單向固化製程中合金的缺陷產生原因，與固化過程中在固液介面的過冷現象有關。近幾年來商品朝著輕薄短小發展,造成對固化過程缺陷控制要求的嚴苛，合金固化因此受到許多學者廣泛的研究。 為了改善這種缺陷的情況，本文將模擬鉛-錫單向固化合金流場，研究在固液介面形態的變化情形，並嘗試經由控制某些特定參數，來分析對固液介面形態不穩定(morphological instability)的影響，藉由對單向固化流場作濃度週期性調變，探討基態系統的變化，利用解析解的方法求解基態；接著對基態流場作線性穩定分析，就同步及次調和兩種不穩定模態來探討固液介面的形態不穩定現象。 We study the morphological instability of the melt-solid interface of a dilute binary alloy. The alloy is assumed to undergo directional solidification into a modulated solutal field. Under such a circumstance, the molten zone is oscillated back and forth in a periodic way. The basic state is solved analytically assuming the melt-solid interface is flat and the bulk melt is quiescent by expanding the governing equation in terms of the assumed infinitesimal modulation amplitude. By further neglecting the flow field, we investigate the interfacial stability of the base state by considering two specific instability modes: the synchronous and subharmonic modes. The synchronous modes vary with time having the same frequency as that of the oscillatory molten zone, while the sudharmonic modes are of the half frequency.
