Analysis of a Directionally Solidified (DS) GTD-111 Turbine Blade Failure
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TECHNICAL ARTICLE—PEER-REVIEWED
Analysis of a Directionally Solidified (DS) GTD-111 Turbine Blade Failure Khier Sabri
. Mohamed Gaceb . Mohamed Ouali Si-Chaib
Submitted: 2 November 2019 / in revised form: 21 January 2020 ASM International 2020
Abstract The purpose of this paper is to clarify the impact of pitting corrosion and erosion on the directionally solidified (DS) GTD-111 turbine blade behavior. Moreover, the pitting corrosion and oxidation phenomena engendered inside cooling channels of the turbine blade are utterly highlighted. Other features such as the g (Ni3, Ti) platelets nucleation, needle r-phase precipitation at the interface NiPtAl/(DS) GTD-111 substrate are exhibited as well. Finally, the different microstructural changes in (NiPtAl) coating strata against hot corrosion, oxidation and interaction with (DS) GTD-111 substrate are revealed and argued. Keywords (DS) GTD-111 superalloy Erosion Pitting corrosion Needle r-phase c0 - Ni3 (Al, Ti) precipitates
Introduction During service operations, row-1 gas turbine blades are exposed to stresses caused by high temperature or static and dynamic loading such as creep, low-cycle fatigue and high-cycle fatigue [1–4]. Furthermore, steady stresses of the rotating blades are based on centrifugal and gas bending loads and thermal gradients [5]. Contributing factors often include environmental attacks such as the hot corrosion and oxidation phenomena, erosive wear, timedependent plastic deformation (neck-down). Moreover, the
K. Sabri (&) M. Gaceb M. O. Si-Chaib Laboratory of Petroleum Equipment’s Reliability and Materials, Hydrocarbons and Chemistry Faculty, Universite´ M’Hamed Bougara de Boumerde`s, UMBB, Boumerde`s, Algeria e-mail: [email protected]
blades are prone to overheating and melting caused by long-lasting excessive temperature of exhaust gases, the impact marks from ingestion of foreign or domestic objects (FOD, DOD) attributable to surface scratches and deformation in the form of dents, and intercrystalline corrosion called chemical failure [6]. It is a well-known fact that the running hours, start/stop cycles, and fuel composition factors add insult to injury and may have a noteworthy impact on the turbine blades entire lifetime [7]. In the event of rupture, there is a likelihood risk of compromising the integrity of the turbine unit [8]. In addition, the first-stage gas turbine HP blades’ trailing edges in exploitation are exposed to the life-threatening risk of overheating owing to the fact the high rate of heat exchanges is caused by the impingement of hot gases [9]. However, the blades’ trailing edges were designed with a few thin-walled cooling channels, which are cooled by internal airflow, in comparison with the leading edges [10]. Notwithstanding the air cooling channels conception within blade airfoil hot sections, trailing edges up to the present time are susceptible to overheating, erosion, pitting corrosion, and thermal cracking as exhibited by many sets of degraded HP blades [11]. From previous results [1
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