Glass formation ability and isothermal crystallization of melt-spun NdNiCuAl ribbons

On the basis of the previous work on (Nd_62.5Ni_37.5)₈₅Al₁₅ alloy, Cu is selected to partially substitute Ni to form (Nd_62.5Ni_37.5−xCu_x)₈₅Al₁₅ (x = 0, 10, 20, 30) melt-spun alloys. The glass-forming ability (GFA) of the as-prepared alloys is evaluated by the isochronal differential scanning calorimeter (DSC) measurement. The results show that GFA increases with Cu content according to several different criterions. The isothermal crystallization behaviors in the corresponding supercooled liquid region is discussed by both Johnson–Mehl–Avrami (JMA) equation and some nucleation and growth models. The fitting shows that it is reasonable to divide the whole crystallization processes into two stages. And the fittings with the nucleation and growth models infers that with increasing Cu content, the nucleation mechanism of the primary stage changes from the quenched-in and steady-state nucleation for (Nd_62.5Ni_37.5)₈₅Al₁₅, to the steady-state nucleation for (Nd_62.5Ni_27.5Cu₁₀)₈₅Al₁₅ and (Nd_62.5Ni_17.5Cu₂₀)₈₅Al₁₅, then to the time-dependent nucleation for (Nd_62.5Ni_7.5Cu₃₀)₈₅Al₁₅. And the dependence of crystallization mechanisms on Cu substitution agrees well with the change of their GFAs.     

Effects of Mn addition on the magnetic property and corrosion resistance of bulk amorphous steels

We aim to obtain bulk amorphous steels (BASs) with low magnetic permeability and high corrosion resistance by designing the compositions of (Fe₄₄Cr₁₀Mo_12.5Mn₁₁C₁₅B₆Y_1.5)_100−xMn_x (x = 0, 2, 4, 8). The vibrating sample magnetometer (VSM) tests show that the magnetization of the BASs exhibits linear relationship to applied magnetic field, indicating the BASs are paramagnetic at room temperature. It is measured that by increasing Mn content from x = 0 to 8, the magnetic permeability can be decreased from 1.0036 to 1.0025. The potentiodynamic polarization experiments show that the BASs have a high corrosion resistance in 3.5% NaCl and 1.0 mol/L HCl solutions. Increasing Mn content can improve corrosion resistance of the BASs in 1.0 mol/L HCl solution to a large degree, while it does not take much effect in 3.5% NaCl solution.     

Microstructure evolution and thermal stability of an Fe-based amorphous alloy powder and thermally sprayed coatings

High velocity oxy-fuel (HVOF) thermal spraying has been used to produce coatings of an Fe–18.9%Cr–16.1%B–4.0%C–2.8%Si–2.4%Mo–1.9%Mn–1.7%W (in at.%) alloy from a commercially available powder (Nanosteel SHS7170). X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were employed to investigate the powder, as-sprayed coatings and annealed coatings which had been heated to temperatures in the range of 550–925 °C for times ranging from 60 to 3900 min. Microhardness changes of the coatings were also measured as a function of annealing time and temperature. The powder was found to comprise amorphous and crystalline particles; the former had a maximum diameter of around 22 μm. The coating was composed of splat like regions, arising from rapid solidification of fully molten powder, and near-spherical regions from partially melted powder which had a largely retained its microstructure. The amorphous fraction of the coating was around 50% compared with 18% for the powder. The enthalpies and activation energies for crystallization of the amorphous phase were determined. Crystallization occurred in a two stage process leading to the formation of α-Fe (bcc), Fe_1.1Cr_0.9B_0.9 and M₂₃C₆ phases. DSC measurements showed that the first stage occurred at 650 °C. Annealing the coating gave a hardening response which depended on temperature and time. The as-sprayed coating had a hardness of 9.2 GPa and peak hardnesses of 12.5 and 11.8 GPa were obtained at 650 and 750 °C, respectively. With longer annealing times hardness decreased rapidly from the peak.     

Boron content dependence of crystallization, glass forming ability and magnetic properties in amorphous Fe-Zr-B-Nb alloys

The glass forming ability (GFA) was investigated in Fe_91−xZr₅B_xNb₄ alloys with B contents of 0–36 at.%. The GFA changes with B content, and fully amorphous alloys were prepared by melt spinning for B contents between 5 and 30 at.%. The amorphous alloys crystallize with a primary crystallization mode in the low B content range of 5≤x≤20 at.%, but in the eutectic mode in the high B content range of 20<x<30 at.%. A single new metastable Fe-Zr-B-Nb cubic phase with a lattice constant of 1.0704 nm, a saturation magnetization of 137 emu/g and a coercivity of 7.3 Oe at room temperature is formed when crystallizing in a polymorphous mode at x=30 at.%. The glass transition temperature (T_g), crystallization temperature (T_x), Curie temperature (T_c) and saturation magnetizations (M_s) of the amorphous alloys increase with increasing B content, but the coercivity (H_c) decreases. As the B content exceeds 20 at.%, not only increase the T_g, T_x and GFA sharply, due to the change of crystallization mode, but also the concentration dependence of the T_c and M_s changes. It is concluded that the amorphous alloys have better GFA, thermal stability and soft magnetic properties for the high B contents of 25–30 at.% than for the low B contents of 5–20 at.%.     

Microstructure and properties of cold consolidated amorphous ribbons from (NiCu)ZrTiAlSi alloys

Amorphous ribbons of compositions (Ni₅₆Cu₂)Zr₁₈Ti₁₃Al₆Si₅ and (Ni₃₆Cu₂₃)Zr₁₈Ti₁₄Al₅Si₄ were consolidated by high pressure torsion (HPT) at room temperature. In the HPT experiments a 6 GPa pressure and two turns were applied. Samples in the form of discs, 6–7 times thicker than the ribbons and about 10 mm in diameter were achieved. The minimal deformation for the homogenous consolidation was estimated to be in the range of 400%. XRD showed that the microstructure was dependent on the composition. The sample with high Cu content remained amorphous while the sample with low Cu content revealed some crystallization. DSC experiments allowed a comparison of the glass transition temperature T_g and crystallization process of the amorphous ribbon and HPT sample which were different. The glass transition temperature T_g of the amorphous HPT sample of (Ni₃₆Cu₂₃)Zr₁₈Ti₁₄Al₅Si₄ composition decreased. For both alloys the nanohardness and the elastic modules showed decrease for cold consolidated samples in comparison to the ribbons.     

Preparation and magnetic properties of amorphous Co–Zr–B alloy nano-powders

The magnetic Co–Zr–B amorphous alloy powders, having a nearly spherical morphology with diameters <50 nm, were obtained successfully by the reduction of an aqueous solution of zirconium sulphate and cobalt chloride with an aqueous solution of sodium borohydride. XRD, selected-area electron diffraction (SAED) and differential scanning calorimetry (DSC) studies showed that the resultant were partially amorphous together with a tiny volume fraction of crystalline phases, and the main amorphous phase consisted of the Zr-based amorphous particles and the Co-based Zr-containing amorphous particles. It is found that the Co/Zr ratio in the powders was indistinguishably equal to the Co²⁺/Zr⁴⁺ ratio in the original mixed solution and the boron content of the samples increased along with the addition rate of NaBH₄ solution. The crystallization temperatures of the resultant powders were in the range of 765.1–771.3 K. The thermal stability of amorphous Co–Zr–B powder increased with increasing the zirconium content. When the Co/Zr ratio in the samples increased from 1.94 to 5.14, the saturation magnetization increased monotonously from 4.76 to 8.87 emu/g, but the coercivity increased irregularly from 15.98 to 26.81 Oe.     

Oxidation behavior of amorphous and nanoquasicrystalline Zr–Pd and Zr–Pt alloys

Oxidation behavior of amorphous and nanoquasicrystalline Zr₇₀Pd₃₀ and Zr₈₀Pt₂₀ alloys melt-spun at different wheel speeds has been studied in air by non-isothermal and isothermal techniques. Oxidation resistance of amorphous alloys has been found to be the lowest in comparison to the partially and fully crystallized Zr alloys. It has also been observed that oxidation does not induce crystallization of the amorphous phase. It has been shown that the oxygen diffusion rate increases gradually in the order of crystalline, nanoquasicrystalline, partially nanocrystalline and amorphous states of these alloys. Possible micromechanism of oxidation and the role of different grain/interface boundaries on the oxygen diffusion has been discussed.     

Hydrogen solution properties in a series of amorphous Zr–Hf–Ni alloys at elevated temperatures

Amorphous alloys are anticipated as new membrane materials for high purity hydrogen production, as substitutes for expensive palladium alloys. For amorphous Zr–Ni-based alloys reported to date, hydrogen permeability increases with Zr content. Hydrogen solution properties in a series of amorphous Zr–Hf–Ni ternary alloys were measured carefully using the Sieverts method and residual hydrogen measurements to investigate the reason. Results indicate that hydrogen solubility in the ternary alloys increases with increasing Zr to improve hydrogen permeability, not because of the geometrical atomic structure but because of higher hydrogen affinity of Zr than that of Hf. Increased permeability with Zr in other amorphous Zr–Ni-based alloys is also expected to be attributable to the same reason. Additionally, hydrogen was found with low mobility, and was not removable even after 10 h evacuation at 573 K; the importance of decreasing low mobility hydrogen as a countermeasure against hydrogen embrittlement was pointed out. Equilibrium hydrogen concentration was found not to obey Sieverts’ law with respect to hydrogen pressure. Rather, it was linear roughly to the quarter power. Parameters to reproduce pressure–composition isotherms were determined using Kirchheim's theory.     

Formation and thermal stability of new Zr–Cu-based bulk glassy alloys with unusual glass-forming ability

The simultaneous addition of Al and Ag to Zr–Cu binary alloys increased in the stabilization of supercooled liquid, the reduced glass transition temperature and γ value, leading to greatly enhance the glass-forming ability (GFA). The Zr–Cu–Ag–Al glassy alloy samples with diameters above 15 mm were obtained in the wide composition range of 42–50 at% Zr, 32–42 at% Cu, 5–10 at% Ag, and 5–12 at% Al. The best GFA was obtained for Zr₄₈Cu₃₆Ag₈Al₈ alloy, and the glassy samples with diameters up to 25 mm were fabricated by an injection copper mold casting. The Zr₄₈Cu₃₆Ag₈Al₈ glassy alloy exhibited high tensile and compressive fracture strength of over 1800 MPa.     

The effect of Hf substitution for Zr on glass forming ability and magnetic property of FeCoZrMoBAlY bulk metallic glasses

Bulk metallic glasses (BMGs) Fe₆₁Co₆Zr_8−xHf_xMo₇B₁₅Al₁Y₂ (x = 0–8) have been produced by copper mold casting technique using industrial raw materials. The effect of substitution of Hf for Zr on the glass forming ability (GFA) and the magnetic property has been studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and superconducting quantum interference device (SQUID). It was found that the substitution of an appropriate amount of Hf for Zr can improve the GFA of the base alloy Fe₆₁Co₆Zr₈Mo₇B₁₅Al₁Y₂, as demonstrated by the increase in reduced glass transition temperature T_rg (=T_g/T_l) and GFA parameters of γ (=T_x/T_g + T_l) and δ (=T_x/T_l − T_g). The Fe₆₁Co₆Zr₅Hf₃Mo₇B₁₅Al₁Y₂ alloy exhibits the highest GFA with the largest T_rg (0.612) and δ (1.633), and can cast a fully amorphous rod in 3 mm diameter. The substitution of Hf for Zr also enhances the magnetic properties, as verified by the increase in saturation magnetization (M_s) in the alloy of Fe₆₁Co₆Zr₃Hf₅Mo₇B₁₅Al₁Y₂, whose M_s is approximately 1.5 times higher than that of the base alloy (x = 0) at room temperature. Finally, the effect of the substitution of Hf for Zr on glass forming ability and magnetic properties is discussed.     

Structural, microstructural and magnetic properties of amorphous/nanocrystalline Ni63Fe13Mo4Nb20 powders prepared by mechanical alloying

This paper focuses on the magnetic, structural and microstructural studies of amorphous/nanocrystalline Ni₆₃Fe₁₃Mo₄Nb₂₀ powders prepared by mechanical alloying. The ball-milling of Ni, Fe, Mo and Nb powders leads to alloying the element powders, the nanocrystalline and an amorphization matrix with Mo element up to 120 h followed by the strain and thermal-induced nucleation of a single nanocrystalline Ni-based phase from the amorphous matrix at 190 h. The results showed that the saturation magnetization decreases as a result of the electronic interactions between magnetic and non-magnetic elements and finally increases by the partial crystallization of the amorphous matrix. The coercive force increases as the milling time increases and finally decreases due to sub-grains formation.     

Thermal stability, microstructure and crystallization kinetics of melt-spun Zr-Ti-Cu-Ni metallic glass

Melt-spun Zr_63.33Ti_8.89Cu_15.45Ni_12.33 glassy ribbons display a double-step devitrification behavior characterized by the precipitation of a metastable quasicrystalline phase in the first stage of the crystallization process, followed by the formation of crystalline phases in the following crystallization event. Investigation of the crystallization kinetics reveal that the initial part of the glass-to-quasicrystalline transformation (x ≤ 55 vol.%) occurs by diffusion controlled growth with an increasing nucleation rate (Avrami exponent n ≥ 2.5), whereas the later stage of the transformation (x > 55 vol.%) is dominated by the growth of the formed nuclei rather than by the generation of new nuclei (2.0 ≤ n ≤ 2.5). The activation energy for quasicrystallization is 360 kJ/mol, which is comparable to the values reported for other quasicrystal-forming Zr-based metallic glasses.     

Thermal stability and primary phase of Al–Ni(Cu)–La amorphous alloys

Thermal stability and primary phase of Al_85+xNi_9−xLa₆ (x = 0–6) and Al₈₅Ni_9−xCu_xLa₆ (x = 0–9) amorphous alloys were investigated by X-ray diffraction and differential scanning calorimeter. It is revealed that replacing Ni in the Al₈₅Ni₉La₆ alloy by Cu decreases the thermal stability and makes the primary phase change from intermetallic compounds to single fcc-Al as the Cu content reaches and exceeds 4 at.%. When the Ni and La contents are fixed, replacing Al by Cu increases the thermal stability but also promotes the precipitation of single fcc-Al as the primary phase.     

Microstructural, thermal and magnetic properties of amorphous/nanocrystalline FeCrMnN alloys prepared by mechanical alloying and subsequent heat treatment

Amorphous FeCrMnN alloys were synthesized by mechanical alloying (MA) of the elemental powder mixtures under a nitrogen gas atmosphere. The phase identification and structural properties, morphological evolution, thermal behavior and magnetic properties of the mechanically alloyed powders were evaluated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM), respectively. According to the results, at the low milling times the structure consists of the nanocrystalline ferrite and austenite phases. By progression of the MA process, the quantity and homogeneity of the amorphous phase increase. At sufficiently high milling times (>120 h), the XRD pattern becomes halo, indicating complete amorphization. The results also show that the amorphous powders exhibit a wide supercooled liquid region. The crystallization of the amorphous phase occurs during the heating cycle in the DSC equipment and the amorphous phase is transformed into the crystalline compounds containing ferrite, CrN and Cr₂N. The magnetic studies reveal that the magnetic coercivity increases and then decreases. Also, the saturation magnetization decreases with the milling time and after the completion of the amorphization process (>120 h), the material shows a paramagnetic behavior. Although the magnetic behavior does not considerably change by heating the amorphous powders up to the crystallization temperature via DSC equipment, the material depicts a considerable saturation magnetization after the transformation of the amorphous phase to the nanocrystalline compounds.     

Characterization of crystallization kinetics of a Ni- (Cr, Fe, Si, B, C, P) based amorphous brazing alloy by non-isothermal differential scanning calorimetry

The thermal stability and crystallization kinetics of a Ni- (Cr, Si, Fe, B, C, P) based amorphous brazing foil have been investigated by non-isothermal differential scanning calorimetry. The glass transition temperature T_g, is found to be 720 ± 2 K. The amorphous alloy showed three distinct, yet considerably overlapping crystallization transformations with peak crystallization temperatures centered around 739, 778 and 853 ± 2 K, respectively. The solidus and liquidus temperatures are estimated to be 1250 and 1300 ± 2 K, respectively. The apparent activation energies for the three crystallization reactions have been determined using model free isoconversional methods. The typical values for the three crystallization reactions are: 334, 433 and 468 kJ mol⁻¹, respectively. The X-ray diffraction of the crystallized foil revealed the presence of following compounds Ni₃B (Ni₄B₃), CrB, B₂Fe₁₅Si₃, CrSi₂, and Ni_4.5Si₂B.     

The role of tensides in the covering, formation and power loss properties of amorphous metallic ribbons by glassy coatings

Tensides are surface active substances which play an essential role in the formation of glassy coatings from aqueous solutions of H₃BO₃, H₃PO₄ and their salts. Firstly, they ensure the wettability of the hydrophobic metallic ribbon at the phase boundary in very low concentrations and, in addition, they adjust both specifically and effectively the reaction conditions between the depositing solution and the surface of the amorphous metallic ribbon. They penetrate into the interlayer of the ribbon changing its physico-chemical properties and in this way influence its magnetic characteristics. This paper deals with the effect of commercially produced non-ionic tensides (Slovanik NT, Slovasol EL, Slovasol O) and an anionic tenside (Slovafos 3) in the process of the formation of glassy coatings vs. power loss for amorphous Fe₈₂Si₆B₁₂, Fe₄₀Ni₄₀B₂₀ and Co₇₀Fe₅Si₇B₁₈ ribbons. The influence of different amounts of tensides in borate and phosphate deposition solutions and of heat treatment of these solutions on power loss is discussed.     

Microstructures and mechanical behaviors of Mg58Cu31Gd11 and Mg65Cu25Gd10 amorphous alloys synthesized by injection casting and melt spinning

Mg₅₈Cu₃₁Gd₁₁ and Mg₆₅Cu₂₅Gd₁₀ alloys were synthesized via two processing routes, injection casting and melt spinning. The diameter of the injection-cast bars was 4 mm in diameter. The XRD results obtained for the Mg₅₈Cu₃₁Gd₁₁ are nearly identical to those for the Mg₆₅Cu₂₅Gd₁₀, showing amorphous-like broad characteristic peaks. All the four characteristic temperatures, T_g, T_x, T_m and T_l, of the Mg₆₅Cu₂₅Gd₁₀ are essentially lower than those of Mg₅₈Cu₃₁Gd₁₁, for both injection-cast rods and melt-spun ribbons. The glass forming abilities of the Mg₆₅Cu₂₅Gd₁₀ are similar to those of Mg₅₈Cu₃₁Gd₁₁, for both injection-cast rods and melt-spun ribbons, indicated by T_rg = 0.60 and γ = 0.42. The average microhardness of the Mg₆₅Cu₂₅Gd₁₀ is 2.41 GPa and 2.27 GPa for injection-cast bars and melt-spun ribbons, respectively, which are significantly lower than 2.84 GPa and 2.49 GPa of the Mg₅₈Cu₃₁Gd₁₁. The nanohardness at the maximum load from the multiple loading is 3.5 GPa for Mg₆₅Cu₂₅Gd₁₀, which is lower than 3.9 GPa for Mg₅₈Cu₃₁Gd₁₁. The curves of load vs. the depth obtained from the nanoindentation tests all show stepwise behavior due to the pop-in events, and the step width increases as the indentation rate decreases. The modulus at the maximum load from the multiple loading obtained from the nanoindentation tests is 64.9 GPa for Mg₆₅Cu₂₅Gd₁₀, which is lower than 70.7 GPa for Mg₅₈Cu₃₁Gd₁₁. The fracture stress and strain of the Mg₆₅Cu₂₅Gd₁₀ BMG rod at room temperature are 490 MPa and 3%, respectively, smaller than those of the Mg₅₈Cu₃₁Gd₁₁ BMG rod, 548 MPa and 3.2%, respectively. The Mg₅₈Cu₃₁Gd₁₁ BMG rod is stronger at room temperature, and also shows higher yield stress and less deformable at elevated temperature, than the Mg₆₅Cu₂₅Gd₁₀ BMG rod.     

Wear and thermal properties of Zr-based amorphous surface alloyed materials fabricated by high-energy electron beam irradiation

Zr-based amorphous surface alloyed materials were fabricated by high-energy electron beam irradiation in this study. A mixture of Zr-based amorphous powders and LiF + MgF₂ flux was deposited on a pure copper substrate, and then an electron beam was directed on this powder mixture to fabricate a one-layered surface alloyed material. A two-layered surface alloyed material was also fabricated by irradiating electron beam again onto the powder mixture deposited on the one-layered surface alloyed material. The microstructural analysis results indicated that a number of coarse crystalline phase particles were formed in the one-layered surface alloyed layer, whereas a small amount of fine and hard crystalline particles were homogeneously distributed in the amorphous matrix of the two-layered surface alloyed layer. Owing to these fine and hard crystalline particles, the hardness and wear resistance of the two-layered surface alloyed layer improved over the one-layered surface alloyed layer or other kinds of surface alloyed layers. The thermal conductivity of the two-layered surface alloyed layer was much lower than that of titanium-alloy-based or stainless-steel-based surface alloyed layers. These findings suggested the possibility of applying Zr-based amorphous surface alloyed materials to high wear-resistant thermal barrier coatings or parts.