Contact angles by the solid-phase grain boundary wetting (coverage) in the Co–Cu system
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The microstructure of binary Co–13.6 wt% Cu and Cu–4.9 wt% Co alloys after long anneals (930–2,100 h) was studied between 880 and 1,085 °C. The contact angles between (Co) particles and (Cu)/(Cu) grain boundaries (GBs) in the Cu–4.9 wt% Co alloy are between 50° and 70°. In the Co–13.6 wt% Cu alloy, the transition from incomplete to complete wetting (coverage) of (Co)/(Co) GBs by the second solid phase (Cu) has been observed. The portion of completely wetted (Co)/(Co) GBs increases with increasing temperature beginning from T wss = 970 ± 10 °C and reaches a maximum of 15% at 1,040 °C. This temperature is very close to the Curie point in the Co–Cu alloys (1,050 °C). Above 1,040 °C, the amount of completely wetted (Co)/(Co) GBs decreases with increasing temperature and reaches zero at T wsf = 1,075 ± 5 °C. Such reversible transition from incomplete to complete wetting (coverage) of a GB by a second solid phase is observed for the first time.
KeywordsContact Angle Interphase Boundary Curie Point Complete Wetting Ingot Axis
Authors thank the Russian Foundation for Basic Research (contracts 09-03-92481 and 09-03-00784), the Russian Federal Agency for Science and Innovations (contract 02.740.11.5081) and Israel Ministry of Science (project 3-5790) for the financial support. Authors cordially thank Prof. E. Rabkin, Dr. A. Mazilkin and Dr. S. Protasova for stimulating discussions, Mr. A. Nekrasov for the help with SEM and EPMA measurements.
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