Formation of bulk metallic glasses in Cu45Zr48−xAl7REx (RE = La,Ce, Nd,Gd and 0 ≤ x ≤ 5 at.%)

We report a series of bulk metallic glass-forming alloys of compositions (Cu₄₅Zr_48−xAl₇RE_x, RE = La, Ce, Nd, Gd and 0 ≤ x ≤ 5 at.%). By using a conventional copper mold sucking method, alloys with diameters ranging from 5 to 10 mm can be readily solidified into an amorphous structure without detectable crystallites. The best glass-forming ability is obtained for the alloys Cu₄₅Zr₄₆Al₇RE₂. Possible effects of RE addition on the glass-forming ability are discussed. In addition, the compositional effect on mechanical properties of Zr–Cu–Al–Gd alloys is presented.     

Corrosion behaviour of Al–29at%Co alloy in aqueous NaCl

Microstructure and corrosion behaviour of a binary Al–29 at%Co alloy have been studied. The alloy was prepared by arc-melting of Al and Co in high purity Ar and rapidly solidified on a water-cooled Cu mould. The alloy chemical composition and microstructure were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Furthermore, the corrosion behaviour was studied by potentiodynamic polarization in aqueous NaCl (0.6 mol dm⁻³) at room temperature. The alloy was found to consist of three phases: hexagonal Al₅Co₂, Z-phase and AlCo (β). The corrosion resistance of different intermetallic phases is characterized. The results are compared to previously published results of Al–TM (TM = transition metal) alloys.     

Preparation and characterization of Zircaloy 4-Tantalum alloys for application in corrosive media

Two Zircaloy 4-Ta alloys (14 and 55 wt.% Ta) were produced by arc-melting. The alloys were hot-rolled at 900 °C and heat-treated under argon atmosphere for 100 h at 700 °C. The alloys were analyzed by scanning electron microscopy and X-ray diffractometry. The microstructure of both rolled and heat-treated alloys is constituted of (β Zr,Ta)-II Ta-rich precipitates dispersed in a (α Zr) matrix. Corrosion tests performed in boiling concentrated H₂SO₄ solutions showed that the Zircaloy 4-Ta alloys are more corrosion resistant than Zircaloy 4 and that the corrosion resistance increases with increasing Ta content.     

A new approach to designing a grain refiner for Mg casting alloys and its use in Mg–Y-based alloys

A totally new grain refiner, Al₂Y, for cast Mg alloys has been predicted using the recently developed edge-to-edge matching (E2EM) crystallographic model. An addition of 0.6–1.0 wt.% Al into the Mg–10 wt.% Y melt promotes the in situ formation of Al₂Y, which reduces the average grain size from about 180 to 36 μm. Active nucleation Al₂Y particles were reproducibly observed at the centres of many refined grains. The excellent grain-refining efficiency is comparable to that of Zr for the same alloy, but the thermal stability of the grains refined by Al₂Y is much higher than those refined by Zr up to a temperature of 550 °C for 48 h. The mechanisms of grain refinement and the superior thermal stability of the refined grains due to Al addition in the Mg–Y alloy are discussed based on the current experimental results.     

The ternary Al–Ce–Cu phase diagram in the aluminum-rich corner

The phase diagram of the Al–Ce–Cu system in the aluminum-rich corner (concentrations up to 35 wt.% Cu and up to 16 wt.% Ce) was studied. Phases and invariant reactions were identified. Liquidus and solidus surfaces, three isothermal cross-sections (540, 590 and 200 °C) and five vertical cross-sections were constructed. It was shown that Al₄Ce (Al₁₁Ce₃), Al₈CeCu₄ and Al₂Cu were in equilibrium with the aluminum solid solution (Al). It was determined that about 17 wt.% Cu dissolves in Al₄Ce; the existence of the Al₄CeCu phase was not confirmed. Experimentally determined parameters of the invariant quasi-binary eutectic reaction L → (Al) + Al₈CeCu₄ (610 °C, 14 wt.% Cu and 7 wt.% Ce) were essentially different from those published earlier. This eutectic had a fine microstructure and was stable to coarsening (after fragmentation and spheroidizing) during the heating process even though the average particle size did not grow larger than 2 μm after annealing at 590 °C.     

Laser (Nd:YAG) cladding of AZ91D magnesium alloys with Al + Si + Al2O3

The laser surface cladding of AZ91D magnesium alloy with Al + Si + Al₂O₃ powders (in the wt.% ratio of 7:1:2) was investigated. Laser processing was carried out with a 5 kW Nd:YAG laser. The microstructure and phase analyses of the surface cladding layer were carried out; furthermore, the morphology of the cladding zone, volume fraction and distribution of the Si and Al₂O₃ particles in the laser surface cladding layer were also investigated. The average microhardness of the surface layer was measured in detail as a function of laser parameters. Microhardness of the surface layer was significantly improved to as high as 210 HV_0.05 as compared to 60–70 HV_0.05 of the AZ91D substrate, and the average microhardness of the cladding layer of the composite surfaced specimen decreases with increasing of laser power. However, the rate of decrease is faster at lower power. Though the average microhardness of the surface cladding layer remains constant, there is a little fluctuation in the reading in some regions possibly, because of the random distribution of hard particles in the cladding layer. Finally, the proper processing parameter ranges for formation of a homogeneous microstructure and enhancement of microhardness for laser surface cladding of AZ91D with Al + Si + Al₂O₃ were established.     

A novel high-strength,high-ductility and high-corrosion-resistance FeAlMnC low-density alloy

The as-quenched Fe–8.68 wt.% Al–30.5 wt.% Mn–1.85 wt.% C alloy is plasma-nitrided at 500 °C for 8 h. The nitrided layer obtained is 40 μm thick and composed predominantly of AlN, with a small amount of Fe₄N. The resultant surface hardness (1860 Hv), substrate hardness (550 Hv), ductility (33.6%) and corrosion resistance in 3.5% NaCl solution in the present nitrided alloy are far superior to those obtained previously in optimally nitrided high-strength alloy steels, as well as martensitic and precipitation-hardening stainless steels.     

Effects of Al2O3 addition on the microstructure and properties of Ni activated sintered W matrix composites

In the present investigation, fabrication of high dense (> 97.8%) W matrix composites with increased microhardness values were investigated. W and W–1 wt.% Ni powders were mechanical alloyed for 18 h and sintered at 1400 °C for 1 h under Ar, H₂ gas flowing conditions in order to investigate the effects of 1 wt.% Ni addition on the densification and properties of W. The effects of Al₂O₃ particles additions on the microstructural and physical properties of the sintered W–1 wt.% Ni sample were investigated. A 92.59% relative density value of the sintered W sample increased to 99.47% with the addition of 1 wt.% Ni. Moreover, despite the observed grain growth, microhardness values significantly increased from 2.81 ± 0.34 GPa to 4.07 ± 0.16 GPa with the addition of 1 wt.% Ni. The relative density values of the sintered W–1 wt.% Ni sample slightly decreased with increasing Al₂O₃ additions, a relative density value of 97.81% was measured for the W–1 wt.% Ni sample reinforced with 2 wt.% Al₂O₃ particles. As the average grain size of W in the sintered W–1 wt.% Ni sample decreased from 4.41 ± 1.71 μm to 1.29 ± 0.39 μm with the addition of 2 wt.% Al₂O₃ particles, the microhardness of the sample increased to 5.98 ± 0.31 GPa.     

Investigation the effect of B4C addition on properties of TZM alloy prepared by spark plasma sintering

TZM alloy is one of the most important molybdenum (Mo) based alloy which has a nominal composition containing 0.5–0.8 wt.% titanium (Ti), 0.08–0.1 wt.% zirconium (Zr) and 0.016–0.02 wt.% carbon (C). It is a possible candidate for high temperature applications in a variety of industries. However, the rapid oxidation of TZM alloys at high temperature in air is considered to be one of the drawback. In this study, TZM alloys with additions of 0–5 wt.% B₄C were prepared by spark plasma sintering (SPS) at 1420 °C utilizing 40 MPa pressure for 5 min under vacuum. The effects of B₄C addition on oxidation, densification behavior, microstructure, and mechanical properties were investigated. The TZM alloy with 5 wt.% B₄C have exhibited an approximately 66% reduction in mass loss under normal atmospheric conditions in oxidation tests made at 1000 °C for 60 min. And an increase from 1.9 GPa to 7.8 GPa has been determined in hardness of the alloy.     

Effect of small aluminum additions on microstructure and mechanical properties of molybdenum di-silicide

The effect of Al alloying on the microstructure and properties of MoSi₂ was investigated. MoSi₂–2.8 and 5.5 at% Al (1.5 and 3 wt %, respectively) alloys showed a two phase microstructure comprising of α-Al₂O₃ and MoSi₂–Al alloy, while the MoSi₂–9 at% (5 wt %) Al alloy possessed a 3 phase microstructure: MoSi₂–Al alloy, Mo(Si,Al)₂ and α-Al₂O₃. Al additions to MoSi₂ reduced the SiO₂ phase, which is detrimental for high temperature strength of MoSi₂, forming Al₂O₃. The surplus Al entered into solid solution with the MoSi₂ and altered the lattice parameters. The Al in solid solution was 0.5 at% in MoSi₂–2.8 at% Al alloy, 2.5 at% in MoSi₂–5.5 at% Al alloy and 3.1 at% in the MoSi₂–9 at% Al alloy. The fracture toughness underwent only a moderate improvement in MoSi₂–2.8 at% and 5.5 at% Al alloys, but exhibited a significant 49% rise in the MoSi₂–9 at% Al alloy. Replacement of SiO₂ by Al₂O₃ in MoSi₂–Al alloys led to a significant improvement in the high temperature yield strength between 1100°C and 1250°C.     

High temperature oxidation of AZ31 + 0.3 wt.%Ca and AZ31 + 0.3 wt.%CaO magnesium alloys

Magnesium alloys of AZ31 + 0.3 wt.%Ca and AZ31 + 0.3 wt.%CaO were cast and oxidized between 450 and 650 °C in atmospheric air. The initially added Ca and CaO enabled to cast the alloys in air without using environmentally hazardous SF₆ gas, by forming a thin CaO-rich barrier layer at the surface during casting. A thin CaO-rich barrier layer was also formed at the surface during oxidation in air, thereby increasing the oxidation resistance of the AZ31 alloy considerably. The initially added Ca and CaO reacted with Al to become Al₂Ca along the grain boundaries of the AZ31 alloy during casting.     

Effects of amorphous Co–C on the structural and electrochemical characteristics of La0.8Mg0.2Ni0.8Mn0.1Co0.5Al0.1 hydrogen storage alloy

Amorphous Co–C powder prepared by ball milling was introduced to improve the performance of La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1 hydrogen storage alloy. The structural and electrochemical properties of the as-prepared La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1–x wt.% Co–C composites were investigated systematically. Scanning electron microscopic images show La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1 alloy was coated by Co–C particles. X-ray diffraction patterns suggest that the composite almost remained original phase structures of La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1 and Co–C in both charge and discharge processes. The maximum discharge capacity of the composites reached 414 mAh g^?1 at a current density of 50 mA g^?1 at 298 K. The cyclic stability and the discharge capacities of the composite electrodes were noticeably improved in comparison with single La–Mg–Ni-based alloy due to increased corrosion resistance and the catalysis of the Co–C powder. Cyclic voltammogram and potentiodynamic polarization studies on the composite indicate that the electrochemical kinetics was improved and the corrosion resistance was increased. The cycling performance of the composite electrode at high current density is good as well.     

The effect of silicon on the structure of Fe-40 at.% Al type alloys with high contents of carbon (1.9–3.8 at.%)

The phase compositions of alloys based on Fe-40 at.% Al with additions of carbon ranging from 1.9 to 3.8 at.% and with and without the addition of 1.2 at.% Si were studied by light optical and transmission electron microscopies, X-ray diffraction and electron probe microanalysis. The structure of the matrix of all alloys is a B2 lattice, inherent to the intermetallic compound FeAl. Two main precipitating phases are observed: graphite and aluminium carbide Al₄C₃. The quantity of the phases depends in detail on the chemical composition and the heat treatment. The presence of Al₄C₃ in the alloys with the highest carbon content is in agreement with the recent theoretical prediction of a Fe–Al–C ternary phase diagram by Ohtani et al., as well as with older experiments of Vyklický and T?ma. The occurrence of Al₄C₃ is supported by the addition of silicon. Small traces of carbide κ of perovskite-type Fe₃AlC are observed only in the alloys with the lowest aluminium and carbon contents.     

Electrochemical corrosion behaviors of straight WC–Co alloys: Exclusive variation in grain sizes and aggressive media

The electrochemical corrosion behaviors of straight WC–10Co cemented carbides with grain sizes of 1.2, 2.6, 6.1 and 8.2 μm, were comparatively investigated in the solutions of NaOH (pH = 13), Na₂SO₄ (pH = 7) and H₂SO₄ (pH = 1) respectively. To insure a sole variable of WC grain sizes, specific magnetic saturation values of the alloys are adjusted to be identical. The results show a good linear dependence for R_ct (charge transfer resistance) and I_corr (corrosion current density) against the grain sizes. A high sensitivity of the grain sizes to both R_ct and I_corr are identified in NaOH and H₂SO₄. In the solutions of NaOH and Na₂SO₄, the alloys with smaller WC grain sizes exhibit better corrosion resistances, while the alloys with larger WC grain sizes exhibit better corrosion resistances in H₂SO₄. Additionally, in terms of the corrosiveness, NaOH is the weakest and H₂SO₄ is the most aggressive for all the alloys. The corrosion mechanisms were discussed in light of the SEM surface observation, X-ray photoelectron spectroscope analysis and the electrical equivalent circuits for electrochemical impedance spectroscopy.     

A DSC analysis of thermodynamic properties and solidification characteristics for binary Cu–Sn alloys

The liquidus temperatures and enthalpies of fusion for Cu–Sn alloys are systematically measured across the whole composition range by differential scanning calorimetry (DSC). The liquidus slope vs. Sn content is derived on the basis of the measured results. The measured enthalpy of fusion is related to the Sn content by polynomial functions, which exhibit one maximum value at 55 wt.% Sn and two minimum values around 28.9 wt.% Sn and 90 wt.% Sn, respectively. The undercoolability of those liquid alloys solidifying with primary α (Cu) solid solution phase is stronger and can be further enhanced by increasing the cooling rate. However, other alloys with the preferential nucleation of intermetallic compounds display smaller undercoolings and are not influenced by cooling rate. Microstructural observations reveal that peritectic reactions can rarely be completed. With the increase in undercooling, the primary α (Cu) dendrites are refined in the peritectic Cu–22 wt.% Sn alloy. For the hyperperitectic Cu–70 wt.% Sn alloy, typical peritectic cells are formed in which the peritectic η(Cu₆Sn₅) phase has wrapped the primary ε(Cu₃Sn) phase. The DSC curves of metatectic-type Cu–Sn alloys indicate that the metatectic transformation γ → ε + L upon cooling is an exothermic event, and a large undercooling of 70 K is required to initiate this transformation in metatectic Cu–42.5 wt.% Sn alloy. The metatectic microstructures are characterized by (ε + η) composite structures. The η phase is mainly distributed at the grain boundaries of the coarse ε phase, but are also dispersed as small particles inside ε grains. The volume fraction of the η phase increases with the Sn content.     

Cr effects on magnetic and corrosion properties of Fe–Co–Si–B–Nb–Cr bulk glassy alloys with high glass-forming ability

Effects of the Cr addition on glass formation, magnetic and corrosion properties of {[(Fe_0.6Co_0.4)_0.75B_0.2Si_0.05]_0.96Nb_0.04}_100−xCr_x (x = 1, 2, 3, 4 at.%) alloys have been investigated. It was found that the addition of Cr element slightly decreases the glass-forming ability (GFA), but is very effective in increasing corrosion resistance and improving soft magnetic properties for this Fe–Co–B–Si–Nb bulk glassy alloy within the composition range examined. The Fe–Co–B–Si–Nb–Cr alloys exhibit high GFA. Full glassy rods with diameters up to 4 mm can be synthesized by copper mold casting. The Fe-based bulk glassy alloys (BGAs) exhibit a high saturation magnetization of 0.81–0.98 T as well as excellent soft magnetic properties, i.e., extremely low coercive force of 0.6–1.6 A/m and super-high initial permeability of 26,400–34,100. Furthermore, corrosion measurements show that corrosion rate and corrosion current density of these Fe-based BGAs in 0.5 M NaCl solution decrease from 7.0 × 10⁻¹ to 1.6 × 10⁻³ mm/year and 3.9 × 10⁻⁶ to 8.7 × 10⁻⁷ A/cm², respectively, with increasing Cr content from 0 to 4 at.%. The success of synthesizing the new Fe-based BGAs exhibiting simultaneously high GFA as well as excellent good soft magnetic properties combined with high saturation magnetization and enhanced corrosion resistance allows us to expect future progress as a new type of soft magnetic materials.     

Structure stability and mechanical properties of Mg–Al-based alloy modified with Y-rich and Ce-rich misch metals

Mg–3.4 wt.% Al-based alloy modified with 2.4 wt.% Ce-rich and 0.3 wt.% Y-rich misch metals was prepared by high-pressure die-casting. The microstructure, thermal stability of intermetallic phases and mechanical properties were investigated. The cross-section of test bar is divided into the fine skin region and the wide core region by a narrow band. Two intermetallic phases Al₁₁RE₃ and Al₂RE, with the former being the dominant one, are mainly distributed at the interdendritic regions. The Al₁₁RE₃ intermetallics possess high volume fraction, fine acicular/lamellar morphology and layered arrangement. It is suggests that each rare earth element has the individual preference for the above two Al–RE intermetallics. The thermal stability of Al₁₁RE₃ is conditioned. It is basically stable at temperature up to 200 °C within 800 h, while almost all Al₁₁RE₃ intermetallics transform to Al₂RE at higher temperature of 450 °C for 800 h. The alloy exhibits remarkably improved tensile and compressive yield strengths at room temperature and 200 °C and they are the results of the reinforcement of dendrite boundaries with Al₁₁RE₃ intermetallics, the fine dendritic arm spacing effect as well as the solid solution strengthening with various rare earth elements.     

Erosion wear behaviour of plasma sprayed NiCrSiB/Al2O3 composite coating

In this work, 60 wt.% NiCrSiB–40 wt.% Al₂O₃ composite coating was produced on AISI 304 substrate material using the atmospheric plasma spraying technique. The coating surface has been characterised using a scanning electron microscope (SEM), optical microscope and X-ray diffractometer (XRD). The microhardness, porosity, density and surface roughness of the coating were measured. The adhesion strength of the coating was measured using pull off adhesion tester. The erosion behaviour of plasma sprayed coating was studied at 450 °C using hot air jet erosion testing machine. The erosion rate of coated and uncoated samples was evaluated at 30° and 90° erodent impact angles. The SEM images of the eroded samples were taken to analyse the erosion mechanism. The test results reveal that the coating protects the substrate at both 30° and 90° impact angles.     

Nanocrystalline Fe–C alloys produced by ball milling of iron and graphite

A series of nanocrystalline Fe–C alloys with different carbon concentrations (x_tot) up to 19.4 at.% (4.90 wt.%) are prepared by ball milling. The microstructures of these alloys are characterized by transmission electron microscopy and X-ray diffraction, and partitioning of carbon between grain boundaries and grain interiors is determined by atom probe tomography. It is found that the segregation of carbon to grain boundaries of α-ferrite can significantly reduce its grain size to a few nanometers. When the grain boundaries of ferrite are saturated with carbon, a metastable thermodynamic equilibrium between the matrix and the grain boundaries is approached, inducing a decreasing grain size with increasing x_tot. Eventually the size reaches a lower limit of about 6 nm in alloys with x_tot > 6.19 at.% (1.40 wt.%); a further increase in x_tot leads to the precipitation of carbon as Fe₃C. The observed presence of an amorphous structure in 19.4 at.% C (4.90 wt.%) alloy is ascribed to a deformation-driven amorphization of Fe₃C by severe plastic deformation. By measuring the temperature dependence of the grain size for an alloy with 1.77 at.% C additional evidence is provided for a metastable equilibrium reached in the nanocrystalline alloy.     

Combined effect of Ni and nano-Y2O3 addition on microstructure,mechanical and high temperature behavior of mechanically alloyed W-Mo

Nanostructured tungsten (W) based alloys with the nominal compositions of W₇₀Mo₃₀ (alloy A), W₅₀Mo₅₀ (alloy B), and 1.0 wt.% nano-Y₂O₃ dispersed W₇₉Ni₁₀Mo₁₀ (alloy C) (all in wt.%) have been synthesized by mechanical alloying followed by compaction at 0.50, 0.75 and 1 GPa pressure for 5 mins and conventional sintering at 1500 °C for 2 h in Ar atmosphere. The microstructure, evolution of phases and thermal behavior of milled powders and consolidated products has been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), High resolution transmission electron microscopy (TEM), Energy dispersive spectroscopy (EDS) and differential scanning calorimetry (DSC). Minimum crystallite size of 29.4 nm and maximum lattice strain and dislocation density of 0.51% and 18.93 (10¹⁶/m²) respectively has been achieved in alloy C at 20 h of milling. Addition of nano-Y₂O₃ reduces the activation energy for recrystallization of W based alloys. Alloy C compacted at 1 GPa pressure shows enhanced sintered density, hardness, compressive strength and elongation of 95.2%, 9.12 GPa, 1.51 GPa, 19.5% respectively as well as superior wear resistance and oxidation resistance (at 1000 °C) as compared to other W-Mo alloys.