Influence of Melt-Spinning Parameters on the Structure and Soft Magnetic Properties of (Fe0.65Co0.35)88Zr7B4Cu1 Alloy

Melt-spun ribbons of (Fe_0.65Co_0.35)₈₈Zr₇B₄Cu₁ alloy have been prepared at different wheel speeds, namely, 47, 39, 34, and 17 m/s, and subsequently annealed at 773 K (500 °C) under controlled atmosphere. Structural and soft magnetic properties have been evaluated using X-ray diffraction, differential scanning calorimetry, transmission electron microscopy, and vibrating sample magnetometer. The structure of as-spun ribbons changes from fully amorphous to partially amorphous/nanocrystalline to fully nanocrystalline (bcc α-Fe(Co) + Fe₂Zr) on decreasing the wheel speed. Annealing of amorphous ribbons leads to the precipitation of nanocrystalline bcc α-Fe(Co) phase. The Curie temperature (T _c ) of the amorphous phase is found to increase with decreasing wheel speed possibly due to the effect of exchange field penetration of nanocrystals present in the amorphous matrix. The saturation magnetization (4πM _s ) of as-spun ribbons having partially nanocrystalline bcc α-Fe(Co) phase is high as compared to the ribbons with completely amorphous phase, and it remains almost the same even after annealing. The lowest coercivity has been achieved in the ribbons that are fully amorphous, and the coercivity was found to increase with decreasing wheel speed.     

A Study on Synthesis, Crystallization, and Magnetic Behavior of Nanocrystalline Fe-Based Metallic Glasses

In the present work, structure of the as-cast melt-spun ribbons, nonisothermal crystallization kinetics, and the effect of heat treatment on the magnetic properties have been studied. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses have revealed the presence of amorphous and partly crystalline structures in the as-cast Fe₆₇Co₁₈Si₁B₁₄ and Fe₅₇Co₂₆Cr₃B₁₄C_0.2 metallic-glass ribbons, respectively. The crystalline phase present in the as-cast Fe₅₇Co₂₆Cr₃B₁₄C_0.2 metallic-glass was identified as α-Fe. Direct transformation from liquid to α-Fe has been analyzed from a thermodynamic and kinetics point of view. The differential scanning calorimetry (DSC) studies have shown two-stage crystallization behavior. The primary and secondary crystallization phases were identified as bcc-Fe(Co) and bct-(Fe,Co)₃(Si,B), respectively. Kissinger and Gao et al. methods were employed for nonisothermal crystallization kinetic studies. The activation-energy values obtained by the two models were in good agreement. The nucleation and growth morphologies of crystalline phases have been explained on the basis of the Avrami exponent, which were found to be consistent with the observed microstructures. The magnetic properties of as-cast amorphous ribbons showed low coercivity, and this has been attributed to averaging of magnetocrystalline anisotropy over grains coupled within an exchange length, i.e., based on a random anisotropy model. The influence of microstructure on magnetic properties was studied by crystallizing the amorphous phase at 400 °C for 3 hours. The saturation magnetization and coercivity had increased after crystallization for both alloys. This article is based on a presentation given in the symposium entitled “Materials Behavior: Far from Equilibrium” as part of the Golden Jubilee Celebration of Bhabha Atomic Research Centre, which occurred December 15–16, 2006 in Mumbai, India.

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Effect of vanadium addition on the microstructure, hardness, and wear resistance of Al0.5CoCrCuFeNi high-entropy alloy

The authors studied the effect of vanadium addition on the microstructure and properties of Al_0.5CoCrCuFeNi high-entropy alloy. The microstructure of Al_0.5CoCrCuFeNiV _x (x=0 to 2.0 in molar ratio) alloys was investigated by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. With little vanadium addition, the alloys are composed of a simple fcc solid-solution structure. As the vanadium content reaches 0.4, a BCC structure appears with spinodal decomposition and envelops the FCC dendrites. From x=0.4 to 1.0, the volume fraction of bcc structure phase increases with the vanadium content increase. When x=1.0, fcc dendrites become completely replaced by bcc dendrites. Needle-like σ-phase forms in bcc spinodal structure and increases from x=0.6 to 1.0 but disappears from x=1.2 to 2.0. The hardness and wear resistance of the alloys were measured and explained with the evolution of the microstructure. The hardness values of the alloys increase when the vanadium content increases from 0.4 to 1.0 and peak (640 HV) at a vanadium content of 1.0. The wear resistance increases by around 20 pct as the content of vanadium increases from x=0.6 to 1.2 and levels off beyond x=1.2. The optimal vanadium addition is between x=1.0 and 1.2. Compared with the previous investigation of Al_0.5CoCrCuFeNi alloy, the vanadium addition to the alloy promotes the alloy properties.     

Phase Formation in Isothermally Annealed (Co0.95Fe0.05)89Zr7B4 Nanocrystalline Alloys

This report focuses on the phase relations and transformations in a (Fe_0.05Co_0.95)₈₉Zr₇B₄ melt-spun alloy with an emphasis on crystallization and its effects on thermomagnetic properties. When as-spun ribbons are annealed at relatively low temperatures (near primary crystallization), the nucleation and growth of nonequilibrium body-centered-cubic (bcc) crystallites occurs in a residual amorphous matrix, as determined by transmission electron microscopy (TEM) and X-ray diffraction (XRD). At intermediate temperatures, bcc crystallites continue to grow with the addition of a small volume fraction of the equilibrium face-centered-cubic (fcc) phase. It is expected that after the bcc nuclei are formed, the grains coarsen as bcc phase and do not transform to the more stable fcc phase at intermediate temperatures. At temperatures where the amorphous matrix phase dissociates into Zr intermetallics, the bcc phase is transformed into fcc and the grains coarsen significantly. Thermodynamic modeling has been used to support the nucleation of the nonequilibrium bcc phase during the early stages of crystallization. Thermomagnetic results show little reduction in the saturation magnetization as a function of annealing temperature up to the primary crystallization temperature (~420 °C). This article is based on a presentation made in the symposium “Phase Transformations in Magnetic Materials” which occurred during the TMS Spring meeting, March 12–16, 2006, in San Antonio, TX under the auspices of the Joint TMS-MPMD and ASMI-MSCTS Phase Transformations Committee.

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Ferromagnetic bulk amorphous alloys

This article reviews our recent results on the development of ferromagnetic bulk amorphous alloys prepared by casting processes. The multicomponent Fe-(Al,Ga)-(P,C,B,Si) alloys are amorphized in the bulk form with diameters up to 2 mm, and the temperature interval of the supercooled liquid region before crystallization is in the range of 50 to 67 K. These bulk amorphous alloys exhibit good soft magnetic properties, i.e., high B _s of 1.1 to 1.2 T, low H _o of 2 to 6 A/m, and high μ _e of about 7000 at 1 kHz. The Nd-Fe-Al and Pr-Fe-Al bulk amorphous alloys are also produced in the diameter range of up to 12 mm by the copper mold casting process and exhibit rather good hard magnetic properties, i.e., B _r of about 0.1 T, high H _o of 300 to 400 kA/m, and rather high (JH)_max of 13 to 20 kJ/m³. The crystallization causes the disappearance of the hard magnetic properties. Furthermore, the melt-spun Nd-Fe-Al and Pr-Fe-Al alloy ribbons exhibit soft-type magnetic properties. Consequently, the hard magnetic properties are concluded to be obtained only for the bulk amorphous alloys. The bulk Nd- and Pr-Fe-Al amorphous alloys have an extremely high T _x/T_m of about 0.90 and a small ΔT _m(=T _m−T _x) of less than 100 K and, hence, their large glass-forming ability is due to the steep increase in viscosity in the supercooled liquid state. The high T _x/T_m enables the development of a fully relaxed, clustered amorphous structure including Nd-Nd and Nd-Fe atomic pairs. It is, therefore, presumed that the hard magnetic properties are due to the development of Nd-Nd and Nd-Fe atomic pairs with large random magnetic anisotropy. The Nd- and Pr-based bulk amorphous alloys can be regarded as a new type of clustered amorphous material, and the control of the clustered amorphous structure is expected to enable the appearance of novel functional properties which cannot be obtained for an ordinary amorphous structure. This article is based on a presentation made in the “Structure and Properties of Bulk Amorphous Alloys” Symposium as part of the 1997 Annual Meeting of TMS at Orlando, Florida, February 10–11, 1997, under the auspices of the TMS-EMPMD/SMD Alloy Phases and MDMD Solidification Committees, the ASM-MSD Thermodynamics and Phase Equilibria, and Atomic Transport Committees, and sponsorship by the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory.     

Ductile and High Strength White Cast Iron of Ultrafine Interconnected Network Morphology

Fe_100–x C _x melts (x = 18 to 24) can be cast under B₂O₃ flux into solids of interconnected network morphology, with a wavelength in the submicron range. There are two major constituent subnetworks, which are a brittle Fe₃C subnetwork and a ductile αFe subnetwork. The Fe_100–x C _x network alloys, therefore, are white cast iron of novel microstructure. Fe_100–x C _x specimens of x = 18 to 21 are ductile and the yield strength can be as large as ~3200 MPa. Fe_100–x C _x specimens of x = 22 to 24 are in the regime of a ductile-to-brittle transition. The compressive strength is high, at ~2700 MPa. Microstructural analysis indicates that the ultrafine network morphology and the ductile αFe subnetwork are responsible for the ductility exhibited in Fe_100–x C _x network alloys of x = 17 to 21. They are also responsible for the high compressive strength in Fe_100–x C _x network alloys of x = 22 to 24.     

Electron microscopy of crystalline and amorphous Ni-P electrodeposited films: In-situ crystallization of an amorphous solid

Electron microscopy has been used to study the structure of Ni-P electrodeposited thin films with 7, 12, 20 and 22 at. pct P. For the crystalline as-deposited films with 7 and 12 at. pct P (low P films), the crystal structure is fcc and the grains are a supersaturated solid solution of P in Ni. Grain size decreases with increasing P content; the present findings agree with previous ones. For “amorphous” as-deposited films with 20 and 22 at. pet P (high P content films) the amorphous phase is not completely homogeneous and there are regions in which small microcrystals exist. Electron beam heating a low P con-tent film causes the crystalline array of supersaturated Ni grains to decompose to an equilibrium mixture of Ni and Ni₃P; both types of grains are randomly oriented. Electron beam heating a high P content film causes the amorphous regions to undergo several complex transformations. The first reaction to occur is: Amorphous (Ni-P) -Ni_xP_y + Ni (random) where Ni_xP_y is a newly discovered phase with a variable composition. Further beam heating causes a second transformation to equilibrium phases: Ni_xP_y + Ni → Ni₃P + Ni (random). The microstructure resulting from the above transformations depends on variations in composition of the as-deposited specimens, rates of heating and temperature gradients. The mode of phase transformation in microcrystalline regions and amorphous regions is distinctly different. Crystallization in amorphous regions occurs by a nucleation and growth of Ni_xP_y, and Ni; a crystallization front is seen to advance into the amorphous re-gion. Crystallization in microcrystalline regions occurs by nucleation and growth of the Ni₃P phase and grain coarsening of the Ni phase. No distinct crystallization front is ob-served.     

Effect of Al82.8Cu17Fe0.2 alloy doping on structure and magnetic properties of SmCo5-based ribbons

This work tries to improve the magnetic properties by multi-element doping in the form of a ternary alloy.SmCo₅₊χwt%Al-Cu-Fe(x=0-7)ribbons melt-spun at 40 m/s were produced by adding Al_82.8Cu₁₇Fe_0.2alloy into SmCo₅ matrix,and their phases,microstructure,and magnetic properties were investigated.The results show that both x=0 and 3 ribbons form a cellular microstructure.Al-Cu-Fe addition reduces the content of the Sm₂(Co,M)₇ cell wall,narrows its width,and forms the local disordered micro-regions and solute-segregation nanoclusters in the Sm(Co,M)₅ grains.With x increasing to5,Al-Cu-Fe addition promotes the phase separation between and within grains of the SmCo₅-based alloy.The Al-Cu-Fe addition can simultaneously improve the coercivity and magnetization of the SmCo₅-based ribbons,in particular,the magnetization of the x=3 ribbons increases by 35%,while the coercivity of the x=5 ribbons increases by 3.9 times.Finally,the microstructure evolution models are built up,and the relationship between the microstructure and the magnetic properties is discussed.     

Titanium-Based Metallic Glass Composites with Good Plasticity

Three types of Ti-based alloys (an amorphous material, an amorphous composite with intermetallic crystals, and an intermetallic compound) of the compositions Ti_41.5Zr_2.5Hf₅Cu_42.5−x Ni_7.5+x Si₁ (x = 0, 5, and 15) were fabricated to study the effect of composition on glass formability and microstructure, and the dependence of mechanical properties on microstructure were investigated at room temperature. The results show that the amorphous composite has an excellent combination of both ultrahigh strength (2245 MPa) and large plastic strain (9 pct), which is a significant improvement compared to both the fully amorphous and intermetallic structures. In addition, it is also found that the crystal phases in the amorphous matrix can obstruct the shearing-off of the shear bands by inducing them to interact, deflect, and branch, resulting good plasticity in the amorphous composite. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Investigation of Structure and Magnetic Properties of Rare Earth-Leaned Pr2(Fe,Co)14(C,B)-Type Nanocomposites

The phase evolution and magnetic properties of Pr_xFe_82-x-yTi_yCo₁₀B₄C₄ (x=9–10.5; y=0, 2) melt-spun ribbons have been investigated. The effects of wheel speed and annealing on the crystallization and magnetic properties of the ribbons were emphatically discussed. It was found that Ti substitution enhances the glass forming ability of the Pr₂(Fe,Co)₁₄(C,B)-type ribbons. For the high wheel speed V_s (18 m/s), the Ti-substitution ribbons consist of significant amorphous phase, and show a typical two-step magnetic behavior, while most of Ti-free ribbons are mainly composed of the crystallized 2:14:1, α-(Fe, Co) and 2:17 phases. With decrease in wheel speed, all these composition of ribbons are crystallized, and more magnetically hard 2:14:1 phase is formed in the ribbons. The content of metastable 2:17 phase in the ribbons decreases with increasing Pr and Ti substitution. A B_r of 9.5 kG, _iH_c of 9.8 kOe, and (BH)_max of 16.0 MGOe were obtained in the as-spun Ti-substitution Pr_10.5Fe_69.5Ti₂Co₁₀B₄C4 ribbon prepared at V_s=15 m/s. For all the as-spun Ti-free ribbons prepared at different wheel speed V_s, the (BH)_max is lower than 10 MGOe owing to poor demagnetization-curve shape. Ti substitution also helps suppressing the grain growth of 2:17 phase during annealing process, and simultaneously, gently promoting the growth of magnetically hard 2:14:1 phase. Annealing treatment significantly improves the magnetic properties of the Ti-substitution ribbons with higher Pr content. No obvious promotion of magnetic properties was found in the Ti-free ribbons after annealing.     

[(Fe<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>)<Subscript>0.75</Subscript>B<Subscript>0.20</Subscript>Si<Subscript>0.05</Subscript>]<Subscript>96</Subscript>Nb<Subscript>4</Subscript> Metallic Glasses with Small Cu Additions

Recently, (Fe-Co)-B-Si-Nb bulk metallic glasses (BMGs) were produced. Such BMGs exhibit high glass-forming ability (GFA) as well as good mechanical and magnetic properties. These alloys combine the advantages of functional and structural materials. The soft magnetic properties can be enhanced by nanocrystallization. To force the nanocrystallization, small content of Cu was added to the starting composition. In this article, {[(Fe_0.5Co_0.5)_0.75Si_0.05B_0.20]_0.96Nb_0.04}_100–x Cu _x glassy alloys (x = 1, 2, and 3) were chosen for investigation. The GFA and the thermal stability of these alloys were evaluated. The effects of crystallization during heat-treatment processes on the phase evolution and the magnetic properties, including M _s , H _c , and T _c , in these alloys were investigated. The phase analyses were done with the help of the X-ray diffraction patterns recorded in situ by using the synchrotron radiation in transmission configuration.     

Magnetic properties of melt-spun ribbons(Sm_(1-x)Zr_x)(Fe_(0.92)Ti_(0.08))_(10) with ThMn_(12) structure and their hydrides

The structure and magnetic hysteresis properties of the cast Sm_(1-x)Zr_x(Fe_(0.92)Ti_(0.08))_(10)(x = 0-0.3)alloys and melt-spun ribbons prepared from them were studied.In the cast alloy with x0.2, a considerable amount of the eutectic phase is found in the SEM micrographs.Analysis of the temperature dependences of the magnetic susceptibility and XRD patterns allows amorphous state in the as-spun ribbons with x0.2 to be determined.The specific magnetization measured in a field of 17 kOe and remanence decrease with increasing annealing temperature from 800 to 900 ℃ and weakly depend on Zr concentration.The maximal value of coercivity Hc = 4.7 kOe is obtained on the ribbons with x = 0.2 after annealing at 850℃ for 10 min.After additional hydrogenation of the ribbons,both the coercivity and remanence increase by 54% and 7%,respectively.     

A thermodynamic analysis of the phase equilibria of the Fe-Ni system above 1200 K

A quasi-subregular solution model is used to describe the thermodynamic properties of the liquid phase; values of the solution parameters are obtained from extensive and consistent thermochemical data reported in the literature. For the fcc and bcc phases, the same model is used to account for the nonmagnetic part of the Gibbs energy and the magnetic contribution is taken from the previous paper. Again, the values for the quasi-subregular solution parameters for the fcc phase are obtained from extensive and consistent thermochemical data reported in the literature at high temperatures. The values of the solution parameters for the bcc phase are obtained from the thermodynamic values of the liquid and fcc phases and the known phase boundary data. The calculated phase equilibria are in good agreement with the available data. Based on the thermodynamic data, the metastablel + γ andl + δ phase boundaries as well as theT ₀ (γ + l) andT ₀(δ +l) curves are calculated.     

An analytical electron microscopy study of constituent particles in commercial 7075-T6 and 2024-T3 alloys

To better understand the role of constituent particles in pitting corrosion, analytical electron microscopic studies were performed on the constituent particles in commercial 7075-T6 and 2024-T3 alloys. Five phases, namely, Al₂₃CuFe₄ and amorphous SiO₂ in 7075-T6 and Al₂CuMg, Al₂Cu, and (Fe,Mn) _x Si(Al,Cu) _y in 2024-T3, were identified. The crystal structure and chemistry of the Al₂₃CuFe₄, Al₂CuMg, and Al₂Cu phases in these alloys are in good agreement with the published data. Small deviations from their stoichiometric compositions were observed and are attributed to the influence of alloy composition on the phase chemistry. For the (Fe,Mn) _x Si(Al,Cu) _y (approximately, x=3 and y=11) phase, a rhombohedral structure, with lattice parameter a=b=c=1.598 nm and α=β=γ=75 deg, was identified and is believed to be a modified form of either Al₈Fe₂Si or Al₁₀Mn₃Si. Information from this study provided technical support for studying the electrochemical interactions between the individual particles (or phases) and the matrix. The corrosion results are reported in a companion article.     

Thermodynamics of the solid phases in the system Fe−Mn−C

Phase relationships in the Fe−Mn−C system in the temperature range 600 to 1100°C have been studied using metallographic and X-ray methods and the electron microprobe. Isothermal sections of the phase diagram of the system are reported based on the present results and those of earlier investigators. The fcc λ-phase (austenite) containing carbon is stable at all values ofy _Mn=x _Mn/(x _Mn+x _Fe) in the range 890 to 1100°C and in a more restricted composition range at lower temperatures. Its composition under conditions of equilibrium with the carbides (Fe, Mn)₃C, (Fe, Mn)₂₃C₆, ε, and liquid are shown for several temperatures. The free energy of formation of the cementite phase, (Fe, Mn)₃C, at 1000°C, from γ-Fe, γ-Mn (undercooled) and graphite is ΔG ₁₂₇₃=−35,790y _Mn−2760y _Fe+3RT (y _Mn lny _Mn+y _Fe lny _Fe). The data show that the alloyed cementite is essentially and ideal mixture of Fe₃C and Mn₃C,i.e., the metal atoms are distributed at random on the metal sites in the lattice. ROBERT BENZ, formerly of the Research Staff, Massachusetts Institute of Technology, Cambridge, Massachusetts