Synthesis of metallic glass using femtosecond laser pulsesf

激光被吸收，在质量有时间烧蚀之前，以超音速在样品中发生热传导。发生烧蚀并对材料产生机械冲击。最终热锋冷却，其速度降至以下的烧蚀激波。激波锋面经过热锋面，然后激波穿过未加热的材料。随着传播距离的增加，冲击压力幅值不断减小至零。然而，激波锋面后面的区域仍处于热平衡状态。我们发现利用飞秒激光脉冲可以合成非平衡材料，如非晶结构和高压相。利用飞秒激光烧蚀金属，产生振幅为100 ~ 300gpa的强激波。估计飞秒激光诱导熔层的冷却速率为1013K/s数量级。我们将这两个特性应用于非平衡材料的合成。飞秒激光照射后，用XRD、TEM和EBSD分析了晶体结构。本课题成功合成的非平衡材料有：CuTi非晶合金来源于g-CuTi合金，高压e-Fe来源于a-Fe，高压b-Ti和w-Ti来源于a-Ti，六边形金刚石来源于高取向热解石墨，高压简单六边形结构的Si来源于金刚石结构的Si。

Laser is absorbed, and thermal conduction occurs into the sample at supersonic velocities before mass has time to ablate. Ablation occurs and drives a mechanical shock into the material. Eventually the thermal front cools and its velocity drops below that of the following ablation shock. The shock front passes the thermal front and the shock then traverses unheated material. The amplitude of the shock pressure decreases continuously to zero with increasing propagation distance. However, the region behind the shock front remains in thermal equilibrium.We found that non-equilibrium materials such as amorphous structure and high-pressure phases were synthesized using femtosecond laser pulses. A strong shock wave of which amplitude is 100-300 GPa is driven by the femtosecond laser ablation of metals. The cooling rate of the femtosecond laser induced-molten layer is estimated to be the order of 1013K/s. We appled these two features to synthesize non-equilibrium materials. After the femtosecond laser irradiation, crystalline structures were analyzed using XRD, TEM, and EBSD. Non-equilibrium materials which we succeeded to synthesize in this research project are follows ; CuTi amorphous alloy from g-CuTi alloy, high-pressure e-Fe from a-Fe, high-pressure b-Ti and w-Ti from a-Ti, hexagonal diamond from highly oriented pyrolytic graphite, high-pressure simple hexagonal structure of Si from diamond structure of Si.