Title: Investigation on microstructure and mechanical properties on varying surface region of a service-exposed IN738 turbine blade

Authors: Afolabi Lukmon Owolabi; Puteri Sri Melor Megat-Yusoff; Mior Azman Meor Said

Addresses: Mechanical Engineering Department, University Technology PETRONAS, 32610 Bandar Seri Iskandar, Malaysia ' Mechanical Engineering Department, University Technology PETRONAS, 32610 Bandar Seri Iskandar, Malaysia ' Mechanical Engineering Department, University Technology PETRONAS, 32610 Bandar Seri Iskandar, Malaysia

Abstract: The study investigates the microstructural transformation and mechanical properties of nickel-based IN738 super-alloy turbine blade after service exposure of 52,000 h at temperature of ±720°C for the degradations and stress rupture profile. The grain boundary carbides, decomposition and the transformation of MC carbides (gamma prime (γ′)) and creep cavities are analysed. The growth of γ′ precipitates in the microstructure was investigated using transmission electron microscopy. It was observed that gamma prime (γ′) possesses high coarsening at inter-dendritic area than in the dendrite core. Thus implies a contributing factor in the interface between the carbides, grain boundaries and the gamma prime (γ′) films preferential location for nucleation and propagation of cracks and creep cavities. The coarsening behaviour of γ′ precipitates adhere with the Ostwald ripening. The average hardness values of the inside and outside portion of the turbine blade was 325 and 298 HV10, respectively.

Keywords: super-alloy; carbide decomposition; structure; grain boundary; gamma prime precipitate; tensile stress; creep properties.

DOI: 10.1504/IJMMP.2017.087661

International Journal of Microstructure and Materials Properties, 2017 Vol.12 No.1/2, pp.38 - 54

Available online: 25 Oct 2017 *

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