自由體積對塊體非晶斷裂韌性的影響

1、Company LogoZhen-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 volumeCompany Logo 03 Results and Discussion02 Experimental01 Abstract and Introduction04 ConclusionsComp

2、any LogoAbstract 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

3、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

4、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

5、rods that correspond to cooling rate levels from 40 K/s to 103 K/s.Company LogoAbstract 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

6、. 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

7、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 thechanges in the BMG structure and mechanical responses, and sheds light on the origin responsible for the BMG toughening observed.

8、Company Logo Experimentalu 1.在Ar氣保護氣氛下，使用同模鑄造法制備2-10mm不同直徑the Cu49Hf42Al9 BMG rodsu 2.數(shù)據(jù)的測定 1)密度的測量是通過阿基米德法測的 2)維氏硬度的測量是用MVR-HS硬度計在加壓300N。 保溫時間20S測得。顯微硬度值是20個個體測量的平 均值。并且才三個不同的點進行測量。 3)放熱焓變由DSC-Diamond; PerkinElmer,Shelton, CT 在氧化鋁箱、流動Ar氣保護、加熱速率0.33K/s測得 4)Elastic properties彈性特征由RUS（共振超聲分光鏡檢測）測得back

9、Company Logo Experimental 5) 缺口韌性的測量是通過不同冷卻速率下形成BMG板材測得 6) 材料的斷裂韌性是通過測量單邊切口梁(SENB)測定。3PB(三點彎曲測試)是用Instron 5848micromechanical tester 在線性位移(0.1mm/min)測得 7）通過前面所的實驗數(shù)據(jù)在ASTM standard E399標準之下，得出缺口韌性的值。 8）式樣斷裂面形貌在SEM下觀察。 Company LogoResults and Discussionu3.1. Cooling-rate dependence of the frozen-in exc

10、ess volume and hardnessFig. 1. (a) Changes of density and Vickers microhardness and (b) relative change of frozen-in excess volume, as a function of the diameter of as-cast Cu49Hf42Al9 BMG rods.Company LogoResults and Discussionu3.2. Correlation of frozen-in excess volume with enthalpy recoveryCompa

11、ny LogoResults and DiscussionFig. 3. Correlation between relative change of excess volume and enthalpy recovery (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 exces

12、s volume with enthalpy recoveryCompany LogoResults and Discussionu3.3. Correlation of frozen-in excess volume with elastic constantsFig. 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.材料性能對冷卻速率的敏感

13、性歸納為：Hv (G or E) 泊松比 密度Company LogoResults and Discussionu3.3. Correlation of frozen-in excess volume with elastic constantsCompany LogoResults and Discussionu3.4. Effect of glass-forming cooling rate on notch toughness（缺口韌性）Company LogoResults and Discussionu總結(jié)冷卻速度 維氏硬度 密度 B 泊松比 H fV粘度 斷裂韌性 pr能量釋放率 缺口韌性 源于Company LogoConclusionsuIncreasing 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 an