Synthesis of metallic glass using femtosecond laser pulsesf

激光被吸收，在质量有时间烧蚀之前，热传导以超音速发生在样品中。发生烧蚀并将机械冲击驱动到材料中。最后，热锋冷却，其速度下降到低于下一个烧蚀激波的速度。冲击波阵面通过热阵面，然后冲击波穿过未加热的材料。随着传播距离的增加，冲击压力的幅值连续减小到零。然而，冲击波阵面后面的区域仍然处于热平衡状态。我们发现，非平衡材料，如非晶结构和高压相合成使用飞秒激光脉冲。飞秒激光烧蚀金属产生了振幅为100-300 GPa的强冲击波。飞秒激光诱导熔化层的冷却速率估计为1013 K/s量级。我们利用这两个特性来合成非平衡材料。在飞秒激光照射后，使用XRD、TEM和EBSD分析晶体结构。本课题成功合成的非平衡材料有：由g-CuTi合金合成CuTi非晶合金，由a-Fe合成高压e-Fe，由a-Ti合成高压b-Ti和w-Ti，由高取向热解石墨合成六方金刚石，由Si的金刚石结构合成高压简单六方结构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.