The formation of bulk metallic glasses (BMGs) in ternary Cu-Zr-Ti system was investigated by a copper mold casting method. The nature of the amorphous phase was verified by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). It was demonstrated that the BMGs could be formed in a broad composition range in this system. Cu50Zr42.5Ti7.5, Cu60Zr27.5Ti12.5, Cu60Zr30Ti10 and Cu60Zr32.5Ti7.5 alloys exhibit strong glass-forming ability (GFA), and fully glassy rods of 5 mm in diameter can be obtained. In the center region of the ternary diagram, however, the GFA of the alloys was degraded due to the presence of Laves phase. The degradation of the GFA results from easy nucleation of the Laves phase in the undercooled liquid.
Hua Men, Junying Fu, Chaoli Ma, Shujie Pang, and Tao Zhang Department of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100083, China
The glass forming ability of the [(Fe12/13Y1/13)100?xBx]96Nb2Zr2 (x=9–26) system was investigated using a series of cluster lines. Three types of clusters, an icosahedron (Fe12Y), a capped Archimedes anti-prism (Fe8B3) and a capped trigonal prism (Fe9B), as well as a binary eutectic (Fe83B17) were considered. Bulk glassy alloy rods of 3 mm in diameter were synthesized using a copper mold suction-casting method. The glass transition temperature was observed for all samples in the boron range of 15.9at%-25.7at%, with the alloy at 15.9at% of boron having the best thermal properties. The ferrous-based bulk metallic glasses (BMG) obtained have high reduced glass transition temperatures with the maximum reaching 0.63 and large supercooled liquid regions with the maximum reaching 111 K. Magnetic testing revealed a large value of coercive force and remanent magnetization, being 11 kA/m and 0.1 T, re- spectively.
Similar element substitution has been applied for improving glass forming ability （GFA） in AI86NigLa5 amor- phous alloy. The effects of La-Ce and Ni-Co pairs on the GFA, magnetic properties and hardness of Al-Ni-La alloy were investigated by using X-ray diffraction （XRD）, transmission electron microscopy （TEM）, differential scanning calorimetry （DSC）, magnetometer and hardness-tester. The results show the GFA of the samples in the order of Al86（Ni0.5Co0.5）9（La0.5Ce0.5）5〈 A186Ni9Las〈A186Ni9（La0.5Ce0.5）5, implying that similar element substitution has a limited enhancing effect on the GFA of the present Al-Ni-La alloy. In addition, the measured samples display a diamagnetic behavior at room temperature. The variations of diamagnetic behavior as well as the microhardness of the samples are strongly dependent on the microstructure, i.e., the amounts of the icosahedral structure and precipitates, after the similar element substitution in the Al-Ni-La alloy.
Guihua Li Weimin Wang Xiufang Bian Li Wang Jiteng Zhang Rui Li Tao Huang
Bulk metallic glasses (BMGs) with large supercooled liquid region are promising materials for superplastic forming. In this paper, we demonstrate a microstructure-based strategy to pinpoint the composition with the largest supercooled liquid region in La 86 x Al 14 Cu x (x=16 at%-20 at%) metallic glass system. By monitoring the changes in crystallization behavior of the glassy alloys with composition to search for the alloys exhibiting eutectic crystallization, the glassy alloys with the largest supercooled liquid region in the given alloy system can be found. The metallic glasses with Cu contents of 16 at%-19 at% exhibited two crystallization peaks, and the primary crystallization product was identified to be α-La by means of DSC, XRD and TEM. The increase in Cu content resulted in the decay of the primary crystallization peak and the increase in onset temperature of crystallization, leading to the enlargement of supercooled liquid region. By further suppressing the α-La primary crystallization with increasing Cu content up to 20 at%, the eutectic crystallization of α-La and LaCu 13 through one crystallization reaction occurred upon heating, where the largest supercooled liquid region of 65 K for La 66 Al 14 Cu 20 glassy alloy was located. This study indicats that, in a given glassy alloy system, a larger supercooled liquid region can be achieved by optimizing the alloy compositions to suppress the primary crystallization.
The microstructures and thermal properties of Fe61Co9-xZr8Mo5WxB17 (x=0 and 2) formed under different vacuum conditions were investigated by scanning electron microscopy(SEM), X-ray diffractometry(XRD), transmission electron microscopy(TEM), and conventional dilatometry(DIL). The variation of the non-monotonic effects of tungsten content and vacuum conditions on the glass forming ability(GFA) of Fe-based alloys can be drawn in a schematic diagram. The higher the GFA of alloys, the higher the difference between the thermal expansion coefficients of glassy state and crystalline state(-α), which can be described by the free volume model during dilatometric measurements. Under low and high vacuum conditions, the viscosity and microhardness are improved and the fragility of the Fe-based alloys are decreased by adding tungsten.
To study the influence of Fe addition on the Al-based amorphous alloys,the structure and properties of Al84Ni10La6 and Al84Ni9Fe1La6 alloys were investigated through various techniques.The results show that 1% Fe（molar fraction） addition increases the area of the pre-peak in the structure factor and decreases the thermal expansion coefficient difference between the crystalline and amorphous states.1% Fe addition also improves the glass forming ability（GFA）,micro-hardness,fracture toughness,electric resistivity,absolute diamagnetism and corrosion resistance of Al-Ni-La alloys,which is related to the changes of medium-range order and quench-in free volume caused by 1% Fe addition.
