Newtonian flow of Zr55Cu30Al10Ni5 bulk metallic glassy alloys
Newtonian flow of Zr55Cu30Al10Ni5 bulk metallic glassy alloys
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DOI：
10.1016/s1359-6462(00)00417-6
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发表时间：
2000-08
影响因子：
6
通讯作者：
A. Reger-Leonhard;M. Heilmaier;J. Eckert
中科院分区：
文献类型：
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作者：
A. Reger-Leonhard;M. Heilmaier;J. Eckert
近年来，仅需要1-10 Ks-1的低冷却速率来玻璃化而不结晶的块状形式的金属玻璃合金[1，2]引起了广泛的兴趣，从制备和潜在应用的技术方面到对结构和所得性质的科学好奇心。与以薄带形式生产的二元和三元非晶金属系统相比，这些多组分合金的特征在于强的玻璃形成能力以及宽的过冷液体区域Tx Tx Tg（其中Tx和Tg分别是结晶和玻璃化转变温度），从而产生高的抗结晶热稳定性。除了它们的热力学性质之外，Zr基大块金属玻璃在室温下特别显示出突出的机械性质，即屈服强度值高达2GPa，微塑性高达1%，低杨氏模量和高断裂韧性值与铝合金相当[3，4]。这些性质连同所报道的在玻璃化转变附近的高温下在粘性状态下的易成形能力[5，6]一起承诺在结构部件的近净成形制造领域中的应用。然而，在过冷液态下的确切变形机制，或者更准确地说，块体金属玻璃是否通过牛顿粘性流动变形，在文献中仍然是一个有争议的问题[6-8]。因此，本文的目的是揭示明确的证据牛顿粘性流动在铸造Zr 55 Cu 30 Al 10 Ni 5块体金属玻璃合金在玻璃化转变温度Tg附近的温度。这将以单相无定形结构以及含有高达10体积%的在铸造时形成的微米尺寸结晶沉淀物的无定形基体的情况为例。
In recent years, metallic glassy alloys in bulk form requiring only low cooling rates of 1–10 Ks 1 to vitrify without crystallization [1, 2] have attracted widespread interest ranging from technological aspects of preparation and potential applications to scientific curiosity about the structure and the resulting properties. In contrast to binary and ternary amorphous metallic systems produced in form of thin ribbons, these multi-component alloys are characterized by a strong glass forming ability together with a wide supercooled liquid region Tx Tx Tg (where Tx and Tg are the crystallization and glass transition temperature, respectively), thus giving rise to a high thermal stability against crystallization. This enables the production of bulk amorphous samples with a thickness of up to 30 mm by conventional casting techniques.Besides their thermodynamic properties Zr-based bulk metallic glasses in particular reveal outstanding mechanical properties at room temperature, namely a beneficial combination of yield strength values as high as 2 GPa, microplasticity of up to 1%, low Young’s moduli and high fracture toughness values comparable to those of aluminum alloys [3, 4]. These properties together with the reported easy forming abilities in a viscous state at elevated temperatures around the glass transition [5, 6] promise applications in the field of near-net shape fabrication of structural components. However, the exact deformation mechanism in the supercooled liquid state, or more precisely whether a bulk metallic glass deforms by Newtonian viscous flow or not, remains a controversial issue in the literature [6–8]. Therefore, the purpose of this paper is to reveal clear evidence for Newtonian viscous flow in cast Zr55Cu30Al10Ni5 bulk metallic glassy alloys at temperatures around the glass transition temperature Tg. This will be exemplified for a single-phase amorphous structure as well as for the case of an amorphous matrix containing up to 10 vol% of micrometer-sized crystalline precipitates formed upon casting.