Microstructural Characterization of the Laser Welding in a Nickel Based Superalloy
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.421
Microstructural Characterization of the Laser Welding in a Nickel Based Superalloy Mayra Jurado1, Gerardo Altamirano1, Jorge Leobardo Acevedo2, Alvaro Aguirre2. 1 Instituto Tecnológico de Saltillo, Blvd. Venustiano Carranza #2400, Colonia Tecnológico, Saltillo, Coahuila, México.
2
Corporación Mexicana de Investigación en Materiales, Ciencia y Tecnología #790. Col Saltillo 400. CP 25290 Saltillo, Coahuila, México.
ABSTRACT
In this research it was experimentally analyzed the effect of the parameters of the Pulsed Micro Laser Welding Process Nd:YAG on the microstructural behavior of a nickel base superalloy (IN-738). For this purpose, different laser welding tests were performed on samples subjected to different heat treatment conditions obtained from the gas turbine blades. The influence of the power and the speed welding of the applied process and heat treatment condition on the weld geometry, microstructure and mechanical properties was determined. The microstructures of the obtained welds were characterized by scanning electron microscopy and Vickers hardness tests. In general, alternatives to homogenize and rejuvenate the microstructure of the base material are proposed in order to avoid the formation and propagation of cracks. The results are discussed mainly in terms of the present phases and decomposition of carbides, which considerably affect the weldability of the IN-738 superalloy. This study provides useful information for the subsequent restoration of the 2nd step turbine blades by using of the Laser Welding Process Nd:YAG.
INTRODUCTION Nickel base superalloys are high-temperature structural materials due to their remarkable ability to maintain their properties mechanical at elevated temperatures under considerable load for extended period of life [1]. Inconel 738 superalloy is a vacuum investment cast; this alloy offers excellent properties as corrosion resistance and high mechanical strength at elevated temperatures [2]. This is a precipitation hardened superalloy due to intermetallic elements of the type
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gamma prime, Ni3 (Al-Ti) –γ’, which is used to manufacture components that operate in the hot section of industrial turbines (blades). The main problems of the blades of IN-738 alloy when they are in operation are divided into two groups: the first one is the generation of surface damage, such as corrosion, thermal fatigue, erosion, cracking and fracture. The second one is the internal damage such as the formation of cavities by thermofluence, growth of carbides and intermetallic compounds; in addition to the precipitation of embrittlement phases due to the content and nature of the alloying elements, mainly chromium and molybdenum. This implies the need of a set of parameters experiment
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