Characteristics Of Bulk Metallic Glass Research Articles

Correlations between Thermal Parameters and Glass Forming Abilities of Bulk Metallic Glasses Unveiled by Datamining

Datamining informatics techniques such as principal component analysis (PCA) and partial least squares (PLS) were applied to identify the composition characteristics of bulk metallic glasses with high glass forming abilities. It was pointed out that the reduced glass transition temperature T g /T l was comparatively the best indicator but no single indicator can reflect all the glass forming abilities of different alloy systems.

Composites of amorphous and nanocrystalline Zr–Cu–Al–Nb bulk materials synthesized by spark plasma sintering

The fabrication of Zr70Cu24Al4Nb2 bulk metallic glass composite samples by spark plasma sintering (SPS) process has been successfully realized. The unique characteristics of bulk metallic glasses could lead to the possibility of future applications as new structural and functional materials. The densification of an amorphous Zr70Cu24Al4Nb2 powder was realized in a systematic study changing the sintering temperature in the SPS process leading to stable composites characteristic of amorphous and nanocrystalline structures. X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) analysis, transmission electron microscopy (TEM) as well as hardness tests were applied to determine the structural and mechanical properties of the sintered materials. A stable amorphous bulk metallic glass based on Zr70Cu24Al4Nb2 with a low fraction of crystallites could be fabricated applying a nominal sintering temperature of 400 °C. Higher sintering temperatures lead to composites with high fractions of nanocrystalline material with porosities below 0.5%.

벌크비정질합금(BMG)의 절삭특성 평가

In this study, the cutting characteristics of bulk metallic glass (BMG) cut using a computer numerically controlled (CNC) lathe were investigated for different insert tool materials and cutting speeds. The surface roughness, chip morphology, cutting forces, and tool wear during turning of BMG alloy were examined. Four kinds of tool materials were used to cut an 8-mm-diameter BMG. The examination of the surface roughnesses of the BMG specimens machined at each cutting speed showed that the surface roughness became better as the cutting speed increased, and the tool materials also influenced the surface roughness. The chip morphology investigations showed that the unoxidized BMG chips had serrated curled chips with adiabatic shear bands, while the oxidized chips exhibited local melting and tangling rather than the usual spiral-shaped chips. The cutting force induced during machining of the Zr-based BMG was the largest for the TiN-WC tool, followed by the polycrystalline diamond (PCD) tool. The cermet tool exerted the smallest cutting force.

Fracture characteristics of bulk metallic glass under high speed impact

High speed impact experiments of rectangular plate-shaped Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) were performed using a two-stage light gas gun. Under spherical shock waves with impact velocities ranging from 0.503 km/s to 4.917 km/s, obvious traces of laminated spallation at the back (free) surface and melting (liquid droplets) at the impact point were observed. The angles about 0°, 17°, 36°, and 90° to the shocking direction were shown in the internal samples because of the interaction between the compressive shock waves and the rarefaction waves. The compressive normal stress was found to induce the consequent temperature rise in the core of the shear band.

Sliding tribological characteristics of Zr-based bulk metallic glass

Wear and friction characteristics of Zr-based bulk metallic glass under dry sliding conditions are investigated. This study demonstrates that load and sliding speed significantly affect the wear characteristics of bulk metallic glass material and sliding distance is less effective on wear. Critical sliding speed and normal force limits, 1 m/s and 10 N, respectively, are distinguished. Overall average coefficient of friction value was in the range of 0.35–0.45, better than that of conventional structural materials such as AISI 6061-T6 and AISI 304. Analysis of the worn surface revealed that the bulk metallic glass was exposed to inhomogeneous shear deformation, adhesive wear, and abrasive wear during sliding test. Three sizes of wear debris, oversize flakes, machining chips and powder-like debris, are collected. There was no change recorded in surface and cross-sectional hardness measurements after the sliding test. This study concludes that bulk metallic glass is better in general friction characteristics than conventional structural materials such as AISI 6061-T6 and AISI 304.

Tribological Behaviors of Bulk Metallic Glasses

The tribological properties of Zr-based and Cu-based bulk metallic glasses (BMGs) sliding against discs of SUS 304 and Si3N4 at room temperature under dry and lubrication of fresh plasma, distilled water, and physiological distilled water were investigated on a pin-on-disc testing machine. The results demonstrated the influences of counterface materials, lubrication conditions and the characteristics of BMGs on the frictional behaviors of the Cu- and Zr-based BMGs. It is found that the steady state friction coefficients and the wear rates sometimes are not consistent, and the wear resistance was been improved when the counterface change from SUS304 to Si3N4. Otherwise, wear rates of the BMGs under lubrication conditions are much lower than that of under dry sliding conditions, and the Cu-based BMGs exhibits higher wear resistance than Zr-based BMGs under same experimental conditions because it is a nanocrystalline amorphous alloy and has the higher glass transition and crystallization temperatures.

Finite element analysis of microimprinting of bulk metallic glasses in supercooled liquid regime

A finite element analysis (FEA) model to analyze imprint of a bulk metallic glass (BMG) in the temperature range near the glass transition temperature (Tg) has been developed. The material model includes both Newtonian and non-Newtonian flow behavior. The results reveal that the topology of the imprinted surface depends strongly on temperatures, but only mildly on surface feature scale. As a result of the flow characteristics of BMG in the temperature range above Tg, the lubrication condition has only a slight effect on BMG imprinting.

Bio-Tribological Properties of Bulk Metallic Glasses Sliding Against Si<sub>3</sub>N<sub>4</sub>

Metallic biomaterials are used as bone plate, dental implant, wire, electrode, and so on. For the purpose of providing the medical services with higher quality, the frictional and wear behavior of Cu47Ti34Zr11Ni8, (Cu47Ti34Zr11Ni8)99Si, Zr41Ti14Cu12.5Ni10Be22.5 and Zr57Nb5Cu15.4Ni12.6Al10 bulk metallic glasses (BMG) against ceramic ( Si3N4) at room temperature under dry sliding and lubrication of fresh plasma, distilled water, and physiological saline conditions were investigated on a pin-on-disc testing machine. Under identical sliding condition, the steady state friction coefficients of BMGs were observed with values ranging from 0.6 to 0.9 under dry sliding, 0.5 to 0.8 under lubrication with distilled water, 0.5 to 0.7 under lubrication with physiological saline, and 0.3 to 0.7 under lubrication with fresh plasma, respectively. Wear rates of BMGs indicated significant difference that the Cu-based metallic glasses exhibited higher wear resistance than that of Zr-based glasses. The surface tracks indicated the existence of viscous flow and the material transfer occurred from BMG rod to the ceramic disc. Since tribological properties are not intrinsic properties, those results demonstrated the influences of the environment and the characteristics of BMGs on the frictional behaviors, and furthermore indicated that BMGs may be one of the promising biomaterials in the future.

Cutting Characteristics of Bulk Metallic Glass

The establishment of appropriate machining techniques for bulk metallic glasses (BMGs), which exhibit excellent mechanical, physical and chemical properties, is required to apply the BMGs. In this report, the cutting characteristics of BMGs were examined by turning with different tool materials, nose radii (Rn) and cutting speeds (V). Round bars of Zr65Cu15Ni10Al10 and Pd40Cu30Ni10P20 at% BMGs were used as the workpieces. In order to compare the cuttability of the BMGs with that of crystalline alloys, steel (JIS SGD-400D) and free-cutting brass (JIS C3604) were used. The principal cutting force (FH) and surface roughness (Ra) of the machined surfaces were measured. X-ray diffraction patterns were also obtained from the machined surfaces. The value of Ra in the BMGs exhibit the upper end of precise finishing level (i.e., Ra ¼ 0:2 mm), and was remarkably lower compared with the steel and a little lower compared with the free-cutting brass in spite of the value of V. The value became smaller with increasing values of Rn, exhibiting a very low value of 0.08 mm for an Rn value of 1.2 mm. The values of FH in both BMGs did not show a clear difference and were half that of the steel for a V value less than 40 m/min, even though the tensile strength of the BMGs was twice as large as the steel. The chip of the BMGs showed an ideal flow type with very short and regular intervals, formed by planar slip, and revealed very homogeneous, flat and featureless back surfaces. From these observations of chips, it is presumed that the reason for the excellent cuttability of BMGs is due to a slipping-off mechanism at planes of very short intervals decided only by the maximum shear stress and non-built-up edges caused by a low glass transition temperature.

Sliding and deformation of metallic glass: experiments and MD simulations

The sliding behavior of metallic glass (MG) was studied using pin-on-disk tests and molecular dynamics (MD) simulations. Friction coefficients and wear rates of a Zr–Ti–Cu–Ni–Be alloy were similar to those reported for ductile materials, e.g., normal crystalline metals; i.e., exceptional friction and wear characteristics of bulk MG were not observed. Sliding caused plastic deformation, transfer, mechanical mixing and reamorphizing of devitrified material. In vacuum, a softer layer developed adjacent to the interface. In air, an additional harder layer appeared when oxidation products were incorporated into the near-surface material. MD simulations involved a two-component 2D amorphous system. Simulations of tensile tests showed elastic/perfectly plastic response, strain rate dependence, void formation and shear bands. Simulations of sliding showed decreased density near the interface, suggesting an increase in free volume during shear, but neither voids nor shear bands. Subsurface displacement profiles were similar to those reported in experiments on crystalline materials and were consistent with flow patterns expected for flow near a boundary. The MD results on mechanical mixing suggest relevance to other processes, including mechanical alloying, friction welding, formation of nanocrystals, erosion and deformation at high strain rates.