Evaluation of structure-property relationship in tailor-made metallic glasses

Abstract

Since amorphous alloys have disordered atomic structures that are different from those of crystalline alloys, they exhibit various unique properties that can not be explained by conventional theory. In particular, when the amorphous material increases in size, It is very likely to be applied as However, unlike crystalline alloys, amorphous alloys have disadvantage that surplus breakdown occurs at the same time as breakdown because there are no plastic deformation mechanisms such as slip or dislocation. In addition, due to the amorphous forming ability(which requires a rapid cooling rate), it is difficult to fabricate a general metal manufacturing process

therefore, there is a limitation in the size of amorphous material. Therefore, to expand the possibility of using amorphous materials as structural materials, it is essential to improve the plastic deformation resistances of the materials and to enlarge them while maintaining the amorphous structure. Therefore, in this study, we analyzed the atomic- scale structural change of an amorphous alloy depending on the added element and experimentally investigated the change of physical properties according to the structural change. As a result, we overcame the limit of application of existing amorphous materials as a structural material, We propose a concept to control the structure. In addition, we tried to overcome the limitations of existing amorphous alloys by studying enlargement through additive manufacture of amorphous powders using 3D the printing process, which is a leading innovation in manufacturing technology. To investigate the structural and physical properties of a monolithic amorphous phase, a simple binary system (Ni-Nb) was selected and a series of elements (Zr, Gd, Y) was added to the alloy. When Zr (+4 kJ/mol), which has a relatively small positive heat of mixing, was added to the Ni-Nb binary alloy, no heterogeneity could be confirmed in monolithic amorphous phase through transmission electron microscopy or SAXS (small angle X-ray scattering). However, as a result of confirming the interatomic bonding distance and coordination number using EXAFS (extended X-ray absorption fine structure), local atomic-scale heterogeneity in the single amorphous phase was confirmed due to the addition of Zr. In addition, the local atomic-scale heterogeneity could provide several sites where shear bands can be generated, thereby preventing sudden destruction by a concentrated shear band and ultimately improving the amorphous stretching. These results were the first to be experimentally identified. In addition, the correlation between heterogeneity at the atomic scale and the physical properties was confirmed through bulk specimens. It was influenced by the cooling rate. On the other hand, when Y and Gd (+30 kJ/mol), which have positive heats of mixing with constituent elements, were added to the Ni-Nb binary alloy, a phase-separated amorphous phase was obtained. The microstructures and thermal properties of amorphous phase separation were different despite having the same enthalpy of mixing. Based on the thermodynamic data, we developed a new alloy design concept to control the microstructures of phase separated amorphous alloys by calculating the miscibility gap of the phase separated amorphous material (which can induce differences in microstructure) and examining the governing factor. To overcome the size limitation of amorphous material, we observed that the change of physical properties of the printed result varied according to process variable control, which was confirmed through 3D print(powder bed fusion) processing of the amorphous powder. By using the amorphous powder, the amorphous structure could be enlarged while retaining the amorphous structure when the process parameters and the heat input of 3D printing were controlled appropriately. In addition, the amorphous mechanical behavior experiment (produced by 3D printing) showed a difference in cooling rate within a single amorphous state during amorphous manufacture through 3D printing, unlike conventional amorphous manufacturing, It was found that atomic-scale heterogeneity in the single amorphous phase can increase elongation of the amorphous phase. A broad understanding of the amorphous structure and property relationships from this work will ultimately provide a new way to design and process various alloys to take advantage of the excellent properties of amorphous materials. Furthermore, a new milestone for manufacturing customized amorphous materials for their industrial application is suggested.