As-spun Alloys Research Articles

Revisiting Rare Earth Permanent Magnetic Alloys of Nd-Fe-C

Nd-Fe-C alloys have been reported as hard magnetic materials with a potential higher coercivity than Nd-Fe-B alloys. However, it has been seldom studied since its intrinsic properties were investigated in the last century. Here, we revisited the structure, phase precipitation and magnetic properties of rapidly quenched ternary Nd-Fe-C alloys for further understanding their composition-microstructure-property relationships. The Nd10+xFe84−xC6 (x = −2, 0, 2, 3, 4, 5) alloys with various compositions were prepared by melt spinning. The results show that the hard magnetic Nd2Fe14C phase can be hardly formed in the as-spun alloys. Instead, the alloys are composed of soft magnetic α-Fe phase and planar anisotropic Nd2Fe17Cx phase. After annealing above 650 °C, the Nd2Fe14C phase is precipitated by the peritectoid reaction. All optimally annealed alloys contain Nd2Fe14C and Nd2Fe17Cx phases, while the presence and content of α-Fe phase are determined by the alloy composition. The crystallization degree of the as-spun alloys has an effect on their magnetic properties after annealing. After the annealing treatment, partly crystallized as-spun alloys exhibit better magnetic properties than the amorphous alloys. The intrinsic coercivity Hcj = 847 kA/m, remanence Jr = 0.69 T, and maximum energy product (BH)max = 64.3 kJ/m3 were obtained in the Nd14Fe80C6 alloy annealed at 725 °C. The formation of the Nd2Fe14C and Nd2Fe17Cx phases with the Nd2O3 phase precipitated at the triangular grain boundaries is responsible for its relatively good properties. Although the magnetic properties of Nd-Fe-C alloys obtained in this work are inferior to those of Nd-Fe-B, the present results help us to further understand the magnetic behavior of Nd-Fe-C alloys.

A comparative study on microstructures of a high-Zn AlZnMgCuZr alloy fabricated by casting and melt spinning

A high-Zn Al–27Zn-1.5Mg-1.2Cu-0.08Zr alloy was prepared by traditional casting and melt spinning. The as-casted alloy consists of well-developed α-Al dendrites with many coarse η-phase and low solute concentration, coarse network precipitates at grain boundaries and the α-Al/η-phase eutectic structures at triple junctions. Due to these featured structures, the as-cast alloy exhibits a low tensile strength of 101 MPa with room temperature and high temperature (300 °C) damping capacity of 0.0058 and 0.027 respectively. Comparatively, the as-spun alloy reveals gradient cross-sectional microstructures after solidification: an ultrafine grained region near the wheel surface, a transition region and an equiaxed-grained region near the ribbon free surface, with changes of precipitate morphologies from granular shape to network shape via vermicular. High-density nano-sized η′-phase/GP-zones within α-Al grains result in a higher tensile strength (121 MPa) of as-spun alloy with room temperature and high temperature (300 °C) damping capacity of 0.0049 and 0.048 respectively. Fracture analysis shows that the as-casted alloy fails in a mixed-mode fracture, comprised predominantly of transgranular fracture, quasi-cleavage fracture, cleavage fracture and dimple fracture, whereas the as-spun alloy failed in cleavage fracture and dimple fracture.

Plastic quasicrystal-containing alloys prepared by annealing pseudo-high entropy Zr70–75(Al, Ni, Cu, Ag)25–30 glassy alloys

A glassy (G) phase was formed for Zr-rich Zr70–75(Al, Ni, Cu, Ag)25–30 (atomic percent, at.%) melt-spun alloy ribbons. These glassy alloys exhibit the glass transition, followed by a supercooled liquid region and then three-stage crystallization. The glass transition temperature and the onset temperature for the first-stage crystallization (Tx1) decrease from 630 to 668 K, respectively for the 70Zr alloy to 619 and 652 K, respectively for the 75Zr alloy. The first-stage exothermic peak is due to the precipitation of an icosahedral quasicrystal (IQ) phase. The IQ particle size decreases from 10 nm to 6 nm with increasing Zr content from 70at.% to 74at.%. The [G + IQ] phases change to Zr2Ni + Zr2(Cu, Ag) phases after the second exothermic peak and then Zr2Ni + Zr2(Cu, Ag) + Zr5Al3 phases after the third stage. It is noticed that the as-spun glassy alloy ribbons as well as the annealed [G + IQ] phase ribbons exhibit good bending plasticity. Furthermore, the 70Zr thicker ribbons also exhibit high tensile fracture strength of 1090–1187 MPa and plastic elongation of 0.17 %–0.42 %. The fracture mode is similar to that of ordinary bulk metallic glasses. The Vickers hardness (Hv) is 480 for 70Zr alloy and decreases to 436 for 75Zr alloy. The precipitation of IQ phase causes a significant increase in Hv to about 554. The formations of glassy alloys with high Zr contents of 70at.%–75at.% by melt spinning as well as the [G + IQ] phase alloys with good bending plasticity by annealing hold promise for the creation of a new type of engineering material, transcending mere academic novelty.

Novel Fe–B–P–C–Cu–Co amorphous/nanocrystalline alloys with excellent comprehensive performance via Co substitution for Fe

The amorphous formation ability, thermal properties, crystallization behavior, magnetic properties, resistivity and bending ductility of Fe84.5-xB12P2C1Cu0.5Cox (x = 0, 4, 8) alloys were systematically investigated. It is found that the substitution of Fe by Co promotes the transformation of the as-spun alloys from a completely amorphous structure to an amorphous/nanocrystalline dual-phase structure, which is related to the differences in the interactions between the involved atoms. The saturation magnetization of alloys increases with increasing Co content and can be increased to 1.93 T at x = 8 by heat treatment, but excessive substitution of Co for Fe deteriorates the coercivity and bending ductility due to the pre-existing α-Fe(Co) grains. The resistivity is positively correlated with the disorder of structure, and the as-spun alloy with x = 4 exhibits a high resistivity of 136.2 μΩ cm. As a result, the annealed Fe80.5B12P2C1Cu0.5Co4 alloy with excellent soft magnetic properties (Ms = 1.81 T, Hc = 7.8 A/m) and good bending ductility in combination with high resistivity has potential for application in the field of electronic devices.

Tunable magnetic properties and magnetic domain structure of nanocomposite permanent materials via Ti addition into Nd-Fe-Co-B alloys

In this work, the effect of tunable Ti content on the microstructure, magnetic domain structure, and magnetic properties of as-spun and annealed Nd9.5Fe79-xCo5TixB6.5(x = 0,1,2,3,4) alloys at the quench speed of 18 m/s were investigated. For the as-spun alloy, augmenting the Ti content enhanced the initial crystallization temperature and the stability of the amorphous phase. Simultaneously, the incorporation of Ti led to augmentation in the quantity of nanocrystals within the amorphous matrix, thereby facilitating the formation of vortex-like magnetic domains with large size but reduced the saturation magnetization Ms. For the annealed alloy, the incorporation of Ti inhibited the precipitation of α-Fe phase, refined the grain, enhanced the exchange coupling between the soft and hard magnetic phase and facilitated the formation of smaller, more uniform vortex-like magnetic domains, These alterations were beneficial to improve the comprehensive magnetic properties. Furthermore, the addition of tunable Ti resulted in a remarkable impact on coercivity enhancement. The coercivity value exhibited a significant increase of 54.30%, surging from 374.24 kA/m to 577.51 kA/m. Upon a thorough analysis of the magnetic domains and coercive force mechanisms, it was ascertained that the introduction of Ti substantially augmented the creation of vortex-like domains. These domains effectively impede domain motion, consequently elevating the material's coercivity.

Microstructural characterization of rapidly solidified Al-13.5 at.% Cr and Al-13.5 at.% V alloys for catalytic applications

Intermetallic compounds, due to their well-defined stoichiometry, arrangement of atoms and controlled crystal structure, are a promising alternative to expensive noble metal catalysts. In this paper, the catalytic properties of Al-13.5 at.% Cr and Al-13.5 at.% V alloys, corresponding to the quasicrystalline approximants Al45Cr7 and Al45V7, were investigated for the first time.The alloys in the form of fragmented brittle ribbons were produced by the melt-spinning. The microstructure of the ribbons, both in the as-spun state and after heat treatment (100 h at 600 °C), was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. In the as-spun state, the ribbons showed a multiphase microstructure. In addition to the Al45Cr7 phase in the Al-Cr alloy and the Al3V phase in the Al-V alloy, they also contained α(Al) solid solution and icosahedral quasicrystalline phases. After heat treatment, the alloys became almost single phase, consisting mainly of stable monoclinic phases: Al45Cr7 or Al45V7. The catalytic performance of the phenylacetylene hydrogenation reaction was tested on as-spun and heat-treated alloys that had previously been pulverized and sieved to select a powder fraction of less than 32 µm. All the tested materials show high substrate conversion, above 80% after 1 h reaction, along with high activity rate. The homogenized powders demonstrated a slightly better properties in relation to as-spun materials. These results confirm the potential of intermetallic catalysts, including the tested alloys, in hydrogenation reactions and verify the possibility of using the metallurgical method to obtain catalytically active materials.Graphical abstract

Influence of static magnetic field on rapid solidified structure and nanocrystallization behavior of Fe–Si–B–Cu soft magnetic alloys with pre-existing α-Fe nanocrystals

The effects of static magnetic field strength on the rapid solidified structure, thermal stability, crystallization structure and soft magnetic properties of melt-spun Fe81.6Si4B13Cu1.4 alloys were investigated and the corresponding related mechanism was discussed in terms of formation of pre-existing α-Fe crystals and nanocrystallization behaviors. The rise of magnetic field strength promotes the formation of the α-Fe crystals in as-spun alloy, enhances the competitive growth between the crystals during annealing, and then refines the crystals in the annealed alloy and improves their magnetic softness. The Fe81.6Si4B13Cu1.4 alloy prepared under 200 mT contains α-Fe crystals with a high number density and average size (D) of 8.3 × 1022 m−3 and 5.9 nm, respectively, in as-spun state, and possesses fine crystals with a D of 18.2 nm and excellent soft magnetic properties with a high saturation magnetization of 1.75 T, low coercivity of 9.2 A/m and high effective permeability of 10,160 at 1 kHz after annealing at 633 K for 60 min.

Effect of power spinning and heat treatment on microstructure evolution and mechanical properties of duplex low-cost titanium alloy

• A power spinning process and subsequent three kinds of heat-treatment routines were conducted on the new duplex Ti-5.5Al-1Fe-3.5Cr-3.2Zr-0.2Si alloy. • The microstructure evolution and mechanical properties of low-cost titanium alloy were systematically studied. • The as-spun specimens, subjected to low-temperature annealing at 550°C for a duration of less than 4 h, exhibited a good balance of strength and ductility. • The irregular variation of elongation can be ascribed to the competition of precipitation and spheroidization. The microstructural evolution and mechanical properties of low-cost Ti-5.5Al-1Fe-3.5Cr-3.2Zr-0.2Si alloy during power spinning and after three types of heat-treatment routines (low-temperature annealing, high-temperature annealing, solution and annealing) were systematically studied. An effective heat-treatment routine to fabricate high-strength and acceptable ductile as-spun Ti-5.5Al-1Fe-3.5Cr-3.2Zr-0.2Si alloy tubes was then proposed whereby the relationship between the mechanical performances and microstructures was analyzed. The {0002} α and {001} β textures were formed after multi-pass power spinning. The as-spun LC-Ti alloy exhibited a good combination of strength and elongation after heat treatment at 550 °C for 4 h, which was ascribed to the large plastic induced low-temperature spheroidization of deformed α phase and nanoscale α precipitation from deformed β phase. However, the elongation decreased evidently when Zr2Si/TiCr2 participated at the interphase boundaries after heat treatment at 550 °C for 8 h. In high-temperature annealing, the elongation changed nonlinearly owing to the precipitation of Zr2Si particles at triangular grain boundaries treated at 750 °C for 1 h, and the spheroidization of the deformed α p phase. Under solution and annealing conditions, lenticular α s would participate from the metastable β grains, which contributed to the greatest strength albeit poor ductility. This study provides an effective guidance for the processing and application of the low-cost titanium alloy.

Unusual alloying effects of Co and Ni on structure and magnetic properties of Fe-Si-B-Cu nanocrystalline alloys with pre-existing α-Fe nanocrystals

Alloying Co and Ni in traditional Fe-based nanocrystalline alloys always brings about crystals refinement and magnetic softness improvement, while we found opposite phenomena in Fe81.3Si4B13Cu1.7 nanocrystalline alloy with pre-existing α-Fe nanocrystals in present work and clarified the related mechanism by investigating the structure evolution of melt-spun (Fe, Co, Ni)81.3Si4B13Cu1.7 alloys. The Co and Ni alloying lowers the number density (Nd) of pre-existing α-Fe nanocrystals in the as-spun alloys by suppressing the formation of Cu-enriched clusters. The effect of Ni alloying is more distinct than that of Co and adding 10 at.% Ni completely eliminates the nanocrystals. The decreased Nd leads to the weakened competitive growth between the nanocrystals, combined with the absence of diffusion-suppression, resulting in the slightly crystals coarsening and corresponding magnetic softness deterioration in the annealed Co-containing alloys and much more distinct ones in the annealed Ni-containing alloys.

Excellent soft magnetic properties and enhanced glass forming ability of Fe-Si-B-C-Cu nanocrystalline alloys

In the present investigation, the glass forming ability (GFA), thermal stability, and soft magnetic properties of Fe85Si6-xB8Cu1Cx alloys are investigated by the substitution of C for Si. It was found that the GFA of C-containing alloys is remarkably enhanced when a certain amount of Si is replaced by C in a C-free alloy. The temperature interval between the first and second crystallization temperatures is also improved by C addition and reaches a maximum value of 169 °C for the as-spun Fe85Si2B8Cu1C4 amorphous alloy. The Fe85Si4B8Cu1C2 nanocrystalline alloy exhibits the best soft magnetic properties with the highest saturation magnetic flux density (Bs) of 1.95 T and the lowest coercivity (Hc) of 4.1 A/m, which corresponds to the highest grain number density (Nd). The high GFA, large annealing window, low cost, and excellent soft magnetic properties enable the Fe85Si2B8Cu1C4 nanocrystalline alloy as a material with wide applicability. Moreover, this work is highly beneficial in balancing the relationship between a high Bs and sufficient GFA in the production of Fe-rich nanocrystalline alloys.

Microstructure evolution, magnetic properties and frequency characteristics of Si-rich FeSiBCuNb soft magnetic alloy induced by annealing treatment

The influences of heat treatment on the microstructure, domain structure and magnetic characteristics of the Fe 73.5 Si 15.5 B 7 Cu 1 Nb 3 alloy were investigated. We demonstrated that the as-spun alloy exhibits high amorphous forming ability and good thermal stability with a large annealing interval between the primary and secondary crystallization peaks over 170 °C. Also, the interaction of chemical concentration fluctuations and heterogeneous nucleation is responsible for the nanocrystallization mechanism of alloy. Furthermore, the magnetic structures change from the narrow and zigzag-like branched domains to wide and regular striped domains with increasing annealing temperature, which leads to a decrease in pinning effects. Appropriate magnetic anisotropy introduced by heat-treatment process has effect on the magnetic mechanism and the shape of magnetic hysteresis loops, which adjusts the frequency characteristics. After the optimum annealing, the alloy exhibits the excellent magnetic properties including high Ms. of 135.4 emu/g and low Hc of 0.56 A/m, together with good low-frequency characteristics. • Nanocrystallization mechanism of the Si-rich Finemet amorphous alloy were studied roundly. • High volume fraction, fine, and uniformly distributed nanocrystalline structure was obtained. • Optimal Ta induced wide magnetic domains achieves high Ms., low Hc and high L. • High-temperature annealing introduced anisotropy improves high frequency characteristics.

Direct synthesis of Fe-Si-B-C Cu nanocrystalline alloys with superior soft magnetic properties and ductile by melt-spinning

Structure, magnetic properties and ductile of melt-spun Fe83-xSi4B13-yCyCux (x = 0–1.7; y = 0–8) alloys were investigated. The addition of 1.7 at.% Cu in a Fe83Si4B13 amorphous alloy generates abundant α-Fe crystals by providing nucleation sites, and further C doping promotes the growth of the crystals by suitable turning amorphous-forming ability, hence they increase saturation magnetic flux density (Bs) and slightly worse magnetic softness of the as-spun alloys. The as-spun Fe81.3Si4B7C6Cu1.7 alloy possesses a combined structure of a fully amorphous layer in wheel side surface and predominating nanocrystalline structure with gradually enlarged α-Fe crystal, whose average size and volume fraction are determined as about 12 nm and 32%, respectively, therefore superior soft magnetic properties and ductile with a high Bs of 1.74 T, coercivity (Hc) of 32.7 A/m, effective permeability (μe, at 1 kHz) of 3200 and high relatively strain at fracture (εf) of 3.61% can be achieved directly in this alloy by only using melt-spinning. The annealing at 578 K releases internal stress, promotes the growth of the α-Fe crystals and remains the amorphous layer of the Fe81.3Si4B7C6Cu1.7 alloy, then improves the soft magnetic properties and maintains the superior ductile with increasing the Bs and μe to 1.80 T and 14,100, respectively, lowering the Hc to 9.4 A/m and slightly reducing the εf to 2.39%. The combination of superior soft magnetic properties and ductile and simplified synthesis process entitles the Fe-Si-B-CCu nanocrystalline alloys great potentials in high performance electromagnetic applications.

Effect of Ge Addition on Magnetic Properties and Crystallization Mechanism of FeSiBPNbCu Nanocrystalline Alloy with High Fe Content

In this work, new Ge-containing Fe-based nanocrystalline alloys with the composition of Fe80.2Si3B12-xP2Nb2Cu0.8Gex (x = 0, 1, 2 at.%) were developed, and the effects of Ge content on the magnetic and crystallization processes of the alloys were investigated. The addition of Ge extends the annealing window of the present Fe-based alloys, which reaches 173.6 K for the alloy of x = 2. The nanocrystalline alloy of x = 2, composed of dense and uniformly distributed α-Fe grains with an average grain size of 15.7 nm precipitated in the amorphous matrix, was obtained by conventional annealing treatment at a temperature of 843 K for 10 min, and this nanocrystalline alloy exhibited excellent magnetic properties with the Hc of 3 A/m and Bs of 1.65 T, which has great potential for industrial application. Non-isothermal crystallization kinetics studies show that the nucleation activation energy of the alloys gradually decreases with the increase in Ge content. The primary crystallization process is dominated by the direct growth of pre-existing nuclei in the as-spun alloy ribbons, and these pre-existing nuclei provide numerous heterogeneous nucleation sites to form dense and uniform α-Fe nanocrystals with a fine grain size, which leads to the excellent magnetic properties of the present Ge-containing Fe-based nanocrystalline alloys.

Phase precipitation and magnetic properties of melt-spun ternary Gd2Fe14B alloy and advantages of gadolinium substitution in Y2Fe14B alloy

To take the advantage of gadolinium (Gd) in developing and manufacturing RE-permanent magnets, the magnetic properties and phase precipitation behavior of Gd2Fe14B alloys prepared by melt spinning were investigated in this work. The results show that optimally direct quenched nanocrystalline Gd2Fe14B alloy exhibits the magnetic properties with remanence Jr of 0.51 T, coercivity Hc of 187 kA/m, and maximum energy product (BH)max of 33.1 kJ/m3. It also shows excellent thermal stability with a small negative temperature coefficient of Jr (α = −0.066%/K) and a positive temperature coefficient of Hc (β = 0.171%/K). The phase precipitations of as spun Gd2Fe14B alloy during melt spinning and over-quenched amorphous Gd2Fe14B alloy during heat treatment were clarified. The magnetic properties of the crystallized alloys annealed at 800 °C are close to those of the optimized directly quenched as-spun alloys, indicating good performance stability under various processes. In addition, the role of Gd substitution in (Y1–xGdx)2Fe14B alloys was systematically studied. Gd substitution can significantly enhance the thermal stability and decrease the irreversible remanence loss of Y2Fe14B alloy. With increasing Gd content, Gd-doped Y2Fe14B alloys show continuous enhancement of Hc at elevated temperatures. The highest β value of 0.22%/K was obtained in (Y0.2Gd0.8)2Fe14B alloy at 300–400 K. Gd substitution is not only effective in improving the exchange coupling effect and corrosion resistance of Y2Fe14B alloy but also superior to Nd in terms of improving the oxidation resistance. The present work has certain instructions for designing and developing new low cost RE permanent magnets with improved thermal and environment stability.

Magnetic properties and phase constitution of rapidly quenched nanocrystalline Gd-Fe-B alloys with various Gd contents

To fully understand the performance of nanocrystalline ternary Gd-Fe-B alloys, an detailed investigation on the phase precipitation and magnetic properties of Gd10+xFe84-xB6 alloys (x = 0, 2–6) were carried out. The enhanced remanence Jr of 0.62 T and maximum energy product (BH)max of 37 kJ/m3 were obtained for Gd10Fe84B6 alloy. The coercivity significantly increased from 145 to 453 kA/m with the increase of Gd content from 10 to 16 at.% due to the formation of continuously distributed intergranular phase. Compared to many other RE-Fe-B alloys, Gd-Fe-B alloys show superior magnetic stability to withstand alternating temperature, demonstrated by lower irreversible loss. For the rapidly quenched amorphous Gd-Fe-B alloys, after annealing treatment, in addition to the Gd2Fe14B phase, the α-Fe, FexB, and GdFe2 phases also precipitated from the amorphous matrix for the alloys with x = 0, 2, and 4, respectively. Interestingly, the crystallized alloys annealed at optimum temperature exhibit similar hard magnetic properties as those of the optimized as-spun alloys, suggesting that the properties of Gd-Fe-B alloys are not sensitive to the process.

Effects of La substitution on microstructure and hydrogen storage properties of Ti–Fe–Mn-based alloy prepared through melt spinning

The as-spun Ti1–xLaxFe0.8Mn0.2 (x=0, 0.01, 0.03, 0.06, 0.09, molar fraction) alloys were prepared by melt spinning. The effects of La substitution for Ti on the microstructure, hydrogen storage kinetics and thermodynamics of TiFe-type Ti–Fe–Mn-based alloy were investigated. The as-spun alloys hold the TiFe single phase, which transforms to TiFeH0.06, TiFeH, and TiFeH2 hydrides after hydrogenation. La substitution promotes the formation of micro-defects (such as dislocations and grain boundaries) in the alloys, thus facilitating hydrogen diffusion. In addition, the hydrogen storage kinetics properties are improved after introducing La element. With the rise of La content, the hydrogen storage capacity decreases firstly and then increases, but the absolute value of hydriding enthalpy change (|ΔH|) increases firstly and then reduces. When x=0.01, the maximum value of |ΔH| is obtained to be (25.23±0.50) kJ/mol for hydriding, and the alloy has the maximum hydrogen absorption capacity of (1.80±0.04) wt.% under the conditions of 323 K and 3 MPa.

Fundamental properties of melt-spun stoichiometric Y2Fe14B alloy and the advantages of Nd substitution

Here we investigate the effects of wheel speed and heat treatment on the melt-spun ternary Y2Fe14B alloy, aiming to clarify its structure, phase precipitation and magnetic properties. For directly quenched alloys, the optimum magnetic properties can be achieved when the wheel speed is within a relatively wide range of 30–40 m/s. The Y2Fe14B alloy prepared at 36 m/s shows the highest coercivity of 149 kA/m and remanence of 0.88 T with the maximum energy product (BH)max of 6.8 MGOe due to the single hard magnetic phase structure. For the amorphous ribbons prepared at 50 m/s, when the annealing temperature increases from 773 to 1073 K, the α-Fe phase precipitates first accompanied by the appearance of Y2Fe14B phase and a small quantity of Fe-B phase. The magnetic properties of annealed samples are much lower than those of the optimized as-spun alloys. The effects of Nd substitution for Y on the structure, magnetic properties and thermal stability of (Y1-xNdx)2Fe14B (x = 0–1) alloys have been systematically investigated. The Hcj and (BH)max exhibit almost linear increase with the increasing Nd substitution. Relatively low temperature coefficients can be obtained in the Nd substituted alloys. The current results are important for exploring high performance and low cost Y­based rare earth permanent magnets with improved thermal stability.

Influence of Co on microstructure and coercivity of (Ni0.5Fe0.5)80B10Si2Cu1Zr7 alloy

The effects of Co on microstructure, crystallization behavior and magnetic properties of (Ni0.5Fe0.5-xCox)80B10Si2Cu1Zr7 (x = 0~0.5) alloys were investigated. The results show that, the as-spun alloys remain lower coercivity (Hc) values (5 A/m ~ 14 A/m) over the whole Co content range, owing to their amorphous structure. After being annealed for 20 min above the onset temperatures of primary crystallization (Tx1), amorphous and nanocrystallines are coexisted in the alloys, and the crystal structure of nanocrystallines changes between fcc-(Ni, Fe, Co) and bcc-(Fe, Ni, Co) with the increasing Co content. In particular, it was found that Hc of the annealed alloys changes anomalously between 40 A/m and 1529 A/m with the increasing Co content, owing to the integrated action of grain size (D), magnetocrystalline anisotropy (K1) and lattice distortion. Especially for the alloys with x = 0.2 and x = 0.3, serious lattice distortion is the dominant factor for their higher Hc value than 1000 A/m.

Achieving high porosity and large recovery strain in Ni-free high Zr-containing Ti-Zr-based shape memory alloy scaffolds by fiber metallurgy

Highly porous Ti-40Zr-8Nb-2Sn (at.%) shape memory alloy scaffolds were prepared by fiber metallurgy using rapidly solidified alloy fibers for the application of cancellous bone replacement. The phase constituents of alloy fibers and scaffolds were investigated by means of X-ray diffraction (XRD), superelastic behavior of alloy fibers was investigated by means of the dynamic mechanical analyzer (DMA), microstructures and mechanical properties of scaffolds were investigated by means of scanning electron microscopy (SEM) and compressive test, respectively. As-spun alloy fibers consisted of only β phase at room temperature. Clear superelastic behavior was observed in the as-spun alloy fibers at temperatures between 153 K and 298 K. The scaffolds showed three-dimensional networks with fiber-fiber bonds, whose porosity and pore size was about 80% and larger than 100 μm, respectively. The compressive yield stress and elastic modulus of the scaffold annealed at 973 K for 1.8 ks were about 4.0 MPa and 0.3 GPa, respectively, similar to those of cancellous bone. Recoverable strain in the scaffold was improved from 2.8% to 4.0% after annealed at 973 K due to the absence of α phase formed in the as-sintered scaffold. Stable cyclic superelastic behavior was observed in the annealed scaffolds at room temperature.

Thermal behavior, microstructure and magnetic properties of (FexNiyCoz)80B10Si2Cu1Zr7 alloys

Amorphous (FexNiyCoz)80B10Si2Cu1Zr7 (x + y + z = 1) alloys were prepared by melt spinning. By investigating the glass-forming ability, thermal behavior, crystallization and magnetic properties of alloy ribbons, detailed and integral pseudoternary diagrams of (FexNiyCoz)80B10Si2Cu1Zr7 alloys were constructed, which can make one clearly understand the effects of ferromagnetic elements (Fe, Co, Ni) on microstructure and physical properties. Results show that, all as-spun alloys show a fully amorphous structure and the coercivity (Hc) can be tuned to a lower value than 45 A/m. After being annealed, alloys with Ni content lower than 64 at.% (y < 0.8) show a refined structure of nanocrystals with an average size about 3–14 nm uniformly dispersed in the residual amorphous matrix, and the Fe-rich and Ni-rich alloys exhibit Hc < 155 A/m comparing with the Co-rich alloys (155–416 A/m). No matter as-spun or annealed alloys, (Co + Ni):Fe = 3:7 is the optimal composition to obtain the maximum saturation magnetization (Ms) when y is a certain value in the range of 0–0.2. In addition, alloys in the whole range of composition were classified according to comprehensive magnetic properties of Ms and Hc. The Fe-rich alloys exhibit typical soft magnetic characteristics of simultaneously high Ms and low Hc, as well as high thermal stability of fully amorphous structure or uniform “primary crystalline phase + residual amorphous” structure. All results give a better insight for amorphous and nanocrystalline (FexNiyCoz)80B10Si2Cu1Zr7 alloys to further analyze more efficient magnetic alloys in inductors, transformers, magnetic recording and other magnetic functional materials.