Dissertation > Excellent graduate degree dissertation topics show

Effect of Melt Hydrogenation on the Glass Forming Ability and Mechanical Properties of Zr-based Bulk Metallic Glasses

Author: DongFuYu
Tutor: SuYanQing
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: Amorphous alloy Melt hydrogenation Melt purification Glass-formingability Mechanical property
CLC: TG139.8
Type: PhD thesis
Year: 2013
Downloads: 74
Quote: 0
Read: Download Dissertation

Abstract


Bulk metallic glasses （BMGs） have a series of superior mechanical properties,e.g., high yield strengths, large elastic strain limits, good corrosion resistance, andgood soft magnetism and hard magnetism, which is a popular research for currentmaterial world. In this dissertation, hydrogen is added to Zr-based bulk metallicglasses （BMGs） by melt hydrogenation. Melt hydrogenation is a new hydrogenationmethod. In this method, the alloys are melted in the gaseous mixture of hydrogenand argon, and the hydrogen diffuses into alloy melt. The effects of melthydrogenation on the melt purification, glass-forming ability （GFA）, mechanicalproperties and mechanisms are studied.The removal effect of melt hydrogenation on the impurities of oxygen inZr55Cu30Ni5Al10alloy is studied first, and it is found that this method has significantdeoxidation effect in the process of melt hydrogenation. When the hydrogenpercentage in gaseous mixture and melting time are increased, oxygen content ofthe alloys gradually decreases. A hydrogen percentage of15%and melting durationof400s are effective in deoxidizing of these alloys and gaining the completelyamorphous alloy structure. Based on the change of Gibbs free energy, the Gibbsfree energy of reaction hydrogen with oxygen is lower than oxygen with zirconium.Therefore, hydrogen and oxygen is more prone to react. It will avoid the formationof zirconium oxide or zirconium/oxygen clusters which can deteriorate the GFA ofBMGs due to heterogeneous nucleation.The melt hydrogenation is applied to Zr55Cu30Ni5Al10master alloys, and it isfound that the volume fraction of crystalline phases CuZr3and AlZr2graduallydecreases with the increase of hydrogen percentage in the gaseous mixture ofhydrogen and argon, and the crystalline phases completely disappear when thehydrogen percentage increases up to10%, indicating the structure of the sample ismostly amorphous. The GFA of Zr55Cu30Ni5Al10alloys before and after melthydrogenation is comparatively investigated using wedge shaped samples. Criticalsection size of Zr55Cu30Ni5Al10alloys gradually increases with the increase ofhydrogen percentage in the gaseous mixture of hydrogen and argon. When thehydrogen percentage increased up to10%, critical section size reaches maximumvalue.After melt hydrogenation, the fragility parameter and critical cooling rate arestudied. In contrast to non-hydrogenated Zr55Cu30Ni5Al10alloy, hydrogenated alloypossesses smaller fragility parameter and critical cooling rate. In addition, the change of Gibbs free energy difference of Zr55Cu30Ni5Al10alloy before and aftermelt hydrogenation is compared. It is found that the Gibbs free energy difference ofhydrogenated Zr55Cu30Ni5Al10alloy is samller than that of non-hydrogenatedZr55Cu30Ni5Al10alloy. They explain that hydrogenated Zr55Cu30Ni5Al10alloy has ahigh GFA from thermodynamics and dynamics.The structural change of Zr55Cu30Ni5Al10alloys after melt hydrogenation isinvestigated based on positron annihilation life time spectroscopy （PALS） analysisand Bernal holes in dense random packing of hard spheres model. Three lifetimecomponents are identified, indicating the presence of three distinct size ranges foropen volume defects in the glass. The components are assigned to annihilation inthe interstitial holes in the densely packed, flow defects and sub-nanometer voids.The increase of the concentration of interstitial holes in the densely packed showthat the efficiently packed regions are increased after melt hydrogenation, lead to adenser random packed structure, which explains the increase of GFA in terms ofstructural points of view.Room temperature mechanical properties of Zr55Cu30Ni5Al10andZr57Al10Cu15.4Ni12.6Nb5are studied, and it is found that room temperaturecompression plasticity does not decrease, but it is greatly improved. Hydrogen-enhance plasticity is attributed to the formation of stress concentration induced byhydrogen which promotes proliferation and stability of shear band. Thus it canweaken the highly localized shear deformation, leading to larger plastic strain ofamorphous alloy.

Related Dissertations

  1. Study on the Synthesis and Properties of Copolyimides Derived from ODPA/Isomeric ODA,TQ323.7
  2. Research on High Aluminum Zinc-Based Alloy Tyre Valves,U463.341
  3. Study of the Polymer Synthetic Paper Formula and Papyraceous Performance,TS71
  4. Low-Frequency Magnetic Pulsing Effect as Well as EET Study of Amorphous Alloy Fe43Co43Hf7B6Cu1,TG139.8
  5. Study on Electromagnetic Roll-Casting and Succeed Rolling of AZ61 Magnesium Alloy,TG339
  6. Study on Microstructure and Performance of Laser Cladding Ni-Based Amorphous Alloy Coatings,TG174.4
  7. Research on the Properties of Basalt Fabric/PPS Needle Punched Filter,TS176.5
  8. The Preparation, Microstructure and Propertities of the New Type 3D-Meshy SiC/Cu-Fe Composite Material,TB33
  9. The Effect of Electric Current Pulses on Microstructure and Mechanical Properties of 14Cr2MoV Steel,TG142.11
  10. Research of Modification and Property of Starch,TS236.9
  11. Research knitted cashmere fiber blends performance fox,TS104.5
  12. Study of Mechanical Property on Special-shaped Girder Cable-Stayed Bridge,U448.27
  13. Properties on Aramid 1313 Fabric and the Compound Silastic Rubber Composite Material with This Fabric,TB332
  14. Study on Amorphous Formation Ability and Performance of Pt-Pd-Cu-P Alloys,TG139.8
  15. Study on the Performance of Double-combined with Mineral Admixture Concrete and Prediction Model of Compressive Strength,TU528
  16. Synthesis and Modification of IPDI-Based Waterborne Polyurethane,TQ323.8
  17. Control of the Microstructure of Cu/ldpe Composites and Its Influence on Their Properties,TB333
  18. Research on Fabrication and Mechanical Properties of Palm Fiber Reinforced Polypropylene Composites,TB332
  19. Research on Formation and Mechanical Properties Characteristic of Laser Welded Frame-covering Structures of Titanium Alloy,TG456.7
  20. Effects of Activating Flux on the Microstructures and Mechanical Properties of Tungsten Inert Gas and Laser Beam Welded AZ31 Magnesium Alloy Joints,TG407
  21. Research on Squeeze Casting Technology for High Strength and Toughness Aluminum Alloy Parts,TG249.2

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
© 2012 www.DissertationTopic.Net  Mobile