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Designing Microstructure through Reverse Peritectoid Phase Transformation in Ni₃Mo Alloy

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dc.contributor.authorKhalfallah, Ibrahimen
dc.contributor.committeechairAning, Alexander O.en
dc.contributor.committeememberReynolds, William T. Jr.en
dc.contributor.committeememberSuchicital, Carlos T. A.en
dc.contributor.departmentMaterials Science and Engineeringen
dc.date.accessioned2017-06-13T19:43:39Zen
dc.date.adate2017-02-03en
dc.date.available2017-06-13T19:43:39Zen
dc.date.issued2016-12-07en
dc.date.rdate2017-02-03en
dc.date.sdate2016-12-14en
dc.description.abstractHigh-energy ball milling and powder metallurgy methods were used to produce a partially alloyed nickel and molybdenum of γ-Ni₃Mo composition (Ni-25at.%Mo). Milled powders were cold-compacted, sintered/solutionized at 1300°C for 100h sintering followed by quenching. Three transformation studies were performed. First, the intermetallic γ-Ni₃Mo was formed from the supersaturated solution at temperatures ranging between 600°C and 900°C for up to 100h. The 100% stable γ-Ni₃Mo phase was formed at 600°C after 100h, while aging at temperatures ranging between 650°C and 850°C for 25h was not sufficient to complete the transformation. The δ-NiMo phase was observed only at 900°C as cellular and basket strands precipitates. Second, the reversed peritectoid transformation from γ-Ni₃Mo to α-Ni and δ-NiMo was performed. Supersaturated solid solution samples were first aged at 600C for 100h followed by quenching to form the equilibrium γ-Ni₃Mo phase. After that, the samples were heat treated between 910°C and 1050°C for up to 10h followed by quenching. Regardless of heat-treatment temperature, samples heat-treated for shorter times exhibited small precipitates of δ-NiMo along and within grain boundaries of α-Ni phase, and it coarsened with time. Third, the transformation from the supersaturated solution α-Ni to the peritectoid two-phase region was performed. The samples were aged between 910°C and 1050°C for up to 10h followed by quenching. Precipitates of δ-NiMo were observed in the α-Ni matrix as small particles and then coarsened with aging time. In all three cases, hardness values increased and peaked in a way similar to that of traditional aging, except that the peak occurred much rapidly in the second and third cases. In the first case, hardness increased by about 113.6% due to the development of the new phases, while the hardness increased by 90.5% and 77.2% in the second and third cases, respectively.en
dc.description.abstractgeneralMechanical milling and powder processing methods were used to produce Ni-25at.%Mo alloy. Nickel and molybdenum powders were milled for 10h, pressed, and then sintered at 1300°C for 100h followed by quenching. Three different phase transformation studies were performed. The goal of the first study was to investigate the formation of γ-Ni<sub>3</sub>Mo phase from the solid solution Ni at temperatures ranging between 600°C and 900°C followed by quenching. The 100% γ-Ni3Mo phase was formed at 600°C after 100h. In the second study, the formation of α-Ni and δ-NiMo from γ-Ni<sub>3</sub>Mo phase was performed. The heat treatments were done between 910°C and 1050°C for up to 10h followed by quenching. The γ-Ni<sub>3</sub>Mo phase was not stable at temperatures between 910°C and 1050°C. Small precipitates of δ-NiMo along and within grain boundaries of α-Ni phase were observed, and they coarsened with time. The third study included the formation of α-Ni and δ-NiMo from solid solution Ni. The heat treatments were performed between 910°C and 1050°C for up to 10h followed by quenching. Precipitates of δ-NiMo were observed in the α-Ni matrix. In all three cases, hardness value increased and peaked with heat treatment times as particles coarsened. In the first case, hardness increased by about 113.6% due to the development of the new phases, while the hardness increased by 90.5% and 77.2% in the second and third cases, respectively.en
dc.description.degreeMaster of Scienceen
dc.identifier.otheretd-12142016-092226en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-12142016-092226/en
dc.identifier.urihttp://hdl.handle.net/10919/78058en
dc.language.isoen_USen
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectNi3Mo Alloyen
dc.subjectAge Hardeningen
dc.subjectReverse Peritectoiden
dc.subjectBulk Processingen
dc.titleDesigning Microstructure through Reverse Peritectoid Phase Transformation in Ni₃Mo Alloyen
dc.typeThesisen
dc.type.dcmitypeTexten
thesis.degree.disciplineMaterials Science and Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.levelmastersen
thesis.degree.nameMaster of Scienceen

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