Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA.
Nano Lett. 2009 Nov;9(11):3954-62. doi: 10.1021/nl9032704.
The in situ martensitic phase transformation of iron, a complex solid-state transition involving collective atomic displacement and interface movement, is studied in real time by means of four-dimensional (4D) electron microscopy. The iron nanofilm specimen is heated at a maximum rate of approximately 10(11) K/s by a single heating pulse, and the evolution of the phase transformation from body-centered cubic to face-centered cubic crystal structure is followed by means of single-pulse, selected-area diffraction and real-space imaging. Two distinct components are revealed in the evolution of the crystal structure. The first, on the nanosecond time scale, is a direct martensitic transformation, which proceeds in regions heated into the temperature range of stability of the fcc phase, 1185-1667 K. The second, on the microsecond time scale, represents an indirect process for the hottest central zone of laser heating, where the temperature is initially above 1667 K and cooling is the rate-determining step. The mechanism of the direct transformation involves two steps, that of (barrier-crossing) nucleation on the reported nanosecond time scale, followed by a rapid grain growth typically in approximately 100 ps for 10 nm crystallites.
利用四维（4D）电子显微镜实时研究了铁的原位马氏体相变，这是一种涉及集体原子位移和界面运动的复杂固态相变。通过单个加热脉冲，将铁纳米薄膜样品以大约 10(11) K/s 的最大速率加热，通过单脉冲、选区衍射和实空间成像来跟踪相变从体心立方到面心立方晶体结构的演变。在晶体结构的演变中揭示了两个明显的成分。第一个成分在纳秒时间尺度上是直接马氏体相变，它在加热到 fcc 相稳定温度范围 1185-1667 K 的区域中进行。第二个成分在微秒时间尺度上代表了激光加热最热中心区域的间接过程，其中温度最初高于 1667 K，冷却为速率决定步骤。直接转变的机制涉及两个步骤，即在报道的纳秒时间尺度上跨越（势垒）成核，随后是快速晶粒生长，对于 10nm 晶粒通常在大约 100 ps 内完成。
