Disorder trapping during the solidification of beta Ni3Ge from its deeply undercooled melt

作者：Ahmad R; Cochrane R F; Mullis A M^*

来源：Journal of Materials Science, 2012, 47(5): 2411-2420.

DOI：10.1007/s10853-011-6062-y

A melt encasement (fluxing) technique has been used to solidify the congruently melting intermetallic beta Ni3Ge from its deeply undercooled parent melt. High speed photography and a photo-diode technique have been used to measure the resulting growth velocity. The maximum undercooling achieved was 362 K, wherein a growth velocity of 3.55 m s(-1) was recorded. At an undercooling of 168 K, an abrupt increase in the gradient of the velocity-undercooling curve is observed and this is attributed to a transition from growth of the ordered L1(2) compound at low undercooling, to growth of the fully disordered compound at high undercooling. A change in the microstructure, from a distribution of very coarse (700 mu m), randomly oriented grains to a fine-grained structure (15-20 mu m) with a large number of low-angle grain boundaries is observed coincident with this transition in the velocity-undercooling curve, a grain refinement pattern that is different to that observed either in deeply undercooled solid solutions or other intermetallics. This transition is ascribed to a recovery and recrystallisation process in the disordered phase due to the low post-recalescence cooling rate.

• 出版日期2012-3