Mg-Er based bulk amorphous alloys and their composites
W.Y. Liu (Materials Science)
Supervised by Prof. H.F. Zhang, Vice Prof. A.M. Wang and Prof. Z.Q. Hu
Mg based amorphous alloys are regarded as a new family of the promising structural materials for their high strength and low density. Generally, multi-component system shows good glass forming ability (GFA) which has the characters of large atomic size mismatch and negative mixing heat amongst the constituent elements. But no method or theory can solve the challenge of quantified relationship between alloy component and glass forming ability. In this paper, the main purpose is to build the quantified relationship and then to explore new Mg based bulk amorphous alloy system.
Firstly, we build the model to calculate GFA of alloys, using the intrinsic material properties (atomic size, electro-negativity, melting point and valence electron of the constituent element), through analyzing the character of typical glass forming formers. Comparing with the experimental results, the model can be applied in GFA calculation successfully with high precision. The statistical correlation parameter R2 is as high as 0.85.
Secondly, based on the GFA calculation model we developed a new Mg-Er based bulk amorphous alloy system. Through modification the GFA calculation model, the relationship between alloy constituents and its glass forming ability are clarified very well. Calculation values agree well with experimental values. With the guide of calculation model, exploring new amorphous alloy progress smoothly。
Thirdly, after testing their mechanical properties, the Mg-Er based amorphous alloys show high fracture strength and high micro-hardness, but plastic strain is limited at ambient temperature. In order to solve the problem, the Nb particles (Nbp) strengthened metallic glass matrix composites, Nbp-Mg60Cu30Er10 composites have been fabricated, which have high plastic strain values about 5-6%. The effect of Nbp is helpful of inducing to generate more shear bands, promoting their bifurcation and hindering their free propagation.
Nbp-Mg60Cu30Er10 composites posses a certain amount of plastic strain, but their matrixes are still deformed by the mode of localized shear bands. Plastic shaping is still unsolved. So it is proposed to investigate the deformation behavior of Mg60Cu30Er10 amorphous alloy in the supercooled liquid region. The supercooled liquid can show remarkable homogeneous plastic strain (about 50-60%) with rather low flow stress (less than 100MPa). This property can help us to shaping Mg-Er based bulk amorphous alloys.
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