High-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. / Master of Science / Mechanical 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.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/78058 |
| Date | 03 February 2017 |
| Creators | Khalfallah, Ibrahim |
| Contributors | Materials Science and Engineering, Aning, Alexander O., Reynolds, William T. Jr., Suchicital, Carlos T. A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Thesis, Text |
| Format | application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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