Mechanism,condition and characteristics for the formation of the network structure in a group of Zr-Al-Ni-Cu bulk metallic glasses(BMGs) were investigated.The results show that the constituent segregation and/or the symplastic growth would be the mechanisms for the formation of the cell structure in the present Zr-Al-Ni-Cu BMGs.The cell structure can be easily obtained for the glass forming alloys whose compositions locate nearby the eutectic point.The shorter the distance is from the eutectic point,the larger the cell and the thicker the cell wall of the network structure will be.The present investigation would provide useful information for the development of the BMG with the network structure.
AN WeiKeDING DaWeiCAI AnHuiZHOU GuoJunLUO YunLI JiangHongPENG YongYi
Effect of network structure on plasticity and fracture mode of Zr？Al？Ni？Cu bulk metallic glasses （BMGs） was investigated. The microstructures of transversal and longitudinal sections were exposed by chemical etching and observed by scanning electron microscopy （SEM）. The mechanical properties were examined by room-temperature uniaxial compression test. The results show that both plasticity and fracture mode are significantly affected by the network structure and the alteration occurs when the size of the network structure reaches up to a critical value. When the cell size （dc） of the network structure is ~3μm, Zr-based BMGs characterize in plasticity that decreases with increasingdc. The fracture mode gradually transforms from single 45° shear fracture to double 45° shear fracture and then cleavage fracture with increasingdc. In addition, the mechanisms of the transition of the plasticity and the fracture mode for these Zr-based BMGs are also discussed.
Cu50Zr40Ti10 bulk amorphous alloys were fabricated by hot pressing gas-atomized Cu50Zr40Ti10 amorphous powder under different consolidation conditions without vacuum and inert gas protection. The consolidation conditions of the Cu50Zr40Ti10 amorphous powder were investigated based on an L9（34） orthogonal design. The compression strength and strain limit of the Cu50Zr40Ti10 bulk amorphous alloys can reach up to 1090.4 MPa and 11.9 %, respectively. The consolidation pressure significantly influences the strain limit and compression strength of the compact. But the mechanical properties are not significantly influenced by the consolidation temperature. In addition, the preforming pressure significantly influences not the compression strength but the strain limit. The optimum consolidation condition for the Cu50Zr40Ti10 amorphous powder is first precompacted under the pressure of 150 MPa, and then consolidated under the pressure of 450 MPa and the temperature of 380 °C.
An artificial neural network （ANN） model was developed for simulating and predicting critical dimension dc of glass forming alloys. A group of Zr-Al-Ni-Cu and Cu-Zr-Ti-Ni bulk metallic glasses were designed based on the dc and their de values were predicted by the ANN model. Zr-Al-Ni-Cu and Cu-Zr-Ti-Ni bulk metallic glasses were prepared by injecting into copper mold. The amorphous structures and the determination of the dc of as-cast alloys were ascertained using X-ray diffraction. The results show that the predicted de values of glass forming alloys are in agreement with the corresponding experimental values. Thus the developed ANN model is reliable and adequate for designing the composition and predicting the de of glass forming alloy.
Phase formation, glass forming ability, mechanical and thermal properties of Cu50Zr50-x Alx(0?x? 11.0) glass forming alloys were systematically investigated. The results show that Cu50Zr47Al3 alloy has the best glass forming ability(GFA), lowest fragility index(m) and highest fracture strength. There are B2 Cu Zr and B19' Cu Zr phases for Cu50Zr50-x Alx(0?x?5.0) alloys. B2 Cu Zr phase disappears and two new phases(Cu10Zr7 and Cu Zr2) appear when 5.05.0). Cu50Zr50-x Alx(0?x?4.0) alloys are off-eutectic compositions while near-eutectic compositions for Cu50Zr50-x Alx(5.0?x?11.0) alloys. The Eg, Ex, and Ep decrease with increasing sensitive factor(β) for the studied Cu-based alloys characterized in the room-temperature brittleness. The dependence of the phase formation and GFA on the Al content is discussed.
Zr-Al-Ni-Cu bulk metallic glasses （BMGs） were developed and their fragility parameters （m） were calculated by Arrhenius and Vogel-Fulcher-Tammann （VFT） equations. The results show that the m values of the Zr-Al-Ni-Cu BMGs derived by Arrhenius equation are in agreement with the corresponding m values derived by VFT equation. These Zr-Al-Ni-Cu BMGs characterize in low m values. The low m values for these BMGs would be due to their network microstructures. In addition, the m values of Zr-Al-Cu-Ni BMGs could be obtained by regulating Zr content. The composition of Zr-Al-Cu-Ni BMGs with the lowest m value would be near 54%Zr （mole fraction） because the m value about 13 of Zr 54 Al 13 Cu 18 Ni 15 BMG is the lowest among these Zr-Al-Ni-Cu BMGs developed.
