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Contemporary Machining Processes for New Materials
Published in E. S. Gevorkyan, M. Rucki, V. P. Nerubatskyi, W. Żurowski, Z. Siemiątkowski, D. Morozow, A. G. Kharatyan, Remanufacturing and Advanced Machining Processes for New Materials and Components, 2022
E. S. Gevorkyan, M. Rucki, V. P. Nerubatskyi, W. Żurowski, Z. Siemiątkowski, D. Morozow, A. G. Kharatyan
Attempts at the production of TiN-coatings in reactive atmospheres by means of laser irradiation were undertaken in the 1980s and 1990s, providing an enormous improvement to surface properties (Höche et al., 2015). With a CO2 laser, it was possible to obtain a hundred micrometers thick coatings. The surface of commercially pure titanium (cp-Ti) after laser nitriding contains a mixture of α'-Ti and δ-TiN. When nitrogen content of the processing gas is increased, the volume fraction of δ-TiN rises at the expense of the α'-Ti which causes surface hardness to grow. Laser nitriding of high-strength (α+β)-Ti alloy Ti-6Al-4V can increase hardness to moderate values in the range of 400–600 HV, improving cavitation and water droplet erosion resistance. Values above 600 HV could significantly improve sliding wear resistance, while abrasive wear resistance of Ti–6Al–4V can only be improved if thick layers exhibiting hardness above 800 HV are generated. Similarly, (α+β)-Ti alloys like Ti-4, 5Al–3V–2Mo–2Fe (SP700), and β-Ti alloys like Ti–10V–2Fe–3Al can be enhanced by laser nitriding (Höche et al., 2015).
Failure analysis of a low-pressure stage steam turbine blade
Published in Nondestructive Testing and Evaluation, 2023
Modern turbine blade’s last two low-pressure (LP) stages are expected to operate in a wet steam medium in steam turbines. Condensation during steam expansion typically produces fine mist droplets.This study analysed stainless steel ex-service steam turbine blades. (Water droplet erosion) WDE on different portions of the blade was identified.No crack or any other defect-like appearance was noticed on the surface during visual inspection of the turbine blade. No sign of corrosion or thermal fatigue was found on the surface. However, considerable erosion damage was observed in the edge sections of Blade.It was determined that the blade material was not faulty based on chemical analysis and mechanical testing.The turbine blade under inquiry did not fail due to a material flaw, according to the dye penetration testing and microstructure study.The defective sections were carefully analysed in order to determine the causes of failure, and it was found that water droplet erosion was the cause of blade damage. Identifying the deteriorating mode in advance allows us to replace and repair turbine parts at the best possible moment, reducing the need for unneeded replacement and preventing unscheduled outages.The airfoil’s edges are scarred by water droplets leaving behind microscopic notches. As stress concentrators, these notches compromise the integrity of the blade in areas of high stress. If left ignored, the notches serve as crack initiators that eventually lead to spreading cracks. This could soon progress to a blade failure if combined with dynamic loads. Each facet of a failure inquiry contributes to figuring out what went wrong and how to prevent such incidents in the future. Failure analysis is thus crucial for enhancing turbine system reliability and avoiding similar failure incidences.