一般的鑄造過程不易控制凝固結構之形態，最多只能改變晶粒大小，而方向性凝固與單晶成長均屬於難度高之鑄造技術，需使用適當的鑄造機制，來控制凝固結構形態，其中以單晶之製程最為困難，方向性凝固則次之，不過方向性凝固是單晶製程之基礎。針對方向性凝固，本文設計五種不同之鑄造實驗模式，探討於此五種模式之凝固微結構與鑄件軸向溫度分布之相關性。於實驗研究中，以錫鉛合金作為鑄件材料，使用光學顯微鏡觀察凝固微結構以及計算鑄件的橫截面晶粒數目，並利用熱偶線與溫測擷取系統量測鑄件軸向之溫度分布。本文經由橫截面與縱切面之顯微組織觀察、橫截面晶粒數及鑄件軸向溫度分布，分析於五種實驗模式中，晶粒型態之大小跟凝固時之熱傳環境的關聯性，由其分析結果，可掌握方向性凝固之控制機制。

　To control the morphology of solidifying microstructure is difficult in a casting process, in which only the grain size can be easily changed. To perform advanced casting techniques such as directional solidification and the growth of single crystal, a proper casting mechanism is needed to control solidifying microstructures. The fabricating technique of single crystal is based on that of directional solidification. Among these solidification processes, the growth of single crystal is the most difficult one and directional solidification the second. To obtain directional solidification, in this paper, five different kinds of experiment models are designed to investigate the resulting microstructures and their relationships with the axial temperature profiles. In this study, Pb-Sn alloy is used as the testing material and the optical microscope is utilized to observe the solidifying microstructures. The grain number of the lateral cross section is counted and thermal couples are used to measure the temperatures along the axial direction of the cylindrical casting. From the microstructures on the lateral and longitudinal cross sections, the grain number and axial temperature distributions, the relationship among the morphology and size of grain and the solidifying environment is investigated for those five experimental models. From the analysis results, the controlled mechanism of directional solidification can be regulated.

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