M. Sameezadeh, M. Vaseghi, H. Zafari,
Volume 5, Issue 1 ((Journal OF Welding Science and Technology 2019)
Abstract
In this paper, failure mechanism of a 17th stage blade of an 82.5 MW steam turbine that caused damage to the internal turbine compartment and the adjacent blade equipment has been studied. In order to determine the cause of failure and prevent similar events, various metallurgical and mechanical investigations including chemical composition analysis, metallography and microstructural analysis, fractography using scanning electron microscope and hardness and tensile tests were carried out. The initial results showed that the alloy had a chemical composition, microstructure and mechanical properties in the acceptable range, and the fracture failure was not due to the mechanical and metallurgical degradation during the service. The results of the fractography indicate high cycle fatigue as the main mechanism of the failure and shows that the fatigue crack has initiated from the adjacent hole relative to the vibration damped wire near to the brazing region on the blade, due to inadequate quality and incomplete connection of the brazing and its stress concentration effect the hole, which eventually has propagated and reached a critical level, and a sudden failure of the blade has occurred.
M. Talebipour, R. Shoja Razavi, R. Mozafarinia, M. Barekat, A. Khorram,
Volume 12, Issue 1 (Journal OF Welding Science and Technology 2026)
Abstract
Selective laser melting (SLM) has been considered as a method for manufacturing large and complex industrial parts. Considering that structural defects are generally caused by process parameters, the optimal evaluation of parameter selection to minimize localized defects has been of interest. Therefore, a model was presented to predict the optimal single-pass geometric characteristics based on the main process parameters, namely laser power and scanning speed, to prevent defects in single-pass Inconel 738LC on Inconel 738 casting substrate. An optimal process map was obtained based on the use of linear regression method combined with genetic optimization algorithm with optimal combination parameters (PαVβ). Finally, based on the geometric characteristics of single-passes, an optimal region was identified on the process map. At a power of 325 W and a laser scanning speed of 800 mm/s, due to the decrease in the G/R ratio, the microstructure from the junction to the substrate to the top of the single pass has changed from columnar to coaxial dendritic.
