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oai:www.ideals.illinois.edu:2142/97793 2023-07-11 col_2142_5131 col_2142_14837 com_2142_5130 com_2142_14836 com_2142_234

Stubbins, James F. Zhang, Yang Wang, Jinsheng 2017-08-10T20:33:28Z 2017-08-10T20:33:28Z 2019-08-11T09:15:17Z 2017-04-27 2017-05 T91 ferritic-martensitic (F/M) steel is one of the leading candidates for high temperature structural materials in advanced nuclear power applications. In situ Wide-angle X-ray Scattering (WAXS) was used to investigate T91 during tensile test under 3 different temperatures: room temperature (RT), 450C, 550C, respectively. By fitting scattering patterns, information of diffraction peaks and their variation trends with respect to macroscopic strain were recorded for further analysis of Fe matrix, M23C6 and MX precipitates. Lattice strain of Fe matrix and precipitates were obtained from peaks shift in WAXS pattern during tensile test. Load partitioning effect, which is known as precipitates can bear higher load than Fe matrix, was found to be less obvious within plastic regime with the increase of temperature from RT to 550C. Peak broadening, represented by full width at half maximum (FWHM), was carefully analyzed using modified Williamson-Hall (W-H) plots to separate strain and crystalline size effects due to their different theta dependence. It was found that dislocation density rho in Fe matrix behaved differently within different tensile regimes: before Ultimate Tensile Strength (UTS), they all increased; after UTS, it plateaued first then increased at end for RT, remained stable for 450C while decreased continuously for 550C. Coherent scattering length L310 calculated by Scherrer Equation using Fe(310) plane behaved as below: before UTS, they all decreased; after UTS, it decreased continuously for RT, remained stable for 450C and rose dramatically for 550C. The variation trends of both dislocation density and coherent scattering length L310 were impacted by combination effect from high temperature and tensile flow stress evolution. Scanning Electron Microscopy (SEM), Optical Micropy (OM) and Transmission Electron Microscopy (TEM) were also used to study the post-tensile samples. SEM found that at RT tensile fracture happened violently with huge cracks on necking center cross-section, while fracture happened slowly with voids and dimples on cross-section under higher temperatures. SEM Energy Dispersive Spectroscopy (EDS) mapping also found that rupture protrusions on necking center edges had higher C and N concentration than that of metallic elements. OM revealed the martensitic plates and ferrites in T91 after polishing and etching. Lastly, TEM experiment was also carried out using Focused Ion Beam (FIB) prepared specimen to characterize precipitates, dislocations and other microscale features, and to compare with the previous X-rays Diffraction (XRD) results. Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2019-05-01 The student, Jinsheng Wang, accepted the attached license on 2017-04-26 at 14:06. The student, Jinsheng Wang, submitted this Thesis for approval on 2017-04-26 at 14:09. This Thesis was approved for publication on 2017-04-27 at 16:30. DSpace SAF Submission Ingestion Package generated from Vireo submission #11091 on 2017-08-10 at 15:07:09 Made available in DSpace on 2017-08-10T20:33:28Z (GMT). No. of bitstreams: 2 WANG-THESIS-2017.pdf: 18246513 bytes, checksum: c3ad44c8406396d9424d67840f3cb1c5 (MD5) LICENSE.txt: 4210 bytes, checksum: 0844f02cf46a24336170c0213900027e (MD5) Previous issue date: 2017-04-27 Embargo set by: Colleen Fallaw for item 102846 Lift date: 2019-08-10T21:27:21Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system U of I Only Restriction Lifted for Item 102846 on 2019-08-11T09:15:17Z. application/pdf http://hdl.handle.net/2142/97793 en Copyright 2017 Jinsheng Wang T91 steel In-situ X-rays diffraction (XRD) tensile test Study of microstructure evolution in F/M steel T91 by in-situ synchrotron wide-angle X-rays scattering text text Nuclear, Plasma, & Rad Engr Nuclear, Plasma, Radiolgc Engr University of Illinois at Urbana-Champaign Thesis M.S.