The effect of tin (Sn) addition on the glass forming ability (GFA) and mechanical properties of the Ni-Nb-Zr ternary alloy system has been studied. The addition of Sn improves the GFA; Ni61Nb35.5-xZr3.5Snx (in at.%) alloys with x=1 can be cast into amorphous samples at least 3 mm in diameter using a copper mold injection-casting method. The critical size for glass formation decreases to 2 mm when x=5 because Ni2SnZr phase precipitates readily. The addition of Sn is also effective in enhancing the stability of the supercooled liquid; a maximum supercooled liquid region of 48 K was attained for the Ni61Nb30.5Zr3.5Sn5 alloy. Compression tests reveal that the Ni61Nb33.5Zr3.5Sn2 alloy possesses the best mechanical properties,with yield strength～3180 MPa,fracture strength～3390 MPa and plastic strain ～1.3%. The fracture surfaces examined by scanning electron microscopy indicate that the alloys have a transition from ductility to brittleness in fracture behavior. The combination of high GFA,high thermal stability,high strength and compressive plasticity makes these alloys potentially attractive for engineering applications.
LI DengKeZHANG HaiFengWANG AiMinZHU ZhengWangHU ZhuangQi
118 kinds of Pt-Zr phases were established and investigated by considering various structures. Then the related physical properties, such as structural stability, lattice constants, formation enthalpies, elastic constants and bulk moduli, are obtained by ab initio calculations. Based on the calculated results of formation enthalpies, the ground-state convex hull is derived for the Pt-Zr system. The calculated physical data would provide a basis for further thermodynamic calculations and atomistic simulations. For these Pt-Zr compounds, it is found there are a positive linear correlation between the formation enthalpies and atomic volumes, and a negative linear correlation between the bulk modules and atomic volumes.
The influence of Zr content on corrosion behaviors of the Ni61.5Nb 38.5xZrx(x=1,3,5,7,9 at.%) bulk metallic glasses(BMGs) in 1 M HCl aqueous solution was investigated by potentiodynamic polarization measurements and X-ray photo-electron spectroscopy(XPS).It was found that these BMG alloys possess superior corrosion resistance,that is,with large passive region of about 1.5 V and low passive current density(as low as 0.05 Am-2 for Ni61.5Nb31.5Zr7).XPS analysis indicates that the high corrosion resistance is attributed to the formation of Nb-and Zr-enriched surface films formed in the aggressive acid solution.The Zr substitution for Nb effectively reduces the Ni content,particularly the metallic state Ni content in the surface films,which depresses the electrical conduction of the surface films and reduces the passive current density,thus leading to the enhancement of the corrosion resistance of these Ni-Nb-Zr BMGs.These alloys may potentially be useful for engineering applications.
LI DengKeZHU ZhengWangZHANG HaiFengWANG AiMinHU ZhuangQi
An Fe-based amorphous alloy was found to significantly enhance the reductive degradation of an azo dye in aqueous solution. The surface-area normalized rate constant was up to 2.0 L m-2 min-1 at room temperature,an order of magnitude larger than any previously reported value. The activation energy of the degradation process was calculated according to the Arrhenius equation,and a much lower value than those previously reported was obtained. Valence band measurement indicated that a depressed valence band maximum and a widened empty band were established in the amorphous ribbon. The unique structure of the amorphous alloy is important-it may reduce the activation energy of the degradation process and enhance the activity of the electrons,thus accelerating the degradation process.
