Formation and evolution characteristics of bcc phase during isothermal relaxation processes of supercooled liquid and amorphous metal Pb

The formation and evolution characteristics of bcc phase during the isothermal relaxation processes for supercooled-liquid and amorphous Pb were investigated by molecular dynamics simulation and cluster-type index method （CTIM）. It is found that during the relaxation process, the formation and evolution of bcc phase are closely dependent on the initial temperature and structure. During the simulation time scale, when the initial temperature is in the range of supercooled liquid region, the bcc phase can be formed and kept a long time; while it is in the range of glassy region, the bcc phase can be formed at first and then partially transformed into hcp phase; when it decreases to the lower one, the hcp and fcc phases can be directly transformed from the glassy structure without undergoing the metastable bcc phase. The Ostwald＇s ＂step rule＂ is impactful during the isothermal relaxation process of the supercooled and glassy Pb, and the metastable bcc phase plays an important role in the precursor of crystallization.

Interfacial features of TiAl alloy/316L stainless steel joint brazed with Zr−Cu−Ni−Al amorphous filler metal

TiAl alloy and 316L stainless steel were vacuum-brazed with Zr−50.0Cu−7.1Ni−7.1Al(at.%)amorphous filler metal.The influence of brazing time and temperature on the interfacial microstructure and shear strength of the resultant joints was investigated.The brazed seam consisted of three layers,including two diffusion layers and one residual filler metal layer.The typical microstructure of brazed TiAl alloy/316L stainless steel joint was TiAl alloy substrate/α2-(Ti3Al)/AlCuTi/residual filler metal/Cu9Zr11+Fe23Zr6/Laves-Fe2Zr/α-(Fe,Cr)/316L stainless steel substrate.Discontinuous brittle Fe2Zr layer formed near the interface between the residual filler metal layer andα-(Fe,Cr)layer.The maximum shear strength of brazed joints reached 129 MPa when brazed at 1020℃ for 10 min.The diffusion activation energies ofα2-(Ti3Al)andα-(Fe,Cr)phases were−195.769 and−112.420 kJ/mol,respectively,the diffusion constants for these two phases were 3.639×10^(−6) and 7.502×10^(−10)μm^(2)/s,respectively.Cracks initiated at Fe2Zr layer and propagated into the residual filler metal layer during the shear test.The Laves-Fe2Zr phase existing on the fracture surface suggested the brittle fracture mode of the brazed joints.

STRUCTURE AND GLASS FORMING ABILITY(GFA)OF AMORPHOUS ALLOYS

A new microstructure model is developed for amorphous alloys,so called Cluster medel, in which the amorphous phase is thought of composing of randomly distributed ordered clusters of different sizes.Thermodynamic calculation on this model deduces a parameter describing the glass forming ability of metallic alloys:α_c=(1-2.08/Φ_m)T_g/T_m,where T_g is gass transition temperature,T_m is the melting temperature,and Φ_m is entralpy change of melting.It is believed that easy glass forming alloy systems have larger values of a_c.This new criterion of GFA not only provides the theoretical background for several GFA criteria in the literature cited,but also can predict the GFA of many alloy systems more reasonably and accurately.

Strength and interfacial microstructure of Si3N4 joint brazed with amorphous Ti-Zr-Ni-Cu filler metal

In this paper, the vacuum brazing of Si3N4 ceramic was carried out with Ti40Zr25Ni15Cu20 amorphous filler metal. The interfacial microstructure was investigated by scanning electron microscopy （ SEM ）, energy dispersive spectroscopy （EDS） etc. According to the analysis, the interface reaction layer was mode up of TiN abut on the ceramic and the Ti-Si, Zr-Si compounds. The influence of brazing temperature and holding time on the joint strength was also studied. The results shows that the joint strength first increased and then decreased with the increasing of holding time and brazing temperature. The joint strength was significantly affected by the thickness of the reaction layer. Under the same experimental conditions, the joint brazed with amorphous filler metal exhibits much higher strength compared with the one brazed with crystalline filler metal with the same composition. To achieve higher joint strength at relatively low temperature, it is favorable to use the amorphous filler metal than the crystalline filler metal.

Structural and mechanical properties of amorphous carbon films deposited by the dual plasma technique

Direct current metal filtered cathodic vacuum arc （FCVA） and acetylene gas （C2H2） were wielded to synthesize Ti-containing amorphous carbon films on Si （100）. The influence of substrate bias voltage and acetylene gas on the microstructure and mechanical properties of the films were investigated. The results show that the phase of TiC in the （111） preferential crystallographic orientation exists in the film,and the main existing pattern of carbon is sp2. With increasing the acetylene flow rate,the contents of Ti and TiC phase of the film gradually reduce; however,the thickness of the film increases. When the substrate bias voltage reaches -600 V,the internal stress of the film reaches 1.6 GPa. The micro-hardness and elastic modulus of the film can reach 33.9 and 237.6 GPa,respectively,and the friction coefficient of the film is 0.25.

Vacuum brazing TiAl intermetallic to K4169 alloy using amorphous filler metals Ti_(56.25–x)Zr_(x)Ni_(25)Cu1_(8.75)

A series of Ti_(56.25-x)Zr_(x)Ni_(25)Cu1_(8.75)(x=0–25,at.%) filler metals were designed based on a cluster-plus-glue-atom model to vacuum braze TiAl intermetallic to K4169 alloy. The impact of Zr content on the interfacial microstructure and shear strength of joints was examined. And the relationship between the interfacial lattice structure and the fracture behavior of the joint was investigated. The findings reveal a sectionalized characteristic with three reaction zones (Zone I, Zone II and Zone III) in the microstructure of the TiAl intermetallic to K4169 alloy joint. As the Zr content in filler metals increased, the diffusion of Ti transitioned from long-distance to short-distance in Zone I, changing the initial composition from TiNi_(3) /TiNi/NiNb/(Cr, Fe, Ni)SS to NiCrFe/(Cr, Fe, Ni)SS /TiNi. In Zone II, the initial composition altered from TiNi_(3) /TiNi to TiNi/Ti_(2) Ni/TiNi_(3) /TiCu/TiNi. The interface between Zones II and III altered from a non-coherent and semi-coherent interface of TiNi/TiAl/Ti_(3) Al with significant residual stress to a semi-coherent interface of TiNi/TiNi_(3) /TiAl_(2) /Ti_(3) Al with a gradient distribution. The shear strength of the joint initially decreased and then increased. When the Zr content of filler metal was 25 at.%, the shear strength of the joint reached 288 MPa. The crack initiation position changed from non-coherent TiNi/TiAl interface with high angle grain boundaries (HAGBs) and lattice mismatch of 65.86 at.% to a semi-coherent Ti3 Al/TiAl2 interface with a lattice mismatch of 20.07 at.% when the Zr content increased. The brittle fracture was present on the fracture surfaces of all brazed joints.

Microstructures and properties of Fe-Co-B-Si-Nb coating prepared by laser cladding and remelting

High power laser cladding of [ （ Fe0. 5 Co0. 5 ） 0. 75 B0. 2 Si0.05 ] 95. 7 Nb4. 3 powder mixture afier-remelting was performed to fabricate Fe-based metallic glass coating on the surface of steel of China Classification Society： Grade B （CCS-B）. Scanning electron microscopy （SEM）, X-ray diffraction （XRD）, transmission electron microscopy （TEM） with energy dispersive spectrometer （EDS）, Vickers hardness tester and corrosion resistance tester were employed to characterize microstructures and evaluate properties of this coating. According to the results of SEM, XRD and TEM, the cladding coating consisted of nanocrystalline embedded in amorphous phase. EDS data indicated that Nb segregated in the amorphous matrix. The results of hardness test revealed that the hardness of the top layer was higher than that of the inner layer of the coating. The coating exhibited excellent corrosion resistance in a 3.5% NaCl solution.

非晶态介孔FeAlP催化剂用于合成1,5-苯二氮类化合物(英文)

A simple and versatile method for the synthesis of 1,5-benzodiazepines from o-phenylenediamine and ketones in the presence of solvents and under solvent-free conditions that used an amorphous mesoporous iron aluminophosphate as catalyst was developed.High yields with excellent selectivity were obtained with a wide variety of ketones under mild reaction conditions.The catalyst had the advantages of ease of preparation,ease of handling,simple recovery,reusability,non toxicity,and being inexpensive.

Microstructure and Wear Properties of Fe-based Amorphous Coatings Deposited by High-velocity Oxygen Fuel Spraying

Fe-based powder with a composition of Fe_（42.87）Cr_（15.98）Mo_（16.33）C_（15.94）B_（8.88）（at.%）was used to fabricate coatings by high-velocity oxygen fuel spraying.The effects of the spraying parameters on the microstructure and the wear properties of the Fe-based alloy coatings were systematically studied.The results showed that the obtained Fe-based coatings with a thickness of about 400μm consisted of a large-volume amorphous phase and some nanocrystals.With increasing the fuel and oxygen flow rates,the porosity of the obtained coatings decreased.The coating deposited under optimized parameters exhibited the lowest porosity of 2.8%.The excellent wear resistance of this coating was attributed to the properties of the amorphous matrix and the presence of nanocrystals homogeneously distributed within the matrix.The wear mechanism of the coatings was discussed on the basis of observations of the worn surfaces.

Synthesis and properties of ionic conduction polymer for anodic bonding

In this study,powders of polyethylene oxide（PEO） and lithium perchlorate（Li Cl O4） were used as the raw materials for producing the ionic conduction polymer PEO–Li Cl O4 with different complex-ratios and used for anodic bonding through high energy ball milling method,and meanwhile,X-ray diffraction,differential scanning calorimetry（DSC）,ultraviolet absorption spectrum test analysis,and other relevant methods were adopted to research the complexation mechanism of PEO and Li Cl O4 and the impact of the ionic conduction polymer with different complex-ratios on the anodic bonding process under the action of the strong static electric field.The research results showed that the crystallization of PEO could be effectively obstructed with increased addition of Li Cl O4,thus increasing the content of PEO–Li Cl O4 in amorphous area and continuously improving the complexation degree and the room-temperature conductivity thereof,and that the higher room-temperature conductivity enabled PEO–Li Cl O4 to better bond with metallic aluminum and have better bonding quality.As the new encapsulating material,such research results will promote the application of new polymer functional materials in micro-electromechanical system（MEMS） components.

Advances in Investigation of Fe-based Glass-forming Alloy Melts

Continuous precision casting is an important trend in modern industrialization.Clustering effects in glassforming metallic liquids tremendously influence the properties of rapidly quenched ribbons;therefore,much attention has been paid to the study of Fe-based glass-forming melts at high temperatures.Recent investigations of these melts are categorized and reviewed.It is concluded that more efforts are still required to reveal the discipline of amorphization brought about by rapid quenching of Fe-based glass-forming melts.