Access Type

Open Access Dissertation

Date of Award

January 2019

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical Engineering

First Advisor

Guru P. Dinda

Abstract

Nickel-based superalloys are substantially used in the manufacturing of boilers for ultra-supercritical power plants and gas turbine hot-section as this grade of alloys provide higher yield strength with the rise in operating temperature and pressure owing to the presence of γʹ second phase precipitates. Conventionally, casting techniques such as centrifugal casting, investment casting, vacuum molding and several other casting based methods are used to fabricate the hot-section components. Nevertheless, a need for designing advanced materials with complex designs such as geometry, microstructure control, compositional changes, microstructure and property varying with the location as in functionally graded materials is not viable for manufacturing using traditional processing routes. Moreover, if the components have manufacturing defects or subjected to degradation during extended exposure in the course of service, it is unfeasible to repair the superalloy parts by conventional routes as these alloys are prone to cracking employing welding.

Advanced manufacturing processes such as additive manufacturing (AM) based techniques presents an opportunity to fabricate various metallic alloy systems resulting in controlling the desired microstructure and property under regulated processing environment by optimizing the parameters by design of experiments. As AM is relatively a new method of fabricating advanced structural high-performance materials there is a substantial need to systematically investigate several materials developed for conventional manufacturing routes, develop new materials suitable for AM and finally investigate how the process-structure-property relationship affects the competency of AM in building high-grade components in nickel-based superalloy.

The objective of this research is to facilitate the fundamental scientific understanding of melting and remelting of layers using a laser beam as the energy source, solidification and re-solidification theory, precipitation kinetics, structure-property-relationship of various nickel-based superalloys employing direct laser metal deposition (LMD)-based AM process. Thermodynamic simulation coupled with experimental proof, post-processing and advanced materials characterization methods are amalgamated to deepen the understanding of LMD processed nickel-based superalloys, thus, validating the feasibility of repair and fabrication of high-performance structural components with required microstructure and property.

Download

Share

COinS