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Preparation of the CeGa-based Metallic Glasses and Their Kinetic Properties

Author: XuBaoChen
Tutor: ZuFangZuo
School: Hefei University of Technology
Course: Materials Processing Engineering
Keywords: CeGa-based bulk metallic glasses Glass forming ability Density Fragility Dynamic mechanical relaxation
CLC: TG139.8
Type: Master's thesis
Year: 2013
Downloads: 31
Quote: 0
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Abstract


Metallic glasses possess the amorphous structure compared with thecrystalline matter thus have special properties. The Ce-based metallic glass is aspecial family of metallic glasses because of their low glass transition temperaturesand their abnormal properties under high pressure. However the previous Ce-basedalloys can only form10mm fully glassy rod with a bad glass forming ability. In thiswork, a new CeGa-based alloy system was discovered to improve the glass formingability based on the former knowledge and experience. In addition the dynamicmechanical properties of a representative Ce70Ga8.5Cu18.5Ni3glassy alloy among thealloy system were investigated in the supercooled liquid region by dynamicmechanical analysis method.Ga element with larger Pauling electric negativity than Al was selected toreplace Al in the Ce-based alloys to change the glass forming ability of theCe-based alloys. The results prove that the new Ce-Ga-Cu alloys have super glassforming ability in a wide composition range compared with the Ce-Al-Cu alloys.The Ce70Ga8.5Cu21.5alloy can form fully glassy rod with diameter of12mm, whichmakes the Ce-Ga-Cu alloy be one of the few ternary alloys with best glass formingability. Also we got the density data of the ternary glassy alloys. The resultsindicate that there is a good corresponding relationship between density and glassforming ability in the present alloy system. Our experiment proved the densitydependent glass forming ability for the first time in multicomponent alloys.The Ni addition to the Ce-Ga-Cu alloy further enhanced the glass formingability of CeGa-based alloy. The Ce-Ga-Cu-Ni alloys can form glassy rods withdiameter of14mm in a large composition range. The critical diameter is20mm forthe best glass former Ce70Ga8.5Cu18.5Ni3alloy. The dynamic properties wereexplored by DSC method and we got the fragility parameter m of the quaternaryalloys. A good glass forming ability dependence on fragility was discovered in thisquaternary alloy family. Also we calculated the critical cooling rate of six newCeGa-based metallic glasses (Ce70Ga8.5Cu21.5-xNix(x=0,1.5,3,5,8.5,10.5)) with theglass forming ability criterion formula proposed by Limin Wang. And thecalculated critical cooling rates deviate from the experimental critical cooling rateto a large degree. The calculation results proved that the Limin Wang’s formula didn’t work well in these CeGa-based metallic glasses. Taking into account theinfluence of supercooled liquid region to glass forming ability, γ was used tooptimize Limin Wang’s formula. Then a new glass forming ability criterion formulawas proposed in this work by numerical fitting method. The new formula can workmore universally than the existing criterion.In addition, we investigated the dynamic mechanical properties of theCe70Ga8.5Cu18.5Ni3glassy alloy in the supercooled liquid region. The results showthat the srong CeGa-based glass also shows an excess wing on the high frequencyside of the loss modulus peak. This phenomenon indicates that the slow βrelaxation may also exist in this strong metallic glass.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > The alloy learn with a variety of properties of alloys > Other special nature of the alloy > Amorphous alloy
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