The correlation between dendritic microstructure and melt undercooling is investigated to present a new technique for rapid single crystal growing, or high undercooling directional solidification (HUDS). In a certain range of undercooling for stable dendrite growth in a negative temperature gradient, this new technique is employed to prepare single crystal Ni50Cu50 bars of approximately 10 mm in diameter and 65 mm in length. Optical metallography and X-ray diffraction experiments indicate that the resulting single crystals in the directionally solidified bars are composed of dendrites approximately parallel to each other and growing mainly in the (100) directions. The formation process and growth velocity of single crystals in an undercooled liquid are analyzed according to the obtained results and calculated by a current dendrite growth theory, respectively. A comparison of the HUDS technique with the as-proposed autonomous directional solidification (ADS) process is made also in the present paper.
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