Decoupled bulk and surface crystallization in Pd85Si15 glassy metallic alloys: Description of isothermal crystallization by a local value of the Avrami exponent

1988 ◽  
Vol 3 (1) ◽  
pp. 59-66 ◽  
Author(s):  
A. Calka ◽  
A. P. Radliński
Keyword(s):  
Amorphous Alloys ◽  
Transition Process ◽  
Avrami Exponent ◽  
Surface Crystallization ◽  
Scanning Calorimetry ◽  
Avrami Model ◽  
X Ray ◽  
Bulk Crystallization ◽  
Phase Transition Process ◽  
Local Value

Isothermal devitrification of Pd85Si15 amorphous alloys has been analyzed using differential scanning calorimetry (DSC) and x-ray diffractometry. Both as-quenched and aged amorphous ribbons were investigated. Crystallization of aged samples starts from the surface and proceeds several micrometers into the bulk. The product of this process is a layer of strongly textured palladium (111) followed by a mixture of Pd2Si, Masumoto MSI phase, and untextured palladium. Next, the crystallization occurs via a different (bulk) mechanism, resulting in a mixture of Masumoto MSII phase and untextured palladium. The bulk mechanism is the only one observed in as-quenched samples. The surface and bulk crystallization mechanisms are spatially decoupled and, therefore, the corresponding DSC data can be analyzed separately. This has been done according to the Kolmogorov–Johnson–Mehl–Avrami model and also using the recently developed concept of local value of Avrami exponent n. For both the surface and bulk crystallization the phase transition process cannot be characterized by a single value of n. Observed variation of n with the crystallized fraction x is explained by a considerable variation of the nucleation rate that takes place during devitrification.

Comparative study of the crystallization behavior and morphologies of carbon and glass fiber reinforced poly(ether ether ketone) composites

2020 ◽  
pp. 096739112096510
Author(s):  
Pan Wang ◽  
Qing Lin ◽  
Yaming Wang ◽  
Chuntai Liu ◽  
Changyu Shen
Keyword(s):  
Carbon Fiber ◽  
Glass Fiber ◽  
Isothermal Crystallization ◽  
Crystallization Behavior ◽  
Unit Cell ◽  
Fiber Reinforced ◽  
Scanning Calorimetry ◽  
Avrami Model ◽  
X Ray ◽  
Glass Fiber Reinforced

This work aims to perform a systematic investigation on the crystallization behavior and morphologies of carbon and glass fiber reinforced PEEK. The nonisothermal and isothermal crystallization behavior was investigated by differential scanning calorimetry (DSC). The resultant morphologies were assessed by wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), and polarized optical microscopy (POM) to provide details on spherulitic level, crystalline structure at unit cell, and lamellar levels. It was found that the crystallization ability of carbon fiber filled PEEK was better than that of neat PEEK, while the behavior of glass fiber filled PEEK was in an opposite trend. The incorporation of carbon fiber (or glass fiber) led to a looser packing of the unit cell or a less crystal perfection of PEEK but did not change its crystal form as well as its long period of lamellae. The isothermal crystallization kinetics was analyzed by the Avrami model, suggesting that the crystallization mechanism of carbon fiber filled PEEK was different from that of neat PEEK and its glass fiber filled composites. Nevertheless, the POM results showed that fiber-induced transcrystallization in PEEK matrix was not evidenced for either carbon or glass fiber filled PEEK. Finally, the effect of carbon and glass fiber on the crystallization of PEEK matrix was discussed to some extent.

The Composition Effect on the Nanocrystallization of Finemet Amorphous Alloys

1996 ◽  
Vol 457 ◽  
Author(s):  
J. Zhu ◽  
T. Pradell ◽  
N. Clavaguera ◽  
M. T. Clavaguera-Mora
Keyword(s):  
Amorphous Alloys ◽  
Nucleation And Growth ◽  
Secondary Crystallization ◽  
Composition Effect ◽  
Phase Precipitation ◽  
X Ray Diffraction ◽  
Initial Composition ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Diffusion Controlled

ABSTRACTDifferential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Neutron Diffraction (ND) and Mössbauer Spectroscopy (MS) were used to study the nanocrystallization process of Fe73.5Cu1Nb3Si22.5–xBx (x=5, 7, 8, 9 and 12) amorphous alloys. Both the temperature range and the activation energy of Fe(Si) phase precipitation from the amorphous martrix increase with the initial B composition. The initial Si composition influences the mechanism of the nanocrystallization: for the Si rich samples, the beginning of nucleation and growth processes is interface controlled, for the B rich samples it is diffusion controlled. Secondary crystallization from the remaining amorphous is mainly Fe3B and Fe2B, the ratio of Fe3B/Fe2B being dependent on the initial composition too.

Structure, Annealing Characteristics and Mechanical Properties of Mg60Cu30-yY10Siy Bulk Amorphous Alloys

2002 ◽  
Vol 754 ◽  
Author(s):  
U. Wolff ◽  
B. Yang ◽  
N. Pryds ◽  
J.A. Wert
Keyword(s):  
Mechanical Properties ◽  
Amorphous Alloys ◽  
Simple Technique ◽  
Partial Substitution ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Glass Forming ◽  
Si Content ◽  
Constant Heating

ABSTRACTThe effect of different Si contents on the glass forming ability (GFA) and the amorphous-to-crystalline transformation has been investigated for the Mg-Cu-Y-Si system. Four Mg60Cu30-yY10Siy (y = 1–5 at.%) alloys were prepared using a relatively simple technique of rapid cooling of the melt in a copper mould. Crystallization was induced by heat treatment of the alloys and the samples were then characterized concerning their microstructure and thermal stability by X-ray diffraction (XRD), optical (OM) and scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) at a constant heating rate. Partial substitution of Cu by Si leads to a transition of the as-cast structure at a constant cooling rate from amorphous to crystalline with increasing Si content. Furthermore, the glass transition temperature (Tg) of the Mg-Cu-Y-Si alloy is lower compared to the Mg-Cu-Y system. The mechanical properties of the bulk Mg-Cu-Y-Si alloys have been investigated and found to vary with the Si content.

Thermal and Mechanical Properties of the (Cu36Zr48Al8Ag8)100-xSix (x = 0–1) Amorphous Alloys

2010 ◽  
Vol 638-642 ◽  
pp. 1627-1631 ◽  
Author(s):  
N.Y. Wu ◽  
C.J. Hsieh ◽  
Jason S.C. Jang ◽  
S.R. Jian ◽  
Y.T. Chen
Keyword(s):  
Amorphous Alloy ◽  
Amorphous Alloys ◽  
Microstructure Development ◽  
Thermal And Mechanical Properties ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Arc Melting ◽  
Diffraction Patterns ◽  
Si Content ◽  
Supercooled Region

In this study, (Cu36Zr48Al8Ag8)100-xSix (x = 0–1) amorphous alloy rod with (2~4) mm diameter were prepared by arc melting. The thermal properties and microstructure development during the annealing of amorphous alloys have been investigated by the combination of differential scanning calorimetry (DSC),, X-ray diffractometry (XRD) and Vickers indentation. The XRD result reveals that all these as-quenched, (Cu36Zr48Al8Ag8)100-xSix alloys exhibit the broad diffraction patterns of amorphous phase. A clear Tg (glass transition temperature) and supercooled region (about 102 K) were revealed for all of those amorphous alloy rods. The crystallization temperature (Tx), (ΔTx) , and micro-hardness of (Cu36Zr48Al8Ag8)100-xSix amorphous alloys is increased as the Si content.

scholarly journals Crystallization of Fe-Based Bulk Amorphous Alloys

2015 ◽  
Vol 60 (1) ◽  
pp. 7-10 ◽  
Author(s):  
K. Błoch ◽  
M. Nabiałek ◽  
M. Dośpiał ◽  
S. Garus
Keyword(s):  
Amorphous Alloys ◽  
Rapid Quenching ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Transmission Electron ◽  
Two Stages ◽  
Two Peaks ◽  
Structure Investigations ◽  
Dsc Curves

Abstract The aim of this paper is to present the results of crystallization studies for the bulk amorphous (Fe0.61Co0.10Zr0.025Hf0.025 Ti0.02W0.02B0.20)98Y2, Fe61Co10TixY6B20, Fe61Co10Ti2Y7B20 alloys. The crystallization of the alloys was studied by differential scanning calorimetry (DSC). The amorphicity of the investigated alloys in the as-quenched state was testified using Mossbauer spectroscopy, X-ray diffractometry and transmission electron microscopy. Moreover, X-ray diffractometry was applied to structure investigations of partially crystallized samples. The crystallization process in the investigated alloys occurs in one or two stages. Two peaks in the DSC curves can be overlapped or well separated indicating the complex crystallization processes. From X-ray diffraction we have stated that in both types of devitrification the crystalline phase can be ascribed to the α-FeCo. In the first stage the crystalline grains seem to grow from the nuclei frozen in the samples during the rapid quenching, whereas in the second one both the growth of the existed grains and creation of new ones during annealing may occur.

DSC Kinetic Studies on Glass Ceramic System Crystallizing Indialite (Mg2Al4Si5O18)

2006 ◽  
Vol 45 ◽  
pp. 25-29
Author(s):  
Giovanni Baldi ◽  
Valentina Dami ◽  
V. Faso
Keyword(s):  
Mechanical Characteristics ◽  
Kinetic Studies ◽  
Surface Crystallization ◽  
Initial Surface ◽  
Scanning Calorimetry ◽  
Isothermal Method ◽  
Bulk Crystallization ◽  
Dimensional Growth ◽  
Avrami Parameter ◽  
Different Grain Size

A formulation belonging to the CaO-MgO-SiO2-Al2O3 system was characterized in order to found a monophase system based on indialite (Mg2Al4Si5O18), known for its good mechanical characteristics. The classical kinetic studies performed in the muffle kiln show an initial surface crystallization followed from immediate bulk crystallization. The kinetic results obtained via differential scanning calorimetry (DSC) were treated with isothermal method, Kissinger, Ozawa and Matusita and Sakka approaches and compared. These results partially explain the macroscopic behavior, because the studies performed on sample of different grain size show a typical trend for a surface crystallization, while the value of Avrami parameter calculated from the kinetics is 2.3, demonstrating a bi-dimensional crystallization. The value of crystallization energy EC calculated with the isothermal method is 517.8 kJmol-1 and the comparison with nonisothermal studies suggests bulk crystallization to occur with an increasing number of nuclei and a two-dimensional growth of crystals.

Investigation of the Bulk Nd60-xDyxFe30Al10 (x=0, 2, 5) Amorphous Alloys

2005 ◽  
Vol 475-479 ◽  
pp. 3393-3396
Author(s):  
Hui Xu ◽  
Xiao Hua Tan ◽  
Nannan Qi ◽  
Qing Wang ◽  
Yuanda Dong
Keyword(s):  
Saturation Magnetization ◽  
Amorphous Alloys ◽  
Magnetic Behavior ◽  
Glass Forming Ability ◽  
X Ray Diffraction ◽  
Soft Magnetic ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Glass Forming ◽  
Intrinsic Coercivity

The glass-forming ability, thermal stability and magnetic properties of the Nd60-xDyxFe30Al10 (x=0, 2, 5) bulk amorphous alloys were investigated by x-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscope (SEM) and the vibrating sample magnetometer (VSM). The results show that the glass forming ability of the Nd60-xDyxFe30Al10 (x=0, 2, 5) alloys decrease with increasing Dy content. The as-cast Nd60-xDyxFe30Al10 (x=0, 2, 5) alloys show hard magnetic behavior at room temperature. With increasing Dy content, the intrinsic coercivity of the alloys increase significantly while the saturation magnetization and remanence of the alloys decrease monotonously. With increasing annealed temperature, the intrinsic coercivity of the Nd55Fe30Al10Dy5 alloy decreased significantly, while the saturation magnetization and remanence decrease monotonously. The Nd55Fe30Al10Dy5 alloy shows soft magnetic behavior after annealed at 773K for 30 min.

Reversible Structural Relaxation in Fe-Ni-B-Si Metallic Glasses

1986 ◽  
Vol 80 ◽  
Author(s):  
R. Brüning ◽  
Z. Altounian ◽  
J. O. Ström-Olsen
Keyword(s):  
Metallic Glasses ◽  
Structural Relaxation ◽  
Short Range ◽  
Short Range Order ◽  
Composition Dependence ◽  
Published Data ◽  
Surface Crystallization ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray

AbstractReversible structural relaxation has been studied in (Fe1-xNix)80B10Si10 by differential scanning calorimetry and X-ray diffraction. It is found that surface crystallization plays a major role in inhibiting reversibility. In consequence previously published data have presented a misleading picture about the composition dependence of the reversible effect in Fe-Ni-B-Si, which simply increases monotonically with Ni composition. There is no evidence that chemical short range order plays any role in reversibility.

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