Liquidus temperatures and solidification behavior in the copper–niobium system
1998; Elsevier BV; Volume: 46; Issue: 11 Linguagem: Inglês
10.1016/s1359-6454(98)00063-9
ISSN1873-2453
AutoresD Li, Michael B. Robinson, T. J. Rathz, Gareth R. Williams,
Tópico(s)Metallurgical Processes and Thermodynamics
ResumoThe copper–niobium phase diagram has been under active debate; thus, a corroboratory experimental study is needed. In this investigation, the melts of Cu–Nb alloys at compositions ranging from 5 to 86 wt% Nb were processed in different environments and solidified at relatively low cooling rates of 50–75°C/s to determine liquidus temperatures and to study solidification behavior. For all samples processed under very clean conditions, only Nb dendrites in a Cu matrix were observed; while in the presence of oxygen impurities, the alloys containing 5–35 wt% Nb exhibited microstructure of Nb-rich spheroids and Nb dendrites in the Cu matrix. The results obtained from clean conditions are in fair agreement with the Cu–Nb phase diagram having an S-shaped, near-horizontal appearance of the liquidus. The formation of Nb-rich droplets at slow cooling rates is discussed in terms of a stable liquid miscibility gap induced by oxygen.
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