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第二讲马氏体相变形核第一讲讨论了马氏体相变的基本特征,得出其定义,这一讲将转向讨论马氏体形核机制。图2—1表示奥氏体与马氏体单位体积自由能随温度的变化。奥氏体自由能随温度降低而增加,马氏体自由能也是随着温度降低而增加,两条曲线在T_温度处相交,在T_点,单位体积马氏体与奥氏体具有相同的自由能。当温度降低到T_下时,马氏体的自由能低于奥氏体的自由能,因此比奥氏体更稳定。所以,T_0点以下,马氏体与奥氏体自由能之差△g(△g=g~M—g~A)变为负值。相变驱动力定义为-△g,所以在T_0以下驱动力就变为正值。冷
Lecture 2: Martensite Phase-Change Nucleation Lecture 1 discusses the basic characteristics of martensitic transformation and concludes its definition. This talk will turn to discuss the nucleation mechanism of martensite. Figure 2-1 shows the volumetric free energy per unit volume of austenite and martensite as a function of temperature. Austenite free energy increases with decreasing temperature, and martensite free energy also increases with decreasing temperature. The two curves intersect at T_temperature. At T_point, the unit volume martensite and austenite have the same Free energy. When the temperature is lowered to T_, the free energy of martensite is lower than the free energy of austenite and is therefore more stable than austenite. Therefore, below the T_0 point, the difference Δg (△ g = g ~ M-g ~ A) between the martensitic and austenitic free energies becomes negative. The phase change driving force is defined as - Δg, so the driving force becomes positive under T_0. cold