College - Author 1
College of Engineering
Department - Author 1
Materials Engineering Department
Degree Name - Author 1
BS in Materials Engineering
College - Author 2
College of Engineering
Department - Author 2
Materials Engineering Department
Degree - Author 2
BS in Materials Engineering
Date
6-2020
Primary Advisor
Blair London, College of Engineering, Materials Engineering Department
Abstract/Summary
Inconel 718 is a nickel-based superalloy and commonly used rocket engine material due to its excellent properties at elevated temperatures. Its fatigue life relies heavily on the surface roughness, as fatigue introduces and propagates cracks at the surface. Part standards set by Aerojet Rocketdyne typically necessitate surface roughness values from 64 to 125 Ra. However, surface topography and residual stresses incurred from the finishing process also affect the fatigue performance. The specific goal of the project is to perform a literature review and write experimental methods to determine how the surface roughness, topography, and residual stresses from turning, grit blasting, and polishing cumulatively affect mid-to-high cycle fatigue. Available literature shows that solution treated and aged, polished Inconel 718 reaches a high cycle fatigue regime within the stress amplitude range of 500 to 600 MPa. This range will be the starting point for producing useful S-N curves for the common finishing processes, polishing, turning, and grit blasting, used by Aerojet. Testing methods and analysis techniques will include surface roughness measurements using an Ambios XP1 stylus profilometer, scanning electron microscopy (SEM) imaging of surface topographies, fully reversed cantilever bending fatigue testing, and SEM fracture analysis. The safety issues addressed are relevant for fatigue testing, grit blasting, and using Kalling’s solution to etch Inconel 718 metallography samples.
URL: https://digitalcommons.calpoly.edu/matesp/229