Effects of Undercooling and Cooling Rate on Peritectic Phase Crystallization Within Ni-Zr Alloy Melt
The liquid Ni-16.75 at. pct Zr peritectic alloy was substantially undercooled and containerlessly solidified by an electromagnetic levitator and a drop tube. The dependence of the peritectic solidification mode on undercooling was established based on the results of the solidified microstructures, crystal growth velocity, as well as X-ray diffraction patterns. Below a critical undercooling of 124 K, the primary Ni{sub 7}Zr{sub 2} phase preferentially nucleates and grows from the undercooled liquid, which is followed by a peritectic reaction of Ni{sub 7}Zr{sub 2}+L → Ni{sub 5}Zr. The corresponding microstructure is composed of the Ni{sub 7}Zr{sub 2} dendrites, peritectic Ni{sub 5}Zr phase, and inter-dendritic eutectic. Nevertheless, once the liquid undercooling exceeds the critical undercooling, the peritectic Ni{sub 5}Zr phase directly precipitates from this undercooled liquid. However, a negligible amount of residual Ni{sub 7}Zr{sub 2} phase still appears in the microstructure, indicating that nucleation and growth of the Ni{sub 7}Zr{sub 2} phase are not completely suppressed. The micromechanical property of the peritectic Ni{sub 5}Zr phase in terms of the Vickers microhardness is enhanced, which is ascribed to the transition of the peritectic solidification mode. To suppress the formation of the primary phase completely, this alloy was also containerlessly solidified in free fall experiments. Typical peritectic solidified microstructure forms in large droplets, while only the peritectic Ni{sub 5}Zr phase appears in smaller droplets, which gives an indication that the peritectic Ni{sub 5}Zr phase directly precipitates from the undercooled liquid by completely suppressing the growth of the primary Ni{sub 7}Zr{sub 2} phase and the peritectic reaction due to the combined effects of the large undercooling and high cooling rate.
- OSTI ID:
- 22857983
- Journal Information:
- Metallurgical and Materials Transactions B, Process Metallurgy and Materials Processing Science, Vol. 49, Issue 2; Other Information: Copyright (c) 2018 The Minerals, Metals & Materials Society and ASM International; http://www.springer-ny.com; Country of input: International Atomic Energy Agency (IAEA); ISSN 1073-5615
- Country of Publication:
- United States
- Language:
- English
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