自由体积对块体非晶断裂韧性的影响

1、Zhen-Dong Zhu a, Evan Mab, Jian Xu a,* Intermetallics 46(2014)164e172Elevating the fracture toughness of Cu49Hf42Al9 bulk metallic glass: Effects of cooling rate and frozen-in excess volume 03 Results and Discussion02 Experimental01 Abstract and Introduction04 ConclusionsAbstract and Introduction He

2、re 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

3、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

4、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

5、 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 stud

6、y 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 in

7、dicators of, the BMG internal structure. Such a systematic characterization provides us with a comprehensive picture of thechanges in the BMG structure and mechanical responses, and sheds light on the origin responsible for the BMG toughening observed. Experimentalu 1.在Ar气保护气氛下，使用同模铸造法制备2-10mm不同直径th

8、e Cu49Hf42Al9 BMG rodsu 2.数据的测定 1)密度的测量是通过阿基米德法测的 2)维氏硬度的测量是用MVR-HS硬度计在加压300N。 保温时间20S测得。显微硬度值是20个个体测量的平 均值。并且才三个不同的点进行测量。 3)放热焓变由DSC-Diamond; PerkinElmer,Shelton, CT 在氧化铝箱、流动Ar气保护、加热速率0.33K/s测得 4)Elastic properties弹性特征由RUS（共振超声分光镜检测）测得 Experimental 5) 缺口韧性的测量是通过不同冷却速率下形成BMG板材测得 6) 材料的断裂韧性是通过测量单边切口梁

9、(SENB)测定。3PB(三点弯曲测试)是用Instron 5848micromechanical tester 在线性位移(0.1mm/min)测得 7）通过前面所的实验数据在ASTM standard E399标准之下，得出缺口韧性的值。 8）式样断裂面形貌在SEM下观察。 Results and Discussionu3.1. Cooling-rate dependence of the frozen-in excess volume and hardnessFig. 1. (a) Changes of density and Vickers microhardness and (b)

10、relative change of frozen-in excess volume, as a function of the diameter of as-cast Cu49Hf42Al9 BMG rods.Results and Discussionu3.2. Correlation of frozen-in excess volume with enthalpy recoveryResults and DiscussionFig. 3. Correlation between relative change of excess volume and enthalpy recovery

11、(DH) associated with structure relaxation of Cu49Hf42Al9 BMG fabricated with different glass-forming cooling rates. The dash line is from linear fittingu3.2. Correlation of frozen-in excess volume with enthalpy recoveryResults and Discussionu3.3. Correlation of frozen-in excess volume with elastic c

12、onstantsFig. 4. Change of (a) shear modulus (G) and bulk modulus (B) and (b) Youngs modulus (E) and Poissons ratio (n) with rod diameter of as-cast Cu49Hf42Al9 BMG.材料性能对冷却速率的敏感性归纳为：Hv (G or E) 泊松比 密度Results and Discussionu3.3. Correlation of frozen-in excess volume with elastic constantsResults and

13、Discussionu3.4. Effect of glass-forming cooling rate on notch toughness（缺口韧性）Results and Discussionu总结冷却速度 维氏硬度 密度 B 泊松比 H fV粘度 断裂韧性 pr能量释放率 缺口韧性 源于ConclusionsuIncreasing the cooling rate during BMG fabrication, such as casting under argon atmosphere mixed with helium, has a remarkable effect to significantly improve the toughness of BMGuThe enhanced BMG toughness is associated with