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Characterization and Analysis of Nanoindentation Behavior for Bulk Amorphous Alloys

Author: PengJian
Tutor: LongZhiLin
School: Xiangtan University
Course: General and Fundamental Mechanics
Keywords: Bulk amorphous alloy Nanoindentation Serrated flow Creep
CLC: TG139.8
Type: Master's thesis
Year: 2010
Downloads: 185
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Abstract


Amorphous alloys have aroused extensive interest since they weresynthesized in the 1960s because of their superior physical, chemical andmechanical properties. However, the lack of room-temperature plasticitybefore fracture for this alloys, has hampered their developments andapplications. Therefore, the study of plastic deformation mechanism and themethod of improving plastic deformation have being hot and difficult issuesin the area of amorphous alloys. In this thesis, the plastic and creepdeformation behaviors and their mechanisms of Pd40Cu30Ni10P20,Zr48Cu32Ni4Al8Ag8, Zr48Cu34Pd2Al8Ag8 and [(Fe0 .6Co0 .4)0 .75B0 .2Si0 .05]96Nb4bulk amorphous alloys were investigated by depth-sensing nanoindentationand atomic force microscopy (AFM) nanoindentation experiments. Some ofthe main results and conclusions are listed as follows:1. Pd40Cu30Ni10P20 and Zr48Cu32Ni4Al8Ag8 exhibited serrated flow(pop-in) phenomenon during nanoindentation experiments, which wassignificantly dependent on loading rates. According to the analysis of singlepop-in event and AFM topography, we consider that there exists someconnection between pop-in event and shear band, and each shear band is notcorresponding to single pop-in event but to multiple pop-in events.2. Single pop-in event data was extracted from P-h curve, and eachpop-in event consists of three steps: acceleration, steady state, anddeceleration. Furthermore, the shear band sliding speed was estimated.Based on the viscosity value and three steps properties of shear bands, arheological model was proposed, which can fit experimental pop-in data andexplain serrated flow phenomenon well.3. On the basis of free volume theory, the expression betweenconcentration of flow defects and indentation loading rate, and theexpression between concentration of flow defects and depth were deduced,which successfully predict the rate-dependent flow serration andindentation size effect (ISE) phenomena, respectively.4. Room-temperature creep phenomenon was observed inPd40Cu30Ni10P20, Zr48Cu32Ni4Al8Ag8, Zr48Cu34Pd2Al8Ag8 and[(Fe0 .6Co0 .4)0 .75B0 .2Si0 .05]96Nb4 bulk amorphous alloys duringnanoindentation tests. The creep deformation increased with increasing indentation load and loading rate, and attained steady state after holdingtime of 10 s. During holding segment, creep contains two steps: there is aninitial sharp rise in creep displacement at the primary part, followed by asteady-state creep where creep depth changes little with time. The creepdeformation behaviors of studied bulk amorphous alloys were modeledusing the elastic-viscoelastic-viscous (EVEV) model. It was found that thiscreep behavior can be well described by the EVEV model. According to theEVEV model, the creep strain rate, stress exponent, creep compliance andretardation spectrum were further calculated.5. Based on free volume theory, shear transformation zone (STZ)activation volume was calculated by nanoindentation creep experiment.6. The deformation behaviors of Pd40Cu30Ni10P20, Zr48Cu32Ni4Al8Ag8and Zr48Cu34Pd2Al8Ag8 BMG in shear band, between shear band and inundeformed regions were studied by AFM nanoindentation, and theirload-displacement curves and hardness values were obtained.

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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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