ABSTRACT

To be used as a new kind of three-dimensional printing material, rheological behaviour of a La-based bulk metallic glass (BMG) was studied over a wide range of high temperatures and strain rates by uniaxial compression experiments. The variations in peak stress and steady stress with temperature and strain rate were analysed. Three rheological regions were revealed for the BMG: a non-Newtonian, a Newtonian and an abnormal region which are determined by the temperature and strain rate. The variation on viscosity further indicates that the rheological mode transforms from Newtonian fluid to non-Newtonian fluid with the increase of strain rates at the same temperature. The results from scanning electron microscope test also confirm the microstructural changes that occurred at three different rheological modes. The crystallisation kinetics of La₅₅Al₂₅Ni₅Cu₁₀Co₅ was studied by thermal analysis and the result show that the crystallisation process of La₅₅Al₂₅Ni₅Cu₁₀Co₅ glassy alloy is the diffusion-controlled growth. The relationship among steady-state stress, strain rates and temperatures are determined by using hyperbolic function under high-temperature compression test. The curve shows that the logarithmic relationship between the steady-state stress and strain rates satisfies the linear relationship. Besides, the activation energy Q of this amorphous alloy in Newtonian rheological region is 131.31 kJ/mol.

摘要

作为一种新型的三维印刷材料，通过单轴压缩实验研究了La基大块金属玻璃（BMG）在宽范围的高温和高应变速率下的流变行为。分析了峰值应力和稳态应力随温度和应变率的变化。揭示了BMG的三个流变区：非牛顿区，牛顿区和异常区，这是由温度和应变率确定的。粘度的变化进一步表明，在相同温度下，随着应变速率的增加，流变模式从牛顿流体转变为非牛顿流体。扫描电子显微镜测试的结果还证实了在三种不同流变模式下发生的微观结构变化。La的结晶动力学通过热分析对₅₅ Al ₂₅ Ni ₅ Cu ₁₀ Co ₅进行了研究，结果表明，La ₅₅ Al ₂₅ Ni ₅ Cu ₁₀ Co ₅玻璃态合金的结晶过程是扩散控制的生长。稳态应力，应变速率和温度之间的关系是通过在高温压缩试验下使用双曲线函数来确定的。该曲线表明稳态应力和应变率之间的对数关系满足线性关系。此外，该非晶态合金在牛顿流变区的活化能Q为131.31kJ / mol。