Search

The investigation addresses the influence of tensile deformation on the magnetic properties of 304SS samples in their as-received state as well as those with martensite content of 12 and 17%. Non-destructive electromagnetic techniques like magnetic Barkhausen emission (MBE) and magnetic hysteresis loop have been used to measure variation in MBE voltage and coercivity, respectively, during plastic deformation through tensile loading. As both the techniques use surface probe, the present investigation will be useful for in situ evaluation of structural components. With progressive plastic deformation, those measurements revealed different stages of deformation indicated by change in MBE signal and magnetic coercivity. The stages of magnetoelastic response, strain-induced martensitic transformation, dislocation pile-ups and formation of voids reflected different patterns of magnetic Barkhausen emission and magnetic coercivity variation with progressive straining of austenitic stainless steel samples. The changes in true strain with variation in martensite content along gauge length of fractured samples have been analyzed with respect to martensite transformation kinetics. Mathematical fitting methodology has been adopted to distinguish as-received and pre-strained martensitic transformation characteristics. In situ magnetic NDE and associated martensitic transformation parameters may be useful for structural health monitoring of in-service components.

The electromagnetic interference shielding effectiveness (EMI SE) of amorphous and annealed melt-spun ribbons having typical composition of Co72.5Si12.5B15, (Fe0.65Co0.35)83Si1.3B11.7Nb3Cu1, Fe80Si8B12 and Fe83Si2B13Nb2 were studied in the 0.2–8.5 GHz microwave range. The amorphous nature of the as-quenched ribbons was confirmed by X-ray diffraction patterns and differential scanning calorimetry (DSC). The flexible electromagnetic wave absorber ribbons of CoSiB, FeSiB, and FeCoSiBNbCu based alloys exhibit ∼99.99% attenuation of electromagnetic waves in the entire 0.2–8.5 GHz (L, S and C-band) range. Both as-quenched and annealed amorphous ribbons of Co72.5Si12.5B15 and Fe80Si8B12 are electromagnetically active and total electromagnetic shielding effectiveness (SET) of ribbons found to be ∼36 dB, ∼34 dB throughout the test range. The EMI shielding properties deteriorates for FeCoSiBNbCu and FeSiBNb based nanocomposite ribbons achieved by in-situ crystallization annealing. The electromagnetic shielding of magnetic ribbons is effected mainly by absorption mechanism due to high electrical resistivity and magnetic permeability. The CoSiB and FeSiB melt-spun ribbons can be a potential magnetic filler for military and stealth applications in L, S and C-band range.

The substitution of Fe with Co and B with Si is investigated in a series of high induction Fe84B13Nb2Cu1 amorphous alloys. The as-quenched melt-spun alloys are structurally amorphous in wheel side and a mild crystallites alongwith amorphous phase in air side. The alloy with 35 at% Co addition depicts improved thermal stability, saturation induction and coercivity, and the optimal combination of soft magnetic properties is achieved for an extended annealing temperature range. The additional 10 at% Si deteriorates soft magnetic properties.

Rapidly quenched Co- and Fe-based monolayer and their bilayer prepared through double nozzle technique have been characterized to investigate its microstructural and magnetic properties and their possibility as high-temperature magnetocaloric material. The Co- and Fe-based monolayer ribbons displayed Curie temperatures (TC) of 463 K and 700 K, respectively. Magnetic entropy change ∆SM of the bilayer was measured at a low magnetizing field of 1 T in the temperature spans covering separately for TC of Co- and Fe-based ribbons corresponding to separate entropy at low- and high-temperature regime. The ∆SM value at TC of Fe-based ribbon displayed values in the span of 1.13–1.71 J kg−1 K−1 in their monolayer and bilayer state. On incipient nanocrystallisation at 773 K, the ∆SM and refrigerant capacity (RC) around TC of cobalt-based bilayer ribbon revealed comparable values as in their as-quenched state. However, nanocrystallisation elevated the ∆SM of bilayer across TC of the Fe-based regime to a high value close to 4.6 J kg−1 K−1 with a fairly elevated RC of 96 J kg−1. The enhanced ∆SM associated with the formation of Fe-based nanocrystallites is evidenced through transmission electron microscopy. The interdiffusion of ferromagnetic elements Fe and Co is also supposed to elevate the ∆SM as well as the RC of the glassy system in the bilayer ribbons.

The recovery and recrystallization behaviors of low-carbon interstitial-free steel are investigated at different annealing temperatures (200-690 °C) through correlation between the changes in magnetic parameters (coercivity and r.m.s. voltage), hardness, tensile strength and high-angle grain boundary fractions (HAB). Magnetic parameters and tensile strength show a significant change within recovery region (200-500 °C), while the hardness variation is very minimal at this temperature region. On the other hand, the hardness is abruptly changed compared to magnetic properties at higher annealing temperature (550-640 °C). The grain boundary characteristics and microtexture evolution occurring at recrystallization regime are evaluated by orientation imaging microscopy (OIM) and orientation distribution function (ODF) through electron backscattered diffraction (EBSD). The increase in recrystallization fraction noticeably affects microtexture property, justifying with the strengthening of γ-fiber, weakening of α-fiber and disappearance of rotated cube component with increasing annealing temperatures.

The effect of tempering treatment has been investigated on water quenched P22 steel with the chemical composition of 0.13C, 0.24Si, 0.47Mn, 0.012P, 0.005S, 2.19Cr, 0.93Mo and balance Fe (all in wt%) within the temperature ranges of 650–900 °C. The microstructural, mechanical and magnetic properties of as-quenched and tempered steels have been investigated through optical and scanning electron microscopy, hardness and universal tensile testing, electromagnetic sensor (Magstar), respectively. The water quenched sample consists of fine martensitic structure with a hardness of 381 HV. With the progress of tempering, the martensite becomes coarse till 800 °C, decreasing the hardness of steel samples. The tempering at 700 °C results in martensite coarsening and precipitation of rod and globular shaped carbides; while a fraction of globular carbide is observed to increase in the matrix after 750 °C of tempering. Beyond 800 °C, the ferrite and bainite phases gradually form by replacing martensite, and the ferrite structure is prevalent after 900 °C. Due to microstructural changes, the magnetic properties are also affected as a function of tempering temperature. The coarsening of martensite causes the decrease in coercivity with increasing tempering temperature, leading to magnetic softening.

The recovery and recrystallisation behaviours of cold rolled IF steel have been investigated by destructive (optical microscopy and hardness) and non-destructive electromagnetic sensor, (which allo...

In our research we studied the influence of bending on the total magnetic losses, the coercivity of minor hysteresis loops and the virgin magnetization curves of amorphous ribbons and microwires prepared from Finemet-type alloy wound on a mandrel of different diameters. The impact of various factors contributing on static and dynamic magnetic properties through bending stress are discussed. The factors pertain to contribution of the magnetoelastic anisotropy, the onset of the strain-induced magnetization, the changes of domain structure and the mobility of domain walls. The major contribution of hysteresis losses as-compared to the eddy-current losses have been observed on changing the mandrel diameter in wound ribbons and wires. The total specific losses of the Finemet-type ribbons are lower than that of microwires at the frequencies ranging from 50 to 400 Hz. Observed difference in the magnetic properties is attributed to different magnetization processes of amorphous microwires and ribbons. A different geometry and magnetoelastic anisotropy of studied materials are most likely to influence the formation of different domain structures.

The investigation is focussed on phase generation and magnetocaloric properties of a series of Ni 77-X Mn X Ga 23 (x = 22, 23, 24, 25, 27) alloys prepared through arc melting furnace. With increase in Mn content, the alloys showed systematic transition from a non-modulated martensite (NM) to a fully austenitic parent phase through an appearance and coexistence of modulated (M) structure. Intermediate Mn containing alloy (#Mn 24 ) not only displayed high magnetic entropy change (ΔS M ) of −7.7 J/kg −1 K −1 but also large Refrigerant Capacity (RC) of 169 J.Kg −1 at magnetic field change of 3 T compared to other alloys. The coexisting martensite (NM, M) and parent austenite as well as overlapping thermomagnetic and structural transformation was deliverable through tuning of alloy chemistry wherein Ni was systematically substituted by Mn. Transmission electron microscopy (TEM) supported the proposition with existence of martensite plates of different morphology in Mn 24 alloy exhibiting superior magnetocaloric properties.

The present work is focused on the effect of annealing on the magnetic, microstructure, and mechanical properties of 50% cold-rolled IF steel. The heat treatment is carried out at different temperatures ranging from 200 to 700 °C for 15 min holding time, to monitor the recovery and recrystallization process. The microstructure is observed by optical microscopy, and analyzed by image analysis software for quantification of recrystallization fractions and grain size. At 200–550 °C temperatures, no significant microstructural change is observed, indicating the dominancy of recovery at these temperatures. It is also confirmed by a nominal variation of hardness and tensile properties at the aforementioned temperature ranges. The magnetic parameters of coercivity (Hc) and remanent (Br) are measured through the electromagnetic sensing device, indicating a significant change during recovery. The recrystallization completion takes place at 660 °C, confirmed by mechanical and magnetic softening.

The progressive addition of P in Fe-rich FeSiB(P)NbCu nanocomposite alloy leads to grain refinement of α-Fe nanocrystals i.e, dense nucleation and grain growth inhibition. The P addition leads to linear reduction of α-Fe nanocrystallite size (D) and increases nucleation density (Nd) from ~ 30 nm and 2.5 × 1022 (0 at% P) to ~ 15 nm and 0.9 × 1023 for (8 at% P). The refined microstructure leads to coercivity reduction from 74 A/m (0 at% P) to 9.4 A/m (8 at% P), in agreement with Random-Anisotropy Model. The P assisted synergistic grain refinement mechanism is explained in the context of crystallization activation energy, selective solute re-distribution and enhanced stabilization of intergranular amorphous matrix. The 4 at% P alloy shows optimal soft-magnetic properties of 10.2 A/m and 1.64 T.

The investigation addresses the scope of rapidly quenched Fe80Si8B12 ribbons as magnetostrictive sensor (MsS) material to generate guided waves in galvanised iron pipe and evaluation of defects with different geometries and dimensions. Enhancement in the effective defect size (EDS) of transverse and pit type defects increased the MsS signal. However, the backwall echo showed opposing trend (transverse: reduced and pit: increased) with increase in dimensions of these defects. Such behaviour of backwall intensities has been correlated to different type of guided wave strain field distributions around these defects and reflection coefficients.

Anisotropic behaviors of cold rolled and annealed ULC steels are evaluated by orientation imaging microscopy (OIM) and magnetic Barkhausen emission (MBE) techniques. The MBE voltage is found higher along RD than TD, indicating the presence of favorable magnetic easy axis along RD for both 50 and 80% cold rolled steels. The recovery occurred at low temperature (T 500 °C) annealing leads to an abrupt drop of ‘k’ value for both cold rolled steels. Furthermore, the kernel average misorientation map, obtained from OIM, decreases with increasing annealing temperatures.

The investigation addresses the impact of stress on soft magnetic and giant magneto-impedance (GMI) of rapidly quenched Fe77.5Si7.5B15, (Co94Fe6)72.5Si12.5B15 and (Co94Fe6)72.5Si12.5B12.5Nb0.5Cr2 microwires. Differential scanning calorimetry revealed interesting phase stability in the later alloys. The vitrified microwires contained dominant Co and a lean Fe content showed much superior soft magnetic properties and high magnetoimpedance. The alloy microwires incorporated with Nb and Cr manifested lowest coercivity value of 0.034 Oe with a high GMImax value of 425% in the as-quenched state. The uniaxial stress applied on the microwires modified the shape of the hysteresis loops and GMI plots. The hysteresis loops showed stress dependence of coercivity based on alloy chemistry, phase stability and consequent magnetostriction. The GMImax revealed sensitive change with respect to the applied stress in all the alloy microwires. In addition to GMImax interesting features were observed in the GMI profile pertaining influence of stress on the anisotropy field. The anisotropy field shifted systematically in one of the alloy microwires which displayed symmetric dual GMI peaks. The stress was also found to modify the asymmetric characteristics in a microwire.

Polytropic gas spheres of index 1 and extremely high central densities are analysed with the help of general relativistic field equations. Parameters such as the radius and mass are calculated for different central densities. The limiting values of these quantities are obtained and the physical nature of sound waves in these bodies is verified.

The sequential, multi-stage crystallization and magnetic hardening behaviour of Fe82B14Si2Nb2, Fe83B13Si2Nb2, Fe83B12Si2Nb2Cu1 and Fe85B13Nb2 melt-spun alloys have been investigated. The microstructure-crystallization-magnetic property relationship was established using X-ray diffractometry (XRD), differential scanning calorimetry (DSC), magnetometry, transmission electron microscopy (TEM) and magneto-optical Kerr effect microscopy (MOKE) techniques. The increase of Fe content (>82 at%) of as-quenched ribbons imparts microstructural heterogeneity across the ribbon cross–section; i.e., textured α-Fe crystals at the free surface to hetero-amorphous microstructure in the bulk matrix. The isochronal annealing of hetero-amorphous alloys depicts simultaneous surface and bulk crystallization process occurring before and after the crystallization onset temperature (Tx1) temperature. The annealing temperature range (Ta

The effect of varying thickness on structure and thermal properties is investigated in Fe–B–Nb and Fe–B–Si–Nb glassy alloy systems with the addition of different Nb and Co content, respectively. Accordingly, four alloys with the nominal compositions of Fe76-xB18Nb6+x (x = 0, 2) and (Fe1-yCoy)72B12Si12Nb4 (y = 0, 0.5) are processed in the forms of ribbon and rod. All alloys of ribbons represent amorphous structure, while those of rods explain the crystalline structure with the exception of heteromorphous structure for Co added alloy. The Nb addition causes about same glass transition temperature (Tg) but increases crystallization onset (Tx), resulting in a wider supercooled liquid region (ΔTx = Tx-Tg). Moreover, Nb also improves glass forming ability (GFA) with more free volume generation and higher structural relaxation exothermic heat (ΔH0). The Co addition also improves free volume generation and higher ΔH0 for ribbon, but lower amount free volume generation in bulk alloys (rod) than ribbon.

Glass forming ability (GFA) and soft-magnetic behaviour of melt-spun Fe69C5.5P11.5Mn0.4Si2.3Cr1.8Mo1B8.5 (alloy 2) and Fe68C9P12Mn1Si3Nb2B5, (alloy 3) alloys prepared using high phosphorous pig iron (h-PI, Fe80C14P2.2Mn0.4Si3.4) has been studied. The glass formation, thermo-physical and soft-magnetic properties of the alloys were analyzed for different quenching rates by varying wheel speed as 23, 26, 33, 39 and 43 m/s. The simultaneous incorporation of alloying elements (Cr, Mo, Nb) and metalloids (C, B, P, Si) transforms h-PI to complete glassy alloy, even at low quenching rates. The melt quenching rate influences the thermal parameters and Curie temperature of glassy ribbons in an opposite way. Amongst all, FeCPMnSiCrMoB glassy alloy show superior combination of higher glass transition temperature of 788 K, super cooled region of 34 K, glass Curie temperature of 552 K, coercivity less than 13 A/m and maximum saturation magnetization of 1.1 T. In addition, the annealing treatment at 758 K improves magnetic softness (1.7 A/m) of the alloy by relaxation of quenched-in stresses. The comparison of developed glassy alloy with similar Fe-glassy alloys and SENNTIX type alloys show best combination of thermo-physical and magnetic properties. The glassy alloy prepared using blast furnace high phosphorous pig iron can be used for uniformly gapped soft-magnetic cores.

The present investigation addresses the magnetocaloric behaviour in a series of Ni 77− x Mn x Ga 23 ( x =23, 24, 25, 27 and 29) rapidly solidified alloys prepared in the form of ribbons by melt spinning technique. The approach of the study is to identify the off-stoichiometric composition wherein room temperature magneto-structural transformation is achieved. The alloy chemistry was tailored through Mn incorporation for Ni such that the magnetic and structural transitions were at close proximity to achieve highest entropy value of Δ S equal to 8.51 J Kg −1 K −1 for #Mn 24 ribbon measured at an applied field of 3 T. When such transitions are more staggered as in #Mn 29 the entropy value of ribbon reduced to as low as 1.61 J Kg −1 K −1 . Near room temperature transformations in #Mn 24 ribbon have been observed through calorimetric and thermomagnetic evaluation. Reverse martensitic transformation (martensite→autstenite) temperature indicates not only distinct change in the saturation flux density but also an inter-martensitic phase. Microstructural analysis of #Mn 24 alloy ribbon revealed structural ordering with the existence of plate morphology evidenced for martensitic phase.

Soft magnetic materials rich on iron or cobalt have found vast range of usability for sensors such as fluxgates [1] and also, the recently re-invented, magneto-impedance sensors [2]. Giant magneto-impedance (GMI) has experienced huge increase of interest since the late 80's. Although the fluxgate sensor is commercially available, the easy manufacturing of GMI sensors, possibility of miniaturization put attention to many scientists for developing such sensor in many applications. However, GMI sensor has major drawback of large temperature sensitivity [3]. In precise applications, fluxgate sensors are preferred over GMI, which do not saturate the ferromagnetic core and therefore may exhibit perming error. On the other side, the GMI sensors compete with significantly longer period of the development of fluxgates and recently are commercially used for evaluation of microstructural degradation in ferromagnetic materials [4]. Mostly for GMI sensors, amorphous/ nanostructured wires are used rather than ribbons as wire shaped sample has better GMI characteristics than ribbon [5] due to the formation of circumferential anisotropy in wire. On the other hand wires can be used for orthogonal fluxgates but ribbons are preferred over wires for commercial use as they have been tested for last few decades. The magnetization process for the ribbon and the wire shaped samples are assumed to be different presumably due to the difference in cooling process. However, in both cases, the materials should have very low saturation magnetostriction constant and high permeability. The present paper is to understand the variation of sensing properties of the ribbon and wire shaped materials having the same composition, which can be operated both in the GMI and the fluxgate sensing cores and test them in both sensors.

In the present investigation, powders of as-cast ingots of Al–25 at%Fe and Al–34.5 at%Fe alloys close to Al 3 Fe and Al 2 Fe intermetallic phases are subjected to high energy ball milling to understand the possibility of formation of amorphous and/or nanocrystalline phases or any other metastable phases. The development of microstructure, evolution of various metastable phases and their stability are investigated by x-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Mechanical milling of the alloys, up to 50 h, was carried out in high energy planetary ball mill. It resulted in phase transformation from monoclinic and triclinic structures of Al 3 Fe and Al 2 Fe, respectively, to orthorhombic structure pertaining to Al 5 Fe 2 phase and structural transformation from crystalline to amorphous phase. Hardness measurements revealed a transition from hardening to softening behavior in these mechanically milled alloys undergoing prolonged milling. The softening effect in the milled powders, having a composite structure involving nanocrystalline and amorphous phases, is attributed to the competing phenomenon of grain size reduction and amorphous phase formation with increasing milling time.

Rapidly quenched bilayer magnetostrictive ribbons have been prepared and characterized to investigate phase transformations, interfacial activity and their potentiality as bend sensors. The bilayer ribbons were processed in a way to make the positively magnetostrictive layer Fe77.5Si7.5B15 as the free surface while negatively magnetostrictive Co72.5Si12.5B15 layer as the one in contact with the quenching copper wheel. Elemental concentration profiles obtained through electron probe microanalysis (EPMA) revealed synergistic variation in Fe and Co content at the interface. Devitrification process was also observed from atomic migrations and combinations influencing the interface width. Configuration of the bent layers showed interesting bending parameter output which could be further enhanced through stress relaxation. A detrimental effect of devitrification on bend sensitivity of rapidly quenched bilayers was also displayed.

An electromagnetic sensing device, MagStar, has been developed by authors, measure both magnetic hysteresis loop and magnetic Barkhausen emission. The device explains its credibility for characterizing different types steels, SA213T22 and IF steel with varying microstructural phases treated at different heat treatment conditions. MagStar is also very versatile to be applicable for both industries and educational research due to its portability and low cost.

Investigation is focused on the effect of different parametric controls like driving frequency, amplitude of the alternating current (ac), direct current (dc) bias field and anisotropy field (Hk) on the Giant Magneto-Impedance (GMI) properties of rapidly quenched soft magnetic Co66Fe2Si13B15Cr4 amorphous wires developed by in-water quenching technique. Optimal controls of these parameters like driving frequency and amplitude of the ac were found to display a sensitive change in GMI properties at optimal frequency of 5 MHz and 5 mA driving current. The influence of these controls on the output factors like maximum GMI ratio (GMImax), transition from single peak (SP) to double peak (DP), field sensitivity of GMI (η) and anisotropy field (Hk) throw light on the application of the developed wires for sensors. In addition to high Hk, driving frequency of 5 MHz also delivered a combination of desirable sensor properties like high level of sensitivity and its enhanced span of stability. Joule heating further improved the GMI response of the material through current annealing at a current density of 5 A/mm2.

The butt joint of two sight tubes of modified 9Cr–1Mo steel is welded by TIG technique. Subsequently, the post-weld heat treatment (PWHT) of the tubes has been carried out at 650, 700 and 750 °C temperatures for 3 h. Magnetic Barkhausen emission (MBE) measurements are performed in fusion zone, heat affected zone (HAZ) and base metal region of as-welded and all the post-weld heat treated samples. In each weldment, the variation of the MBE signal emanated from fusion zone, HAZ and base metal has been examined. It is found that the RMS voltage of MBE signal increases with PWHT temperature. The conversion of retained austenite to alpha ferrite during PWHT makes the fusion region as a softer zone in the weldment. The variation of magnetic parameters with different PWHT is correlated with hardness and microstructures. This study can be used as an effective tool in evaluation of PWHT parameters in modified 9Cr–1Mo weld joint.

Giant magnetoimpedance (GMI)-based devices offer potential as next-generation low-cost, flexible, ultrasensitive sensors. They can be used in applications that include current sensors, field sensors, stress sensors, and others. Challenging applications involve operation at high temperatures, and therefore studies of GMI temperature dependence and performance of soft magnetic materials are needed. We present a high-temperature GMI study on an amorphous soft magnetic microwire from room temperature to 560°C. The GMI ratio was observed to be nearly constant at ∼86% at low temperatures and to decrease rapidly at ∼290°C, finally reaching a near-zero value at 500°C. The rapid drop in GMI ratio at 290°C is associated with a reduction in the long-range ferromagnetic order as measured by the spontaneous magnetization (M) at the Curie temperature (Tc). We also correlated the impedance with the magnetic properties of the material. From room temperature to 290°C, the impedance was found to be proportional to the square root of the magnetization to magnetic anisotropy ratio. Lastly, M(T) has been fit using a Handrich–Kobe model, which describes the system with a modified Brillouin function and an asymmetrical distribution of exchange interactions. We infer that the structural fluctuations of the amorphous phase result in a relatively small asymmetry in the fluctuation parameters.

The failure mechanism of two economizer tubes of a fossil fuelled 260 MW power plant has been investigated through the magnetic Barkhausen emission (MBE) technique along with the conventional and established materials characterization and evaluation techniques (like microstructures, mechanical properties and X-ray diffraction). The longer service exposer period results in the breaking of ferrite–pearlite structure and spheroidization lamellar cementite in ferrite matrix, associating with high magnetic r.m.s. voltage for former structure. The failure mechanism was governed by the cold end corrosion process with the presence of sulfates, and the subsequent erosion through hard quartz particles leads to a localized thinning of outer surface. Accordingly, the hoop stress was operative in tube walls and failed through fish-mouth opening. The MBE r.m.s. voltage response and pulse height distribution throw light on microstructural changes with duration of service exposure as well as leaked and non-leaked regions of economizer tubes.

The influence of P on amorphizing ability, as-quenched microstructure, thermo-physical and soft magnetic properties of Fe–rich (i) Fe81B15-xPxSi2Nb1Cu1 (ii) Fe82B14-xPxSi2Nb1Cu1 and (iii) Fe83B13-xPxSi2Nb1Cu1 (x = 0, 2, 4, 6, 8 at%) melt-spun alloys are investigated. The substitution of P improves amorphization of alloys and restricts the formation of hetero-amorphous microstructure for Fe 83 at% ribbons at around (x = 8). The improvement in short range ordering of P containing clusters with varying Fe content has been discussed within the framework of Cluster-Glue atom model and supported by experimental thermal parameters. The optimal P content in Fe-rich alloys in the range of 4 ≤ x ≤ 6 delivered favourable thermal properties of high primary and secondary crystallization onset temperature viz; Tx1, Tx2 and temperature span ΔT between these onsets. The P substitution drastically restricts the precipitation of secondary crystallites with reduced enthalpy of secondary crystallisation (ΔH2) during annealing and favourably assists in attaining maximum magnetic moment during the primary crystallization stage. Moreover, the P substitution (4–8 at%) effects refinement of α-Fe nanocrystallites and promotes low coercivity (Hc

The influence of melt spinning and heat treatment on the structure, phase transformation and magnetic field induced strain (MFIS) properties have been investigated for Ni55Mn22Ga22Al1 (at%) alloy. The microstructure showed distinct improvement in morphology of as spun ribbon as compared to ingot. Annealing further enhanced martensite state and displayed systematic arrangement of dislocations. It contributed to increase MFIS to 482 ppm in annealed ribbon as compared to 190 ppm and 28 ppm for as-spun ribbon and ingot, respectively.

Two types of rapidly solidified filler alloys of nominal composition Cu–40Mn–10Ni (C50) and Ni–7Cr–3·2B–4·5Si–3Fe (N82) were used for stainless steel (SS304) brazing joints. The C50 foil is crystalline in nature, whereas N82 foil shows amorphous structure. The SS304/C50/SS304 joint shows solid solution phases at interfacial area, with maximum bond strength of 500 MPa, which qualifies to 80% of base metal strength. Conversely, the SS304/N82/SS304 joint develops brittle CrxBy intermetallic phases, which lowers bond strength to 330 MPa.

DOI: http://dx.doi.org/10.3329/medtoday.v23i2.13098 Medicine TODAY Vol.23(2) 2011 pp.67-71

The effects of process parameters for the in-rotating-water quenching technique have been investigated with respect to structural, magnetic and giant magneto-impedance (GMI) properties of FeCoSiB alloy microwires. Continuous and ductile amorphous wires have been found with the optimization of process parameters. The structural, magnetic and GMI behaviors have been evaluated as a function of wire diameter. The crystallinity of the wires increases with wire diameter, affecting soft magnetic and GMI properties. Consequently, it is found that the wire of 110 μm diameter shows superior soft magnetic and GMI properties.

Rapidly quenched microwires with a nominal composition of Fe 39 Co 39 Si 8 B 14 (#A O ), Fe 37 Co 37 Nb 4 Si 8 B 14 (#A N ) and Fe 36 Co 36 Nb 4 Cr 2 Si 8 B 14 (#A NC ) have been investigated. Devitrification of as-quenched microwires showed that crystallization temperatures increased with simultaneous incorporation of Nb and Cr as in #A NC alloy. Addition of these elements also contributed to an increase in activation energy in #A N and #A NC alloys. Nb addition reduced the particle size, which became much finer in the case of the Cr-containing alloy. Although Nb addition did not have much effect on lowering the Curie temperature T C of the amorphous phase, Cr substitution lowered T C to 698 K from high values of 785 K and 787 K observed in the #A O and #A NC alloys, respectively. However, the Cr addition revealed a better Giant magneto-impedance (GMI) response compared to the other alloys. Such improved GMI properties in the Cr-containing alloy are attributed to lower values of the coercivity and magnetostriction in the alloy containing both Nb and Cr.

The investigation is focused on the effect of Cr incorporation for Co/Fe in (Co 0.5 Fe 0.5 ) 78− x Cr x Si 8 B 14 ( x =0–12) amorphous microwires of 110 μm diameter prepared by in-water quenching technique. The rise in crystallization onset T X1 with Cr addition revealed the elemental contribution against devitrification and a consequent thermal stability. Cr is unfavorable towards ferromagnetic ordering leading to a linear drop in Curie temperature T ca with its rise in concentration. The presence of low Cr content upto Cr-4 at.% has been effective in drastically improving the Giant magneto-impedance (GMI) property. Cr content in the range of 4≤ X ≤10 has low magnetostriction and maximum field sensitivity in the as-quenched state. The GMI properties are further improved after annealing treatment. High content of Cr>10 is found to be deleterious towards GMI behavior and its consequent application as sensor material.

Dependence of Curie temperature (Tc) on time and temperature of annealing for Finemet-type amorphous alloys is studied by DSC. Structural relaxation of an amorphous phase at annealing is accompanied by increase of Tc. The σ-shaped time dependencies, however, are not characterized by the definite final value of Tc: long-term annealing of amorphous phase results in continuation of slow increase of Tc for every temperature. Apparent values of activation energy of relaxation were evaluated from the Tc time–temperature dependencies. It is found that the average value of activation energy increases with progress of the relaxation process. Correlation of the Tc data with structural alterations reflects redistribution of components in amorphous phase during annealing. Further increase of the annealing temperature results in precipitation of α-Fe(Si) nanograins in an amorphous matrix, that accompanied by gradual degradation of corresponding to Tc heat capacity peak. DSC measurements of Tc allow to detect the starting moment of amorphous phase crystallization.

The joining behavior of 304SS and Cu joint is important for the component materials of the first wall and divertor in the International Thermonuclear Fusion Experiment Reactor (ITER). In this research, the joining of 304 stainless steel (SS) and pure copper is done by rapidly solidified Cu-40Mn-10Ni brazing alloy at 920 °C for 5 min. The SEM-BSE image of joint area shows homogeneous microstructure. The butt joint of 304SS and pure Cu breaks at the tensile strength of 260 MPa and several dimples are observed at the fracture surface. It reveals ductile nature and strong bonding between two dissimilar metals. The X-ray diffraction of fracture surface explains the formation of solid solution phases with a little amount of intermetallics.