块状非晶剪切带和微裂纹形核扩展的SEM原位研究

IN SITU SEM STUDY OF INITIATING AND GROWING OF SHEAR BAND AND MICROCRACK IN BULK METALLIC GRASS

在扫描电镜(SEM)中对Zr_(57)Cu_(15.4)Ni_(12.6)Al_(10)Nb_5块状非晶单边缺口试样进行了原位拉伸;用原子力显微镜(AFM)研究了剪切带的三维形貌。研究表明,拉伸时缺口前方产生剪切带,它们逐步发展、长大,尽管剪切带由剪应力产生,正应力在其形成和扩展过程中起重要作用。两剪切带相交时会形成割阶,其长度随相交剪切带中应变量升高而增大,当主剪切带中应变集中足够大后,剪切微裂纹沿主剪切带和基体的交界线形核扩展,并沿剪切面向试样内部扩展几十微米;在正应力作用下,该剪切(Ⅱ型)裂纹张开成Ⅰ型,并快速贯穿试样厚度,然后沿横向快速扩展导致断裂。

In situ tensile tests in scanning electron microscope (SEM) were carried out using a single-edge notched specimen of Zr57Cu15.4Ni12.6Al10Nb5 metallic grass. Three-dimension pattern of shear bands was investigated using atom force microscopy(AFM). The result shows that the shear bands form and grow firstly during loading. The normal stress plays important role in forming and growing of shear bands through shear stress is necessary. A jog can form in a shear band which is intersected by a growing shear band, and the length of the jog increases with increasing the strain concentration in the growing shear band. A shear microcrack (or microcracks) initiates and propagates along the main shear band/matrix interface on the surface of the specimen, and propagates on the shear plane about 20 mum toward the interior of the specimen. During further extending, the shear (mode II) crack opens into mode I crack, and propagate fastly along the shear plane into a through crack, then the specimen failures by fastly propagating of the through crack.