As-quenched State Research Articles

Magnetocaloric Effect in Amorphous and Partially Crystallized Fe-Zr-Nb-Cu-B Alloy

This paper presents the results of an investigation into the: microstructure, magnetic properties and influence of annealing temperature on the magnetocaloric effect of Fe82Zr7Nb2Cu1B8 alloy in the as-quenched and partially crystalline state. The microstructure was investigated using Mossbauer spectroscopy. The magnetocaloric effect was observed as a change in the magnetic entropy, which was calculated from isothermal magnetization curves. Fullyamorphous Fe82Zr7Nb2Cu1B8 alloys, in the as-quenched state, exhibit a Curie temperature equal to (340±5) K. The transmission Mossbauer spectrum for the as-quenched Fe82Zr7Nb2Cu1B8 alloy is typical for weak ferromagnets with the average hyperfine field of 9.86(2) T. For this alloy in the as-quenched state, the changes in maximum magnetic entropy occur near the Curie points and are equal to 0.95 J/(kg K). Also, the maximum magnetic entropy changes decrease after partial crystallization.

The Influence of Heat Treatment on Irreversible Structural Relaxation in Bulk Amorphous Fe61Co10Ti3Y6B20Alloy

Amorphous materials contain structural defects, which play a key role in the magnetization process within the condition known as the approach to ferromagnetic saturation . This paper presents the results of magnetization studies, carried out on bulk Fe61Co10Ti3Y6B20 alloy when under the in uence of a strong magnetic eld. The alloy samples were obtained in the form of a rod 1 mm in diameter, and tested in the as-quenched state and after an isothermal annealing process, at a temperature below the crystallization temperature. It was observed that the heat treatment, carried out below crystallization temperature Tx, leads to irreversible structural relaxations, speci cally reorganizing the atomic con guration within the volume of the alloy into an amorphous structure.

Structural transformation in quasicrystal-forming Al-Cu-Fe alloys

Three Al-Cu-Fe alloys with various iron contents (6 at.%, 12 at.% and 15 at.%), were synthesized by fusion under high-frequency magnetic induction and characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry(DSC). The microstructure evolution was carried out both in the as-quenched state as well after heat treatment at 500 ◦ C in relation to iron composition. Particular attention was been paid to the alloy containing 15%, and we were been able to determine by DSC that a massive transformation from crystal (β ) to quasicrystal i-ψ (Al6 Fe2 Cu) occurs for this composition.

Relationship between Microstructure, Mechanical Properties and Damage Mechanisms in High Martensite Fraction Dual Phase Steels

The relationships between microstructure, mechanical properties and damage mechanisms in as-quenched and in quenched-and-tempered high martensite fraction (>60%) dual phase (DP) steels were investigated. The mechanical behaviour was determined by tensile and hole expansion (HE) tests. In the as-quenched condition, the HE ratio decreased with increasing ferrite content and showed a non-linear inverse relation to the uniform elongation. Tempering significantly improved the HE ratio for all studied martensite fractions; the increase in HE was found to be monotonic for tempering temperatures between 230 degrees C and 460 degrees C, even though the yield stress dependence was complex in this range. Tempering studies showed that, at constant martensite fractions, there was a linear dependence between the HE ratio and the ductile fracture strain, epsilon(f). However, the parameters of the linear relation changed significantly when the martensite fraction was varied. The dominant damage mechanism in simple tensile tests evolved from ferrite/martensite or martensite/martensite interface decohesion in the as-quenched state to martensite/ carbide interface decohesion after tempering. The damage mechanisms were qualitatively described using the Beremin local criteria.

The role of heat treatment and alloying elements on hydrogen uptake in Aermet 100 ultrahigh-strength steel

In this research we aim to present a fast and semi-quantitative electrochemical method – based on cyclic voltammetry (CV) – to easily screen the H uptake of materials. We used Aermet 100, an ultrahigh-strength steel, in its as-quenched (martensitic) state and an aged state to investigate the H-desorption properties of different microstructures. The CV-based method clearly shows the influence of the alloying elements, the microstructure and the effect of hydrogen recombination poisons on the H uptake. The experiments indicate that a significant part of the uptake of hydrogen is due to (i) the presence of Ni as an alloying element and (ii) the presence of austenite that forms during the heat treatment.

Competition driven nanocrystallization in high Bs and low coreloss Fe–Si–B–P–Cu soft magnetic alloys

Based on experimental results and Johnson–Mehl–Avrami analysis, we have identified the nanocrystallization mechanism of newly developed Fe-rich Fe–Si–B–P–Cu soft magnetic alloys. Competition for growth among a large number of nuclei that are present in as-quenched state (grain density ∼3 × 1021 m−3) and nucleated after annealing above the critical temperature for new nucleation (grain density ∼8 × 1022 m−3) governs the grain size. A model of nanocrystallization is made to predict the magnetic/structural properties.

The Influence of Heat Treatment on Soft Magnetic Properties of the Fe60Co10Mo2Y8B20Alloy

This paper presents the results of studies on the magnetic properties of the Fe60Co10Mo2Y8B20 alloy. The samples were fabricated in the form of plates by the injection-casting method. The structure of the investigated alloy, in the as-quenched state and after annealing, was veri ed by using X-ray di ractometry. The magnetization curves as a function of temperature were measured by a force magnetometer. From thermomagnetic curves the Curie temperature of the alloy was determined. As a critical parameter β was chosen to be equal to 0.36 for these calculations, it con rmed that the alloys may be considered as ferromagnetic of the Heisenberg type. Additionally, using a vibrating sample magnetometer the magnetization and coercivity eld were studied (in magnetic eld up to 2 T).

냉간금형강의 미세조직과 기계적 특성: STD11과 8%Cr 강의 비교

Abstract A comparative study was performed on the microstructures and the mechanical properties of STD11and 8Cr steel. The specimens were quenched from 1030 o C and tempered at 240C and 520C. Vickers hard-ness, impact toughness and tensile tests were conducted at various tempering temperatures. Microstructuralcharacterization to measure grain size, volume fraction of retained austenite and distribution of carbides was car-ried out by using SEM, EBSD, TEM and X-ray diffraction techniques. Due to finer M 7 C 3 carbides dispersed, 8Crsteel showed larger impact toughness and plasticity than STD11 irrespective of the tempering temperature. While8Cr steel had lower hardness in as-quenched state and after tempering at 240 o C owing to smaller carbide con-tent and more retained austenite, it was harder after tempering at 520 o C due to larger precipitation hardeningfrom finer M 23 C 6 .(Received August 25, 2014; Revised September 12, 2014; Accepted September 18, 2014)Key words : Cold-work tool steel, 8Cr steel, STD11, Microstructure, Mechanical property

Induction Hardening vs Conventional Hardening of a Heat Treatable Steel

This study focuses on the comparison of mechanical and microstructural properties of induction and conventionally heat-treated steels in the as-quenched state. The investigated steel is a heat treatable 42CrMo4 steel. In order to characterize the mechanical properties, tensile tests and Vickers hardness tests are performed. The yield strength and hardness of the induction hardened condition turn out to be slightly lower compared to the conventionally hardened one. Light optical and scanning electron microscopy show no differences in the martensitic structure of the induction and conventionally hardened condition. However, electron back scatter diffraction investigations reveal a smaller block size within the conventionally hardened specimen. Carbon mappings by electron probe micro analysis show a homogenous carbon concentration in the conventionally hardened and a non-uniform distribution in the induction-hardened case. The segregation of the carbon exhibits line-type features in the induction hardened condition, lowering the total amount of carbon in the matrix. Therefore, the carbon content in the matrix of the conventionally hardened condition is slightly higher, which causes a smaller block size. The smaller block size is believed to be the reason for the higher hardness and yield strength.

Radiofrequency magnetoelastic resonators for magnetoelectric applications

Magnetoelastic resonance measurements are carried out in short ribbons (down to 1 cm length) of Fe59Co16Si15B10 metallic glasses, both as-quenched and after annealing at 400 °C for 10 min. The resonant frequency exceeds 200 kHz with good Q factors for the shortest elements in the as-quenched state. Sandwich-type laminated magnetoelectric (ME) composites are prepared by gluing these ribbons to a PVDF piezoelectric polymer layer, showing good ME response. This effect is discussed as a function of the as-quenched or annealed state, and the length of the magnetoelastic ribbon, and is of interest for near field communication applications.

Depth-Selective Study of Surface Crystallization in NANOPERM-Type Alloys

Evolution of structure and magnetic order is studied in the (Fe81Mo8Cu1B10)-Fe-57 alloy by conversion electron and conversion X-ray Fe-57 Mossbauer spectrometry. Surface features exhibit differences at both sides of ribbon-shaped samples with respect to the screening depth. In the as-quenched state, traces of magnetite (in addition to bcc-Fe) are revealed only at the wheel side of the ribbon to the depth of about 200 nm. It is present also after annealing up to 510 degrees C, then it disappears. In deeper regions (down to 1 mu m), magnetite is less abundant. At the air side, only bcc-Fe is detected, though the progress of crystallization is more pronounced here than at the wheel side. Vibration properties of the bulk of amorphous and nanocrystalline samples are obtained from experiments of nuclear inelastic scattering of synchrotron radiation using partial densities of phonon states.

Nanocrystallization and magnetocaloric effect in amorphous Fe–Mo–Cu–B alloy

Nanocrystallization revealed by X-ray diffraction, transmission electron microscopy and conventional Mössbauer spectroscopy in connection with specific magnetization versus temperature and magnetizing field induction and isothermal magnetic entropy change, as a measure of magnetocaloric effect, in the amorphous Fe76Mo10Cu1B13 alloy are studied. The annealing temperatures are chosen according to a DSC curve to fulfill conditions for the primary crystallization. There are no distinct changes in the crystallization process near the outer and inner surfaces of ribbons. The granular α-Fe phase with some Mo atoms incorporated into BCC lattice appears in the residual amorphous matrix. The grains diameter is almost independent of annealing temperature. The lattice parameter decreases on annealing and approaches to the value proper for pure bulk α-Fe. Such behavior is also confirmed by hyperfine parameters of the crystalline component. For all annealed samples in Mössbauer spectra analysis the component ascribed to the interface should be introduced even at early stages of crystallization. The Curie point of the amorphous phase is lower than the room temperature and increases on annealing. Such behavior makes the investigated material interesting for magnetic refrigerant application. The magnetic entropy change (ΔSM) is rather modest and has its maximum in the as-quenched state and distinctly decreases on annealing. ΔSM is analyzed qualitatively considering the different magnetic phases.

Mössbauer and MFM Investigations of Surface Magnetism in NANOPERM Nanocrystalline Alloys

Structurally di erent surface regions are identi ed at both sides of the ribbon-shaped Fe90Zr7B3 NANOPERM alloy. Though paramagnetic in the as-quenched state, the air side shows signi cant contribution of crystalline bcc-Fe that decreases towards the interior of the ribbon. After annealing at 480 ◦C, magnetic dipole interactions develop that are associated with enhanced number of ferromagnetic nanograins. Signi cant increase in the number of nanograins was revealed at the wheel side, while the one at the air side is almost saturated. The observed maze-type magnetic domains exhibit well developed structure with equally wide strips.

Amorphous Soft Magnetic Fe_{80}B_{11}Si_{9} Alloy in Tensile Stress Sensors Application

Paper presents the results of investigations of the in uence of the tensile stresses on magnetic characteristics of Fe80B11Si9 amorphous alloy in as quenched and annealed state. For the tests, a special methodology of application of uniform tensile stresses to the ring shaped sample was developed. Due to special non-magnetic pads, the magnetizing and sensing coils can be wound around the core. Experimental results indicate high stress sensitivity of Fe80B11Si9 alloy in both as-quenched and annealed state. Permeability of the core decreases over 64% and 58% for as-quenched and annealed core respectively, especially for lower values of the amplitude of magnetizing eld.

Interaction of surface of ribbons of amorphous soft-magnetic iron-based alloys with vapor

The interaction with water vapor of the surface of ribbons of amorphous soft-magnetic iron-based alloys with positive saturation magnetostriction and an effect of the interaction on the magnetization distribution and magnetic properties have been investigated. The results of the investigation showed that, during in-air heat treatment, the interaction of the surface of ribbons of amorphous soft-magnetic alloys with water vapor upon the heating of samples and at the initial stage of isothermal holding exerts a substantial effect on the magnetization distribution and the level of magnetic properties formed. Preliminary room-temperature treatment of the ribbon surface in the as-quenched state with water vapor favors an increase in pseudo-uniaxial tensile stresses along the ribbon axis because, during annealing, the enhanced concentration of hydrogen and oxygen atoms introduced into the ribbon surface is formed in this direction. When certain regimes of heat treatment are used, this leads to an increase in the volume of domains with magnetization oriented along the axis of the ribbon in its plane and allows a significant enhancement in the efficiency of the in-air heat treatment.

Tempering of Direct Quenched Low-Alloy Ultra-High-Strength Steel, Part I – Microstructure

The direct quenching of low-carbon steel has been shown to be an effective way of producing ultra-high-strength, tough structural steels in the as-quenched state without tempering. However, in the present study, the influence of tempering at 500 °C has been studied in order to evaluate the possibilities of widening the range of strengths that can be produced from a single base composition. The chosen composition was 0.1C-0.2Si-1.1Mn-0.15Mo-0.03Ti-0.002B. In order to compare direct quenching with conventional quenching, two pre-quench austenite states were studied: a thermomechanically rolled, non-recrystallized, pancaked austenite grain structure and a recrystallized, equiaxed grain structure. Quenched and quenched-and-tempered microstructures were studied using FESEM and FESEM-EBSD. The as-quenched microstructures of the reheated and quenched and direct quenched specimens were fully martensitic and martensitic-bainitic, respectively. In both cases, tempering made the needle-shaped auto-tempered carbides of the as-quenched materials more spherical. In the case of the direct quenched (DQ) material, tempering led to a notable increase in the size of the grain boundary carbides. Prior austenite grain size and effective grain size after quenching were larger in the case of reheated and quenched material (RQ). Tempering had no effect on effective grain size. The crystallographic texture of the DQ material showed strong {112}<131> and {554}<225> components. The RQ material also contained the same components, but it also contained an intense {110}<110> and {011}<100> components. The effects of these microstructural changes on tensile, impact toughness and fracture toughness are described in part II.

Atomic-scale characterization of prior austenite grain boundaries in Fe–Mn-based maraging steel using site-specific atom probe tomography

The embrittlement and de-embrittlement behavior of an Fe–10Mn–1Pd (wt.%) maraging steel upon isothermal aging at 500°C is related to microstructural changes at prior austenite grain boundaries (PAGBs). Site-specific atom probe tomography measurements were performed to analyze the local chemistry of the PAGBs. Tensile tests and hardness measurements were conducted of the ternary alloy and of a binary non-hardenable Fe–10Mn alloy for comparison. Isothermal aging of the binary steel led to a decrease in strength along with a considerable increase in uniform elongation. The Pd-containing alloy, on the other hand, showed significant age-hardening, and an embrittlement and de-embrittlement transition was revealed. Ductile behavior was observed in the initial as-quenched and over-aged states, but there was zero tensile elongation in the intermediate under- and peak-aged regions, where intergranular fracture along the PAGBs occurred. In the brittle peak-aged state a large number of small nanometer-sized particles rich in Mn and Pd formed inside the grains and decorated the PAGBs. The precipitates grew in size on prolonged aging. Mn segregation to the PAGBs was revealed; the Mn concentration level at the boundaries varied with aging time and was highest in the peak-aged condition. Embrittlement and de-embrittlement mechanisms are discussed and compared to these observations.

Microstructure and some thermomagnetic properties of amorphous and partially crystallized Fe–(Pt)–Zr–Nb–Cu–B alloys

Microstructure and magnetic entropy changes in amorphous and partially crystallized Fe86−xPtxZr7Nb1Cu1B5 (x=0 or 5) alloys are studied. The transmission Mössbauer spectrum for the as-quenched Fe86Zr7Nb1Cu1B5 alloy is typical of weak amorphous ferromagnets with the average hyperfine field of (4.78±0.02)T. The replacing of 5% of Fe atoms by Pt increases the average hyperfine field up to (13.12±0.02)T. High resolution electron microscopy and transmission Mössbauer spectroscopy do not reveal the existence of medium range ordering regions. In the as-quenched state of both alloys the maximum magnetic entropy change occurs near the Curie points and is equal to 0.51Jkg−1K−1 and 0.85Jkg−1K−1 for Fe86Zr7Nb1Cu1B5 and Fe81Pt5Zr7Nb1Cu1B5, respectively. The maximum magnetic entropy change decreases after partial crystallization of the alloys. Both alloys in the as-quenched state above their Curie points behave like Curie–Weiss paramagnets with the paramagnetic Curie temperature equals to Θ1=(330±1)K for Fe86Zr7Nb1Cu1B5 alloy and Θ2=(370±1)K for Fe81Pt5Zr7Nb1Cu1B5 alloy.

Impact of plastic deformation and shear band formation on the boson heat capacity peak of a bulk metallic glass.

The effect of annealing on the low-temperature heat capacity of a bulk Pd38.5Ni40P21.5 metallic glass is investigated for as-quenched and deformed (rolled) states. Although the boson heat capacity peak increases with increasing strain, it relaxes faster and to a lower level compared to that of the as-quenched state after annealing treatments both below and above the glass transition temperature Tg. The glass is found to retain a certain "memory" on the room-temperature plastic deformation even after annealing above Tg. Indications for two counteracting processes that might be related to different types of shear bands are observed.

Microstructure and Magnetic Entropy Change in Amorphous <inline-formula> <tex-math notation="TeX">${\rm Fe}_{76}{\rm Mo}_{10}{\rm Cu}_{1}{\rm B}_{13}$ </tex-math></inline-formula> Alloy

Microstructure and some thermomagnetic properties of the amorphous ${\rm Fe}_{{76}}{\rm Mo}_{{10}}{\rm Cu}_{{1}}{\rm B}_{{13}}$ alloy in the as-quenched state and after annealing at 623 and 673 K are studied. High-resolution electron microscopy, apart from the amorphous phase, reveals the existence of medium range ordered (MRO) regions 1–2 nm in size. Transmission Mossbauer spectroscopy confirms that these regions are $\alpha$ -Fe MRO ones and grow during annealing. The Curie point of the alloy is 277, 272, and 284 K in the as-quenched state and after mentioned above heat treatments, respectively. The maximum of the magnetic entropy change is rather modest and equal to $0.88~{\rm J}\cdot{\rm kg}^{{-1}}\cdot{\rm K}^{{-1}}$ in the as-quenched state and reaches the value of $1.12~{\rm J}\cdot{\rm kg}^{{-1}}\cdot{\rm K}^{{-1}}$ after annealing at 673 K. Magnetic entropy change depends not only on the temperature, but on the maximum of the magnetizing flux density, ${{B_{m}}=\mu_{0}{H_{m}}}$ (according to ${{\Delta}}{S_{M}}={C(T)}\cdot{B_{m}^{{n}}}$ ) as well. The exponent ${n}$ is close to 1 below the Curie point and does not reach 2 in high and equal to 2 in low magnetizing flux density range above the Curie point like in Curie–Weiss paramagnets. Such behavior is ascribed to the presence of MRO regions beside the amorphous phase and the material can be treated as biphasic.