Volumetric manifestation of grain refinement in undercooled metal

Journal Article · Wed Oct 01 04:00:00 EDT 1997 · Scripta Materialia

DOI:https://doi.org/10.1016/S1359-6462(97)00203-0· OSTI ID:541012

Xiao, J Z; Kui, H W ^[1]

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1. Chinese Univ. of Hong Kong (Hong Kong). Dept. of Physics

Experience indicates that when a molten metal crystallizes below its melting temperature T{sub 1} (T{sub 1} stands for the thermodynamic melting temperature of pure metallic elements or the liquidus of alloys), the microstructure of the undercooled specimen depends on the initial bulk undercooling {Delta}T of the undercooled melt, which is defined as {Delta}T = T{sub 1} {minus} T where T is the kinetic crystallization temperature. For instance, Walker found that the grain size of undercooled Ni undergoes a rapid drop by as much as two orders of magnitude in a narrow temperature range, from {Delta}T = 155 to 170 K. This phenomenon is termed grain refinement. Xiao et al. on the other hand demonstrated that grain refinement in undercooled Cu{sub 30}Ni{sub 70} is brought about by a re-melting of dendrites. The re-melting mechanism as occurred in undercooled Cu{sub 30}Ni{sub 70} is made possible by a substantial composition variation, or equivalently varying liquidus T{sub 1}, across the length of the dendrites at {Delta}T {ge} {Delta}T*. Upon solidification, the heat of crystallization can bring the temperature of the system back to T{sub 1} causing re-melting of the inhomogeneous dendrites. It is also noted that during microstructural analysis, voids are always present in an undercooled Cu{sub 30}Ni{sub 70} specimen. Furthermore, their distribution varies from one specimen to another of different {Delta}T. More importantly, it appears that the total volume of the voids present in one undercooled specimen differs from that of another undercooled specimen of different {Delta}T. In this paper, the specific volume of undercooled Cu{sub 30}Ni{sub 70} was measured as a function of {Delta}T in order to establish a correlation between the grain refinement transition and the specific volume.

• OSTI ID: 541012
• Journal Information: Scripta Materialia, Journal Name: Scripta Materialia Journal Issue: 7 Vol. 37; ISSN 1359-6462; ISSN SCMAF7
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COPPER ALLOYS
DENSITY
EXPERIMENTAL DATA
GRAIN REFINEMENT
GRAIN SIZE
LIQUID METALS
NICKEL ALLOYS
SOLIDIFICATION
TEMPERATURE DEPENDENCE
VOIDS