Abstract
We study the effects of Ag addition on thermal stability and thermophysical properties of Ti-Zr-Ni icosahedral quasicrystals. The Ag addition results in increasing the coherence length and thermal stability of the icosahedral phase (i-phase) of the as-cast Ti35.2Zr43.8Ni21 alloy, which are maximized at around 4 at.% Ag addition. Differential scanning calorimetry (DSC) and electrostatic levitation (ESL) experiments reveal that the addition suppresses the i-phase decomposition on heating and cooling. We find that considerable amount of the i-phase remains in the samples processed by radiational cooling in ESL as the Ag concentration increases. These results demonstrate that Ag addition stabilizes the i-phase of the Ti35.2Zr43.8Ni21 alloy. No anomalous effect of Ag addition is found on density and viscosity of the Ti35.2Zr43.8Ni21 liquid.
Highlights
Small additions of elements onto matrix materials often have a dramatic influence on physical, chemical, and mechanical properties [1,2]
We showed that a small Ag addition to the Ti-Zr-Ni alloy significantly reduces the crystal–liquid interfacial free energy and this is attributed to the formation of icosahedral medium range order (IMRO) by pairing with Zr atoms in the liquid, based on electrostatic levitation experiments and ab-initio molecular dynamic (MD) simulation [7]
We investigate the effects of Ag addition on the thermal stability and thermophysical properties of Ti-Zr-Ni quasicrystals using electrostatic levitation (ESL), differential scanning calorimetry (DSC), and X-ray diffraction (XRD)
Summary
Small additions of elements onto matrix materials often have a dramatic influence on physical, chemical, and mechanical properties [1,2]. Since the icosahedral ordering is incompatible with the well-defined long-range periodic order that characterizes crystals, the prevalence of those orderings in liquids can increase the nucleation barrier for crystal formation (i.e., improving glass forming ability (GFA)), but lower it for quasicrystal formation This is true even in the case of simple binary Cu-Zr alloys. Minute compositional change strongly impacts the GFA by changing the number of ISRO or IMRO in the liquid [17,18,19,20] As for another example, Ag addition significantly affects glass forming [21,22,23,24,25] and quasicrystal forming abilities [7,26,27]. We showed that a small Ag addition to the Ti-Zr-Ni alloy significantly reduces the crystal–liquid interfacial free energy and this is attributed to the formation of IMRO by pairing with Zr atoms in the liquid, based on electrostatic levitation experiments and ab-initio molecular dynamic (MD) simulation [7]
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