H.F. Zhang

Mechanical properties of tungsten fiber reinforced ZrAlNiCuSi metallic glass matrix composite

Tungsten fiber reinforced (Zr55Al10Ni5Cu30)(98.5)Si-1.5 metallic glass composites were fabricated and characterized. The mechanical properties of the composite under compression and tension were investigated. Tungsten reinforcement greatly increased compressive strain to failure compared to the unreinforced (Zr55Al10Ni5Cu30)(98.5)Si-1.5 metallic glass. The compressive failure mode changed from a single shear band to multiple shear bands and to localized fiber buckling and tilting as the volume fraction of tungsten fiber increased. The maximum tensile strength and strain to failure of each of the composites were lower than those of unreinforced material due to the lack of substantial shear bands. Tensile toughness changed to some extent due to different interface reactions. The reason for the improved mechanical properties is discussed

TiZr-base Bulk Metallic Glass with over 50 mm in Diameter

Low-cost TiZr-base bulk metallic glasses (BMGs) (Ti(36.1)Zr(33.2)Ni(5.8)Be(24.9))(100-x)Cu(x) (x=5, 7 and 9) with a maximum size of over 50 mm in diameter were developed by optimizing the alloy composition. The idea is initiated by selecting a particular microstructure comprising primary beta-Ti dendrite and amorphous phase. Afterwards, based on this composition of amorphous phase, a class of TiZr-base bulk metallic glasses was designed step by step to reach the optimum composition range. The glass transition temperature (T(g)), initial crystallization temperature (T(x)) and width of supercooled region (Delta T) of (Ti(36.1)Zr(33.2)Ni(5.8)Be(24.9))(91)Cu(9) BMG are 611, 655 and 44 K, respectively. The (Ti(36.1)Zr(33.2)Ni(5.8)Be(24.9))(91)Cu(9) BMG exhibits low density of 5.541 g.cm(-3) and high compressive fracture strength of 1800 MPa, which promises the potential application as structural materials.

Hydrogenation characteristics of Mg-TiO2 (rutile) composite

The nanostructured composite Mg-TiO2 (rutile) was prepared by reaction ball milling (RBM). Under the combined effects of the catalyst n-TiO2 and the mechanical driving force, Mg was hydrided into MgH2 and gamma -MgH2 directly during RBM. The addition of TiO2 resulted in a markedly improved hydrogenation performance of Mg, rapid kinetics, low working temperature and excellent oxidation-resistance. A hydrogenation mechanism of the composite was proposed on the basis of microstructure analysis

Enhanced plasticity in Mg-based bulk metallic glass composite reinforced with ductile Nb particles

The authors report the synthesis of Mg-based metallic glass composite reinforced with Nb particles which are simply added during melting process. The ductile Nb particles effectively impede shear band propagation and upon yielding, deformed Nb particles distribute the load uniformly to the surrounding glassy matrix to promote the initiation and branching of abundant secondary shear bands. In contrast to the previous Mg-based metallic glass composites which fracture with very little plasticity, the composite shows great resistance to crack growth. The high strength of 900 MPa and large plasticity of 12.1 +/- 2% have made it comparable to excellent Zr- or Ti-based metallic glass composite. (c) 2006 American Institute of Physics.

Behaviour of AZ31 magnesium alloy during compression at elevated temperatures

Abstract The hot deformation of AZ31 magnesium alloy has been studied by compression testing using a Gleeble 1500 machine at temperatures between 250 and 450°C and at strain rates ranging from 0·005 to 5 s−1. Optical microscopy and transmission electron microscopy (TEM) have been used to observe microstructures of the alloy. The experimental results show that the flow stress behaviour can be described by an exponential law at temperatures below 350°C. At higher temperatures a power law of deformation is valid. The hot deformation activation energy Q derived from the experimental data is 112 kJ mol−1 with a stress exponent n=7. Optical microscopy and TEM observations show that dynamic recrystallisation (DRX) takes place during the deformation process and the formation of new grains occurs by conventional DRX nucleation by bulging. The average DRX grain size Drex is sensitively dependent on deformation temperature T and strain rate ϵ and is also a function of the Zener–Hollomon parameter Z. The relationship between Z and Drex has been experimentally constructed using linear regression. In the present work, DRX grains nucleate by bulging of some portions of serrated grain boundaries, accompanied by the formation of twinning.

Large reversible magnetocaloric effects in ErFeSi compound under low magnetic field change around liquid hydrogen temperature

Magnetic properties and magnetocaloric effects (MCEs) of ternary intermetallic ErFeSi compound have been investigated in detail. It is found that ErFeSi exhibits a second-order magnetic transition from ferromagnetic to paramagnetic states at the Curie temperature TC = 22 K, which is quite close to the liquid hydrogen temperature (20.3 K). A thermomagnetic irreversibility between zero-field-cooling and field-cooling curves is observed below TC in low magnetic field, and it is attributed to the narrow domain wall pinning effect. For a magnetic field change of 5 T, the maximum values of magnetic entropy change (−ΔSM) and adiabatic temperature change (ΔTad) are 23.1 J/kg K and 5.7 K, respectively. Particularly, the values of −ΔSM and refrigerant capacity reach as high as 14.2 J/kg K and 130 J/kg under a magnetic field change of 2 T, respectively. The large MCE without hysteresis loss for relatively low magnetic field change suggests that ErFeSi compound could be a promising material for magnetic refrigeration...

Electrochemical characteristics of amorphous Mg0.9M0.1Ni (M=Ni, Ti, Zr, Co and Si) ternary alloys prepared by mechanical alloying

Abstract Mg0.9M0.1Ni (M=Ni, Ti, Zr, Co or Si) ternary alloys were prepared by mechanical alloying (MA). The XRD result showed that all ternary alloys were of amorphous structure, with a trace of substitution elements, except for Co. Electrochemical characteristics of all ternary alloys were studied which were compared to MA amorphous MgNi alloy. Experimental results showed that the ternary alloys had a large discharge capacity at room temperature but lower than that of the MA MgNi alloy. Partially substituting Mg with Ni, Ti, Co, Si could lead to the improvement of cyclic stability and high rate discharge capability. Over all, amorphous Mg0.9Ti0.1Ni showed the best synthesis properties.

Elevated temperature compression behaviour of Mg-Al-Zn alloys

Abstract Flow stress behaviour of Mg–Al–Zn alloys was studied by compression testing using a Gleeble 1500 machine at temperatures of 200–450°C and at strain rates ranging from 0·005 to 5 s−1. The experimental results show that initial grain size and a distinctive basal texture lead to the great difference between as extruded AZ31 alloy and other two groups of cast alloys AZ31 and AZ80, including the variation in the flow stress equations and dynamic recrystallisation behaviour. The increment of alloying element Al will decrease stacking fault energy and enhance the process of dislocation climb, and therefore reduce the tendency for dislocation pile-up to cross-slip. The presence of the second phase particles will hinder both the formation and migration of recrystallisation fronts. As a result, for cast AZ80 alloy, dynamic recrystallisation is delayed and the activation energy for the plastic deformation process sharply increases from 166·75 to 220 kJ mol−1 as compared with cast AZ31 alloy under the same deformation condition.

Structural and hydriding properties of composite Mg-ZrFe1.4Cr0.6

The composite system Mg-ZrFe1.4Cr0.6 was synthesized by mechanical grinding of Mg mixed with various amounts of ZrFe1.4Cr0.6. The hydrogenation performance of Mg in the composite system was markedly enhanced, especially for Mg-40 wt.% ZrFe1.4Cr0.6. SEM, TEM, EDS and X-ray diffraction were used to characterize the composite. The full exploitation of the catalytic function of ZrFe1.4Cr0.6 and the nanostructure of Mg were found to be the main reasons for the markedly improved hydriding kinetics of the composite

Reduction of hysteresis loss and large magnetocaloric effect in the C- and H-doped La(Fe, Si)13 compounds around room temperature

The effects of the interstitial C and H atoms on the phase formation, the hysteresis loss, and magnetocaloric effects of the NaZn13-type La(Fe, Si)13 compounds are investigated. It is found that the annealing time to obtain a 1:13 structure is significantly reduced from 40 days for LaFe11.7Si1.3 to a week for LaFe11.7Si1.3C0.2. The introduction of C and H atoms can adjust Curie temperature to around room temperature and leads to the decrease in magnetic entropy change (ΔSM) and magnetic hysteresis loss due to the weakening of itinerant-electron metamagnetic transition. Large −ΔSM of 19.0 J/kg K at room temperature without hysteresis loss for LaFe11.7Si1.3C0.2H1.7 is obtained for a field change of 5 T.