Microstructure refinement and bicontinuity formation by distributed internal melting at the Ni3Sn4 peritectic

Guided by a current interest in processing schemes, such as liquid-metal dealloying, providing fine-scale bicontinuous metal microstructures, we investigate the microstructure evolution during the peritectic melting of Ni 3 Sn 4 . The product microstructure is an interconnected array of spherical clusters of crystallographically aligned Ni 3 Sn 2 ligaments, interpenetrated by a contiguous liquid phase. When quenched to room temperature, the prevalent microstructure consists of two interpenetrating solid phases. Leaching the solidified Sn melt produces monolithic porous bodies of Ni 3 Sn 2 . The characteristic structure size can reach down to 2 μ m, a microstructure refinement by almost 2 orders of magnitude as compared to the 150 μ m grain size of the master alloy. Remarkably, a more severe refinement is achieved at higher annealing temperatures. Our experiments identify liquid-film migration as the controlling process, here concurrent with constitutional supercooling and cellular solidification. We argue that peritectic melting exemplifies a more general family of processes of distributed internal melting (DIM). These processes exploit the abundant nucleation of regions of melt, finely distributed throughout a parent microstructure, when the alloy is heated into a two-phase solid–liquid regime of its phase diagram. DIM provides a novel and versatile pathway to fine-scale bicontinuous microstructures.