Microstructure and mechanical property of Zr<Subscript>65</Subscript>Al<Subscript>7.5</Subscript>Ni<Subscript>10</Subscript>Cu<Subscript>12.5</Subscript>Ag<Subscript>5</Subscript> bulk metallic glass subjected to rolling

The as-cast and the pre-annealed Zr₆₅Al_7.5Ni₁₀Cu_12.5Ag₅ bulk metallic glasses were rolled at room temperature to different deformation degrees, and the microstructure and microhardness were examined. It is revealed that no phase transformation occurs in the as-cast/rolled specimen except for localized shear bands, indicating that the material has a good structural stability against plastic deformation. When the glass is pre-annealed in the supercooled liquid region for a short time, however, the stability deteriorates significantly. In this case, rolling deformation results in nanocrystallization in the specimen. The pre-annealed glass has less free volume than the as-cast glass, but it does not exhibit a quicker increase in free volume content during the rolling, suggesting that free volume is prone to annihilate at the crystal/glass interfaces. With nanocrystallization occurred, the microhardness of the pre-annealed specimen decreases at a slower rate than that of the as-cast one during rolling deformation.     

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.     

XPS study of the initial oxidation of the bulk metallic glass Zr<Subscript>46.75</Subscript>Ti<Subscript>8.25</Subscript>Cu<Subscript>7.5</Subscript>Ni<Subscript>10</Subscript>Be<Subscript>27.5</Subscript>

The surface oxidation behaviour of the bulk metallic glass Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 was investigated in situ by using X-ray photoelectron spectroscopy (XPS). The initial stages of oxidation at room temperature were studied by exposing the clean alloy specimen surface to varying doses of pure oxygen (up to 1,000 L) in an UHV chamber. Progressive oxidation of Zr, Be and Ti was observed with increasing doses, the major species in the oxide layer being Zr(IV) and Be(II) possibly existing as ZrO₂, BeO, while Cu and Ni remained in their elemental forms. High temperature in situ oxidation in the temperature range 423–653 K for a fixed oxygen dose of 300 L was also investigated. Oxidation of Be was observed at all temperatures, while a sharp decrease in the oxidation of Zr and Ti was observed for temperatures at 573 K and above. The results show a preferential oxidation of Be and Zr at room temperature, while at higher temperatures oxidation is controlled by the reduction of oxides of Zr and Ti and the diffusion of oxygen into the alloy bulk. The role of the dissolved carbon impurity in the reduction of the oxides is discussed.     

Effect of thermo-mechanical histories on the microstructure and properties of Zr<Subscript>65</Subscript>Al<Subscript>10</Subscript>Ni<Subscript>10</Subscript>Cu<Subscript>15</Subscript> metallic glassy plates

Effect of thermo-mechanical histories during hot rolling in the supercooled liquid region on the microstructure and properties of Zr₆₅Al₁₀Ni₁₀Cu₁₅ metallic glassy plates was investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), differential scanning calorimetry (DSC), microhardness and electrical resistivity measurements. It was found that some nano-scale clusters and a few crystalline phases were dispersed in the amorphous matrix, which may depress the crystallization onset temperature (T_x). The microhardness increased while the electrical resistivity first increased and then decreased with hot rolling times. So, it is important for the working and forming of bulk metallic glasses in the supercooled liquid region to take the thermo-mechanical histories into account.     

Fabrication and mechanical properties of WC particulate reinforced Cu<Subscript>47</Subscript>Ti<Subscript>33</Subscript>Zr<Subscript>11</Subscript>Ni<Subscript>6</Subscript>Sn<Subscript>2</Subscript>Si<Subscript>1</Subscript> bulk metallic glass matrix composites

The mechanical behavior of the WC particulate (WC_p) reinforced Cu₄₇Ti₃₃Zr₁₁Ni₆Sn₂Si₁ bulk metallic glass (BMG) matrix composites has been examined. The mechanical properties are improved with increasing WC_p content up to 20 wt%. The ultimate compression strength and plastic strain of the composite containing 20 wt% WC_p are 2.4 GPa and 2.4%, while those of the monolithic BMG are 1.6 GPa and ∼0%, respectively. The multiple shear band formation and crack deflections through WC particles have been identified as the main mechanism for the improved toughness.     

Crystallization and thermally induced surface relief effects in a Mg<Subscript>65</Subscript>Cu<Subscript>25</Subscript>Y<Subscript>10</Subscript> bulk metallic glass

The crystallization behaviour of Mg₆₅Cu₂₅Y₁₀ bulk metallic glass (BMG) under different reheating conditions was investigated. X-ray diffraction spectrometery (XRD), differential scanning calorimetery (DSC), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to examine the crystallization of different samples and the surface relief generated on as-polished surfaces during heat treatment. Different phase constituents were found in samples that experienced different reheating stages. It is proposed that both the reheating temperature and holding time have a significant effect on the phase constituents. The BMG was found to generate surface corrugations of amplitude 1–2 μm during annealing above its crystallization temperature. Such thermally induced surface relief effects are probably a result of the development of surface stresses generated by volumetric changes associated with crystallization of the residual amorphous phase.     

Failure of Zr<Subscript>50</Subscript>Ti<Subscript>16.5</Subscript>Cu<Subscript>15</Subscript>Ni<Subscript>18.5</Subscript> amorphous metallic ribbon

The deformation and fracture behavior of Zr₅₀Ti_16.5Cu₁₅Ni_18.5 bulk amorphous metal in the form of a thin ribbon have been determined in tensile test at room temperature. The fracture is localized in a major shear band and the fracture angle between the tensile stress axis and the fracture plane is close to 45°. Fractographic observations have revealed that the fracture surface of the amorphous metallic glass consists mainly of a vein-like pattern morphology. We present a scheme of three zones of fracture surface morphology: progressive smooth sliding region (A), dominating vein like pattern (B), and river-like ripples (C). __________ Translated from Problemy Prochnosti, No. 1, pp. 28–31, January–February, 2008.     

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.     

The influence of the cooling rate on bulk metallic glass formation in Mg<Subscript>80</Subscript>Cu<Subscript>15</Subscript>Y<Subscript>5</Subscript> and Mg<Subscript>80</Subscript>Cu<Subscript>10</Subscript>Y<Subscript>10</Subscript>

The Mg–Cu–Y system is known to be one of the best glass formers among the various existing magnesium alloys. The compositions chosen for the current study were Mg₈₀Cu₁₅Y₅ and Mg₈₀Cu₁₀Y₁₀. Different casting processes yielded four different microstructures that were analyzed by means of X-ray diffraction, scanning electron microscopy, high resolution scanning electron microscopy, and energy-dispersive X-ray spectroscopy chemical analysis. The different casting procedures were gravity castings of 3 mm diameter specimens into a copper mold held at different temperatures (cooled to −195 °C with the aid of liquid nitrogen, held at room temperature and heated up to 300 °C) and melt-spinning. Detailed microstructure study was then performed on the melt-spun specimen using transmission electron microscopy and high resolution transmission electron microscopy. The above-mentioned investigation revealed a crystalline rather than amorphous structure. The observed microstructure could not be explained on the basis of current models referring to the frequency of nucleation events.     

Crystal structure of Gd<Subscript>14</Subscript>Cu<Subscript>48</Subscript>Ga<Subscript>3</Subscript> and Tb<Subscript>14</Subscript>Cu<Subscript>48</Subscript>Ga<Subscript>3</Subscript>

The compounds Gd₁₄Cu₄₈Ga₃ and Tb₁₄Cu₄₈Ga₃ have been synthesized, and their structures have been determined by powder x-ray diffraction (Gd₁₄Ag₅₁ type).     

Study of air oxidation of amorphous Zr<Subscript>65</Subscript>Cu<Subscript>17.5</Subscript>Ni<Subscript>10</Subscript>Al<Subscript>7.5</Subscript> by X-ray photoelectron spectroscopy (XPS)

The oxidation of the bulk amorphous alloy Zr₆₅Cu_17.5Ni₁₀Al_7.5 in air in its amorphous and the supercooled liquid states was studied in the temperature range 573–663 K using X-ray photoelectron spectroscopy (XPS). The oxide film mainly consisted of the oxides of Zr (as ZrO₂) and Al (as Al₂O₃). No Cu or Ni was found in the oxide film formed on the amorphous state of the alloy while significant Cu (as CuO) was present in the oxide film formed on the alloy in its supercooled liquid state. The role of the various alloying elements during oxidation at high temperatures in air is discussed in the paper. The XPS data from oxide film support the previously suggested mechanism for oxidation of this alloy, i.e. the rate controlling process during oxidation of the alloy at low temperatures (in the amorphous state) is the back-diffusion of Ni and Cu, while the oxidation at high temperatures (in the supercooled liquid state) is dominated by the inward diffusion of oxygen.     

Anelastic behavior of 8Y-FSZ/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite

This paper has clarified the anelasticity of 8Y-FSZ/α-alumina composites wherein the 8Y-FSZ phases are dispersed like islands. The amount of anelastic strain generated and the manner of anelastic deformation were compared to those of monolithic 8Y-FSZ. The anelastic strains of six kinds of 8Y-FSZ/α-alumina, as well as of monolithic 8Y-FSZ and monolithic α-alumina, were measured. The results showed that the anelastic strain was produced even in the composite where 8Y-FSZ phases existed as islands, and that the more the anelastic strain produced, the higher the volume fraction of 8Y-FSZ. In addition, the composition with a fully densified alumina phase had the effect of inhibiting anelastic strain in the 8Y-FSZ phase.     

Temperature-gradient-driven silver transport in the superionic conductor Ag<Subscript>1.9</Subscript>Cu<Subscript>0.1</Subscript>Se

A steady state silver transport in the superionic conductor Ag_1.9Cu_0.1Se in a temperature gradient has been analyzed. The parameters of the Soret effect have been determined, and the conditions for silver precipitation have been identified. The rate of silver precipitation is shown to increase with increasing temperature gradient and heat of silver transport.     

Nucleation behavior and microstructure of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-poor LAS glass–ceramics

Influence of MgO and K₂O on the nucleation behavior of Al₂O₃-poor LAS (Li₂O–Al₂O₃–SiO₂) base glasses was investigated by thermal analysis and, the effect on microstructure and surface topography of glass–ceramics was also examined by SEM, AFM and TEM. According to results of thermal analysis, the exothermic peak temperature of the glass showed a decrease with increase of nucleation temperature to nucleation time of 6 h. But some glasses nucleated for 9 h showed nucleation rate-like curve with maximum point. The dependence of reciprocal value of the exothermic peak temperature on the nucleation temperature indicated that an introduction of MgO might accelerate the nucleation of the base glass and thus result in rough surface topography of glass–ceramics. On the other hand, in the case of glass–ceramics containing K₂O the main crystalline phase was lithium metasilicate and they showed fine microstructure resulting in smooth surface topography. TEM micrographs of as-quenched and nucleated glasses showed no trace of phase separation affecting nucleation or final microstructure.     

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.     

High-temperature thermodynamic properties of the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

High-temperature mass spectrometry is used to investigate vaporization processes and determine SiO₂ activity in the Al₂O₃-SiO₂ system between 1850 and 1970 K. The results are consistent with the known phase equilibria in this system.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 4, 2005, pp. 434–441.Original Russian Text Copyright © 2005 by Bondar, Lopatin, Stolyarova.     

Refractive index of Al<Subscript>3</Subscript>C<Subscript>2</Subscript>B<Subscript>48</Subscript> aluminum borocarbide crystals

Aluminum borocarbide single crystals have been grown from an Al-based solution melt. The crystal lattice parameters have been determined, the dispersion of the refractive index in a 0.55–1.3 μm wavelength interval has been studied, and the temperature coefficient of the refractive index in a 300–600 K range has been measured. The crystals are characterized by a high refractive index in the visible spectral range in combination with at a high hardness, which makes them of interest for jewelry, as well as for both traditional and X-ray optics.     

Preparation of fine-grained ceramics by hot-pressing of Ce<Subscript>0.09</Subscript>Zr<Subscript>0.91</Subscript>O<Subscript>2</Subscript>/MgO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanopowder

We have studied the effect of hot-pressing conditions (different pressure rise rates and isothermal holding temperatures in the range 1450–1550°C) on the microstructure of ceramics produced from nanopowder with the composition Ce_0.09Zr_0.91O₂/MgAl₆O₁₀/γ-Al₂O₃ (20.6, 37.4, and 42.0 wt %, respectively). Firing at 1450°C for 1 h made it possible to obtain fine-grained ceramics with less than 3 μm in grain size. The compaction pressure rise rate was shown to be a key parameter under such thermal conditions (20 + 10°C/min → 1450°C). Grain growth was prevented most effectively when the maximum load, 30 MPa, was reached at a temperature of 1000°C. Under such conditions, the grain size was 0.4–0.8 μm and the relative density reached 98.8%.     

Phase relations in the Ag<Subscript>8</Subscript>SnS<Subscript>6</Subscript>-Ag<Subscript>2</Subscript>SnS<Subscript>3</Subscript>-AgBr system and crystal structure of Ag<Subscript>6</Subscript>SnS<Subscript>4</Subscript>Br<Subscript>2</Subscript>

The T-x phase diagram of the Ag-Sn-S-Br system has been studied in the composition region Ag₈SnS₆-Ag₂SnS₃-AgBr, and a compound of composition Ag₆SnS₄Br₂ has been identified. Ag₆SnS₄Br₂ has a new structure, closely related to that of Ag₆GeS₄Br₂: sp. gr. Pnma, a = 6.67050(10), b = 7.82095(9), c = 23.1404(3) Å, Z = 4, R _B = 0.0519, R _wp = 0.0782, χ² = 1.36.