Comparison of Neutron Irradiation Effects on PM-HIP and Cast Grade 91 Steels
Abstract
In recent years Powder Metallurgy Hot Isostatic Pressing (PM-HIP) alloys have been of interest to the nuclear power industry to replace alloys fabricated through typical manufacturing processes. However, irradiation effects on PM-HIP alloys have not yet been thoroughly researched. These alloys offer many advantages over typically cast alloys such as more uniform microstructures, higher quality, ease of inspectability, and lower costs. Gaining a better understanding of the evolution of the microstructure under various irradiation conditions is important. The objective of this thesis is to compare irradiation effects on Grade 91 steel that has been cast and produced by PM-HIP. Samples were subjected to fast spectrum neutron irradiation at the Advanced Test Reactor (ATR) at Idaho National Lab (INL). They were irradiated at 400oC to 1 dpa.Tensile testing was conducted on both irradiated and unirradiated samples to quantify the increase in yield stress due to irradiation. General microstructure characterization was conducted through Scanning Transmission Electron Microscopy (STEM) on both irradiated and unirradiated samples, this allows for a better understanding of dislocation evolution and the effect dislocation loops have on strengthening. Atom Probe Tomography (APT) was utilized to create three-dimensional reconstructions of the samples to characterize the precipitates that have formed and to gain a better understanding of how those precipitates aid in strengthening. Various strengthening models are then applied to understand how each of these defects affects the increase in yield strength in this alloy. The PM-HIP alloy exhibits higher strengthening due to irradiation compared to the cast alloy, therefore increasing the interest in this type of manufacturing for nuclear applications.
Degree
M.Sc.
Advisors
Wharry, Purdue University.
Subject Area
Atomic physics|Materials science|Mechanics|Medical imaging|Nuclear engineering|Physics
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