冷却速度对Cu_(46)Zr_(44)Al_5Nb_5块体非晶合金组织和力学性能的影响

Microstructure and Mechanical Properties of Cu_(46)Zr_(44)Al_5Nb_5 Bulk Amorphous Alloy Prepared with Cooling Rates

通过磁悬浮熔炼-水冷铜模吸铸法制备了Cu46Zr44Al5Nb5块体非晶合金阶梯形试样,由X射线衍射(XRD),差示扫描量热仪(DSC)和万能试验机分别表征试样的结构、热力学和力学行为,研究其组织、热稳定性和力学性能与冷却速率的关系。结果表明,Cu46Zr44Al5Nb5合金具有较强的非晶形成能力和良好的热稳定性,其热力学行为表现出尺寸效应。熔体凝固冷却速率对试样尺寸变化敏感,随着试样尺寸的增加,冷却速度呈倍数递减、合金结构的无序度下降,原子排列向稳态转变,导致非晶合金的热稳定性降低。合金的玻璃转变温度不是定值,而是随冷却速度增加而升高,过冷液相区宽度ΔTx、约化玻璃转变温度Trg和晶化放热ΔH随直径的增加而降低,玻璃转变温度向低温漂移。随着直径的增加,冷却速度的降低,非晶合金的短程有序范围增大,最近邻原子间距减小,非晶合金结构的无序密堆性下降,原子排列向稳态转变,导致抗压强度降低,合金的断裂强度随试样直径的增大而减小。

Cu46 Zr44Al5 Nb5 bulk amorphous alloys with step-shape were fabricated by magnetic levitation melting under an argon at- mosphere using a water-cooled Cu mold. Microstructure, thermal stability and mechanical properties were studied by X-ray diffraction （XRD）, differential scanning calorimetry （DSC） and universal testing machine. The effect of cooling rates on microstructure and me- chanical properties of the samples with different diameters was investigated. The results showed that Cu46 Zr44Al5 Nb5 bulk metallic glas- ses （BMG） exhibited good thermal stability and strong glass-forming ability as well as a size effect. The cooling rates of the fusion were sensitive to the size of different samples. With the increase of sample size, the cooling rates exhibited a muhiplicative decrease. And the disorder degree of microstructure decreased, as well as a steady transition of atoms arrangement occurred. Thus, thermal stability of bulk amorphous alloy decreased with the diameters increasing. The glass-transition characteristic temperature was not a constant but avariable one changing with the cooling rates, which increased as a rise of cooling rate. Super-cooled liquid region △Rx, the reduced glass-transition temperature Trg and the crystallization exothermic calories △H decreased as the diameters increased. The glass-transition temperature drifted to lower temperature. The short-range order scope was broaden with the nearest atomic distance decreasing as a re- sult of the increasing diameter and decreasing cooling rate. And the fracture strength of the bulk amorphous alloy decreased with the in- crease of sample size, as a result of the decrease of disorder degree in lager samples.