Papers by Keyword: Bulk Amorphous Alloy

Abstract: Microfracture mechanisms of Zr-based bulk metallic glass (BMG) alloy containing ductile crystalline particles were investigated by directly observing microfracture processes using an in situ loading stage. Strength of the BMG alloy containing crystalline particles was lower than that of the monolithic BMG alloy, while ductility was higher. According to the direct microfracture observation, crystalline particles initiated shear bands, acted as blocking sites of shear band or crack propagation, and provided the stable crack growth which could be confirmed by the R-curve analysis, although they negatively affected apparent fracture toughness. This increase in fracture resistance with increasing crack length improved overall fracture properties of the alloy containing crystalline particles, and could be explained by mechanisms of blocking of crack or shear band propagation, formation of multiple shear bands, crack blunting, and shear band branching.

Abstract: Dynamic deformation and fracture behavior of Zr-based bulk metallic glass (BMG) and BMG composite containing dendritic β phases was investigated in this study. Dynamic compressive test results indicated that both maximum compressive stress and total strain of the BMG and BMG composite decreased with increasing test temperature because shear bands could propagate rapidly as the adiabatic heating effect was added at high temperatures. Above the glass transition temperature, total strain decreased more abruptly due to crystallization of amorphous phases. Maximum compressive stress and total strain of the BMG composite were higher than those of the BMG because β phases played a role in forming multiple shear bands. The BMG composite having more excellent dynamic properties than the BMG can be more reliably applied to the structures or parts requiring dynamic properties.

Abstract: In the present study, fatigue tests of sharp-notched Zr-based bulk metallic glass (BGM), were conducted under fully reversed cyclic bending, and the fatigue crack initiation mechanisms were clarified by using AFM. The fracture surface was also observed to examine the crack propagation mechanism. The fatigue notch factor was 2.0, while the elastic stress concentration factor is 2.7. From the macroscopic observations of fractured specimen, either tension mode or shear mode fracture morphologies were observed. Either in smooth specimens or notched specimens, no prodigious sign of crack initiation were observed, i.e., fatigue cracks were initiated from shear bands those were formed just before the crack initiation.

Abstract: Recent interest in bulk-metallic glasses (BMGs) has led to the development of amorphous alloys designed for structural applications in various fields as aircraft frames, rotating equipment, automobiles, and medical implants. Although the mechanical behavior of BMGs is being studied extensively, little attention has been paid to their fatigue behavior. Moreover, early fatigue characteristics have exhibited contradictory results. In the current research, uniaxial tension-tension fatigue experiments were performed on notched Zr52.5Cu17.9Al10Ni14.6Ti5 button-head fatigue specimens with various surface finishes. The fatigue studies were designed to better understand the influence of the average surface roughness and/or critical surface defects on the fatigue behavior of glassy alloys. It was hypothesized that geometric surface flaws would lower the observed life of a BMG sample by shortening the crack initiation phase and providing local stress concentrators. The current studies of surface conditions indicate that fatigue-endurance limits are greatly impacted by the average surface roughness with possible reductions of greater than fifty percent.

Abstract: The formability of several Zr-based bulk metallic glasses in the supercooled liquid region has been estimated. Using the data obtained from compression tests, normalized processing maps based on a dynamic materials model (DMM) have been constructed to evaluate feasible forming conditions. Laboratory-scale hot extrusion of the Zr44Ti11Cu9.8Ni10.2Be25 BMG has also been carried out to clarify the effectiveness of the normalized processing maps established in this study. The influence of thermal properties and microstructural differences on the formability of BMGs is interpreted in terms of a normalized temperature within the supercooled liquid region.

Abstract: There are presented original experimental results of studying rheological behavior of Vitralloy 1 (Zr41Ti14Cu12.5Ni10Be22.5), which shows in the certain strain rate range stable linear viscous (Newtonian) flow. Comparative analysis of these results and the results related to other superplastic alloys as well as to crystallizing metallic melts has been carried out.

Abstract: Bulk armorphous Mg65Cu25Gd10 alloy of 12mm rods were prepared by water quenching the molten alloy in the stainless steel tube. Neither cavities nor voids are seen over the whole range and no contrast revealing a crystalline phase is seen over the transverse cross section. The glass transition temperature (Tg), crystallization temperature (Tx), the melting temperature (Tm) and the liquidus temperature (Tl) are measured to be 419K, 492K, 702K, 735K, respectively, for the Mg65Cu25Gd10 alloy with a diameter of 12mm. These temperatures are similar with those of the alloy with a diameter of 8mm produced by metallic mould casting. Both alloys have the same Vickers hardness about 260. Water quenching can further improve the critical diameter of glassy rods, so it is qualified for the formation of the bulk alloys.