High temperature low cycle fatigue behaviour of cast nickel-based superalloy Inconel 738LC in as-received condition and coated with an Al-Si diffusion layer was studied. The Al-Si protective layer was deposited on the gauge section of cylindrical specimens using the slurry technique. Fatigue tests were performed on cylindrical specimens under total strain control in symmetrical cycle at 800 °C in air. The coating has a beneficial effect on fatigue life in the low amplitude domain. The stress response of the coated material is higher for high amplitudes in comparison with the uncoated one. Fracture surfaces and sections parallel to the specimen axis have been examined to study fatigue damage mechanisms.

Abstract: Protective layers are used to improve high temperature performance of structural materials. However, the effect of coatings on mechanical and fatigue properties is not sufficiently known because it is a combination of many factors as high-temperature exposure time, thermal cycle and coating deposition technique. Interactions between the coating and the substrate under high-temperature conditions influence the life time of coated blades. This paper is focused on the study of microstructure and properties of aluminide protective layers deposited on cast polycrystalline nickel base superalloy Inconel713LC. The light microscopy with image analyses and scanning electron microscopy with energy dispersion spectroscopy were used. The surface treated specimens exposed at 800 °C in air and cylindrical specimens with protective layer cyclically loaded under strain control at 800 °C in air were studied. Experimental data on thickness, uniformity and chemical analysis of individual phases are obtained for as-coated specimens, for specimens exposed to 800 °C for 500 hours in air and for specimens fatigued to fracture at 800 °C in air.

Abstract: Cylindrical specimens of Inconel 713LC in as-cast condition and with Al diffusion coating by the CVD technique were cyclically strained under total strain control at 800 °C. Hardening/softening curves, cyclic stress-strain curves, and fatigue life curves are obtained. The coating has a beneficial effect on the Manson-Coffin curve while the fatigue life is reduced in the Basquin representation. The stress response of the coated material is lower in comparison with the uncoated one. Sections parallel to the specimen axis have been examined to study fatigue damage mechanisms.

Abstract: High-temperature constructional parts of aircraft engines and energy units are exposed to high dynamic stress (fatigue processes and creep) and various temperatures in dioxide-corrosion condition (hot corrosion, oxidation and erosion). The improvement of aero-engine and turbine efficiency is possible through the increase of temperature in front of turbine. This requires the use of heat-resistant and creep-resistant materials, especially nickel-base superalloys which resist mentioned effects for a limited period of time. A deposition of protective layers should improve hot corrosion resistance. This paper is focused on microstructure of protective layers created by codeposition of Al and Si on nickel-base superalloys INCO 713 LC and INCO 738 LC after thermal and thermal-stress exposition and on microstructure of basic materials (substrates). The contribution also shows creep tests results for both superalloys with and without a protective layer.