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Preparation And Corrosion Properties Of Zr-based Bulk Metallic Glasses

Posted on:2013-02-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:X P NieFull Text:PDF
GTID:1111330371465798Subject:Materials science
Abstract/Summary:PDF Full Text Request
Zr-based metallic glasses (BMG) exhibit excellent mechanical properties such as high strength and low elastic modulus. But the low plastic strength severely limits the application and developments of metallic glass. Therefore it is of great importance to develop novel metallic glasses with both large plastic strain and high glass-forming ability. In addition, one of the most important criterions for application of the engineering materials is high environmental stability (such as corrosion and oxidation resistance), therefore it is essential and meaningful to conduct researches on corrosion and oxidation behavior of BMG.In this paper, we firstly chose Sn, V, Si, Hf, Nb and Ti as the microalloying elements, to investigate the effects of microalloying effect on the glass-forming ability, thermal stability and mechanical property of Zr46Cu37.6Ag8.4Al8 BMG. The results indicate that only adding 1 at.% of Ti can greatly improve the plasticity from 2% for as-cast alloy to 16%. Furthermore, the BMG still keeps its large glass forming ability after microalloying of Ti.Then the effects of V, Hf, Ni, Nb and Ti addition on the corrosion behavior of Zr-based BMG were investigated. It is demonstrated that the microalloying of Ti, Nb and Ti can greatly enhance the stability of passive film formed on the BMG, and improve the corrosion resistance. The reason may be related with the enrichment of Zr, Ni, Nb or Ti elements which have the high passive ability on the surface of BMG. This is proved by the EDX results.Moreover, we conducted TG tests to investigate the oxidation behavior of Zr46Cu37.6Ag8.4Al8and Zr64Cu16Ni10Al10 BMGs respectively. The structure and composition of the oxide film were studied by the XRD, SEM and XPS. The effects of thermal oxidation on the corrosion behavior of BMG were also investigated. It is found that the Zr64Cu16Ni10Al10 after oxidation at low temperature exhibits excellent passive behavior in 0.5 M NaCl and the corrosion resistance was also enhances after oxidation. That is mainly due to the formation of a 100 nm tetragonal ZrO2-enriched oxide layer in the oxide film. In contrast, both the passive stability and corrosion resistance of the Zr46Cu37.6Ag8.4Al8 BMG were severely deteriorated after oxidation. That is caused by the special structure and composition of the oxide film formed after oxidation.The effects of rolling on the corrosion behavior of Zr64Cu16Ni10Al10 BMG were also investigated. The corrosion mechanism and the phenomenon of preferential pitting initiation at shear band were carefully discussed. It was demonstrated that it was the structural changes on shear band dominated the preferential pitting at shear band behavior rather than shear offset, residual stress or free volume.
Keywords/Search Tags:Bulk amorphous alloy, Glass forming ability, Mechanical property, Oxidation, Corrosion
PDF Full Text Request
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