Effects of Mischmetal Addition on the Microstructural Characteristics of BCuP-2 Brazing Filler Metal
In this work, the effect of mischmetal (48wt%Ce–27wt%La–14wt%Nd–6wt%Pr) additions on the microstructural characteristics of an Cu-7wt%P brazing filler metal (BCuP-2) were investigated. The volume fraction of primary Cu was considerably increased with increasing mischmetal addition in the BCuP-2. Also, the eutectic structure was changed from lamella to fibrous morphology and the pseudo-eutectic phase (Cu3P) was formed around the primary Cu with the mischmetal addition above 0.03wt%. Compound containing a small amount of mischmetal was formed in the primary Cu phase and this compound acts as the nucleation sites of primary Cu. The fraction of primary Cu was increased by about 1-2wt% due to the mischmetal rich phase. The mischmetal rich phase also formed in the pseudo-eutectic phase and this enhanced the formation of pseudo-eutectic phase. The addition of mischmetal changes the eutectic phase lamella to fibrous by suppressing both the solid-liquid interfacial energy and the surface energy of the solid. The mischmetal additions showed a very strong influence on the nucleation process of primary Cu and the subsequent formation of Cu3P phase as well as the eutectic structure change.
Byung Tae Ahn, Hyeongtag Jeon, Bo Young Hur, Kibae Kim and Jong Wan Park
B.K. Lee et al., "Effects of Mischmetal Addition on the Microstructural Characteristics of BCuP-2 Brazing Filler Metal", Solid State Phenomena, Vols. 124-126, pp. 1421-1424, 2007