Crystallization Behaviour and Mechanical Properties of Zr65Cu18Ni9A18 Bulk Metallic Glass

Designing and synthesis of cost effective bulk metallic glasses （BMGs） has been of considerable interest during the last decade so that they can be made commercially viable. Among these, Zr-based BMGs have been reported extensively due to their attractive properties, An alloy having composition Zr65Cu18Ni9A18 was designed and synthesized using 2-3 N pure materials by Cu mould casting. The alloy was characterized by X- ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS） and high temperature differential scanning calorimetry （DSC）. Thermal parameters like supercooled liquid region △Tx, reduced glass transition temperature Trg, γ and δ parameters were evaluated. Mechanical properties like microhardness, nanohardness, elastic modulus and fracture strength were measured. The alloy showed wide supercooled liquid region of 129＋1 K with improved thermal stability. The alloy has considerable fracture strength along with fair amount of ductility.

Influence of Small Cr Addition on Thermal Stability and Magnetic Properties of Fe-Co-Zr-Nb-B Glassy Alloys

Fe62Cos-xCrxZr6Nb4B20 （x=0-4 at. pct） metallic glasses show high thermal stability with a maximum supercooled liquid region of about 84.8 K. The addition of 2 at. pct Cr causes the extension of the supercooled liquid region remarkably, leading to the enhancement of thermal stability and glass-forming ability. The crystallization of the Fe-based glassy alloys takes place through a single exothermic reaction, accompanying the precipitation of more than three kinds of crystallized phases such as α-Fe, Fe2Zr and ZrB2. The long-range atomic rearrangements required for the precipitation of the multiple crystalline phases seem to play an important role in the appearance of the large supercooled liquid region through the retardation of the crystallization reactions. The Fe-based alloys exhibit soft ferromagnetic properties. The saturation magnetization decreases with increasing Cr content while the saturated magnetostriction increases as a function of Cr content. There is no distinct change in the saturation magnetization and coercive force with annealing temperature below the crystallization temperature. The devitrification gives rise to a considerable enhancement in both as and He.

Oxidation of a Co-base Superalloy

The oxidation behavior of a cast polycrystalline Co-base superalloy was studied at temperatures from 900 to 1050℃ and analyzed by thermogravimetric analysis （TGA）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results indicate that a cast Co-base superalloy follows the subparabolic oxidation kinetics at 900 and 1000℃, which are controlled by the growth of the inner Cr-rich layer, and that after oxidation at 1050℃ for 200 h, it almost exhibits the linear oxidation kinetics possible due to the volatility of Cr-rich oxide. A mixed scale forms on the alloy after prolonged oxidation. The oxide scale formed at 900 and 1000℃ is composed of an outer layer of spinel and an inner continuous Cr-rich layer and at I050℃ is composed of a very discontinuous Cr-rich layer.

Evolution of Grain Selection in Spiral Selector during Directional Solidification of Nickel-base Superalloys

The process of grain selection in the spiral selector was investigated by both a ProCAST simulation based on a cellular automaton finite element（CAFE） model and experimental confirmation.The results show that the height of starter block,the spiral diameter and initial angle play an important role in grain selection.The dimension of selector should be maintained in a stable range to optimize the grain orientation and select a single crystal efficiently.A selector which can efficiently select a single crystal had been successfully designed.Grain orientation fluctuation in the spiral part was also studied by means of the variation of thermal condition.

Effect of Solidification Parameters on the Microstructure and Creep Property of a Single Crystal Ni-base Superalloy

A single crystal Ni-base superalloy was processed with withdrawal rates between 2 and 7 mm/min.The ascast microstructures,heat treatment response and creep property have been characterized as a function of the withdrawal rate.As expected,the primary and secondary dendrite arm spacing decreased with increasing withdrawal rate; microsegregation degree and porosity distribution were also varied with different withdrawal rates.The withdrawal rate of 2 mm/min resulted in a noticeable residual microsegregation even after full heat treatment.The samples solidified at 7 mm/min exhibited a high density of cast porosities,and this led to a dramatical decline of the creep strain.4 or 6 mm/min appeared to be the optimum withdrawal rate in the present study,which resulted in a uniform microstructure and an optimum density of cast porosity.

Rapid decolorization of Acid Orange Ⅱ aqueous solution by amorphous zero-valent iron

Some problems including low treatment capacity,agglomeration and clogging phenomena,and short working life,limit the application of pre-treatment methods involving zero-valent iron （ZVI）.In this article,ZVI was frozen in an amorphous state through a melt-spinning technique,and the decolorization effect of amorphous ZVI on Acid Orange II solution was investigated under varied conditions of experimental variables such as reaction temperature,ribbon dosage,and initial pH.Batch experiments suggested that the decolorization rate was enhanced with the increase of reaction temperature and ribbon dosage,but decreased with increasing initial solution pH.Kinetic analyses indicated that the decolorization process followed a first order exponential kinetic model,and the surface-normalized decolorization rate could reach 2.09 L/（m^2 ·min） at room temperature,which was about ten times larger than any previously reported under similar conditions.Recycling experiments also proved that the ribbons could be reused at least four times without obvious decay of decolorization rate and efficiency.This study suggests a tremendous application potential for amorphous ZVI in remediation of groundwater or wastewater contaminated with azo dyes.

Magnesium Alloy for Repair of Lateral Tibial Plateau Defect in Minipig Model

Bone graft substitutes are widely-studied as alternatives to bone grafts in the clinic. The currently available products are mostly ceramics and polymers. Considerable progress has been made in the study of the biodegradable magnesium alloys, which possess the necessary attributions of a suitable substitute, including an excellent mechanical property. In the present study, a minipig model of a lateral tibial plateau defect was used to evaluate the effectiveness of a magnesium alloy in the repair of a critical-sized defect. The micro-arc oxidation （MAO）-coated ZK60 alloy tablets and medical-grade calcium sulfate pellets were used as the test and control materials, respectively. Bone morphology was monitored by computed tomography after the implantation for 2 and 4 months. It was found that the bone morphology in minipigs following magnesium treatment was similar to that of the normal bone, whereas an abnormal and concave morphology was displayed following the calcium sulfate treatment. The average bone healing rate for the magnesium-treated defects was higher than that of the calcium sulfate-treated defects at the first 4 months following the implantation. Overall, magnesium treatment appeared to calcium sulfate treatment. Thus, the MAO-coated ZK60 al substitute, and further research on its biological activity in improve the defect repair as compared with the oy appears to be a useful biocompatible bone graft vivo is needed.

Influence of the Substrate Orientation on the Isothermal Solidification during TLP Bonding Single Crystal Superalloys

Angle deviations between the two substrates during transient liquid phase （TLP） bonding single crystal superalloys cannot be avoided. In the present work, specimens have been prepared to investigate the influences of the various substrate orientations. It is found that the width of the non-isothermal solidification zone （NSZ） is linear with the square root of the isothermal solidification time. This suggests that the isothermal solidification process is B-diffusion controlled in different substrate orientation deviations. And also the width of the NSZ increases with increasing angle deviation, indicating that the isothermal solidification time needed in the TLP bonding increases with increasing orientation deviation between the two substrates.

Effect of Threshold Stress on Anisotropic Creep Properties of Single Crystal Nickel-Base Superalloy SRR99

The influence of orientation on the creep properties of the nickel-base single crystal superalloy SRR99 was investigated at 760℃ and various levels of applied stress.It was found that the effect of anisotropy was strikingly prominent at this temperature.Deformation mechanisms of single crystals with three principal orientations at 760℃/790 MPa were explained according to detailed observations of dislocation arrangements by means of transmission electron microscopy （TEM）.Liability to shearing γ＇ precipitates for [011] orientation and co-planar slip for [111] orientation resulted in poor creep strength and short stress rupture life.It was also found that the apparent primary creep strain could be measured when the applied stress was increased to 565 MPa.Modified power law equation was adopted and the concept of a threshold stress σ 0 which determines dislocation looping or shearing to be activated was then involved.Through detailed calculations,the threshold stress was obtained to further analyse the distribution of the applied stress and better rationalize the anisotropic creep behaviour in the stereographic triangle in combination with TEM observations.

Effect of Minor Alloying on Crystallization Behavior and Thermal Properties of Zr_(64.5)Ni_(15.5)Al_(11.5)Cu_(8.5) Bulk Amorphous Alloy

Minor alloying plays an important role in the synthesis and improvement of thermal stability of bulk metallic glasses（BMGs）.The present study was conducted to investigate the effect of minor additions of Y,Ti and Nb on the crystallization behavior and the thermal properties of Zr64.5Ni15.5Al11.5Cu8.5 alloy.Thermal parameters and the activation energies for crystallization were calculated for four（Zr0.645Ni0.155Al0.115-Cu0.085）100-xMx（M=Y,Ti and Nb,while x=0,2 at.） alloys.The present alloys have wide supercooled liquid region of ≥87 K.Maximum activation energy was found to be greater than 300 kJ/mol for the base alloy.Four crystalline phases were identified in the samples annealed at 823 K for 20 min.Reduced glass transition temperature（Trg） and other thermal parameters such as γ,δ and β were improved by Y and Ti addition.Nb addition resists crystallization below annealing temperature 713 K,however,its effect on thermal properties is not very promising.

Precipitation Behaviors in the Diffusion Affected Zone of TLP Bonded Single Crystal Superalloy Joint

The single crystal superalloys were joined by transient liquid phase(TLP) bonding. The precipitating behavior in the diffusion affected zone(DAZ) was studied and the hardness across the DAZ was analyzed. Results have shown that there existed M3B2,M5B3 and M23B6 borides in the DAZ. With increasing bonding time,fine M3B2 precipitates formed first near the isothermal solidification zone(ISZ)/matrix interface. Then,the dendritic M5B3 precipitates formed with an obvious orientation relationship with the substrate. The acicular precipitates were constituted by M23B6 and M5B3 phases with continuous or discontinuous morphologies. The hardness of the DAZ reached a summit in the fine M3B2 region and decreased with the increase of the distance away from the ISZ/matrix interface.

Friction Stir Welding of Zr_(55)Al_(10)Ni_5Cu_(30) Bulk Metallic Glass to Crystalline Aluminum

The Zr55Al10Ni5Cu30 bulk metallic glass plate were successfully welded to crystalline aluminum plates by using a friction stir welding （FSW） method. The welded zone was examined. No defects, cracks or pores were observed and no other crystalline phases except for aluminum were found in the welded joint. The strength of the joint is higher than that of aluminum. The glassy phase in the stir zone keeps the amorphous state, showing a successful welding. The storage modulus softens over the glass transition. And the weldability was discussed according to this phenomena.

Interfacial morphologies between iron and Ag-Cu-Sn alloy

A series of experiments have been designed to investigate the effect of different space positions between liquid Ag-Cu-Sn alloy drop and iron substrates on the liquid/solid inter-facial morphologies by a sessile drop method. The results show that Ag-Cu-Sn alloy diffuses into the solid iron substrate, and the amounts are greater and the distances are longer when it dif-

Prediction of Dendrite Orientation and Stray Grain Distribution in Laser Surface-melted Single Crystal Superalloy

A vectorization analysis technique for crystal growth and microstructure development in single-crystal weld was developed in our previous work. Based on the vectorization method, crystal growth and stray grain distribution in laser surface remelting of single crystal superalloy CMSX-4 were investigated in com- bination of simulations with experimental observations. The energy distribution of laser was taken into consideration in this research. The experimental results demonstrate that the simulation model applies well in the prediction of dendrite growth direction. Moreover, the prediction of stray grain distribution works well except for the region of dendrites growing along the [100] direction.

High Temperature Stress Rupture Anisotropy of a Ni-Based Single Crystal Superalloy

High temperature stress rupture anisotropies of a second generation Ni-base single crystal（SC） superalloy specimens with [001], [011] and [111] orientations under 900 ℃/445 MPa and 1100 ℃/100 MPa have been investigated in the present study, with attentions to the evolution of γ/γ′ microstructure observed by scanning electron microscopy and the dislocation configuration characterized by transmission electron microscopy in each oriented specimen. At 1100 ℃/100 MPa as well as 900 ℃/445 MPa, the single crystal superalloy exhibits obvious stress rupture anisotropic behavior. The [001] oriented specimen has the longest rupture lifetime at 900 ℃/445 MPa, and the [111] oriented sample shows the best rupture strength at 1100 ℃/100 MPa. While the [011] oriented specimen presents the worst rupture lifetime at each testing condition, its stress rupture property at 1100 ℃/100 MPa is clearly improved, compared with900 ℃/445 MPa. The evident stress rupture anisotropy at 900 ℃/445 MPa is mainly attributed to the distinctive movement way of dislocations in each oriented sample. Whereas, at 1100 ℃/100 MPa, together with the individual dislocation configuration, the evolution of γ/γ′ microstructure in each orientation also plays a key role in the apparent stress rupture anisotropy.

Amorphous alloys——A kind of promising high-performance materials

Amorphous alloys, relatively recent metallic materials, exhibit many excellent properties because of their unique structure. They have attracted tremendous attention from both scientists and engineers since their initial discovery 50 years ago. In the early stages, scientists focused on developing new alloy systems with good amorphous structure forming ability and to un-