摘要
An interesting phenomenon of cooling-rate induced brittleness in Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass （BMG） was reported. It was found that the as-cast BMG specimens exhibited a brittle-ductile transition when the larger specimens were machined into smaller specimens through removing the cast-softening surface layer by layer. After compression tests, the as-machined small specimens, owing to the absence of the cast-softening surface, displayed highly dense and intersecting shear bands, and extensive plastic deformation. This is in contrast to the catastrophic failure and low deformability in the as-cast large specimens. More free volume was detected in the smaller as-fractured specimens, by differential scanning calorimetry, which may be attributed to the occurrence of strain softening and increased plasticity. Compared with the relatively smooth fracture surface in the smaller specimens, the larger specimens showed more diverse features on the fracture surface due to their graded structures.
研究Zr52.5Cu17.9Ni14.6Al10Ti5块体非晶合金由于铸造过程中表面与心部冷却速率差异诱发的表面软化层对其室温压缩行为的影响。通过逐层除去铸造表面软化层,块体非晶试样表现出脆性-韧性转变。在室温压缩时,除去表面软化层的试样呈现大量致密、均匀分布的剪切带和较好的塑性;而未除去表面软化层的试样仅萌生出少量剪切带,且发生灾难性断裂。除去软化层的试样变形后自由体积增加,说明在压缩过程中发生了应变软化。除去软化层的试样组织结构相对均匀,剪切带稳定扩展,断面平滑;而未除去表面软化层的试样则呈现出多样的断面形貌。
基金
Project(2012M511401)supported by China Postdoctoral Science Foundation
Project(12JJ5018)supported by Hunan Provincial Natural Science Foundation of China
Project(2012RS4006)supported by Hunan Provincial Science and Technology Plan of China
Project(CSUZC2012028)supported by the Open-End Fund for the Valuable and Precision Instruments of Central South University,China
