Crystallization behavior,mechanical properties,and corrosion resistance of an amorphous Fe<Subscript>76.5</Subscript>P<Subscript>13.6</Subscript>Si<Subscript>4.8</Subscript>Mn<Subscript>2.4</Subscript>V<Subscript>0.2</Subscript>C<Subscript>2.5</Subscript> alloy

We have studied the mechanical properties and corrosion resistance of an amorphous Fe_76.5P_13.6Si_4.8Mn_2.4V_0.2C_2.5 alloy and their response to nanocrystallization as a result of brief lamp processing and heat treatment. The results demonstrate that the lamp processing time needed to obtain a given phase composition through partial crystallization of the amorphous alloy is two orders of magnitude shorter than the corresponding heat treatment time. We have found lamp processing conditions that ensure the formation of an amorphous–nanocrystalline composite with a twofold increase in hardness, without loss of plasticity. It has been shown that, with increasing loading rate during nanoindentation, the hardness of the alloy decreases because of the increase in plasticity, which shows up as the formation of a larger number of shear bands. Under uniaxial tension, the material exhibits microplasticity, which may be due to intercluster sliding, with the amorphous structure retained. The corrosion resistance of the as-prepared amorphous alloy in a medium contaminated with sulfur dioxide exceeds that of the partially crystallized alloys.     

Microstructure of laser-induced combustion synthesis of Cu<Subscript>59.6</Subscript>Zr<Subscript>36.9</Subscript>Al<Subscript>3.5</Subscript> alloy

Cu_59.6Zr_36.9Al_3.5 alloy are prepared by laser-induced combustion synthesis technology. The microstructure and phases formed of the product is studied by XRD and TEM. The product consists of mixtures of amorphous and crystalline phases, mainly(α-Zr, Zr₂Cu, Zr₁₀Cu₇ and Cu₈Zr₃. The amorphous and nanocrystalline phases content over 50% in volume estimated from the broad peak in the XRD spectrum. TEM and HRTEM results show that the microstructure is characterized by inhomogeneously distributed amorphous, nano Zr₂Cu, relatively gross (∼100 nm) Zr₂Cu, and large grain Cu₁₀Zr₇.     

Laser multi-layer cladding of Zr<Subscript>65</Subscript>Al<Subscript>7.5</Subscript>Ni<Subscript>10</Subscript>Cu<Subscript>17.5</Subscript> amorphous alloy on magnesium substrates

A coating about 3-mm thick of the amorphous alloy, Zr₆₅Al_7.5Ni₁₀Cu_17.5 was fabricated on magnesium substrates using the technique of laser multi-layer cladding protected under an atmosphere of argon gas. The coating exhibited a graded microstructure, which could be generally categorized into three classes: an amorphous phase, an amorphous–nanocrystalline composite, and one which is predominantly crystalline. Formation of the latter two was due to the reheating effect of the laser cladding process. With regard to properties, the microhardness and the wear resistance of the composite material were both higher than that of the monolithic amorphous material; both materials showed excellent corrosion resistance in a 3.5% NaCl solution.     

Metastable phases in the Ni<Subscript>75</Subscript>Nb<Subscript>12</Subscript>B<Subscript>13</Subscript> alloy prepared under nonequilibrium conditions

The structure of Ni₇₅Nb₁₂B₁₃ alloys prepared by liquid quenching (LQ) and mechanical alloying (MA) has been studied by x-ray diffraction. The alloy prepared by LQ at a cooling rate of ～10⁶ K/s is shown to be fully amorphous, while MA yields an amorphous-crystalline material in which the predominant phase is an fcc Ni〈Nb,B〉 solid solution. The thermal stability of the alloys and their structural transformations on heating have been studied by differential scanning calorimetry. The amorphous phase obtained by LQ is shown to crystallize at 490°C. After heating to 720°C, the alloy consists of two equilibrium phases: Ni₂₁Nb₂B₆ (τ) and Ni₅Nb₃B₂ (z). Heating the MA alloy to 720°C leads to the formation of a stable τ-phase, while the Ni-based fcc solid solution remains supersaturated and, hence, metastable. Increasing the milling time leads to the formation of nanocrystalline τ and Ni₃B phases, in addition to the Ni-based fcc solid solution, which corresponds to the equilibrium phase composition of the Ni₇₅Nb₁₂B₁₃ alloy in the Ni-Nb-B phase diagram. The effect of high-energy milling on the phase composition of the alloy is similar to that of heat treatment.     

Inverted surface hysteresis loops in heterogeneous (nanocrystalline/amorphous) Fe<Subscript>81</Subscript>Nb<Subscript>7</Subscript>B<Subscript>12</Subscript> alloys

Inverted hysteresis loops were observed for the first time in the near-surface layers of heterogeneous (nanocrystalline/amorphous) Fe₈₁Nb₇B₁₂ alloys. In particular, a negative residual magnetization is retained when a positive magnetic field applied in the sample plane is decreased to zero. The inverted hysteresis is qualitatively explained within the framework of a two-phase model, according to which the heterogeneous alloys contain two dissimilar phases exhibiting uniaxial magnetic anisotropy and featuring antiferromagnetic exchange interaction.     

Fe<Subscript>73.5</Subscript>Cu<Subscript>1</Subscript>Nb<Subscript>3</Subscript>Si<Subscript>15.5</Subscript>B<Subscript>7</Subscript> Thin Films Deposited by HiPIMS: Magnetic and Magnetostrictive Behavior

Results concerning the magnetic, magnetostrictive, structural, morphological, and topological properties of amorphous and nanocrystalline Fe _73.5Cu ₁Nb ₃Si _15.5 B ₇ thin films deposited using the high power impulse magnetron sputtering (HiPIMS) technique are reported. In as-deposited state, the samples are amorphous, the nanocrystalline state being achieved for samples isothermally annealed at adequate temperatures, in an electric furnace. For the optimum annealing temperature (475 ^°C), a decrease by about 70 % for the coercive magnetic field (50 A/m) and up to 1 order of magnitude for the saturation magnetostriction (~1×10^?6), compared to the as-deposited state, was obtained. The X-ray diffractometry (XRD) and scanning electron microscopy (SEM) results for samples thermally treated at 475 ^°C revealed a 53.6 % crystalline volume fraction of α-Fe(Si) nanograins with an average size of about 15 nm and a Si content of 10.78 %, uniformly dispersed in a residual amorphous matrix. Using the saturation magnetostriction values determined using the cantilever deflection method and the crystalline volume fraction of α-Fe(Si) nanograins, the contribution of crystalline phase to the saturation magnetostriction was also determined.     

Crystallization behaviour and mechanical properties of rapidly solidified Al<Subscript>87.5</Subscript>Ni<Subscript>7</Subscript>Mm<Subscript>5</Subscript>Fe<Subscript>0.5</Subscript> amorphous alloy

The crystallization behaviour and the mechanical properties of rapidly solidified Al_87.5Ni₇Mm₅Fe_0.5 alloy ribbons have been examined in both as-melt-spun and heat-treated condition using differential scanning calorimetry, X-ray diffractometry (XRD), transmission electron microscopy (TEM), tensile testing and Vicker’s microhardness machine. XRD and TEM studies revealed that the as-melt-spun ribbons are fully amorphous. The amorphous ribbon undergoes three-stage crystallization process upon heating. Primary crystallization resulted in the formation of fine nanocrystalline fcc-Al particles embedded in the amorphous matrix. The second and third crystallization stages correspond to the precipitation of Al₁₁(La,Ce)₃ and Al₃Ni phases, respectively. Microhardness and tensile strength of the ribbons were examined with the variation of temperature and subsequently correlated with the evolved structure. Initially, the microhardness of the ribbon increases with temperature followed by a sharp drop in hardness owing to the decomposition of amorphous matrix that leads to formation of intermetallic compounds     

Co,Ni-base alloy thin films deposited by r.f. magnetron sputtering in Ar/N<Subscript>2</Subscript> atmosphere

Phase composition and microstructure of CoNiCrAlY thin films deposited by r.f. Magnetron Sputtering in reactive Ar/N₂ atmosphere were determined by X-ray Diffraction. Three basic phases were observed, for increasing nitrogen partial pressure: (a) a nanocrystalline supersaturated solid solution of the alloy elements with fcc structure and interstitial nitrogen (up to 10–15%), with a sharp [111] fibre texture turning into a broad [200] component for increasing N₂ content; (b) an amorphous phase with nominal composition M₂N (with M as the alloy elements); and (c) a nanocrystalline nitride approaching the nominal composition MN. Nanocomposite coatings made of nanocrystalline fcc metal phase embedded in an amorphous matrix can be formed in a relatively narrow N₂ partial pressure range, whereas at high nitrogen content the thin films tend to form an increasing fraction of a nanocrystalline nitride in addition to the amorphous matrix.Scratch test results are different for the various systems: thin films made of (a) behave as typical plastic metals, with an increased scratch test resistance for increasing N₂ content; amorphous (b) films show a very good scratch test behaviour and tend to fail in a plastic mode, with optimal properties for systems made of fcc metal nanocrystalline/amorphous nanocomposites; thin films with a high N₂ content tend to behave in a brittle way for increasing content of the nanocrystalline nitride phase.     

Effect of 0.1 M Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> solution on the structure and properties of amorphous and nanocrystalline Fe-P-Mn alloys

We have studied the electrochemical behavior of amorphous and nanocrystalline Fe-P-Mn alloys with different Mn contents in 0.1 M Na₂SO₄ as a model contamination. The results demonstrate that the alloys rapidly dissolve during anodic polarization, like an Fe-Si-B-Nb-Cu (Finemet) electrochemical alloy. The process involves the dissolution of both Fe and a metastable Fe₂P-based phase.     

Effect of 0.1 M Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> solution on the structure and properties of soft-magnetic Fe-P-Mn-V alloys

A large number of amorphous and nanocrystalline inexpensive alloys have been prepared from ferrophosphorus naturally doped with Si, V, Mn, and C. The alloys appear attractive for use in parts of transformers intended for operation in SO₂-contaminated atmospheres. Electrochemical characterization results demonstrate that amorphous and nanocrystalline alloys of the Fe-P-Mn-V system, a part of the Fe-P-Si-Mn-V-C system, are comparable in corrosion resistance to the Fe₇₇Si₁₃B₇Nb₂Cu₁ (Finemet) alloy, doped with expensive, deficient metals in the presence of boron and copper.     

Mechanochemical synthesis and characterization of Ni<Subscript>25</Subscript>Te<Subscript>75</Subscript> nanocrystalline alloy

Ni₂₅Te₇₅ nanocrystalline alloy containing trigonal NiTe₂ and Te nanocrystals was prepared through mechanochemical processing of pure elemental tellurium and nickel powders in argon atmosphere. The Ni₂₅Te₇₅ samples processed from 3 h to 30 h milling times were characterized by X-ray powder diffraction, transmission electron microscopy, magnetization and Raman spectroscopy. Trigonal NiTe₂ crystals with average size of 16 nm can be obtained after only 3 h of processing time. For longer milling times, the trigonal NiTe₂ phase becomes majority (about 70% with 30% for nanometric Te and no pure Ni was detected) and its average crystallite size slightly increases to 20 nm. Transmission electron microscopy images and electron diffraction patterns confirm the nanometric size of the crystalline domains in the agglomerated particles. The magnetic properties of the Ni₂₅Te₇₅ powders are dependent on synthesis time, suggesting a paramagnetic behavior mainly associated with the NiTe₂ nanophase. Raman spectra showed peaks that can be associated with unreacted Te and tellurium oxides modes, but it also showed several modes that can be attributed to trigonal NiTe₂ nanophase. The high-pressure experiments showed no phase transitions for NiTe₂ up to 17 GPa and Te phase transitions from form I to forms II and III occurred simultaneously at 4.5 GPa, remaining up to 12 GPa; after that, only reflections of Te-III and the NiTe₂ were observed. All the phase transitions observed with pressure are reversible after decompression. The bulk modulus determined from the least-squares fit of first-order Murnaghan equation of states is 110 GPa for the NiTe₂ nanophase and 28 GPa for Te-I.     

Crystallization kinetics of an amorphous Al<Subscript>75</Subscript>Ni<Subscript>10</Subscript>Ti<Subscript>10</Subscript>Zr<Subscript>5</Subscript> alloy

The formation and crystallization behaviors of a mechanically alloyed Al₇₅Ni₁₀Ti₁₀Zr₅ amorphous alloy were studied by X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry in the present study. The effective activation energy of the crystallization was determined by the Kissinger and Ozawa equations, respectively. The two equations yield close results and the average activation energy is 252 ± 13 kJ/mol. The resultant crystalline products were Al and Al₃Ni, and the crystallization mechanism is two- or three-dimensional nucleation and growth controlled by the diffusion of atoms. The thermal stability of the alloy was evaluated by a continuous transformation diagram obtained by the extended Kissinger equation.     

Effect of dispersion and polymeric coatings on the magnetic properties of the Fe<Subscript>73.1</Subscript>Cu<Subscript>1.0</Subscript>Nb<Subscript>3.0</Subscript>Si<Subscript>15.5</Subscript>B<Subscript>7.4</Subscript> amorphous alloy

We tested Fe_73.1Cu_1.0Nb_3.0Si_15.5B_7.4 amorphous alloy for changes in the magnetic properties accompanying the transition from the strip form into a powder and after modification with polymeric coatings. It is shown that the dispersion down to particles smaller than 10 μm in size and the procedure of modification do not, in fact, worsen the magnetic properties of the alloy.     

Influence of wheel speed during planar flow melt spinning on the microstructure and soft magnetic properties of Fe<Subscript>68.5</Subscript>Si<Subscript>18.5</Subscript>B<Subscript>9</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> ribbons

The structure and soft magnetic properties of Fe_68.5Si_18.5B₉Nb₃Cu₁ (at.%) alloy ribbons produced through planar flow melt spinning at different wheel speeds viz. 34, 17 and 12 m/s have been investigated using X-ray diffraction, differential scanning calorimetry, transmission electron microscopy, vibrating sample magnetometer and positron lifetime spectroscopy. Amorphous ribbons formed with different wheel speeds manifested different enthalpy and activation energy of crystallization. The volume fraction of nanocrystalline phase, saturation magnetization and permeability are found to increase whereas coercivity is found to decrease with increasing wheel speed on annealing. A detailed analysis of positron lifetime spectra obtained from the as-spun ribbons has been used to rationalize the variation in microstructure and magnetic properties. The presence of larger number of defects at higher wheel speed increases the volume fraction of nanocrystalline phase on annealing which improves the soft magnetic properties.     

Microstructural evolution during direct laser sintering in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The microstructural evolution during direct laser sintering of LSD (Layerwise Slurry Deposition)—samples in the Al₂O₃–SiO₂ system has been investigated. Slurries with a water content of 34 wt.% and a SiO₂/Al₂O₃—ratio of about 3:1 have been used to manufacture layers which—after consecutive drying—have been sintered and laminated by laser treatment. Densified samples can be obtained with laser irradiances from 190 to 270 kW/cm² and scan velocities between 35 and 65 mm/s. Elemental mappings of the layers’ cross sections suggest an inhomogeneous phase distribution in the laser sintered LSD samples with a slight alumina concentration gradient. A lower degree of particle melting in the bottom region of the layers is plausible due to attenuation of the laser beam intensity. SEM and HRTEM micrographs show that after a few seconds of laser treatment relictic starting phase, crystalline alumina plus amorphous silica, occur together with needle like mullite, the latter formed within an amorphous aluminosilicate phase. The resulting phase assemblage reflects the non-equilibrium conditions which can be expected for short time laser treatments. Mullite nucleation within the bulk of the liquid phase rather than in the vicinity of the parent alumina phase suggests that dissolution of alumina is the rate controlling step. Subsequent thermal post treatment in air in a conventional sintering furnace causes an increase of density to about 96% and leads to additional phase reactions. Amorphous silica transforms into cristobalite and the amount of alumina is reduced by additional mullite formation. By both coalescence of individual crystals and grain growth the morphology of the newly formed mullite changes during post heat treatment.     

Effect of heating rate on the microstructural and magnetic properties of nanocrystalline Fe<Subscript>81</Subscript>Si<Subscript>4</Subscript>B<Subscript>12</Subscript>P<Subscript>2</Subscript>Cu<Subscript>1</Subscript> alloys

The effect of heating rate on the structural and magnetic properties of the nanocrystalline Fe₈₁Si₄B₁₂P₂Cu₁ alloy has been investigated. Amorphous Fe₈₁Si₄B₁₂P₂Cu₁ alloy was annealed at 753 K for 180 s at different heating rates ranging from 0.05 to 5 K/s in protective argon atmosphere. The structural and magnetic properties of the as-quenched and annealed alloys were studied using X-ray diffractometer (XRD), differential scanning calorimeter (DSC), vibrating sample magnetometer (VSM), and B–H loop tracer, respectively. Amorphous precursor prepared by industry-grade raw materials is obtained. The increase of heating rate is found to be significantly effective in decreasing the grain size of α-Fe(Si) phase, but the grain size increases at higher heating rate. The volume fraction of α-Fe(Si) phase shows a monotonic decrease with the increase of the heating rate. The coercivity H _c markedly decreases with increasing heating rate and exhibits a minimum at the heating rate of 0.5 K/s, while the saturation magnetization, M _s, shows a slight decrease. These results suggest that the effect of heating rate on H _c and M _s is originated from the changes of grain size and the volume fraction of α-Fe(Si) phase.     

The domain structure and barkhausen effect in Fe<Subscript>78</Subscript>B<Subscript>12</Subscript>Si<Subscript>9</Subscript>Ni<Subscript>1</Subscript> amorphous alloy

There is no correlation between dimensions of the domain structure elements in an Fe₇₈B₁₂Si₉Ni₁ amorphous alloy ribbon and the Barkhausen effect characteristics in this alloy in various states: initial, hydrogenated, and annealed. Traditional notions of the Barkhausen effect, the nature of which is related to the domain size and the domain wall mobility, are inapplicable to disordered systems such as magnetically soft amorphous metal alloys.     

Mechanical properties of HfB<Subscript>2.7</Subscript> nanocrystalline thin films

The paper describes comparative nanoindentation tests of an HfB₂ single crystal and an HfB_2.7 nanocrystalline thin film deposited on a steel substrate by magnetron sputtering. The boron superstoichiometry and small grain size are shown to result in a significant increase in hardness and decrease of elastic modulus of the thin HfB_2.7 film in comparison to the bulk single crystal. The abnormally high (for inorganic materials) value (87%) of elastic recovery of the impression depth in the thin HfB_2.7 film upon the indenter unloading suggests that the film can be considered as a promising wear-resistant coating.     

Corrosion resistance of amorphous Fe<Subscript>82</Subscript>P<Subscript>16</Subscript>Si<Subscript>2</Subscript> in 0.1 M Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>

A soft-magnetic amorphous Fe-P-Si alloy prepared using ferrophosphorus waste was tested for corrosion in 0.1 M Na₂SO₄. In a nonequilibrium state, the Fe₈₂P₁₆Si₂ alloy interacts with the medium, but annealing and relaxation reduce the interaction, without influencing the magnetic properties of the alloy. The corrosion resistance of the alloy is comparable to that of Finemet (Fe-Si-B-Nb-Cu) materials.