COBEM99

S18 Processos Mecânico-Metalúrgicos

Title:

EFFECT OF THE UNDERCOOLING LEVEL ON THE MICROSTRUCTURE OF SN-PB ALLOYS

Summary :

RAPID SOLIDIFICATION PROCESS (RSP), FOR METALS AND ALLOYS, CAN BE ESTABLISHED BY APPLYING HIGH COOLING RATES OR HIGH UNDERCOOLINGS UNDER LOW COOLINGS RATES, AS LOW AS 1 K/S, WHICH OCCURS WHEN NUCLEATION SITES ARE REDUCED OR EVEN ELIMINATED. MELT UNDERCOOLING OPENS NEW SOLIDIFICATION PATHWAYS FOR NEW NON-EQUILIBRIUM PHASES AND UNUSUAL MICROSTRUCTURES. SEVERAL TECHNIQUES HAVE BEEN DEVELOPED IN ORDER TO REDUCE NUCLEATION SITES AND TO PRODUCE HIGH UNDERCOOLINGS FOR METALS AND ALLOYS INCLUDING THE FLUXING TECHNIQUE. IN THIS WORK, THE FLUXING TECHNIQUE WAS APPLIED TO HYPOEUTECTIC, EUTECTIC AND HYPEREUTECTIC PB-SN ALLOYS. AS INCREASE UNDERCOOLING, PRIMARY SN DENDRITE ARM SPACING DECREASE IN THE HYPEREUTECTIC ALLOY, AND FOR HYPOEUTECTIC, EUTECTIC AND HYPEREUTECTIC ALLOYS, A MICROSTRUCTURE MORPHOLOGY TRANSITION FROM REGULAR LAMELAR EUTECTIC INTO ANOMALOUS EUTECTIC OCCURS. THUS, AT A LOW SOLIDIFICATION RATE OR AT A LOW UNDERCOOLING, THE MICROSTRUCTURE EVOLUTION IS NEAR TO EQUILIBRIUM, HOWEVER, A HIGH UNDERCOOLING LED TO A HIGH GROWTH RATE IN THESE ALLOYS AND SEVERAL MORPHOLOGICAL CHANGES TAKE PLACE. KEY WORDS: UNDERCOOLING, PB-SN ALLOYS, MICROSTRUCTURE.

Author :

Bolfarini, Claudemiro 0
de Castro, Walman Benício
Kiminami, Claudio Shyinti
Maia, Manuel de Lucena

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