Annihilation Of Free Volume Research Articles

Enhancement in bio-corrosion resistance of metallic glass by severe surface deformation

Amorphous metals, also known as bulk metallic glasses, are promising materials for advanced healthcare applications. This is attributed to their exceptional properties, unseen in crystalline materials. Their unique ability to undergo relaxation during low temperature annealing provides opportunity to develop tailored properties. Here, we show a new pathway to significantly accelerate the relaxation kinetics in a zirconium based metallic glass through severe surface deformation using thermo-mechanical processing. The combined strain and thermal field during thermo-mechanical processing significantly reduced the relaxation time compared to vacuum annealing concurrent with remarkable enhancement in its bio-corrosion resistance. The corrosion resistance was found to have a direct correlation with the wetting behavior and oxide layer composition. The surface of relaxed glass was found to be rich in zirconium oxide compared to its as-cast state with higher fraction of aluminum oxide. The difference in oxide layer composition was attributed to annihilation of free volume in relaxed glass resulting in limited atomic transport. Relaxed metallic glass exhibited more hydrophobic nature likely due to its lower surface energy state as a consequence of structural densification. In addition, the relaxed glass showed better cell proliferation, thereby, enhancing its appeal as a next-generation biomaterial.

Novel corrosion behaviours of the annealing and cryogenic thermal cycling treated Ti-based metallic glasses

Effects of structural relaxation and cryogenic thermal cycling on corrosion resistance of the Ti50Zr20Be20Ni10 bulk metallic glass (BMG) was investigated in 3.5 wt% NaCl solution. The annealed Ti-based BMGs exhibited striking high pitting potentials with low corrosion current densities, while cryogenic thermal cycling treated BMGs performed poor corrosion resistance. More stable passive films were found to form on the surfaces of annealed BMGs through electrochemical impedance spectra analysis. Sub-sized pits that evolved along with micrometre-sized pits on corroded morphologies of the as-cast and cryogenic thermal cycling treated samples clarified the aggressive corrosion. Annealing treatment gave rise to the annihilation of excessive free volume within BMGs, while cryogenic thermal cycling induced the proliferation of free volume. Moreover, the variation of microhardness further reflected the fluctuation of free volume. The XPS analysis revealed that the superior corrosion resistance of the annealed samples could be attribute to the increment in the concentration of Ti, Zr and distinct decrement in the concentration of Be. It is concluded that excessive free volume would deteriorate stability of surface passive film.

The effect of hydrostatic pressure on the shear deformation of Cu symmetric tilt interfaces

The effect of hydrostatic pressure on the shear deformation behavior of 10 Cu symmetric tilt interfaces has been investigated in the athermal deformation regime (10 K) using molecular dynamics simulations. Cu bicrystals were deformed under shear with a superimposed hydrostatic stress, until initial yield. For most interfaces, the shear strength increased with increasing compressive hydrostatic pressure. However, for the Σ9{221} and Σ5{210} interfaces, this trend was reversed. Neither the sign nor the magnitude of the pressure-induced elevation in shear strength was found to correlate with interface structure or particular deformation mechanism(s). The findings suggest that in general, metrics of interfacial excess volume and dilatation cannot reliably predict the pressure-sensitivity of shear strength; however, for interfaces containing the E structural unit, the annihilation of free volume appears to correlate well with the observed pressure-sensitivity.

High-Pressure Low-Temperature Sintered Dense Amorphous SiBCN Monoliths with Ultrahigh Hardness

An attractive way to prepare dense amorphous Si2B1.5-4C2N monoliths at low temperature was proposed and the effects of applied high-pressure on mechanical properties have been assessed. A monotonous behavior of the bulk density, hardness and modulus as a function of applied pressure was identified. The observed increasing hardness should result from the microstructural changes. The river-like shear band occurs preferentially in locations where the free volume is relative high and high-pressure effectively promoted the densification leading to free volume annihilation.

Correlation between the atomic configurations and the amorphous-to-icosahedral phase transition in metallic glasses

Abstract

Metallic glass hardening after thermoplastic forming

Thermoplastic forming is an important manufacturing technique for the shaping of metallic glass (MG) components. However, property changes of MGs after such forming are unclear. This paper systematically studied the effect of thermoplastic forming on the structure and mechanical properties of a Zr-based MG. It was found that the MG after forming is of higher hardness; yet this effect increases with the forming temperature rise. Localized shear deformation as commonly observed around a Vickers indentation mark in MGs was not found around the indentation mark of the thermoplastically formed MG. The study concluded that the primary mechanism of such property change of the MG is due to the free volume annihilation induced by the structural relaxation during the thermoplastic forming.

Rapid and partial crystallization to design ductile CuZr-based bulk metallic glass composites

Transformation-induced plasticity in CuZr-based bulk metallic glass (BMG) composites opens up a new perspective for the design of ductile BMG composites. In this work, rapid and partial crystallization of BMGs is proposed to tailor microstructures of ductile BMG composites. During the early crystallization stage, the precipitation of B2 CuZr crystals in the Cu42Zr42Al10Co6 BMGs is growth-controlled at low or high heating rates after having passed through a nucleation-dominated temperature region. Abundant nucleation is beneficial for the uniform precipitation of B2 crystals in the glassy matrix. Compared with annealing processes at slow heating, the degree of the free volume annihilation could be reduced to some content by employing a high heating rate. The microstructures of CuZr-based BMG composites can be effectively tuned by changing rapid annealing parameters, which enhances the ductility of the resulting BMG composites. This approach proves to be efficient for the development of ductile metastable alloys and composites.

Quantifying the microstructural inhomogeneity of Zr46Cu46Al8 metallic glasses based on change ratio of polyhedral volume

The microstructural inhomogeneity of Zr46Cu46Al8 metallic glasses is investigated quantitatively by molecular dynamics simulation. A parameter, the change ratio of polyhedral volume, is used to characterize the microstructural inhomogeneity in metallic glasses. Based on identifying the polyhedral volume expansion and contraction around each atom, the microstructural heterogeneity of metallic glasses can be revealed and quantified. The relation between the redistribution of the free volume and production or annihilation of defects has been established. By molecular dynamics simulations of dynamic mechanical tests, the distribution of the change ratio of polyhedral volume is correlated to dynamic heterogeneities in metallic glasses at the atomic level. Our work opens a new technologically avenue towards the characterization of microstructural inhomogeneity that affects the thermodynamics, dynamics and deformation in metallic glasses.

Composition dependent relaxation in La-Al-Ni/Cu metallic glasses

We investigate structural relaxations in La-Al-Ni/Cu metallic glasses and find that the La-Al-Ni glasses tend to have a significant β-relaxation, which becomes more pronounced and shifts to high temperatures when increasing Ni content from 10 to 30 at.% in La85-xAl15Nix or Al content from 10 to 25 at.% in La70AlxNi30-x glasses. In contrast, the β-relaxation in La-Al-Cu glasses is weak and almost disappears after annealing. Compared with La-Al-Cu glasses, La-Al-Ni glasses usually have higher Tg temperatures and bigger changes in Tg by sub-Tg annealing. Different relaxation behaviors between La-Al-Ni and La-Al-Cu glasses changing with compositions and thermal history indicate that the free volume annihilation is not the key factor in controlling the β-relaxation in La-Al-Ni glasses.

Mössbauer spectroscopy research on magnetic softening of Fe84B10C6 amorphous alloy during low-temperature annealing

The mechanism of magnetic softening in Fe84B10C6 amorphous alloys annealed at a temperature below the crystallization temperature has been investigated by Mössbauer spectroscopy. With the prolongation of annealing time, saturation flux density increases gradually but coercivity firstly declines to a minimum and then increases drastically. All the modulations of local structure strengthen the magnetic exchange between Fe neighbor atoms during low-temperature annealing. The structural relaxation at the early stage of annealing including annihilation of excess free volume and residual stress rotates the easy axis to the ribbon plane and weakens magnetic anisotropy, while the subsequent structural relaxation contributing to chemical inhomogeneity results in the inverse situation. Thus, appropriate annealing can magnetically soften amorphous alloys. For the Fe84B10C6 amorphous alloy, soft magnetic properties are optimized when annealed at 493 K for 100 s.

Amorphous Metallic Alloys: Pathways for Enhanced Wear and Corrosion Resistance

Amorphous metallic alloys are widely used in bulk form and as coatings for their desirable corrosion and wear behavior. Nevertheless, the effects of heat treatment and thermal cycling on these surface properties are not well understood. In this study, the corrosion and wear behavior of two Zr-based bulk metallic glasses were evaluated in as-cast and thermally relaxed states. Significant improvement in wear rate, friction coefficient, and corrosion penetration rate was seen for both alloys after thermal relaxation. A fully amorphous structure was retained with thermal relaxation below the glass transition. There was an increase in surface hardness and elastic modulus for both alloys after relaxation. The improvement in surface properties was explained based on annihilation of free volume.

Mechanical Properties Transformation On Zr54Al17Co29 Bulk Metallic Glass by Partial Crystallization

Study on biomaterials is recently essential for rapid development of medical application and Zr 54 Al 17 Co 29 BMGbecomes promising candidate due to the lack of toxic elements. Partial crystallization by isothermal annealing at SCL region was used to variate the crystallinities of BMG. The structural and thermal properties of as cast and partially crystallized samples were confirmed by XRD and DSC test, while microvickers and compression test were further utilized to investigate their mechanical properties. By the higher crystallinity, the hardness could be slightly increased in range 540 ± 5 to 575 ± 5 H v. As-cast sample shows the yield strength and plastic strain of 2130 ± 75 MPa and 2.2 ± 1.6%. The yield strength is increased by the presence of 10% nanocrystal, afterwards, fall and raise phenomena are obtained with further crystallinity. However, with higher crystallinity, the plasticity is significantly degraded and no more plastic strain observed at sample with 50% of crystallinity. Both the presence of nanocrystalline phase and free volume annihilation are the reason of mechanical properties change on the Zr-based BMG.

A size-dependent free volume prediction model of Zr55Cu30Al10Ni5 bulk metallic glass in the supercooled liquid region

The specimen size has a significant influence on the flow behavior of Zr55Cu30Al10Ni5 bulk metallic glass throughout thermoplastic compression processes in the supercooled liquid region. Due to enhanced structural relaxation, the recovery enthalpy increases with specimen size decreasing. Based on combined differential scanning calorimetry experiments and finite element modeling simulations, the different free volume annihilations caused by the specific surface area discrepancy are considered as the main cause of size-dependent free volume variation during the pre-heating process. Thermodynamics and structural relaxation theory are introduced to provide a reasonable explanation of the size-dependent flow behavior at elevated temperatures. A novel prediction model involving size-induced free volume variations has been established by considering the influences of compression deformation variables. The quantitative theoretical prediction agrees well with experimental data, which indicates that the developed prediction model can accurately describe the size-dependent free volume annihilation and generation during the thermoplastic forming process. Furthermore, the reasonable theoretical analysis and size-dependent free volume prediction model provide a profound understanding of the size-dependent flow behavior and its relation to internal structural evolution behaviors of metallic glasses.

Dry Sliding Wear Behavior of Hafnium-Based Bulk Metallic Glass at Room and Elevated Temperatures

Dry sliding wear behavior of hafnium-based bulk metallic glass was studied at two loads (5 and 15 N) and two temperatures (298 and 673 K) using aluminum oxide (Al2O3) ball as a wear counterpart. At 5 N load, wear reduced by ~71% on increasing the temperature from 298 to 673 K. At a higher load of 15 N, the weight loss reduction was much lower (45%) on increasing the temperature from 298 to 673 K. Decreased wear weight loss on increasing the temperature was attributed to the increased hardness of the Hf-based metallic glass at high temperatures. Micro-hardness of the alloy at 293 K was found to be 636 Hv, which gradually increased to 655 Hv on annealing at 673 K. Improvement in the hardness at elevated temperature is attributed to: (1) free volume annihilation, (2) surface oxide formation and (3) nano-crystallites precipitation. Reduced wear at elevated temperature resulted in smaller volume of debris generation that restricted three-body wear to obtain lower coefficient of friction (COF) (0.25-0.35) compared to COF (0.65-0.75) at room temperature.

Mechanical Strength and Surface Roughness of Magnesium-Based Metallic Glasses

This work evaluated the mechanical strength and surface roughness of MgZn30Ca5 ribbon manufactured via a melt spinning technique for applications in the biomedical field. Annealing was performed at 280°C. The inner side (in contact with the wheel) and the outer side (not in contact with the wheel) of the ribbons were mechanically evaluated using nanoindentation, and its surfaces were analyzed by an optical profilometer. Differential scanning calorimeter (DSC) and X-ray diffraction (XRD) analyses were also performed to identify the structure and devitrification of the magnesium metallic glass (MgMG). The nanohardness and elastic modulus increased after annealing (p 0.05). Although both sides of the ribbons showed different surface profiles (p < 0.0001), no statistical difference was detected in roughness parameters on either ribbon side before (p = 0.3094) and after (p = 0.8742) annealing. DSC curves showed disturbances in enthalpy attributed to a relaxation in the MgMG structure and free volume annihilation. The DRX diffractogram showed sharp peaks after annealing, with MgZn and Ca2Mg5Zn13 phases being identified. Although the use of MgMG in biomedical applications is promising, the ribbons displayed limited ductility, toughness, and a relevant embrittlement after the annealing procedure. There were significant changes in the surface profile of both sides of the ribbons. Nevertheless, neither annealing nor the ribbon side had influenced surface roughness parameters.

Low-Temperature Annealing on Treated of Pulsating Magnetic Field Fe-Co-M-B-Cu Amorphous

After the medium-frequency magnetic pulse treating (frequency 1500-2000Hz, field intensity 200-250Oe) on amorphous Fe (Co)-M-B-Cu alloys, the vacuum anealing at low-temperature were in progress at 50°C-100°C for 30 min and 60 min. The soft magnetic properties of nanocrystalline alloy obtained by above mentioned treatments were measured by the vibrational specimen magnetometer. The results show that the structral relaxation , free volume migration and annihilation during the vacuum annealing will lead to the reduction of like-vacancy defects concentration and distortion stress. So the soft magnetic properties of nanocrystalline alloy will be improved further.

Mechanism for microstructural evolution induced by high temperature deformation in Zr-based bulk metallic glasses

In the Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit1) alloy undergoing high temperature deformation, its thermal properties and microstructure are quite different from those in the annealing alloy. In order to research the coupled effect of temperature and plastic strain on microstructural evolution of Zr-based amorphous, uniaxial compression test of Vit1 alloy with good amorphous nature has been performed, and then the structural state and thermal properties of Vit1 alloy after thermal deformation and isothermal annealing in the supercooled liquid region were investigated. It is revealed that the deformed specimens possess higher characteristic temperature and lower enthalpy change of microstructural relaxation. In addition, the smaller inter-atomic distance and higher order degree of atomic arrangement can be observed in those deformed Vit1 alloy. That can be deduced that thermal deformation is in favor of the microstructural evolution from a metastable amorphous state to stable crystallization state, because plastic strain promotes the annihilation of free volume and provide excess driving force of atomic diffusion. However, upon increasing the ambient temperature, the influence of plastic deformation on microstructure gradually decreased owing to the decreasing proportion of the plastic deformation-induced annihilation of free volume during the whole thermal deformation process.

Co-existence of homogeneous flow and localized plastic deformation in tension of amorphous Ni–P films on ductile substrate

The room temperature mechanical behavior of amorphous Ni–P thin films deposited on Ni substrate under tension was systematically investigated. Due to the effect of substrate confinement, unexpected homogeneous plastic flow occurred in the film simultaneously with cracking or shear banding, which co-contributed to the plastic deformation. The film thickness gradually reduced with increasing tensile strain and the maximum reduction increased up to 69% in 2.6 μm-thick film. Such a severe plastic deformation leads to significant structure change in the film where free volume annihilation dominates, evidently by almost 100% reduction in the total relaxation enthalpy in the deformed film, accompanied by the densification and hardening. The stress required for shear band and crack propagation in Ni–P film was analyzed on the basis of Griffith's criterion. A deformation map is proposed to account for co-existence of homogeneous flow and localized plastic deformation (shear banding or cracking), as well as the transition of deformation modes.

Investigation of Elastic Deformation Mechanism in As-Cast and Annealed Eutectic and Hypoeutectic Zr–Cu–Al Metallic Glasses by Multiscale Strain Analysis

Elastic deformation behaviors of as-cast and annealed eutectic and hypoeutectic Zr–Cu–Al bulk metallic glasses (BMG) were investigated on a basis of different strain-scales, determined by X-ray scattering and the strain gauge. The microscopic strains determined by Direct-space method and Reciprocal-space method were compared with the macroscopic strain measured by the strain gauge, and the difference in the deformation mechanism between eutectic and hypoeutectic Zr–Cu–Al BMGs was investigated by their correlation. The eutectic Zr50Cu40Al10 BMG obtains more homogeneous microstructure by free-volume annihilation after annealing, improving a resistance to deformation but degrading ductility because of a decrease in the volume fraction of weakly-bonded regions with relatively high mobility. On the other hand, the as-cast hypoeutectic Zr60Cu30Al10 BMG originally has homogeneous microstructure but loses its structural and elastic homogeneities because of nanocluster formation after annealing. Such structural changes by annealing might develop unique mechanical properties showing no degradations of ductility and toughness for the structural-relaxed hypoeutectic Zr60Cu30Al10 BMGs.

Thermal Stability and the Matrix Induced Brittleness in a Ti-based Bulk Metallic Glass Composite

Crystallization kinetics and nanocrystalline induced brittleness in an in-situ dendrites reinforced Ti44Zr20Nb12Cu5Be19 bulk metallic glass (BMG) composites were investigated. The activated energy of the present Ti-based metallic glass matrix is obtained to be about 201 KJ/mol. As the annealing temperature rises, the annihilation of free volume is believed to cause the increase of hardness and the decrease of plasticity. Brittle fracture occurs after the precipitation of nanocrystalline, which can be ascribed to the formation of the microcracks in the matrix during deformation.