自由体积对块体非晶断裂韧性的影响.ppt

Zhen-Dong Zhu a, Evan Mab, Jian Xu a,* Intermetallics 46(2014)164e172 Elevating the fracture toughness of Cu49Hf42Al9 bulk metallic glass: Effects of cooling rate and frozen-in excess volume 03 Results and Discussion 02 Experimental 01 Abstract and Introduction 04 Conclusions Abstract and Introduction Here we demonstrate that by increasing the cooling rate during the casting of liquid Cu49Hf42Al9 into BMG, using a mixed argon and helium atmosphere, the notch toughness of the resultant BMG can be tripled relative to that obtained at slower cooling rates. The much elevated toughness is attributed to a ten-fold increase in the size of the plastic zone at crack tip, due to the proliferation of shear banding facilitated by enhanced propensity for shear transformations. The latter propensity is explained by the reduced shear modulus and microhardness, as well as increased enthalpy recovery, all of which are rooted in structural disorder as reflected by the lowered density and increased frozen-in excess volume. Such a structure-property correlation is systematically demonstrated by monitoring all these properties over a range of diameters of the as-cast BMG rods that correspond to cooling rate levels from 40 K/s to 103 K/s. Abstract and Introduction Moving forward from these previous studies, in this paper we focus our attention on a quantitative assessment of the possible change of fracture toughness induced by the variation of cooling rate. The notch toughness characterized in this study showed a large increase for the coolingrate range employed. In addition to fracture toughness, we will also examine the effect of cooling rate on several properties including the density, microhardness, enthalpy recovery, andelastic constants, which are all expected to depend on, and thus to be indicators of, the BMG internal structure. Such a systematic characterization provides us with a comprehensive picture of the changes in the BMG structure a