The compression behavior of the heavy RE-based BMC Gd40Y16Al24Co20 under high pressure has been investigated by in situ high pressure angle dispersive X-ray diffraction measurements using synchrotron radiation in the pressure range of 0-33.42 GPa at room temperature. By fitting the static equation of state at room temperature, we find the value of bulk modulus B is 61.27±4 GPa which is in good agreement with the experimental study by pulse-echo techniques of 58 GPa. The results show that the amorphous structure in the heavy RE-based BMG Gd40Y16Al24Co20 keeps quite stable up to 33.42 GPa although its compressibility is as large as about 33%. The coexistence of normal local structure similar to that of other BMGs and covalent bond structure similar to those of oxide glasses may be the reason for the anomalous property under high pressure of the Gd4oY16Al24Co2o BMG.
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
A new type of Cu-La2O3 composite was fabricated by internal oxidation method using powder metallurgy.Sliding wear behavior of the Cu-La2O3 composite was studied on a pin-on-disc wear tester under various electrical currents and applied loads.The worn surfaces were characterized using scanning electron microscopy and energy dispersive spectroscopy to probe the wear mechanisms.The results indicated that applied load had a significant effect on the wear rate of the Cu-La2O3 composite pins.The wear rate displayed the minimum value at the load of 50 N during electrical sliding processes.The corresponding wear mechanism was identified to be adhesive wear,abrasive wear,oxidation wear and arc erosion.
This paper applies techniques of containerless processing, drop tube and glass fluxing, to undercool and solidify Ni77P23 alloys. Different diameter spheres were collected at the bottom of a 52-m long drop tube. Both crystalline and amorphous phase were formed in various size specimens due to the different cooling rate. The variation of partial undercooling with bulk undercooling is calculated for the Ni77P23 alloys. The deep undercooling and rapid solidification behaviour of Ni77P23 melts has been analysed with respect to microstructure formation and transition during fluxing and 52-m drop process of undercooled melts.
The thermal stability and glass forming ability (GFA) of Zr35-xTi30Cu7.5Be27.5Agx (x = 0-10) alloys were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and ultrasonic techniques. We found that the addition of 1 at.% Ag can considerably enhance the GFA as indicated by an increase in the critical glass dimension from 15 mm in the Zr35Ti30Cu7.5Be27.5 alloy to 20 mm in the Zr34Ti30Cu7.5Be27.5Ag1 alloy. However, with the addition of more Ag the supercooled liquid region (△Tx) and y parameter (defined as Tx/(Tg+Tl)) drastically decreased from 155 K and 0.436 to 76 K and 0.363, respectively, resulting in a decrease in the GFA. Additionally, the elastic constant (the ratio of shear modulus to bulk modulus or Poisson's ratio) was also used as a gauge to evaluate the GFA in Zr35-xTi30Cu7.5Be27.5Agx alloys.
Ternary Zr49Cu44Al7 metallic glass matrix composite rods with CuZr nano-phase,exhibiting an elastic strain of 1.6% and a high strength of 1.78 GPa,have been manufactured. The structural evaluation of the ternary metallic glass matrix composite under high pressure has been investigated using angle dispersive X-ray diffraction with a synchrotron radiation source. The investigation shows that the amorphous matrix structure is stable under pressures up to 40.8 GPa at room temperature. No pressure induced CuZr nano-phase disappearing or growing was detected. According to the Bridgeman equation of state,the bulk modulus B0 =115.2 GPa has been obtained.
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
Electrochemical corrosion and oxidation resistances of Zr 60 Ni 21 Al 19 amorphous alloy were studied. The ternary amorphous alloy exhibits greater positive potential than its crystalline counterpart and 0Cr19Ni9Ti stainless steel. Its weight loss result measured in 2 mol/L HCl solution is in agreement with the potentiodynamic curve. But there is no obvious difference in the oxidation resistances between Zr 60 Ni 21 Al 19 amorphous and its crystalline alloys. They both exhibit high oxidation resistance.
