In English

Development of a γ’ Precipitation Hardening Development of a γ’ Precipitation Hardening

Abdul Shaafi Shaikh
Göteborg : Chalmers tekniska högskola, 2018. 102 s.
[Examensarbete på avancerad nivå]

The performance of superalloy materials at high temperatures is what makes gas turbine technology possible. Continual improvement in superalloy properties and resultant elevation of operating temperatures drives higher efficiency and reduced environmental impact in both aerospace and energy applications. Given the technological and commercial significance of superalloys, their adoption into Additive Manufacturing is of vital importance. The Additive Manufacturing of nickel-base superalloys aims to optimize function through geometric complexity of engineered parts, while reducing product development and marketing times. However, there are challenges to overcome before these materials can be used in serial production. Most superalloys are susceptible to cracking when processed in laser-powder bed fusion processes, and cracking mechanisms must be understood and mitigated in order to produce fully-dense parts. Another challenge is in the postprocessing stage. Additively manufactured microstructures are unlike cast or wrought microstructures, and heat treatment regimens must be re-formulated based on the different starting microstructure. Inconel 939 is a cast Ni-base superalloy for service above 800°C and is widely used in hot-sections of industrial gas turbine engines. This thesis presents a study of the cracking behaviour of IN939, and based on fractographic results, shows solidification cracking to be the primary mechanism responsible. The design of heat-treatment necessitated a comprehensive study of the starting microstructure. This was performed by thermal analysis and metallography and equated to simulation results. Heat treatment trials were conducted and the resulting microstructure and room temperature mechanical properties were characterized. Results showed significant differences in the fractions and morphologies of strengthening phases, compared to the conventionally cast material, while room temperature mechanical properties were better or comparable. The obtained results form a basis for proceeding with high-temperature and creep testing of the material to prove its viability in AM.

Nyckelord: Nickel-base superalloy, cracking, IN939, additive manufacturing, DMLS, laser sintering, laser melting, laser powder bed fusion, heat treatment, microstructural evaluation

Publikationen registrerades 2018-08-06. Den ändrades senast 2018-08-06

CPL ID: 255645

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