As-quenched State Research Articles

Magnetization processes features in the tapes of cobalt-based amorphous alloy

Studies of the amorphous cobalt-based soft magnetic alloy AMAG-172 (Co–Ni–Fe–Cr–Mn–Si–B) from different manufacturers have shown that in the as-quenched state there is nonuniformity of the magnetic characteristics, and therefore the level of internal stresses across the width of the tape produced by MSTATOR (Borovichi) significantly lower. However, similar to the tape produced by NIIMET (Kaluga), there is nonuniformity of the tape in thickness, which contributes to the formation of a bimodal field dependence of magnetic permeability.This may be a consequence of the non-uniform concentration along the width of the tape of hydrogen and oxygen atoms embedded in its surface during interaction with atmospheric vapor and the presence of temperature gradients during the manufacturing process. A stepwise shape of the initial sections of the magnetization curves in the region of the first maximum of magnetic permeability was discovered. The abrupt nature of the magnetization processes in the region of weak fields allows us to conclude that in the samples of tape produced by MSTATOR, the formation of the first maximum of the field dependence is associated with an independent magnetization reversal of the surface layer, while the main layer of the tape participates in the formation of the second maximum. The smoothed shape of the stepped initial section of the magnetization curve of samples produced by NIIMET corresponds to the gradual involvement of the main layer of the tape in the processes of magnetization and remagnetization. A comparison of the hysteresis loops of both parts of the tape, measured in the same magnetic field region, shows that the field shift of the hysteresis loops is associated with the interlayer interaction of the surface and volume of the tape, and the formation of asymmetric hysteresis loops occurs with the participation of the second layer with its gradual involvement in the processes of magnetization and magnetization reversal.

Impact of atomic packing and electronic structure on icosahedral short-range order and glass-forming ability of Zr–Cu metallic glasses

ABSTRACT Chemical and topological short-range ordering are important for glass formation in metallic alloys. Yet, it remains little understood from the viewpoint of the electronic bonding among the constituent elements of the alloys. In this work, we study CuxZr100−x, (46 ≤ x ≤ 70) metallic glasses, where the atomic packing efficiency and the electronic structure of the full icosahedra, the key short-range order structures, have been investigated in detail. To capture a realistic picture of the electronic bonding in the icosahedra in the as-quenched metastable state, DFT study of the electronic structure of the icosahedra extracted from classical molecular dynamics simulation is carried out. Results for the CunZr13−n , (4 ≤ n ≤ 9) clusters reveal that Cu6Zr7, Cu7Zr6 and Cu8Zr5 are the most abundant, electronically stable in Cu50Zr50 , Cu58Zr42 and Cu64Zr36, respectively. These three clusters also exhibit pseudo-gap in the density of states at the Fermi level – a feature linked with glass-forming ability according to the nearly-free electron approach. The partial density of states demonstrates the effect of small changes in the stoichiometry of the clusters on the s, p and d states of Cu and Zr in Cu–Cu and Cu–Zr bonding and hence, the stability of the clusters.

Fabrication of porous high-entropy Mn-Fe-Co-Ni-Cu-Zn alloys by vapor phase dealloying

Porous multicomponent 3d transition-metal (TM) alloys were fabricated by eliminating Zn from rapidly quenched ribbons with distinct compositions, TM7Zn93 and TM4Zn96 (TM – a mixture of Mn, Fe, Co, Ni, and Cu) using vapor phase dealloying (VPD). Phase composition and microstructure of the ribbons in an as-quenched state and resulting porous materials were investigated in detail by S/TEM-EDS, XRD, SEM, and EDXRF methods. In the as-quenched state, the majority of the alloy is composed of the CoZn13 type structure (C2/m space group). Atomically resolved EDS mapping clarified the chemical site occupancy of the TM elements in the structure. The resulting fabricated porous high-entropy alloys (HEA) have a spongy microstructure with a bimodal pore size and their surface area was estimated at 2–4 m2/g. Analysis of pore size distribution revealed their macro-mesoporous structure. The formation of the solid solution with the FCC (Fm3̅m space group) crystal structure during VPD was confirmed by XRD data. STEM-EDS analysis revealed the existence of several FCC solid solution phases within the porous HEA. A nanoscale elemental/phase separation into Co- and Cu-rich FCC solid solution regions with coherent interfaces across the individual crystalline grains has been found. A general route to prepare porous HEA using rapid solidification and vapor phase dealloying has been discussed.

Magnetic properties of the amorphous Co-Fe-Cr-Si-B alloy after annealing in unsaturated magnetic field

The regularities of influence of temperature and intensity of a longitudinal magnetic field significantly less than the saturation field during annealing on the magnetic properties of an amorphous soft magnetic alloy based on Co have been studied. The possibility of the effectiveness of such treatment in comparison with traditional annealing without a field due to partial or complete suppression of stabilization of domain boundaries because of directional ordering is demonstrated. Annealing at temperatures below the Curie point with the application of unsaturated field exceeding the saturation field of the residual induction of an amorphous alloy in as-quenched state (40 A/m) showed the greatest efficiency compared with annealing without a field in terms of simultaneously reducing the coercive force Hc and increasing the low-field permeability µ0.3 and maximum permeability µmax. In comparison with non-field annealing, depending on the conditions of unsaturated magnetic field annealing, the possibility of reducing Hc by 39 %, increasing µmax by 4.5 times and µ0.3 by 3.8 times is shown. After annealing in unsaturated field on the magnetization curve of the alloy Co69Fe3.7Cr3.8Si12.5B11, the perminvar region, as well as the parabolic region where Rayleigh's law is fulfilled, end in lower fields than after annealing without a field. The results obtained are discussed taking into account the occurrence of various physical processes in the alloy during heat treatment.

Peculiarities of Magnetization Processes of Cobalt-Based Amorphous Alloy Ribbons in the As-Quenched State

Peculiarities of Magnetization Processes of Cobalt-Based Amorphous Alloy Ribbons in the As-Quenched State

Uticaj hladne plastične deformacije nakon starenja na mehaničke osobine i mikrostrukturu aluminijumske legure EN AW-7075

This paper presents research on the changes in the mechanical and structural properties of the commercial aluminum alloy EN-AW 7075 during thermomechanical processing. The processing involved artificial aging of the alloy at a temperature of 150°C for 30 minutes, followed by cold rolling after aging. Changes in hardness and impact toughness during the experiment were monitored. Hardness was measured using the Leeb method, while impact toughness was measured using the Charpy method. In the annealed state, the lowest hardness values were recorded, while the highest-impact toughness value was achieved in the as-quenched state. By applying cold plastic deformation after artificial aging, the hardness of the alloy significantly increased, while the impact toughness continuously decreased. After deformation of 20%, cracks appearance prevented further deformation. Optical microscopy was used to follow microstructural changes during the applied processing regime. Precipitates of various sizes and morphologies were observed in the structure. The annealed state results in poorly defined grain boundaries and formation of large precipitates relatively evenly distributed throughout the matrix. Cold plastic deformation after aging has resulted in elongated grain structure aligned with the rolling direction, along with crushing of secondary phase particles.

Stimulating the amorphous structure of Fe56Co24Nb4B13Si2Cu1 ferromagnetic alloy by thermal annealing, laser and electron beam irradiation: A Mӧssbauer spectroscopy investigation

This study presents a Mӧssbauer spectroscopy investigation of the Fe56Co24Nb4B13Si2Cu1 amorphous ferromagnetic alloy in the as-quenched state and after thermal annealing, laser and electron beam irradiation. Thermal treatment at temperatures of 450–750° C caused nano, partial and complete crystallization of the alloy system. Crystalline phases such as α-(FeCo), (FeCo)2(BSi) and (FeCo)3(BSi) were identified in the thermally annealed specimens. By analyzing the hyperfine magnetic field distributions, it was shown that continuous wave (cw) CO2 laser irradiation of fresh samples determined a more pronounced in-plane orientation of magnetic moment directions and caused changes in the chemical short-range order in the system with non-zero magnetostriction. For direct comparison, atomic rearrangements were not observed in the Fe68.5Co5Nb3Cu1Si15.5B7 ferromagnetic alloy having a zero magnetostriction constant. Unlike the case of laser annealing, irradiation with 11 GeV electrons of the Fe56Co24Nb4B13Si2Cu1 alloy determined a pronounced out-of-plane magnetic anisotropy and supported the formation of stress centers in the irradiated system. Both laser and electron beam irradiation were found to essentially preserve the amorphous phase of the processed alloy.

Nonuniformity of magnetization processes of a cobalt-based amorphous alloys in the as-quenched state

The magnetization processes nonuniformity of an amorphous cobalt-based soft-magnetic alloy AMAG-172 (Co-Ni-Fe-Cr-Mn-Si-B) in the as-quenched state were studied. Studies have shown that the main reason of the magnetic characteristics and magnetization processes nonuniformity is the nonuniformity of internal stresses due to the alloy manufacture method. An indirect characteristic of internal stresses is the domains volume with orthogonal magnetization. The observed bimodal field dependence of the magnetic permeability and the field shift of the hysteresis loops in the region of 180-degree domain walls displacement are a consequence of the nonuniformity of the alloy over its thickness. The field shift and the asymmetry of hysteresis loops are explained in terms of the formation of a unidirectional exchange anisotropy at the interface between the ferromagnetic and antiferromagnetic phases of the planar magnetization components oriented along the ribbon axis. The field shift disappearance and the asymmetry of the hysteresis loops along the width of the tape can be interpreted as a decrease in the thickness of the CoO oxide antiferromagnetic layer due to the difference in the concentrations and depth of oxygen and hydrogen atoms penetration induced into the surface of the tape during the manufacture of the tape as a result of interaction with atmospheric vapor.

Nonuniformity of Magnetization Processes of a Co-Based Amorphous Alloy Ribbon in the As-Quenched State

Nonuniformity of Magnetization Processes of a Co-Based Amorphous Alloy Ribbon in the As-Quenched State

Magnetostriction of Fe-rich FeSiB(P)NbCu amorphous and nanocrystalline soft-magnetic alloys

The compositional effect of magneto-elastic and magnetostriction properties of Fe-rich Fe81B15−xPxSi2Nb1Cu1 (ii) Fe82B14−xPxSi2Nb1Cu1 and (iii) Fe83B13−xPxSi2Nb1Cu1 (x = 0, 4, 8) amorphous and annealed nanocrystalline alloy ribbons were investigated. The present study adds knowledge to the limited magnetostriction literature available for Fe-rich nanocrystalline alloys by systematically varying the Fe and P content. A combination of Becker-Kersten and small angle magnetization rotation (SAMR) techniques has been employed for the magnetostriction (λs) evaluation. Both the as-quenched and nanocrystalline ribbons exhibit large positive magnetostriction and show strong compositional dependence to the P content. In the as-quenched condition, 4 at% P addition shows maximum magneto-elastic response and magnetostriction constant, with Fe81B11P4Si2Nb1Cu1 alloy exhibiting a maximum of + 52 ppm and P-free Fe83B13Si2Nb1Cu1 alloy exhibiting a minimum of + 27 ppm. In the nanocrystalline state, a slight reduction of magnetostriction is seen for all alloys, with a maximum of + 32 ppm (4 at% P) and a minimum of + 22 ppm (P-free) in Fe83 at% alloys. The unusual large magnetostriction of optimally annealed samples is attributed to the relatively low crystal volume fraction (30–45%) of nanocrystalline ribbons. The lowest magnetostriction of Fe83B13Si2Nb1Cu1 alloy in both as-quenched and annealed state is explained based on ribbon structural heterogeneity consisting of crystal nuclei and textured α-Fe surface crystallization. The study reveals a contradictory response of magneto-crystal anisotropy (grain size reduction) and magneto-elastic anisotropy to the P addition and ribbon structural heterogeneity. The study discusses the implications of the large magneto-elastic anisotropy associated with Fe-rich nanocrystalline ribbons and the way forward for improving their magnetic softness.

Resistance to Abrasive Wear with Regards to Mechanical Properties Using Low-Alloy Cast Steels Examined with the Use of a Dry Sand/Rubber Wheel Tester.

This paper focuses on relationship between the mechanical properties and abrasive wear resistance, expressed by the Kb index, using an example of low-alloy cast steels. In order to achieve the aim of this work, eight cast steels of varying chemical composition were designed, cast and then heat treated. The heat treatment involved quenching and tempering at 200, 400 and 600 °C. Structural changes caused by tempering are demonstrated by the different morphologies of the carbide phases in the ferritic matrix. In the first part of this paper, the present state of knowledge about the influence of structure and hardness on the tribological properties of steels is discussed. This research involved the evaluation of a material's structure, as well as its tribological and mechanical properties. Microstructural observations were performed using a light microscope and a scanning electron microscope. Next, tribological tests were carried-out with the use of a dry sand/rubber wheel tester. To determine the mechanical properties, Brinell hardness measurements and a static tensile test were carried out. The relationship between the determined mechanical properties and abrasive wear resistance was then investigated. The analyses also provided information regarding the heat treatment states of the analyzed material in the as-cast and as-quenched states. It was found that the abrasive wear resistance, expressed by the index Kb, was most strongly correlated with hardness and yield point. In addition, observations of the wear surfaces indicated that the main wear mechanisms were microcutting and microplowing.

Microstructural and magnetic properties of Mn2FeSi and Mn2FeAl alloys prepared in bulk form

Microstructural and magnetic properties of the Mn2FeSi and Mn2FeAl alloys prepared in the bulk form have been investigated. Cylinder-shaped ingots produced by induction melting technique were analyzed in as-quenched state and additionally annealed at 773 K for 5 days in the protective argon atmosphere. The results show that Si and Al have different effects on the microstructural and magnetic properties of the alloys. The Mn2FeAl ingots are single-phase both before and after annealing, and their diffractograms surprisingly correspond not to the Heusler (L21 or XA) but to the primitive cubic β-Mn structure. Conversely, Mn2FeSi alloys show a two-phase behavior in the as-quenched state. From results of X-ray diffraction it was not possible to judge whether Mn2FeSi alloy has the inverse-Heusler (XA) or full Heusler (L21) structure. Annealing of Mn2FeSi leads to the formation of multiple phases. The EDX chemical area analyses resulted in only slight deviations of compositions compared to the nominal ones. The lattice parameters of 0.5672 nm and 0.6339 nm were estimated for the Mn2FeSi and Mn2FeAl samples from X-ray diffraction measurements. From the magnetic viewpoint, all samples are paramagnetic at room temperature and transform into antiferromagnetic state at the N é el temperatures about 50 K and 36 K for Mn2FeSi and Mn2FeAl, respectively. The negative Curie temperatures determined at all samples by Curie-Weiss law indicate an antiferromagnetic ordering of spins. Positron annihilation investigations revealed that Mn2FeSi contains a high concentration of vacancies. The local chemical environment of vacancies characterized by coincidence Doppler broadening is compatible with L21 rather than with XA structure. In contrast vacancy concentration in Mn2FeAl is very low and almost all positrons are annihilated in the free state.

Anomalous Nernst Effect in Flexible Co-Based Amorphous Ribbons.

Fe3Co67Cr3Si15B12 ribbons with a high degree of flexibility and excellent corrosion stability were produced by rapid quenching technique. Their structural, magnetic, and thermomagnetic (Anomalous Nernst Effect) properties were studied both in an as-quenched (NR) state and after stress annealing during 1 h at the temperature of 350 °C and a specific load of 230 MPa (AR). X-ray diffraction was used to verify the structural characteristics of our ribbons. Static magnetic properties were explored by inductive technique and vibrating sample magnetometry. The thermomagnetic curves investigated through the Anomalous Nernst Effect are consistent with the obtained magnetization results, presenting a linear response in the thermomagnetic signal, an interesting feature for sensor applications. Additionally, Anomalous Nernst Effect coefficient SANE values of 2.66μV/K and 1.93μV/K were estimated for the as-quenched and annealed ribbons, respectively. The interplay of the low magnetostrictive properties, soft magnetic behavior, linearity of the thermomagnetic response, and flexibility of these ribbons place them as promising systems to probe curved surfaces and propose multifunctional devices, including magnetic field-specialized sensors.

Effects of aging treatment on the mechanical properties and corrosion resistance of an Al-Cu-Mg-Li alloy

In this paper, the effects of as-quenched, single aging, and double aging on the mechanical properties, microstructure, corrosion resistance, and electrochemical behavior of an Al-Cu-Mg-Li alloy were investigated. Most changes only improved the mechanical properties or corrosion resistance of aluminum alloy alone, and very few of them improved the mechanical properties or corrosion resistance at the same time. The results showed that double aging treatment improved the strength, hardness, and corrosion resistance of the alloy but decreased its elongation. During the aging treatment, the corrosion morphology of the alloy gradually transformed from pitting corrosion (as-quenched) to a combination of pitting corrosion and corrosion cracks (single aging) and finally to pitting corrosion (double aging). The fracture morphology gradually changed from an uniform distribution of a mixture of large and small dimples (as-quenched) to an intergranular fracture (double aging) as aging progressed. Transmission electron microscopy results showed that the T1 phase within grains and at grain boundaries (GBs) was different between the as-quenched and double aged states. In addition, a precipitate-free zone (PFZ) formed in the double aged state. The optimal process of Al-Li alloy was determined to be pre-aging at 100 ℃ for 4 h and final aging at 160 ℃ for 24 h.

Effect of stress relaxation on soft magnetic properties of Fe76Si9B10P5 metallic glass

Stress relief can improve the soft magnetic properties of Fe-based metallic glasses (MGs) and is vital for industrial applications. In this work, we investigated the evolution of soft magnetic properties, relaxation dynamics, and mechanical properties of Fe-based MGs under different applied tensile strains and stress relaxation times. We found that stress relaxation can significantly reduce coercivity Hc by 95% compared with as-quenched state. Furthermore, the coercivity Hc, apparent activation volume Vact and time constant tr all show analogous two-stage variation with annealing time, accompanied by approximate crossovers. This suggests that the microstructure change emerges, further verified by the domain wall motion and the transition from elastic to plastic. These results are helpful in preparing Fe-based MGs with excellent soft magnetic and mechanical properties by controlling the stress relaxation condition.

Influences of surface state on thermal stability and magnetic properties of Fe-Si-B-C amorphous alloy

Influences of surface state on thermal stability and magnetic properties for Fe82Si1B12C5 completely amorphous alloys and Fe83Si1B12C4 amorphous alloys with partial crystallization at their surface have been investigated by layer polished-removal method. The crystallization enthalpy of α-Fe phase for the two amorphous alloys decreases obviously with polishing removal of surface layer with the thickness of removal, due to the alteration of internal stress state. An increase of only 1.2% in Fe content causes an increase of 8.4% in crystallization enthalpy of α-Fe phase for the alloy system with an initial casting thickness, indicating that the thermal stability is stress-sensitive for Fe-based amorphous alloys with high Fe content close to amorphous forming boundary are easier to crystallize. It was found that in the as-quenched state the coercivity for both of them increases linearly with the thickness of removal, which is caused by an increase in internal stress. And it was confirmed by experiment that adequate annealing can greatly improve the soft magnetic properties and alter thermal stability.

Influence of stress-induced α’’ phase transformation on mechanical properties in metastable β type Ti-5Al-2.5Cr-5Mo-1Sn alloy

The stress-induced α’’ phase transformation in titanium alloys has received extensive attention due to its significant effect on mechanical properties. In this work, by adjusting the heat treatment process, the stress-induced α’’ phase transformation is activated in Ti-5Al-2.5Cr-5Mo-1Sn. The quasi-static tensile mechanical properties of the alloy under air-cooled and as-quenched states have been compared. Further, the morphology and orientation of the stress-induced α’’ phase and its interaction with dislocations are investigated by X-ray diffraction (XRD), optical microscope (OM), electron backscattered diffraction (EBSD) and transmission electron microscope (TEM) experiments. The value of average misorientation at the stress-induced α’’ bands region is larger than that in the β matrix, which indicates that the degree of plastic deformation in the stress-induced phase transformation region is higher. Therefore, the stress-induced α’’ phase exhibits a strong strain partitioning effect during the stretching process and improves the ductility of the material. The β/α’’ interface has a weak effect to hinder the dislocations, which results in low tensile strength of the alloy. This work can provide insight into the influence of stress-induced α’’ phase transformation on the mechanical properties of transformation induced plasticity (TRIP) type titanium alloys. • The Ti-5Al-2.5Cr-5Mo-1Sn alloy is elaborately regulated to produce TRIP effect. • Average misorientation of α’’ band region is generally larger than that of β matrix. • α’’ phase exhibits a strong strain partitioning effect to increase alloy ductility. • The β/α’’ interface is semi-coherent and has a weak effect to hinder dislocations.

Glass formation, crystallization, and magnetic properties of the FeNiCrNbB amorphous ribbons

In present work, the glass forming ability (GFA), crystallization, and magnetic properties of the (Fe1-x-y Ni x Cr y )65Nb7B28 (x = 0.05, y = 0.05; x = 0.05, y = 0.1; x = 0.1, y = 0.05) alloys under both as-quenched and as-annealed state were studied. The results show that the introducing Ni and Cr significantly improves the GFA and thermal stability, while it decreases the soft magnetic properties for the as-quenched (Fe1-x-y Ni x Cr y )65Nb7B28 alloys. The Fe68Nb4Cr8Nb5B15 alloys were regarded as good glass-former with Δ - T x = 59 K and T x1 = 846 K. Isothermally annealing treatment were carried out on the (Fe1-xyNixCry) 80Nb5B15 alloys. The crystallization products are α --Fe and Cr3B4 phases for alloys annealed at low temperature, while mixed structure of α - Fe, Fe2B, Fe3B, Ni3B4 and Cr3B4 phases are identified for alloys annealed at high temperature. Besides, increasing annealing temperature deteriorates their soft magnetic properties. Annealing above T p1 decreases the saturation magnetization. However, further increase of annealing temperature (> T p2) makes the soft magnetic properties almost disappear.

Lath martensite substructure evolution in low-carbon microalloyed steels

Lath martensite substructures in as-quenched plain carbon steels exhibit dislocation-like contrast in the transmission electron microscope. More recent observations reported internal twins and nanoscale auto-tempered intra-lath carbides as additional lath substructures in ultra-low-C binary Fe–C steels. Modern microalloyed steels often have similar ultra-low C contents besides microalloying elements like Ti, Nb or V and, more recently, Mo, to achieve high strength, toughness and weldability. Nonetheless, little is known about the lath substructure evolution in the as-quenched state of microalloyed steels. This study investigates the hierarchical martensite substructure evolution post-quenching of microalloyed Nb and NbMo steels with 0.1 wt% C. Hierarchical microstructure characterization was done using scanning and transmission electron microscopy, and electron backscatter diffraction methods including parent grain reconstructions with MTEX. Thermokinetic simulations using MatCalc to determine the carbide evolution during auto-tempering were corroborated with site-specific transmission electron microscopy. Mo addition led to lowering of the martensite start temperature, yet the Nb steel showed a finer hierarchical microstructure. Finer laths with in-lath dislocations, short and long twins, and lath boundary decoration of carbides were found in the Nb steel. Conversely, laths in the NbMo were wider, with frequent intra-lath auto-tempered precipitates in the vicinity of dislocations, without twins.

Room temperature magnetic properties of Mn-Ga-B melt-spun ribbons

In this study, we synthesized Mn65Ga35-δBδ (δ = 0–10) alloys using the melt-spinning technique. In the as-quenched state, the alloys consisted of the D019 and Mn8Ga5 phases in the as-quenched state. After heat treatments, the Mn65Ga35 alloy consisted of the D022 phase, whereas the Mn65Ga30B5 and Mn65Ga25B10 alloys were mainly composed of the D019 phase. The magnetization of the Mn65Ga30B5 and Mn65Ga25B10 alloys was smaller than that of the Mn65Ga35 alloy, but the Mn65Ga30B5 and Mn65Ga25B10 alloys exhibited higher coercivity than the Mn65Ga35 alloy. The highest coercivity of 8.7 kOe was measured at room temperature in the Mn65Ga30B5 alloy with the fined grains of the D019 phase.