Fig.6.1 l(a): Dependence on the frequency of the imaginary part of the complex permeability of Fe75 5 Cu1 Nb1 Si135 B, alloy at different annealing temperature for 30. 1 5 (a): Dependence on the frequency of the imaginary part of the complex permeability of Fe74 Cu05 Nb3 Si135 139 alloy at different annealing temperature for.
List of Tables
List Symbols
CHAPTER -1 INTRODUCTION
General Introduction
The crystallization behavior of this x = 0 alloy is quite disturbing and leads to a severe deterioration of the soft magnetic properties compared to the original amorphous state. Kubaschewski [1.27] showed that in thermodynamic equilibrium boron is practically insoluble in bce Fe (<< 0.01 at. %); the solubilities of Cu and Nb are low: <0.2 at.
Aim of the present research work
The exact coupling mechanism for this type of behavior at T > 7" can be explained in terms of exchange penetration through the thin intergranular paramagnetic layer and/or dipolar interactions. The effect of annealing temperature on the saturation magnetization (Ms) has been reported by Lovas et al.
Organization of the Thesis Work
CHAPTER -2 AN OVERVIEW OF
NANOCRYSTALLINE MATERIALS
An Overview of Nanocrystalline Materials 2.1 History of amorphous and nanocrystalline materials
Formation of Nanocrystalline State
A typical nanocrystalline structure with good soft magnetic properties occurs if the amorphous state is crystallized provided that the primary crystallization of bce Fe takes place before the formation of secondary intermetallic phases such as Fe-B. Both the formation of Fe borides and grain enlargement significantly weaken the soft magnetic properties.
- Advantages of Soft Nanocrystalline Alloys
- Viscosity condition for the Formation of Metallic glass
- Conditions for the formation of Nanocrystalline alloys
- Grain Size and Coercive force of Nanocrystalline alloys
In the initial stages of annealing, Cu-rich clusters are formed by either an If spinodal process or nucleation in the amorphous state. Because the Nb and B enrichment in the amorphous phase stabilizes the remaining amorphous phase, grain growth of the bcc phase eventually stops.
CHAPTER -3
PREPARATION OF
NANOCRYSTALLINE ALLOY
Preparation of NanocrystaHine Alloy
- Methods used for Preparation of Nanocrystalline Alloy
- The Fast Cooling of the Melt
- Sample Preparation .1 Master alloy Preparation
- Preparation of ribbon by Melt Spinning Technique
- Important Factors to Control the Thickness of Ribbons
- Confirmation of Amorphousity of Ribbons
The temperature was monitored by an external pyrometer from the top surface of the molten alloy through a quartz window. A steady flow of the molten metal onto the surface of the rotating drum must be ensured.
CHAPTER -4
THEORETICAL ASPECTS
Theoretical Aspects
Nature and Formation of Amorphous Alloys
At a temperature close to the melting point Tm, the driving force for crystallization is small, so the rates of nucleation and growth of crystals are small, and the initiation time of crystallization is large. Near the glass transition temperature (T2), the atomic motion is completely suppressed and the amorphous structure is frozen, so that the initiation time of crystallization increases.
Factors Contributing to Glass Transition Temperature
The crystallization process is manifested by an abrupt volume change at T, with glass formation characterized by a gradual break in the slope. The area over which the slope change occurs is called the glass transition temperature (T2).
Temperature, T
- Stability of the Amorphous Nanocrystalline Materials
- Structure and Microstructure of Amorphous and NanocrystaHine alloys
- Determination of Nanometric Grain Size by X-ray Diffraction
- Random Anisotropy Model (RAM)
The theoretical analyzes of the factors determining the ease of formation and stability of the resulting amorphous alloys have been extensively discussed [4.7-4.8]. From a thermodynamic point of view, the ability of an alloy to be quenched into the glassy state is generally measured by the size of its quantity. In a similar example, the stability of the glass after forming is generally measured by the size of the quantity.
Scherrer analysis of the width of the X-ray scattering peaks, one would conclude that the 'crystallite size' was on the order of atomic dimensions.
Theories of Permeability
- Relative Permeability
- High frequency Behavior and Losses
The initial permeability of a ferromagnetic substance is the combined effect of the wall permeability and the rotational permeability mechanism. In the case of amorphous materials containing a large number of randomly oriented magnetic atoms, the permeability will be scalar. Relative permeability, sometimes denoted mej, is the ratio of the permeability of a specific medium to the permeability of free space jt0.
The frequency dependence of the absolute value of complex permeability and its imaginary part ji" is expressed in terms of the relative loss factor.
Magnetic dipole moments and Magnetization
Knowledge of atomic volumes of alloy density then allows direct calculation of the alloy magnetization.
Ferromagnetic ordering (Curie) Temperatures
To consider the ferromagnetic response in applied field, ''a as well as the randomizing effects of temperature, we consider the superposition of the applied and internal magnetic fields. By analogy with the problem of paramagnetic moments, the average atomic dipole moment can be expressed in terms of the Brillouin function. An empirical description of the variations of the exchange energy with interatomic distance called the Bethe–Slater curve is instructive in describing the effect of alloying on ferromagnetic Curie temperatures.
In the first case, a unique constant exchange interaction between magnetic atoms is assumed and the amorphous nature of the bond is taken into account by.
CHAPTER -5
- The Principle of Differential Thermal Analysis
- Apparatus
- Experimental Factors
- Interpretation and Presentation of DTA
- X-ray Diffraction (XRD)
- Iav I X-ray 2
And when the reaction ends, the temperature of the sample gradually reaches the temperature of the inactive sample. The area under a DTA peak can be related to the enthalpy change and is not affected by the heat capacity of the sample. The filling can be made of materials such as pyrex, silica, nickel or platinum, depending on the temperature and nature of the evidence involved.
For porous, compacted, or stacked samples, the pore-filling gas can change the thermal conductivity of the atmosphere surrounding the DTA container and cause large errors in the peak region.
IEIIIIII 0,
X-ray powder method
The term "powder" actually means that the crystal domains in the sample are randomly oriented. Therefore, when a 2-D diffraction pattern is recorded, it shows concentric rings of scattering peaks corresponding to different d spacings in the crystal lattice. Powder diffraction data can be collected using a transmission or reflection geometry as shown in Figure 1.
Because the particles in the powder sample are randomly oriented, these two methods will yield the same data.
Experimental Technique for X-ray diffractometer
The X'Pert Pro diffraction system uses a modular system approach to deliver performance for applications ranging from routine characterization to in-depth research investigation. The powder diffraction technique was used with a primary beam power of 40 kV and 30 mA for Cu radiation. A nickel filter was used to reduce Cu-K(1 radiation, and finally Cu-Ka radiation was used only as the primary beam.
An antiscatter slot was used just after the sample holder to reduce air scattering.
Analysis of XRD data
Lattice parameter of crystalline bcc Fe-Si nanograins has been determined for all two different amorphous compositions at different heat treatment temperatures. Normally, the lattice parameter of an alloy composition is determined by the Debye-Scherrer method after extrapolating the curve. The XRD pattern of (i 10) reflection for different steps of the heat treatment temperature of the alloy composition is used to calculate the grain size.
3cos9 (5.4) . All grain size values for all heat treatment temperature steps of the alloy composition were determined.
- Thermal Treatment of the amorphous ribbon
- Impedance Analyzer
- Preparation of the Samples for Complex Permeability Measurement
- Components of Complex Permeability Measurements
- Curie Temperature Measurements
- Inductance Analyzer
- Magnetization Measurement
- Ir 5.6.1 Principle of Vibrating Sample Magnetometer
- Description and brief working principle of Hirst VSM02
The sweep capabilities of the built-in frequency synthesizer and DC bias source allow fast and accurate measurements. Magnetization is defined as the magnetic moment per unit volume or mass of the substance. Vibrating sample magnetometers, as the name suggests, vibrate the sample as part of the measurement process.
The object using a VSM or any other type of magnetic characterization of the magnetization (J) on the applied field H > J (H).
CHAPTER -6
RESULTS AND DISCUSSION
Results and Discussion
Differential Thermal Analysis of the samples
- DTA Results of Nanocrystalline amorphous ribbon Fe-Cu-Nb- Si-B as Affected by Cu and Nb
Since Cu aids nucleation of Fe(Si) phase and Nb slows the formation of boride phase [6.7], the observed anomalies of crystallization temperatures in these studied samples are clearly understood from their compositional variation of Cu and Nb. The area under the first peak of DTA curve corresponds to the enthalpy of crystallization, Al-I of Fe(Si) from which the volume fraction of crystallization (X1 ) can be estimated according to the formula. 6.1) where AIIa and Al I are respectively the enthalpy of crystallization of the cast alloy and that of the alloy annealed for a time t. When the samples are annealed above the T, the primary crystallization as shown by their DTA curves is so diffuse and smeared that it gives signals of near completion of the primary crystallization of Fe(Si) crystallites.
Table-6.3: Annealing Effects on 1St and 2' crystallization states of the nanocrystalline amorphous band with composition Fe74Cuo.5Nb3SiI3.5B9 at constant heating rate 20°C/mm.
X-ray Diffraction Analysis
- XRD Analysis of the Nanocrystalline ribbon with composition Fe755 Cu1 Nb1 Si13.5 B9
- XRD Analysis of the nanocrystaHine ribbon with composition Fe74 Cu05 Nb3 Si135 139
- Dynamic magnetic properties of Fe75.5Cu1Nb1Si13.5B9 alloy with different annealing temperature
- Dynamic magnetic properties of Fe74 Cu0.5 Nb3 Si135 B9 alloy with different annealing temperature
The low frequency value of t' generally increases with the increase in annealing temperature, while the critical frequency decreases. 6.1 1(a,b,c) Frequency dependence of the imaginary part of the complex permeability of Fe75.5 Cu1 Nb1 Si135 B9 alloy at different annealing temperatures for 30 minutes. 6.12 (a,b,c) Frequency dependence of the relative quality factor of Fe75.5 Cu1 Nb1 Si13.5 B9 alloy at different annealing temperatures for 30 minutes.
It is observed that the low-frequency values of t' increase with increasing annealing temperature and reach a maximum value at T8 = 575 °C.
Curie Temperature (Tv) Measurement of Fe-Cu-Nb-Si-B alloys
- Annealing effects on Curie temperature of Fe75.5 Cu1 Nb1 Si13.5 139 alloy
6.19, the temperature dependence of the initial permeability of the cast amorphous ribbon and the samples annealed at 425°C to 450°C in an interval of 25°C is presented. Table 6.7 Annealing temperature, Ta dependence of the Curie temperature of amorphous matrix Tc of Fe75.5 Cu1 Nb1 Si135 B9. It is observed that the sharpness of the fall of j.t' is gradually smeared with the appearance of a tail in the high temperature region.
A probable reason for the lowering of T of the amorphous phase on annealing at and above the crystallization temperature is that.
Specific Magnetization measurement of Nanocrystalline amorphous ribbons
- Effect of annealing temperature on specific magnetization at
6.10, it was observed that the value of t' dropped to a very low value for the sample with an annealing temperature of 550 °C. Specific magnetization (Ms) at room temperature was measured on as-cast and annealed samples. Figure-6.23 Specific magnetization versus magnetic field as cast and annealed Fe74 Cuo.s Nb3 Si13.5 B9 alloy samples.
Tahle-6.8: The values for saturation magnetization of Fe-Cu-Nb-Si-B alloys at Ar different annealing temperature with constant annealing time 30 minutes.
CHAPTER -7
CONCLUSIONS
From systematic research on crystallization, structural and magnetic properties. the following conclusions can be drawn. The evolution of bcc Fe(Si) nanocrystallites and their sizes are determined by the line broadening of the fundamental (110) peaks from the XRD pattern as affected by annealing around the crystallization temperatures. The onset temperature of crystallization found for sample-A is between 450°C and 475°C while for sample-B it is between 500°C and 525°C.
T of the amorphous interfacial phase has been found to decrease for samples when annealed above the crystallization temperatures due to the depletion of Fe and the increase in the relative amount of Nb in the remaining amorphous phase. v).
Chapter-i
Hakim; “Time and temperature dependence of nanocrystalline and initial permeability of finemet alloys,” Nuclear Science and Applications, June (2006) 15 No. 1 9-13. Kang, "Relationship between crystallization process and magnetic properties of Fe-(Cu-Nb)-Si-B amorphous alloys", J. Mattern, "The influence of refractory element additions on the magnetic properties and on the crystallization behavior of nanocrystalline soft magnetic Fe -B-Si-Cu alloys", J.
Manjura Hoque; "Effect of structural parameters on the soft magnetic properties of two-phase nanocrystalline alloy of Fe73.5Cu1 Ta3Si135B9", J.
Chapter-Ill
Chapter-IV
Prados, "Analysis of the Dependence of Spin-Spin Correlations on Thermal Treatment of Nanocrystalline Materials" Phys.
Chapter-V
Chapter-VI
Balong, "Saturation magnetization and amorphous Curie point changes during the early stage of amorphous-nanocrystalline transformation of a FINEMET-type alloy" J.
