Excitation of collective motion of many atoms in amorphous alloys : Realization and application

利用电脉冲在室温下和液氮（LN2）中对非晶态（a-） Cu_<50>Ti_<50>, a-Cu_<50>Zr_<50>, a- pd_ <80>Si_<20>和a-Zr_<60>Cu_<30>Al_<10>的谐振-电脉冲诱导低温结晶（r-e-LTC）进行了研究。谐振（r-）电脉冲是通过电容器放电产生的，其特征为初始电流密度i_<a0>，衰减时间τ，其中r-电脉冲的主傅里叶本质分量的频率为1/2πτ。i_<a0>的变化范围在10^8 A/m^2 ~ 10^<10> A/m^2之间，τ的变化范围在0.05 ms ~ 20之间。对于所有的a-合金，r-e-LTC发生在单次r-电脉冲过程中，且i_<a0>大于阈值电流密度i_<a0>,c，其中i_<a0>，c是τ的函数。在RT和LN_2条件下，r-e-LTC的最高温度分别为400k和200K，表明r-e-LTC是一个非热过程。LN_2中r-电脉冲的i_<a0>，c对τ的依赖关系与RT中r-电脉冲的基本相同，这表明引起r-e-LTC的共振集体运动相关的密度波动在玻璃化转变温度下被冻结。透射电镜观察表明，r-e-LTC形成的晶体相互排列，晶粒尺寸约为10 nm，排列结晶的可能机制是相对高密度区（RHDR）直接转变为结晶相，其中许多原子的协同运动，如原子的光学声子运动。换句话说，共振集体运动时的位移幅值应该是原子种类的函数，并且该区域的成分波动也应该在所形成的晶相允许的范围内。为了实现RHDR的这种协同运动，在相对低密度区域的非弹性应变容量应该相当大。纳米晶金属的非弹性研究支持了这一观点。本工作展示了非晶合金中多原子集体运动激发的实现和应用。少

The resonant-electropulsing-induced low temperature crystallization (r-e-LTC) of amorphous (a-) Cu_<50>Ti_<50>, a-Cu_<50>Zr_<50>, a-Pd_<80>Si_<20> and a-Zr_<60>Cu_<30>Al_<10> was investigated by means of electropulsing at RT and that in liquid nitrogen (LN2). Resonant (r-) electropulsing was made by means of discharge of a condenser which is characterized by the initial current density, i_<a0>, and the decay time, τ, where the frequency of the principal Fourier constitutional component of r-electropulsing is 1/2πτ. The range of i_<a0> was between 10^8 A/m^2 and 10^<10> A/m^2 and that of τ was between 0.05 ms and 20. ms. For all the a-alloys, the r-e-LTC took place during single r-electropulsing with i_<a0> higher than the threshold current density, i_<a0>,c, where i_<a0>,c was a function of τ. The maximum specimen temperature during the r-e-LTC was, e.g., 400 K for r-electropulsing at RT and 200K for r-electropulsing in LN_2, respectively, indicating that the r-e-LTC is associated with … More an athermal process. The dependence of i_<a0>,c, on τ found for r-electropulsing in LN_2 was essentially the same to that observed for r-electropulsing at RT, indicating that the density fluctuation associated with the resonant collective motion responsible for the r-e-LTC was that frozen at the glass transition temperature. The transmission electron microscopy observation revealed that crystallites formed by the r-e-LTC showed crystallographic alignment with each other and the size of the crystallites was, e.g., the order of ten nm. A possible mechanism for the aligned crystallization is a direct transformation of the relatively high density region (RHDR) to a crystalline phase, where cooperative motions of many atoms such as an optical phonon like motions of atoms should take place. In other words, the amplitude of displacement during the resonant collective motion should be a function of atomic species and the compositional fluctuation in this region should be inside in a permissible range for the crystalline phase formed too. In order to realize such cooperative motion of RHDR, a capacity for the anelastic strain in the relatively low density regions should be considerably large. The anelasticity study of nanocrystalline metals supported this point of view. The present work demonstrated the realization and application of excitation of collective motion of many atoms in amorphous alloys. Less