Glass-formation and hardness of Cu–Y alloys

Metallic glasses exhibit particularly attractive mechanical properties, like high stresses to fracture and large elastic strain (up to 2%), but they show generally low plasticity. Aim of this work is to investigate the glass forming range in the Cu–Y system, in order to form the ductile CuY phase (CsCl structure) upon crystallization. Cu₅₈Y₄₂, Cu₅₀Y₅₀ and Cu₃₃Y₆₇ alloys have been prepared by rapid solidification and copper mould casting, obtaining ribbons and cylindrical shaped ingots, with diameter of 2 mm. Fully amorphous, partially amorphous and fully crystalline samples have been obtained for different compositions and quenching conditions. In some cases, the X-ray diffraction results, analysed using the Rietveld method, showed CuY nanocrystals embedded in an amorphous matrix. The microstructure was studied by transmission electron microscopy (TEM) and the presence of nanocrystals of the ductile phase CuY has been confirmed. Microhardness results showed a softening of the amorphous phase due to the presence of CuY nanocrystals and a hardening due to the Cu₂Y phase.     

Effect of Aluminum and Neodymium Admixtures on Devitrification of Silica Glasses

This investigation concerned the devitrification kinetics (in the temperature range 1100° to 1500°C) of silica glasses doped with aluminum oxide (0.1 and 1.0 mol%), neodymium oxide (0.08 and 0.25 mol%), and with aluminum and neodymium oxides simultaneously, at their mutual molar ratio close to 4. The glasses were obtained by electric melting of quartz under vacuum and by the sol/gel method. On the basis of the obtained results, conclusions have been drawn concerning the mode in which the admixtures become incorporated into the silica glasses as well as the structural differences between the melted and sol/gel glasses.     

Microstructure and Fracture Behavior of Zr55Cu30Al10Ni5 Bulk Metallic Glass and Its Composites Containing ZrO2

The microstructure and fracture behavior of Zr55Cu30Al10Ni5 monolithic glass and Zr55Cu30Al10Ni5 reinforced with 5%-7% ZrO2 particles composites have been studied. Vein-like pattern is the main fracture morphology of the matrix, while the smooth regions can be observed on the composites fracture surface besides vein-like pattern. The fracture strength increases from 1716 MPa to 2138 MPa after adding 7vol% ZrO2 particles with average particle size of 1 μm into the matrix, but the composites show no visible plasticity due to formation of Cu10Zr7 and CuZr phases in the matrix     

一种新型的电焊护目镜

提出了一种新型的电焊护目镜,它是由光电控制电路、变色镜片、双防(防红外、紫外)透明玻璃镜片构成。其特点是护目镜随弧光的开启自动变暗,而随弧光的停止又自动变亮;在弧焊作业过程中,操作者不需移动护目镜;抗各种背景光干扰,该护目镜已通过省科委组织的鉴定。     

Molecular dynamic simulation of heterogeneity and chemical states of fluorine in amorphous alkaline earth silicate systems

Chemical states of fluorine in fluorosilicate glasses in the system MF₂-MO-SiO₂ (M = Ca, Sr and Ba; SiO₂ content < 60 mol%) have been investigated by molecular dynamic (MD) simulations with a perfect ionic two-body potential. Comparison of the results with those derived by X-ray photoelectron spectra of the actual glasses demonstrates that MD simulations reproduce well the bonding states of fluorine in the systems as well as the formation of M-F clusters. The MD generated structure of imaginary glasses, or glasses not obtained by the conventional melt-quench technique, with 70 mol% SiO₂ indicates that an acidic environment induces a greater amount of F---Si bonds. Their M-F pair correlation functions plotted against normalized M-F distances suggest that relative ion positions in the clusters are very similar.     

Structure study of a metallic glass using positron annihilation methods

The effects of vitrification and cold rolling on the structure in a metallic glass of Pd_.775Cu_.06Si_.165 alloy and crystalline Pd have been investigated using positron lifetime and angular correlation measurements. It is concluded that: A) the metallic glass contains a negligible concentration of vacancy-like defects and the crystallite model may be excluded as a possible structure of metallic glasses, B) the glass-crystalline boundaries contain a very small fraction of vacancy-like defects and exhibit a smooth transition structure from glassy to crystalline regions, C) the cold rolling of the metallic glass induces no vacancy or dislocation-like defects and plastic flow in metallic glasses is accompanied by cooperative atomic regroupings somewhat analogous to the visco flow of glasses near the glass transition temperature, D) the electronic structure of the Pd-Cu-Si alloy alters little upon disordering from a crystalline to glassy state, but exhibits a large change from that of crystalline Pd. This is attributed to the valence electrons transferred from Si to the d-shell of Pd in the Pd-Cu-Si alloy.     

Applications of environmental scanning electron microscopy (ESEM) in biomaterials field

Various tasks were undertaken in our laboratory where environmental scanning electron microscopy (ESEM) has been of particular interest within the biomaterials field. The possibility of observing wet samples, as well as the fact that sample preparation is minimal, has improved shorter time scales and lower costs in microscopy. Minimal preparation has also reduced the possibility of introducing artifacts. Examples like cell cultures used for pit resorption assays, calcium phosphate deposition processes, and dissolution of phosphate glasses used as biomaterials are presented. Finally, a servohydraulic testing machine designed for mechanical testing in situ in ESEM has allowed the study of shape memory alloys for orthodontic applications or the behavior of different adhesives used in odontology.     

Strengthening and toughening of Mg-Cu-(Y, Gd) bulk metallic glasses by minor addition of Be

Mg₆₅Cu₂₅Re₁₀ and Mg₆₅Cu₂₄Be₁Re₁₀ (Re = Y, Gd) bulk metallic glasses (BMGs) were successfully fabricated by conventional Cu-mold casting method. By the addition of 1 at.% Be, the compressive strengths of Mg₆₅Cu₂₄Be₁Y₁₀ and Mg₆₅Cu₂₄Be₁Gd₁₀ alloys are increased from 760 MPa and 860 MPa to 930 MPa and 1025 MPa, respectively. The fracture morphology is changed from nanometer scale corrugation to micrometer scale dimple and vein pattern, indicating that the addition of minor Be obviously improves the toughness of the alloys. The fracture morphologies with different size of plastic zone in Mg-based BMGs provide probability for understanding the fracture mechanism of BMGs.     

Spectral properties and energy transfer of Tm~(3 )/Ho~(3 )-codoped Ga_2O_3-Bi_2O_3-GeO_2-PbO glasses

The 2.0 μm emission originating from Ho3 :5I7→5I8 transition in Ho3 /Tm3 -codoped gallate-bismuth-germanium-lead glasses were investigated upon excitation with 808 nm laser diode (LD). Energy transfer (ET) process between Tm3 : 3F4 level and Ho3 : 5I7 level was also discussed. It was noted that the measured peak wavelength and stimulated emission cross-section of Ho3 -doped bis-muth-germanium-lead glasses were ～2.02 μm and 5.1×10–21 cm2, respectively. Intense emission of Ho3 in Tm3 /Ho3 -codoped GBPG glass were observed, which resulted from the ET between Tm3 : 3F4 and Ho3 : 5I7 level upon excitation with 808 nm LD.     

Properties and Microstructure of GeS_2-Ga_2S_3-CdS Glasses

1Introduction OsterbergUetal[1]firstlydetectedtheSecond Har monicGeneration(SHG)bythelaser inducedmethodin GeO2SiO2glassfiber,andMyersRAetal[2]observed SHGeffectinSiO2bulkglassesafterpolarizationwitha strongelectronicfield.Sincethenthescholarsalloverthe w…