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Fe-based bulk metallic glasses (BMGs) are a unique class of materials that are attracting attention in a wide variety of applications owing to their physical properties. Several studies have investigated and designed the relationships between alloy composition and thermal properties of BMGs using an artificial neural network (ANN). The limitation of the wide-scale use of these models is that the required composition is yet to be found despite numerous case studies. To address this issue, we trained an ANN to design Fe-based BMGs that predict the thermal properties. Models were trained using only the composition of the alloy as input and were created from a database of more than 150 experimental data of Fe-based BMGs from relevant literature. We adopted these ANN models to design BMGs with thermal properties to satisfy the intended purpose using particle swarm optimization. A melt spinner was employed to fabricate the designed alloys. X-ray diffraction and differential thermal analysis tests were used to evaluate the specimens.

We present variation of the magnetic properties of Fe77.8Nb0.2B14P6C2 amorphous alloys vitrified at different temperatures by changing the atomic structures dependent on the critical cooling rate. The thermophysical properties of the amorphous state achieved after quenching the melt with cold nitrogen atomization gas are compared with those obtained using hot nitrogen gas with a temperature corresponding to the supercooled liquid of the alloy above the glass transition (Tg) but below crystallization temperature (Tx). The differently vitrified Fe77.8Nb0.2B14P6C2 glasses represent different states of high pressure gas atomized amorphous powder at different temperatures obtained by adjusting the gas temperature during the atomization process. The magnetic properties of these different amorphous powders are also investigated. The saturation magnetic flux density of slowly cooled Glass2 is 1.38 T with 450 A/m coercivity corresponding to “semi-soft” magnetic materials. The fast cooled Glass1 powder shows typical soft magnetic properties with lower coercivity (174 A/m), even though the saturation magnetization flux densities are similar in both identical compositions of amorphous powder due to its entropy difference related to the formation of clusters. We can control the magnetic property of amorphous materials from soft to half-soft by adjusting freezing temperature and ordering of atoms.

Thermal spray coatings of two different Fe-based bulk metallic glasses (BMGs) were prepared using atmospheric plasma spray (APS) technique. Effects of crystallinity and chemical phase composition of the initial feedstock materials and the impact of plasma jet on the properties of the Fe-based metallic glass powders were discussed by characterizing the coating properties. Also, partial and complete melting of powders in plasma and the effects on oxidation and crystallization are discussed. Powder which contains elements such as Al and Si, showed better wear property because of oxidation effect and any deviation from the optimum quantity of elements would affect coating properties.

This study demonstrates that prolonged elastostatic compression imposed on amorphous alloys at room temperature induces permanent (homogeneous) deformation associated with structural disordering. It was found that this structural disordering is accompanied by the creation of excess free volume, which in turn enhances the room temperature plasticity. In this study, we investigated the effects of various parameters, such as stress level, flow rate and preloading time, on structural disordering at room temperature. On the basis of the present findings, a method of enhancing the plasticity of amorphous alloys is proposed.

A bulk amorphous alloy, Zr54Cu36Al4Be6, was synthesized. This alloy shows a large plastic strain of ∼22.1% along with a work hardening of 485 MPa, which have hardly been observed in monolithic bulk amorphous alloys. Microstructures of this alloy were observed to investigate the origin of the extraordinary plasticity of the alloy. The alloy exhibited a unique microstructure characterized by an atomistic-scale phase separation, which probably stems from the large difference in mixing enthalpy between the binary pairs of Zr–Be and Cu–Be. This paper discusses the possible mechanism underlying the extraordinary plasticity of the alloy by considering the atomic packing density and atomistic-scale compositional separation induced by Be.

In this study, we investigated the role of a minor alloying element in improving the plasticity of amorphous alloys. The plasticity of the amorphous alloys, Cu60−xZr30Ti10Bex, was drastically improved with increasing amount of Be and reached a maximum of 23% at Cu53Zr30Ti10Be7. It was observed that an atomistic-scale phase separation existed within the alloy, which resulted from the large difference in mixing enthalpy between the binary pairs (Be–Cu, Be–Zr). This atomistic-scale phase separation resulted in an open structure in which atomic rearrangements in the form of the creation of free volume and crystallization were facilitated during deformation. Here we discuss the origin of the enhanced plasticity by clarifying the effect of an additional element, whose mixing enthalpies with the major elements are significantly different, on the structural change of the amorphous alloy.

The role of nancocrystals on the plasticity of the Cu64Zr36 amorphous alloy was studied in terms of the initiation of shear bands and the propagation of cracks. The plastic deformation behaviors of the fully amorphous and the partially crystallized samples with various degrees of crystallinity were compared. The partially crystallized alloys with an adequate amount of nanocrystals showed a considerable enhancement in their plasticity. Finite element calculations were conducted to qualitatively examine the role of the nanocrystals on the formation of the shear bands, while high-resolution electron microscopy was used to directly observe the crack propagation behavior through the matrix with (or without) nanocrystals.

Impacting behavior and deposition formation of Ni–Ti–Zr–Si–Sn bulk metallic glass during kinetic spraying were investigated in this study. Bulk metallic glass particle deposition was primarily dependent on the impacting particle velocity. Secondly, the impacting particle temperature could transfer the deposition mode from fracture-induced local melting to severe viscous flow, especially for the splat on previously deposited splat. It is suggested that the deposition behavior of bulk metallic glass particles is determined by the competition between fracture and deformation. Fracture and deformation are controlled by adiabatic shear instability at the faying interface during impacting, with causal factors including temperature-dependent superplasticity of the bulk metallic glass and an abnormally high strain rate of the individual particle impact during kinetic spraying.

The vacuum degassing behavior of Zr 55 Al 10 Ni 5 Cu 30 , Ni 59 Zr 15 Ti 13 Si 3 Sn 2 Nb 7 Al 1 , and Cu 54 Ni 6 Zr 22 Ti 18 (numbers indicate at.%) metallic glass powders has been investigated and compared with that of Al alloy powder. It was found that the alloy composition influenced the gas desorption behavior with heating in vacuo . Zr 55 Al 10 Ni 5 Cu 30 and Ni 59 Zr 15 Ti 13 Si 3 Sn 2 Nb 7 Al 1 metallic glass powders exhibited little H 2 gas desorption from powder surfaces during vacuum degassing. Because Zr in the Zr-based and Ni-based amorphous alloy powders produced a native zirconium oxide layer, the surface of the Zr 55 Al 10 Ni 5 Cu 30 and Ni 59 Zr 15 Ti 13 Si 3 Sn 2 Nb 7 Al 1 amorphous alloys had no influence on adsorbed H 2 O. Cu 54 Ni 6 Zr 22 Ti 18 metallic glass powder was the most affected by atmospheric H 2 O among the metallic glass powders examined in this study. The adsorbed H 2 O and Cu metal may react with each other with the formation of Cu 2 O and liberation of H 2 during vacuum degassing. In order to obtain sound P/M final products with Cu-based P/M alloys, oxygen-free copper powders should be used in well-controlled atmospheres with low H 2 O partial pressures.

In this study, vacuum plasma spraying (VPS) was chosen for making Ni–Ti–Zr–Si–Sn bulk metallic glass (BMG) coating and the process parameters were optimized in view of phase composition of as-sprayed BMG overlay. When it comes to the phase evolution of BMG particle in thermal spraying process, the crystallization does occur by chemical instability and/or thermal instability. For the VPS process, the chemical instability such as in-flight particle oxidation can be neglected and thus the crystallization of BMG feedstock can be considered to result from the thermal instability. Actually, the crystalline phase fraction of the as-sprayed coatings was largely affected by the plasma gas composition which determines the plasma jet characteristics and also in-flight particle melting state. As the gas enthalpy is increased with the increase of hydrogen gas flow rate, number density of unmelted particle within the coating and crystalline phase fraction were consistently decreased. It implied that the phase composition of VPS BMG coating was largely dependent on the melting state of the impacting BMG particle.

Spherical Cu54Ni6Zr22Ti18 metallic glass powders were prepared using a high-pressure gas atomizer, followed by consolidation using spark plasma sintering (SPS) process. The glass forming ability of both powders as atomized and bulks as SPSed was investigated by X-ray diffractometer (XRD) and differential scanning calorimeter (DSC) as a function of powder size distribution. The bulk maintains the amorphous structure even after the thermal consolidation. The compressive strength was increased as the powder size decreased due to an increased density. The compression tested BMG presents a fracture pattern occurred along the maximum shear plane declined ∼45° to the loading direction.

The bulk metallic glass matrix composite comprising Cu54Ni6Zr22Ti18 metallic glass powder and ductile brass powder was fabricated by the warm process. The warm process was carried out by spark plasma sintering, which led to the homogeneous distribution of both phases of brass and metallic glass without pores. The metallic glass matrix composite material exhibits the same crystallization behavior of the metallic glass powder. A compressive strength of 1.0 GPa with a plastic strain of 3 % was obtained in the present metallic glass composite. The composite with enhanced strength and ductility was successfully achieved by introducing a ductile phase in the hard bulk metallic glass.

In this work, the superplasticity and brittleness of CuNiTiZr bulk metallic glass (BMG) with different initial powder temperatures (below Tg, between Tg and Tx, and above Tx) are investigated. TEM analysis, together with focused ion beam prepared samples, showed that crystallization of BMG was promoted by increasing initial temperature. Interface heating and deformability upon impact enhance the deposition of BMG particles below Tx, while rebound and fracture occurred above Tx due to the formation of a thick pre-crystallized layer around the particles. Strain induced nanocrystallization of BMGs at the impact interface may improve the bonding between amorphous particles.

This study demonstrates that permanent deformation results when an amorphous alloy is subjected to a stress below yield at room temperature. The resultant deformation was observed to be homogeneous and is thought to occur as a result of the structural disordering, in which densely packed short-range ordered clusters break down to form new, loosely packed ones. It was found that this disordering process is irreversible even if the applied stress is removed, resulting in the creation of excess free volume. These findings were analyzed using the molecular dynamics simulations in the light of atomic-scale structural changes.