Kiriti Mamidi

Graduation Semester and Year

2020

Language

English

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Narges Shayesteh

Abstract

Inconel 718 (IN718) is a nickel-based superalloy which exhibits excellent tensile and impact resistant properties along with good corrosion resistance at high temperatures. However, due to the high toughness and work hardening, the machinability of this superalloy is low. Therefore, the selective laser melting (SLM) process has been adopted as an efficient technique to fabricate IN718 parts as it overcomes the problems associated with conventional manufacturing of superalloys. SLM is a widely used additive manufacturing technique which offers the possibility to induce multi-functionality into a single component, and thus reduce the number of components that are needed. In the SLM process, various process parameters like scan strategy, laser power, scan speed, and energy density are defined for the fabrication to regulate the microstructure and thus control the mechanical properties like tensile strength, yield strength, impact strength, and hardness. Owing to the nature of the SLM process, there are consistent repetitions of thermal cycles, which in turn induce residual stress into the part. These residual stresses can be detrimental to the microstructure and hence mechanical properties of the part. Residual stresses lead to warping of the part during the fabrication process, thereby leading to failure of the component. Although each process parameter has an independent and definitive effect on the overall mechanical and metallurgical properties, scan strategy is an independent process parameter which directly affects the level of residual stresses, microstructure, and mechanical properties of the SLM part, as the heat zones in part can be shifted from location to another by varying the scan strategy. This variation of the area of the heat zone changes the temperature gradient, which thereby determines the grain size ranging from equiaxed to elongated. Hence, the scan strategy is the only parameter that is varied for this study. The various scan strategies adopted here are checkered, stripes, FO1, and customized scan strategy, where the angle between the consecutive layers has?been changed?consistently at an angle of 90o . In this study, the residual stress was deduced using methods like hardness, X-ray powder diffraction (XRD), and direct method (CMM) followed by microstructural and compositional analysis on the parts. Mechanical testing like compression tests, hardness test, and roughness test was performed on the SLM fabricated parts. This effort was undertaken to identify the effect of scan strategy on residual stress and to discuss the metallurgical interactions between the mechanical and microstructural properties within the IN718 superalloy.

Keywords

Selective Laser Melting, Inconel 718, Micro structure, Metallurgy, Hardness

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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