Sanja Petronić

Microstructural changes of Nimonic-263 superalloy caused by laser beam action

Pulsed laser treatments induce changes in the microstructure of materials. We have exposed the Nimonic-263 superalloy to pulsed laser beams of various repetition rates and wavelengths and investigated the changes in microstructure and microhardness. Two types of laser treatment of the material surface occurred: mechanical and thermomechanical. The microstructure changes have been comparatively analyzed by scanning electron microscopy and energo-dispersive spectrometry. The grain size was measured before and after the treatment and microhardness tests were performed. These investigations aim to contribute to the study of the level of improvement of microstructure and mechanical properties because of the interaction with laser beams.

Influence of picosecond laser irradiation on nickel-based superalloy surface microstructure

The investigation presented in this paper was carried out on the nickel-based superalloy, Nimonic 263, a material widely used at elevated temperatures and pressures. The samples were exposed to a Nd3+:YAG pulsed laser, at a wavelength of 1064 nm and a pulse duration of 170 ps, and the estimated threshold damage was 2 mJ. Different pulse energies and numbers of pulses were applied in air and helium-enriched atmospheres. Spots obtained by the laser interaction with the material were observed by optical and scanning electron microscopes and analyzed by energy-dispersive spectroscopy. Vickers microhardness tests were performed. In this paper, the changes that had occurred at the sample surface microstructure as a result of laser–material interaction are discussed with the aim of contributing to the determination of optimal laser parameters in the laser surface treatment process.

Obim ispitivanja zavarenog spoja prema SRPS EN 13445-5

Pressure vessels are, according to the degree of risk that present for humans and the environment, divided into the vessels of high and low level of hazard. One of the most important aspects of the conformity assessment of the new pressure equipment and for the evaluation of their safety for work, are nondestructive testing of welded joints. Given the importance and responsibility carried by these tests, the extents of nondestructive testings are recomanded by the standards depending on the type of welded joint and testing group of materials. However, the recomanded extent of tests are the result of analysis and experience, and are subject to change over the years. In this paper, the changes in the extent of nondestructive testing of welded joints in relation to the EN 13445-5: 2009 and EN 13445-5: 2015 are analysed depending on the groups of materials and the type of welded joint of pressure vessels, with reference to the practical examples.

Definition of welding parameters by cooling time in temperature range 800-500ºC

Cooling time in the temperature range 800 - 500°C has a great effect on the structures that arrise in the heat affected zone of welds steel. Data on optimal cooling time t8/5 for the certain steels can be found in the literature. The period of the cooling time t8/5, during the welding of the particular joints, in addition to the thickness and physical properties of welded steel, depends on shape of the weld, the welding process and welding parameters as well. In this work, the procedure for the selection of welding parameters for a butt joint welded to the microalloyed steel P 460 NL1 is presented. The microstructure in the heat affected zone and the results of measurement of their hardness are showed and analysed. It is concluded that the welding parameters selected with the help of cooling time t8/5 provide the satisfactory structure and hardness of welds.

Stress Analysis of Hyperbaric Chambers of Different Geometries

Hyperbaric Oxygen Therapy (HBOT) is a method used to administer pure oxygen at a pressure which is greater than atmospheric pressure in order to increase the concentration of O2 in the tissues, blood and cells, and correct or improve certain conditions. The hyperbaric chamber is a medical instrument that provides many benefits to the economy and health protection. They are in fact pressure vessels, subjected to the higher stress levels. In this paper, the stress and deformation state of different multiplace hyperbaric chambers are determined. Stress and deformation states are calculated for different geometry models using ABAQUS. Therefore, the aim of this paper is to define the weakest points in the chambers of different geometry with the use of the Finite Element Method.