Materials Science Forum Vols. 745-746

Abstract: The microstructures and mechanical properties of AlCoCrFeNi0.3 high-entropy alloys (HEAs) are tailored through heat treatment. During heat treatment, the dendrite phase with a body-centered-cubic (bcc) structure transformed into the interdendrite phase with a bcc structure. Due to the element accumulation with higher hardness in the interdendrites and the increase of volume fraction of interdendrites, the average hardness of AlCoCrFeNi0.3 HEAs increased with the heat-treatment temperature, and the highest hardness was 625 HV. After 500 heat treatment, the optimized mechanical properties under quasi-static compression were achieved, and the yielding strength and fracture plasticity were 2.30 GPa and 9 %, respectively. Upon dynamic loading, the mechanical properties of HEAs were greatly enhanced.

Abstract: The multi-component AlxCoCrFeNiTi0.5 (x=0, 0.2, 0.5, 0.8, 1.0) high-entropy alloys were prepared by vacuum arc melting. The microstructure and mechanical properties were studied. It was found that the structure transformed from FCC into FCC + BCC + Laves, and finally into BCC with the increase of Al content. The compress test results showed that with the addition of aluminium from 0 to 1.0, the fraction strength increased while plasticity reduced. In the stain rates of 5×10^-3/s and 1×10^-3/s, when x=0.8 the fraction strength achieved maximum and x=0 the plastic was best, the strength of 2879MPa and 2433MPa, the strain of 0.21 and 0.22, respectively. The hardness increased obviously (from Hv479.1 to Hv692.7) when Bcc phase and Laves phase appeared. The analysis revealed that the strengthen mechanism was mainly composed of solid solution strengthening and precipitation strengthening.

Abstract: Viscosity reflects kinetic behaviors of metallic glass liquids, as well as the changes of structures of liquids with temperature. In the present work, the viscosity of superheated Cu-Zr-Al alloys has been detected by a torsional oscillating viscometer, and the experimental parameters have been explored. The experimental results indicate that Cu-Zr-Al alloys react with corundum crucibles and are not oxidated easily in the viscometer. In addition, the influence of thermal history on viscosity measurements is not inconsiderable. By eliminating the above factors, an abnormal three-stage trend of viscosity changes is observed finally. Analysis shows that this abnormal dynamic phenomenon probably is attributed to the transition of clusters in different temperature ranges of the glass liquids, and might correspond to the abnormal thermodynamic behavior observed in Cu-Zr-Al liquids.

Abstract: A copper rod/FeSiB amorphous ribbon/copper rod sandwich laminated composite material has been successfully fabricated by co-pressing at temperatures within supercooled liquid region. The bonding interface has been characterized by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Results showed that a good bonding interface could be obtained only when the initial surface were carefully polished. The diffusion zone confirmed by EDS is about 60nm, indicating the bonding is in atomic metallurgical level via limited diffusion. The present results show that even the diffusion length is very small, diffusion bonding in the supercooled liquid region could be an effective way for fabricating Fe-based metallic glass/Cu laminated composites

Abstract: The formation of Cu-Zr-Nb metallic glass was predicted by thermodynamic calculation and then five Cu-Zr-Nb ternary metallic multilayered films were designed and prepared by electron depositing. The metastable supersaturated solid solutions, amorphous phase as well as their composites were able to be obtained in these Cu-Zr-Nb metallic multilayered films upon ion beam mixing. The observations provided a clew to improve the ductibility of the metallic glasses. Some possible interpretations were presented concerning the formation of the crystalline-amorphous composite.

Abstract: In this work, the critical cooling rate R_c for glass formation of a series of Fe_80-xCo_xP₁₃C₇ (x = 0, 5, 10, 15, 20 at.%) alloys was determined by means of constructing CCT curves using Uhlmanns method. The calculated critical cooling rates for x = 0, 5, 10, 15, 20 at.% are 621, 441, 548, 894, 922 K/s, respectively. These results well coincide with the maximum diameters of Fe_80-xCo_xP₁₃C₇ amorphous alloys determined by experiments varying with the content of Co. The calculated R_c was also on the reasonable order of magnitudes. In addition, the values of three common GFA criterions of T_rg, ΔT_x and γ were calculated according to the thermodynamic data determined from DSC and DTA curves of Fe_80-xCo_xP₁₃C₇ (x = 0, 5, 10, 15, 20 at.%) bulk amorphous alloy. The validity of these GFA criterions in the series of Fe_80-xCo_xP₁₃C₇ (x = 0, 5, 10, 15, 20 at.%) alloys were investigated and it was pointed out that these three GFA criterions were not able to explain the experimental results of the maximum diameters of Fe_80-xCo_xP₁₃C₇ amorphous alloys varying with the content x of Co.

Abstract: A Ti-based metallic glass composite with composition of Ti48Zr20Nb12Cu5Be15 exhibits good ambient plasticity in tensile and compressive loading. The macro and micro mechanisms during deformation have been investigated systematically. Obvious asymmetry between the tensile and compressive properties of the composite has been observed, indicating amorphous matrix effect on the metallic glass composite. The micro fracture mechanism of dendrites in compression can also be attributed to two mechanisms: shear induced fracture in major and tension induced fracture in local, revealing a constraint of matrix induced complex stress state in composite. Pile-ups of dislocations in dendrites cause work-hardening of composite, and the impedance of dendrites to shear bands is responsible for the improvement of plastic strain.

Abstract: The effect of Nb addition on the glass-forming ability (GFA), soft-magnetic properties and mechanical properties of [(Co_0.65Fe_0.35)_0.9Ni_0.1]_73-xB_21.9Si_5.1Nb_x (x=36) alloy system were investigated. The results showed that by adjusting the content of Nb, the thermal stability of the supercooled liquid and the GFA increased effectively. With increasing the amount of Nb, the supercooled liquid region (ΔT_x) increased from 45 to 65 K and the reduced glass transition temperature (T_rg=T_g/T_l) was located in the range of 0.5840.644. As a result, the [(Co_0.65Fe_0.35)_0.9Ni_0.1]_73-xB_21.9Si_5.1Nb_x bulk glassy alloys (BGAs) with diameters up to 5.0 mm were produced by copper mold casting. In addition to the high GFA, the Co-based glassy alloys exhibited excellent soft-magnetic properties, i.e., saturation magnetization of 0.530.81 T, low coercive force of 0.511.75 A/m, and high effective permeability of (1.522.53)×10⁴ at 1 kHz under a field of 1 A/m. Besides, the Co-based BGAs also exhibited super high fracture strength of 42704490 MPa and vickers hardness of 11271182.