Novel multilayer structure design of metallic glass film deposited Mg alloy with superior mechanical properties and corrosion resistance

A novel multilayer structure of metallic glass film deposited Mg alloy was designed and fabricated by combining surface mechanical attrition treatment and magnetron sputtering. The multilayer structure consists of amorphous layer and gradient structure sequentially from surface, following with the coarse grains inside. Gradient structure significantly decreases hardness mismatch between the amorphous layer and the matrix of Mg alloy. Wear resistance is increased by 2 orders for this novel multilayer structure with the simultaneous improvement of corrosion resistance.     

Enhancement of plasticity in Zr-based bulk metallic glasses electroplated with copper coatings

Electrodeposition was used to coat copper films on the surface of the BMG pillars (bulk metallic glasses) of Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ (Vit. 105) with the film thicknesses of 71.5 and 161.1 μm. The experimental results of the compression tests of the bare Vit. 105 pillars and the coated Vit. 105 pillars revealed that the copper costing increased the density of shear bands in the Vit. 105 pillars formed during the tests, resulting in the improvement of plasticity. The plastic strain was 6.1% for the coated pillars with a coating thickness of 161.1 μm, which is 3.59 times of 1.7% of the bare Vit. 105 pillars. The deformation of the copper films dissipated the strain energy and limited the propagation of shear bands, which led to the initiation and formation of multiple shear bands. The technique developed in this work provides an effective way to enhance the plasticity of BMGs at room temperature.     

Effects of ion irradiation on Zr52.5Cu17.9Ni14.6Al10Ti5 (BAM-11) bulk metallic glass

Bulk metallic glasses are intriguing candidates for nuclear applications due to their inherent amorphous structure, but their radiation response is largely unknown due to the relatively recent nature of innovations in bulk metallic glass fabrication. Here, microstructural and mechanical property evaluations have been performed on a Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ bulk metallic glass (BAM-11) irradiated with 3 MeV Ni⁺ ions to 0.1 and 1.0 dpa at room temperature and 200 °C. Nanoindentation hardness and Young's modulus both decreased by 6–20% in samples irradiated at room temperature, with the sample irradiated to 1.0 dpa experiencing the greatest change in mechanical properties. However, no significant changes in properties were observed in the samples irradiated at 200 °C, and transmission electron microscopy showed no visible evidence of radiation damage or crystallization following ion irradiation at any of the tested conditions. These results suggest that BAM-11 bulk metallic glass may be useful for certain applications in nuclear environments.     

Effect of minor Cu content on microstructure and mechanical property of NiTiCu bulk alloys fabricated by crystallization of metallic glass powder

Ultrafine-grained Ni_50.2−xTi_49.8Cu_x (x = 0, 2.5, 5, and 7.5) bulk shape memory alloys were fabricated by sintering of metallic glass (MG) powder and crystallization of amorphous phase. Non-isothermal crystallization kinetic analysis reveals that the crystallization mechanism of the synthesized x = 5 MG powder is typical interface-controlled two dimensional growth of nuclei followed by volume diffusion-controlled three dimensional growth of nuclei. In contrast, the crystallization mechanism of the synthesized x = 7.5 MG powder is typical volume diffusion-controlled three dimensional growth of nuclei in whole crystallization process. Correspondingly to different crystallization mechanisms, the two sintered and crystallized (SCed) bulk alloys have the same crystallized phases of bcc B2, fcc NiTi₂ phases, and monoclinic B19′, but these phases display different morphologies and distributions. The SCed x = 5 bulk alloy has a microstructure of bcc B2 matrix surrounding fcc NiTi₂ phase region, while the SCed x = 7.5 bulk alloy possesses discontinuous bcc B2 phase region. Consequently, the different crystallization mechanisms and microstructures causes extreme high yield strength and large plasticity for the SCed x = 5 bulk alloy and low strength and no plasticity for the SCed x = 7.5 bulk alloy. Especially, the yield strength of the SCed x = 5 bulk alloy is at least two times of that of the counterpart alloy prepared by melt solidification. The results provide a method fabricating high performance bulk alloys by tailoring crystallization mechanism using powder metallurgy.     

In-situ synthesis and mechanical properties of Zr-based bulk metallic glass matrix composites manipulated by nitrogen additions

Our study investigates in-situ synthesis and mechanical properties of Zr-based bulk metallic glass (BMG) matrix composites via arc plasma-induced accelerated displacement reaction (APADR) process. The aluminum nitride precursor under arc plasma-induced ultra-high temperature results in higher contents of dissolved nitrogen as well as precipitation of zirconium nitride (ZrN) particles in a Zr-based amorphous matrix. The nitrogen in the matrix results in a decrease of crystallization resistance (lower T_x and reduced glass-forming ability), but an increase of mechanical stability (a decrease of strain burst sizes). In particular, in-situ formed ZrN, which exhibits a homogeneous distribution and strong interfacial bonding with the matrix, causes an increase in compressive fracture strength and significant plastic deformation in the composite compared with the monolithic BMG. The formation of multiple shear bands and the enhancement of shear band interactions by the dissolved nitrogen as well as the in-situ formed ZrN particles were carefully confirmed by a statistical analysis on serrated flows. These results give us a guideline on how to manipulate nitrogen contents and fabricate in-situ BMG matrix composites with improved mechanical properties via APADR process.     

The effect of size on the elastic strain limit in Ni60Nb40 glassy films

On small-sized Ni₆₀Nb₄₀ magnetron-sputtered glassy films confined by frame, we experimentally revealed a significant size effect on the elastic strain limits by in situ transmission electron microscopy observations. Ni₆₀Nb₄₀ glassy films with thicknesses of 50, 100 and 200 nm exhibit elastic strain limits of 6.5–6.6%, 4.7–4.9% and 3.5–3.6%, respectively. No effects of changing length or width, or the ratio of width or length to thickness on the elastic strain limit are detected in the studied ranges. The size effect could be attributed to different open volumes in the magnetron-sputtered Ni₆₀Nb₄₀ films with various thicknesses, indicating that controlling the open volumes might be a useful way to tailor the properties of metallic glassy materials. The current findings provide a new way to understand the tensile deformation behavior of metallic glasses and supply an effective approach to enhance the elastic strain limit of metallic glasses.     

Tribological behavior of Zr-based bulk metallic glass sliding against polymer,ceramic, and metal materials

The tribological properties of zirconium-based bulk metallic glass (BMG) sliding against polymers, steels, and ceramics at different loads and speeds were investigated. Acoustic emission (AE) technology was used to analyze wear states. The frictional coefficients of the BMG slid against the steel and ceramic balls were high but decreased with increased applied normal load and sliding speed. As the steel balls were more ductile than the ceramic ones, the steel–BMG sliding pairs generated weaker AE signals and exhibited larger wear rates. The BMG tested against the polymer balls had much lower and more stable frictional coefficients than the ones against the steel or ceramic balls because of transferred polymer layers on the BMG surfaces. The BMG against the polymer balls also exhibited the highest AE signals among the three types of counter materials used, indicating that abrasive wear dominated in the polymer-BMG sliding pairs. These results demonstrated the potential application of the BMG as a new tribomaterial that could be an alternative to the traditional crystalline metals for various counter materials.     

Ni- and Cu-free Ti-based metallic glasses with potential biomedical application

In the present work Ti–Fe–Si and Ti–Fe–Si–X (X = Zr, Pd, Ge) glassy alloys are discussed as potential biomedical materials. Depending on composition and experimental conditions these alloys possess glassy, quasicrystalline or crystalline structure. The glassy state and crystallization behavior of the melt spun ribbons were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and the Hank's solution was used as simulated body fluid for corrosion tests. Ternary Ti–Fe–Si alloys near the Ti₆₅Fe₃₀Si₅ eutectic point were prone to form quasicrystals if the cooling rate was not high enough to retain amorphous structure. The compositions on the steeper side of the eutectic point could be vitrified. The results indicate that small additions of Zr can have a positive effect on glass formation, while additions of Ge, Pd may have a detrimental effect by promoting crystallization. Ti–Fe–Si and Ti–Fe–Si–Zr alloys exhibited high corrosion properties, superior to that of pure Ti and most of Ti-based glassy alloys reported in the literature. Being free of Ni and Cu this group of alloys may be considered for possible biomedical application.     

Microstructural analysis of Zr55Cu30Al10Ni5 bulk metallic glasses by laser surface remelting and laser solid forming

The crystallization behavior of Zr₅₅Cu₃₀Al₁₀Ni₅ bulk amorphous alloy during laser solid forming (LSF) was analyzed. Since laser surface remelting (LSM) is a key process for the LSF, the crystallization behavior of as-cast Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glasses (BMGs) during LSM was also investigated. It was found that the amorphous state of the as-cast BMGs was maintained when they were repeatedly remelted four times in a single-trace LSM, and as for the LSF of Zr₅₅Cu₃₀Al₁₀Ni₅ bulk amorphous alloy, the crystallization primarily occurred in the HAZ between the adjacent traces and layers after the two layers were deposited. The as-deposited microstructure exhibited a series of phase evolutions from the molten pool to the HAZ as follows: the amorphous → NiZr₂–type nanocrystal + amorphous → NiZr₂–type equiaxed dendrite + amorphous → Cu₁₀Zr₇–type dendrite + NiZr₂–type nanocrystal. Among these microstructural patterns, the NiZr₂–type nanocrystals and equiaxed dendrites primarily formed from the rapid solidification of the remelted liquid in the laser processing process, and the Cu₁₀Zr₇–type dendrites in the HAZ primarily formed by the crystallization of pre-existed nuclei in the already-deposited amorphous substrate.     

Production methods and properties of engineering glassy alloys and composites

Since the first synthesis of glassy alloys in 1960, a great large number of studies have been carried out in basic science and technological aspects. At present, glassy alloys and composites have been used as functional and structural materials. The production method for their practical materials was limited to a quenching type technique for many years before around 1990, but the finding of bulk glassy alloys caused a drastic change in production method of glassy alloys to a copper mold casting type technique which has enabled the production of glassy alloys in a three dimensional bulk form. Furthermore, glass alloy composites produced by semi-solid progressive solidification have been successfully developed recently, even using impure charge materials. The drastic changes in the production method and material form have also resulted in significant extension of application fields of glassy alloys. This paper aims to review the production methods and properties of glassy alloys and composites with useful critical sizes above 100 μm or below 4 μm in thickness for glassy powder in conjunction with the present situation of applications for their glassy alloys and composites which do not belong to materials with an ordinary thickness size range of 10–50 μm.     

Magnetic properties and magnetocaloric effect of FeCrNbYB metallic glasses with high glass-forming ability

The influences of Cr addition on the Curie temperature (T_C), glass-forming ability (GFA), and magnetocaloric effect were investigated in FeCrNbYB metallic glasses. It was found that the addition of Cr element slightly decreases the GFA and saturation magnetization, whereas effectively modulates T_C. By the method of copper mold casting, bulk metallic glasses (BMGs) with critical diameters up to 5 mm can be obtained in Fe_68−xCr_xNb₄Y₆B₂₂ (x = 2–6) alloys. The resulting metallic glasses exhibit T_C of 271–367 K and excellent magnetocaloric properties, including magnetic entropy change of 0.76–1.05 J/kg K, and refrigerant capacity of 83–93 J/kg under a low field change of 1.5 T. In addition, they exhibit a wide supercooled liquid region of 116–135 K. The successful synthesis of the FeCrNbYB BMGs with near room-temperature magnetocaloric properties is encouraging for the future development of Fe-based BMGs as a new magnetic refrigerant in magnetic cooling system.     

The influence of the transformation of electronic structure and micro-structure on improving the thermoelectric properties of zinc antimonide thin films

Measurements of electronic structure, microstructure and thermoelectric properties of zinc antimonide thin films prepared by direct current magnetron co-sputtering were carried out. The as-deposited zinc antimonide thin film had a very high resistivity similar to insulating ceramics, which was due to a low binding energy of both zinc and antimony, with the electron scattering increases and impedes the current transport. With the increase in annealing temperature, the films became more crystalline and the thermoelectric properties were also improved. The resistivity of the film decreased rapidly with its crystallinity when the annealing temperature was above 350 °C. The Seebeck coefficients of the thin films were positive, indicating that the films were P-type. The Seebeck coefficient of those samples increased with increasing annealing temperature. The thin film annealed at 400 °C has an optimal power factor of 1.87 × 10⁻³ Wm⁻¹ K⁻² with a Seebeck coefficient of 300 μVK⁻¹ and a resistivity of 4.82 × 10⁻⁵ Ωm at 573 K.     

Dynamic fragmentation induced by network-like shear bands in a Zr-based bulk metallic glass

Dynamic fragmentation induced by network-like shear bands is observed in a Zr-based bulk metallic glass subjected to impact loading, which is different from shear failure via one dominant shear band under quasi-static compression. Further, the influence of elastic strain energy on the evolution of shear bands is investigated. It is shown that the shear-band pattern occurring in one dominated mode or in multiple modes strongly depends on the loading rates. Dynamic fragmentation is due to the competition between the elastic strain energy driving a shear band and the dissipated energy along the shear band.     

Direct synchrotron x-ray measurements of local strain fields in elastically and plastically bent metallic glasses

In situ high-energy synchrotron X-ray diffraction was conducted on elastically and plastically bent bulk metallic glass (BMG) thin plates, from which distinct local elastic strain fields were mapped spatially. These directly measured residual strain fields can be nicely interpreted by our stress analysis, and also validate a previously proposed indirect residual-stress-measurement method by relating nanoindentation hardness to residual stresses. Local shear strain variations on the cross sections of these thin plates were found in the plastically bent BMG, which however cannot be determined from the indirect indentation method. This study has important implications in designing and manipulating internal strain fields in BMGs for the purpose of ductility enhancement.     

The magnetocaloric effect of Gd-Tb-Dy-Al-M (M = Fe,Co and Ni) high-entropy bulk metallic glasses

In this article, we report the formation of the high-entropy Gd₂₀Tb₂₀Dy₂₀Al₂₀M₂₀ (M = Fe, Co and Ni) bulk metallic glasses with good magnetocaloric properties. Compared with most of the rare earth based metallic glasses, these alloys are found to have the comparably large maximum magnetic entropy changes (ΔS_M), but much broader widths of the ΔS_M peaks, and hence larger refrigerant capacity (RC). This can be attributed to the combination of the spin glass behaviors and the complicated compositions in these alloys. Our work show that the high entropy bulk metallic glasses is a promising candidate material as the magnetic refrigerant.     

FeSiBPNbCu alloys with high glass-forming ability and good soft magnetic properties

Effects of Cu addition on the glass-forming ability (GFA), thermal stability, magnetic properties and crystallization process of (Fe_0.76Si_0.09B_0.1P_0.05)_99−xNb₁Cu_x (x = 0, 0.25, 0.5, 0.75, 1) alloys were investigated. The introduction of Cu effectively stimulates the precipitation of the α-Fe(Si) without obvious deterioration of the GFA, and successfully modifies the simultaneous precipitation of α-Fe(Si), Fe₂B and Fe₃(B,P) phases in (Fe_0.76Si_0.09B_0.1P_0.05)₉₉Nb₁ alloy into separable precipitation of each phase at different temperatures during annealing, leading to the enhancement of soft magnetic properties. The saturation magnetic flux density of the representative (Fe_0.76Si_0.09B_0.1P_0.05)_98.25Nb₁Cu_0.75 alloy could be enhanced from 1.43 to 1.51 T after annealing at 530 °C for 10 min due to the precipitation of α-Fe(Si) nanoparticles with a diameter of about 22 nm dispersing randomly in the amorphous matrix. The integration of high GFA and excellent soft magnetic properties makes the FeSiBPNbCu alloys promising soft magnetic materials for industrial applications.     

In-situ thermal evolution of Ni/Ti multilayer thin films

Nickel and titanium alternated nanolayers were deposited from Ti and Ni targets. The multilayer thin films were designed in order to have equiatomic overall chemical composition with a period from 5 to 70 nm. The chemical composition, morphology, structure and phase transformation behaviour were studied. The surface and cross-section morphology of the as-deposited thin films was analysed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The Ni/Ti thin films present in their surface nanograins and for higher periods in cross section it was possible to distinguish the alternated layers and measure their thickness. The structural evolution with temperature was analysed by in-situ hot stage X-ray diffraction (XRD). The as-deposited multilayer thin films exhibit a tendency to a transitory disorder as the period decreases. For the smaller periods a disordered phase forms during the deposition process, while in Ni/Ti multilayers with higher periods this phase is only observed during annealing. By increasing the temperature an exothermic reaction occurs with the formation of the B2-NiTi austenitic phase. In spite of moderate enthalpy of mixing, the multilayers with intermediate modulation period of Ni/Ti films show potential to be used for joining purposes.     

Structural bulk metallic glasses with different length-scale of constituent phases

Bulk metallic glass composites containing constituent phases with different length-scales are prepared via an in situ method by copper mold casting homogeneous Zr–Ti–Nb–Cu–Ni–Al melts. The phase formation and the microstructure of the composite materials are investigated by X-ray diffraction, optical, scanning and transmission electron microscopy, and microprobe analysis. The composition of the melt as well as the cooling conditions realized during casting determine the type and the morphology of the phases present in the composite. The mechanical properties of composite materials with quasicrystalline or ductile bcc phase reinforcements are tested in uniaxial compression at room temperature, showing that the deformation is controlled by the type of the constituent phases and their morphology. Ductile phase-containing metallic glass composites demonstrate improved work hardening and ductility compared to monolithic metallic glasses. Similar results are obtained for composites with ductile bcc phase dendrites embedded in a nanocrystalline matrix. The improved ductility of the composites is due to the presence of the ductile second phase, which counteracts catastrophic failure by shear localization.     

Quantitatively defining interconnecting-zone in metallic glasses

The interconnecting-zone(I-zone) concept is important for understanding the nature of metallic glasses, especially the thermal-physical property change around the glass transition. The analyses of the pair-distribution function measured at 15 K using high intensity neutron source on the as-cast amorphous state and its crystallized counterpart of a Zr–Cu–Al alloy provided solid evidence on the I-zone concept. Together with the ab-initio molecular-dynamics simulations, it enables us to quantitatively describe this I-zone concept. The nearest atom pairs in the I-zone were also analyzed.     

Quasi-static and dynamic compression behaviors of metallic glass matrix composites

Compressive tests were conducted on metallic glass matrix composites at a series loading rates. It was found that mechanical properties of the composite, e.g. yielding stress and plasticity, have a week dependence on strain rates of 4.0 × 10⁻⁴ s⁻¹–4.0 × 10⁻¹ s⁻¹. Four composites were tested at a constant strain rate of 2.3 × 10 s⁻¹ to uncover the dynamic deformation behaviors. Compared with the quasi-static case, the yielding strength increased under dynamic loading rate, but the plasticity decreased significantly. On the other hand, the dynamic compressive has closely relation with the dendrite size and volume fraction. The decreasing of the dendrite size and volume fraction leaded to the dynamic yielding strength increased but the plasticity decreased. For a same composite, e.g. T1 alloy, the yielding strengths increased slightly but fracture strain decreased with increasing of dynamic strain rates.