Thermal properties and glass-forming ability of bulk glassy alloys

众所周知，钯基和锆基玻璃合金具有较宽的过冷液相区的玻璃化转变。这些大块非晶合金使我们能够研究这些合金的热性能和电阻率。这项工作的主要目的是在所获得的值的基础上讨论这些合金的非晶形成能力。用激光闪光技术测量了合金的热扩散率。用直流四探针法测量了样品的电阻率。用热流型差示扫描量热仪和三电池系统测量比热。合金在液态下的热扩散系数值可归结为与温度呈正相关的线性方程。合金液相线温度下的热扩散系数越低，获得非晶态合金的临界冷却速度越低。因此，合金液体的热扩散系数值可能是其玻璃形成能力的一个指标。在玻璃态下，合金的热扩散系数与温度呈正相关关系。在晶化温度(T_C)时，合金的热扩散系数突然增大。在结晶温度范围内，随着温度的升高，热扩散系数逐渐增大，呈现出三个阶段。电阻率值在T_c处突然减小并逐渐减小，表现出与热扩散系数值相同的趋势。测得玻璃状态下的比表面积为0.372 Jg^-1；K^&lt；-1。得到了液态Pd基合金的比热值。这些值表现出较小的负温度依赖关系。Wiedemann Franz定律的分析还表明，Pd基合金的主要机制可能是在过冷液和液态下受电子控制。

Pd-based and Zr-based glassy alloys are well known to exhibit glass transition with a wide supercooled liquid region. These bulk amorphous alloys allow us to investigate thermal properties and electrical resistivity of these alloys. The main purpose of this work is to discuss the glass-forming ability of these alloys on the basis of the obtained values. The thermal diffusivity values of the alloys were measured with a laser flash technique. The electrical resistivity was measured by a direct current four probe technique. The specific heat was measured by the heat flux type differential scanning calorimeter with a triple cell system. The thermal diffusivity values of the alloys in the liquid state are summarized in the linear equations with positive temperature dependency. The lower the thermal diffusivity values of the alloys at liquidus temperature, the lower the critical cooling rate to obtain amorphous alloy becomes. Thus, the thermal diffusivity values of alloy liquids might be an indicator of their glass forming ability. The thermal diffusivity values of Zr_<55>Al_<10>Ni_5Cu_<30> alloy show positive temperature dependence in the glassy state. The thermal diffusivity values of the alloy increase suddenly at crystallization temperature (Tc). The thermal diffusivity values increase gradually showing three stages in the crystallization temperature range with increasing temperature. The electrical resistivity values suddenly decrease at Tc and gradually decrease showing same tendency of the thermal diffusivity values. The specific value of Zr_<55>Al_<10>Ni_5Cu_<30> in the glass state was measured to be 0.372 Jg^<-1>K^<-1>. The specific heat values for liquid Pd-based alloys were also obtained. These values show small negative temperature dependence. It was also suggested from analysis with Wiedemann Franz law that principal mechanism of Pd-based alloy is likely to be controlled by electron in the super cooled liquid and liquid states.