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Merton C. Flemings. Bui, Quoc Cuong, 1974- Massachusetts Institute of Technology. Department of Materials Science and Engineering 2005-08-19T18:40:38Z 2005-08-19T18:40:38Z 1998 1998 http://hdl.handle.net/1721.1/9578 42075698 Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998. Vita. Includes bibliographical references (leaves 74-75). The rapid solidification of a Fe-12 wt% Cr-16 wt% Ni alloy in containerless processing conditions was investigated using an electromagnetic levitation facility. High-speed video and pyrometry allowed the study of phase selection and secondary nucleation mechanisms for that alloy as well as measurements of delay times and growth velocities. Double recalescence events were observed for the first time at temperatures near the To temperature of the metastable ferritic phase, defining a value of the critical undercooling for metastable bee nucleation significantly lower than previously reported. Phase selection during recalescence was successfully performed by use of different trigger materials: at temperatures below the bee To , a bee Fe trigger induced the primary nucleation of the metastable bee phase which subsequently transformed into the stable fee phase while an fee Ni trigger caused the nucleation of the equilibrium fee phase. Growth velocities were characterized for the 6 phase growing into the undercooled liquid, the [delta] phase growing into the undercooled liquid and the [gamma] phase growing into the semi-solid primary bee. It was found that a critical undercooling exists at which the growth velocity of the primary ferritic phase is equal to that of the secondary austenitic phase into the primary semi-solid. At undercoolings below this critical value, the equilibrium, can overwhelm the primary a and break into the undercooled liquid. Such a double recalescence event can therefore appear as a single event depending on the geometry of the detection equipment. From this observation, a model based on velocity and delay time arguments was proposed to explain discrepancies with earlier works. by Quoc Cuong Bui. S.M. 76 leaves 4405995 bytes 4405752 bytes application/pdf application/pdf eng Massachusetts Institute of Technology M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 Materials Science and Engineering Containerless processing of stainless steel Thesis application/pdf false Publication unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="123af052-e527-4491-827f-9b81ebd08a8a"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Language>eng</Language> <Title>Containerless processing of stainless steel</Title> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>1998</PublicationDate> <Authors> <Author> <DisplayName>Bui, Quoc Cuong, 1974-</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>http://dspace.mit.edu/handle/1721.1/7582</License> <Keyword>Materials Science and Engineering</Keyword> <Abstract>The rapid solidification of a Fe-12 wt% Cr-16 wt% Ni alloy in containerless processing conditions was investigated using an electromagnetic levitation facility. High-speed video and pyrometry allowed the study of phase selection and secondary nucleation mechanisms for that alloy as well as measurements of delay times and growth velocities. Double recalescence events were observed for the first time at temperatures near the To temperature of the metastable ferritic phase, defining a value of the critical undercooling for metastable bee nucleation significantly lower than previously reported. Phase selection during recalescence was successfully performed by use of different trigger materials: at temperatures below the bee To , a bee Fe trigger induced the primary nucleation of the metastable bee phase which subsequently transformed into the stable fee phase while an fee Ni trigger caused the nucleation of the equilibrium fee phase. Growth velocities were characterized for the 6 phase growing into the undercooled liquid, the [delta] phase growing into the undercooled liquid and the [gamma] phase growing into the semi-solid primary bee. It was found that a critical undercooling exists at which the growth velocity of the primary ferritic phase is equal to that of the secondary austenitic phase into the primary semi-solid. At undercoolings below this critical value, the equilibrium, can overwhelm the primary a and break into the undercooled liquid. Such a double recalescence event can therefore appear as a single event depending on the geometry of the detection equipment. From this observation, a model based on velocity and delay time arguments was proposed to explain discrepancies with earlier works.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>