Metallic Glassy Powders Research Articles

Metastable nanocrystallization behavior of Ti-based metallic glassy powders during post-heating

The crystallization behavior of Ti-based metallic glassy powders was systematically investigated. The results show a novel metastable nanocrystallization process, i.e. the glassy powders exhibit multi-step phase transition behavior. For the first exothermic event, the entire glassy phase crystallized into metastable nanocrystals, then a face-centered cubic structured Ni2SnZr and a monoclinic structured TiNi0.8Cu0.2 phases formed by a solid state transition (the second exothermic event). These crystallizations are believed to be driven by the synergetic effect of thermodynamics and kinetics.

Temperature influence on sintering with concurrent crystallization behavior in Ti-based metallic glassy powders

A large size and high strength Ti-based bulk metallic glass is fabricated from the amorphous powders by the spark plasma sintering (SPS) technique. The sufficient viscous flow induced by the macroscopic temperature under a sintering stress is considered as the main mechanism for the densification. During the SPS process, the microscopic temperature gradient was identified, which directly influences the microstructures and in turn the mechanical properties at different regions of the sample. A new phase with an orthorhombic structure ( a = 0.48 nm, b = 1.03 nm and c = 0.61 nm) is determined.

Ni-Nb-Sn Bulk Metallic Glass Matrix Composites Fabricated by Microwave-Induced Sintering Process

Using a gas-atomized Ni59.35Nb34.45Sn6.2 metallic glassy alloy powder blended with Sn powder of various contents, Ni-Nb-Sn bulk metallic glassy matrix composites were fabricated by a microwave (MW)–induced sintering process in a single-mode 2.45 GHz MW applicator in a separated magnetic field. The Ni59.35Nb34.45Sn6.2 glassy alloy powder and its mixed powders containing Sn particles could be heated well in the magnetic field. The addition of Sn particles promoted densification of the sintered Ni59.35Nb34.45Sn6.2 metallic glassy powder. Bulk samples without crystallization of the glassy matrix and with good bonding state among the particles were achieved at a sintering temperature of 833 K.

Displacement Behavior Study of the Shear Stress Effect on the Early Viscous Flow Nature of Fe-B-Nb-Y Metallic Glassy Powder in Spark Plasma Sintering

(Fe0:72B0:24Nb0:04)95:5Y4:5 metallic glassy powders were fabricated with a gas-atomizing method and then densely consolidated by the spark plasma sintering (SPS) technique. Densification behavior during the SPS procedure enables us to understand the thermal behavior and viscous deformation profiles of glassy particles. The glassy powders were consolidated under various temperatures to determine the effect of applied stress on the viscous densification behavior. Consequently, viscous densification commenced under a preset stress of 600 MPa at a flow temperature of Tf ¼ 663 K, which is approximately 248 K lower than that under a stress of 32 kPa, as shown by thermo-mechanical analysis (TMA). Furthermore, even below Tg, SEM images demonstrated fine imprintability on the glassy powders during this stress-enhanced viscous densification. [doi:10.2320/matertrans.MBW200851]

Densification of Gas Atomized Ni-Based Metallic Glassy Powders by Spark Plasma Sintering

Gas-atomized Ni52:5Nb10Zr15Ti15Pt7:5 metallic glassy alloy powders were consolidated by a spark plasma sintering (SPS) process. The densification behavior during the SPS process as well as the structure, thermal stability and mechanical properties of the sintered specimens were investigated. The glassy alloy powders were densified rapidly when the temperature exceeded about 740 K. The density of the sintered specimens increased with an increase in sintering temperature. The specimens with full densification and no crystallization were obtained by the SPS process at a sintering temperature of 773 K with a loading pressure of 600 MPa. The sintered specimens exhibit high-strength and can meet large-size requirement. [doi:10.2320/matertrans.ME200817]

Consolidation of [(Fe<SUB>0.5</SUB>Co<SUB>0.5</SUB>)<SUB>0.75</SUB>Si<SUB>0.05</SUB>B<SUB>0.2</SUB>]<SUB>96</SUB>Nb<SUB>4</SUB> Metallic Glassy Powder by SPS Method

Metallic glasses have been reported to exhibit excellent properties, such as high strength, high corrosion resistance, high wear resistance, which result from their amorphous structure. Because of a drastic reduction in their viscosities in supercooled liquid region, metallic glasses have an excellent workability through viscous deformation for the production of various industrial parts. Recently, much attention has been paid to Fe-based metallic glasses because of their rich resources in addition to their excellent mechanical and magnetic properties. However, due to their poor glass-forming ability, the size of the Fe-based bulk metallic glass by conventional casting techniques is limited. In the present investigation, nearly fully densified disk-shaped compacts of [(Fe0:5Co0:5)0:75Si0:05B0:2]96Nb4 metallic glass were produced from a gas-atomized amorphous powder by spark plasma sintering (SPS). The processing temperature and the time that assure the supercooled liquid state of the compacts were determined from the Time-Temperature-Transformation (TTT) diagram that was constructed by isothermal differential scanning calorimetry. The mechanical properties of the consolidated samples were evaluated by compression test. Comparatively low values of the fracture stress, Young’s modulus and yielding stress of SPSed sample compared to the casted samples were observed, which is discussed on the basis of the integrity of the interparticle bonding. [doi:10.2320/matertrans.M2009093]

SPS 法による Fe-Co 系金属ガラス粉末の固化成形

SPS 法による Fe-Co 系金属ガラス粉末の固化成形

Effect of Sn on microwave-induced heating and sintering of Ni-based metallic glassy alloy powders

Microwave (MW)-induced heating and sintering was carried out by a single-mode MW applicator in a separated electric field or magnetic field using the gas-atomized Ni 52.5Nb 10Zr 15Ti 15Pt 7.5 metallic glassy alloy powder blended with various contents of Sn powders. The addition of Sn particles was found to promote the densification of the sintered Ni-based metallic glassy powders. With increasing Sn contents, the sintering temperature to obtain bulk sample with the retention of the glassy structure was reduced, and good bonding between powder particles was achieved.

Heating of metallic powders by microwaves: Experiment and theory

It is known that bulk metallic samples reflect microwaves while powdered samples can absorb such radiation and be heated efficiently. In the present work we studied heating mechanisms of metallic powders in a multimode 2.45 GHz microwave applicator. The present paper shows direct evidence of penetration of a layer of metallic powder by microwave radiation and provides theoretical explanation of such behavior.The most effectively heated powder is Fe because both eddy current loss (in alternating H-field) and magnetic reversal loss (in alternating E-field) mechanisms act in case of such metal. Diamagnetic metals Sn and Cu are heated better than paramagnetic Ti while Au is also only slightly heated. Cu- and Ni-based metallic glassy powders are also moderately heated. Weak heating of Au powder (which is a noble metal) can be explained by the absence on the particles of the oxide layer (shell), which allows eddy currents flowing through larger area compared to other metals, and reflection mechanism works much better in such case.

Microwave Radiation Processing of Metallic Glassy Powders

In the present study we investigate the stability of Cu50Zr45, Al5 and Ni59Ti16 Zr20Sn5 glassy powders and the formation of the bulk metallic glassy samples by microwave heating in a single mode cavity (915 MHz) in the alternating magnetic field maximum. Metallic glasses exhibit low viscosity at temperatures close to the glass-transition which allows for the processing of glassy powders. Microwave heating being a volumetric heating has significant advantages over conventional heating in materials processing, such as substantial energy savings, high heating rates and process cleanness.

Microstructure and properties of ceramic particulate reinforced metallic glassy matrix composites fabricated by spark plasma sintering

We fabricated Zr 55Cu 30Al 10Ni 5 bulk metallic glassy matrix composites (MGMCs) containing ceramic Al 2O 3 or Si 3N 4 particulates by a spark plasma sintering (SPS) process. Microstructure, thermal stability and mechanical properties of the fabricated bulk MGMCs were investigated. The matrix of the fabricated MGMC specimens maintained a glassy phase after the SPS process. The fabricated MGMC specimens showed thermal stability similar to that of the original gas-atomized glassy alloy powder. Good bonding between the metallic glassy powder and ceramic particulate was recognized. The added ceramic Al 2O 3 or Si 3N 4 particulates were found to be homogenously distributed within the sintered samples and play an important role in the enhancement of plasticity.

Fabrication of ZrCuAlNi Metallic Glassy Matrix Composite Containing ZrO<SUB>2</SUB> Particles by Spark Plasma Sintering Process

Using a mixed powder of argon gas-atomized Zr 55 Cu 30 Alj o N1 5 metallic glassy alloy powder blended with 10vol% ZrO 2 powder, Zr 55 Cu 30 Al 10 Ni 5 bulk metallic glassy matrix composite was fabricated by a spark plasma sintering process. The structure, thermal stability and mechanical properties of the sintered bulk metallic glassy matrix composite were investigated. The ZrO 2 particles were homogeneously dispersed in the Zr 55 Cu 30 Al 10 Ni 5 glassy matrix. No crystallization of the glassy matrix occurred during the spark plasma sintering process. The crystallization behavior of the sintered composite was similar to that of the metallic glassy powder. The sintered composite specimen exhibited larger plastic ductility than that of the as-cast Zr 55 Cu 30 Al 10 Ni 5 glassy alloy rod specimen. The increase in the plastic ductility is proposed to originate from the structural inhomogeneity caused by the ZrO 2 ceramic particles.

Ceramic Particulate Reinforced Zr<SUB>55</SUB>Cu<SUB>30</SUB>Al<SUB>10</SUB>Ni<SUB>5</SUB> Metallic Glassy Matrix Composite Fabricated by Spark Plasma Sintering

Two-type sintered specimens of Zr55Cu30Al10Ni5 glassy alloy powder blended with and without 10 vol% ZrO2 ceramic powder, which had the similar relative density, were fabricated by a spark plasma sintering process in order to clarify the reinforced mechanical effect of ZrO2 particulates in the metallic glassy matrix composite. The structure, thermal stability and mechanical properties of the two-type sintered specimens were investigated. Two-type sintered specimens as well as original metallic glassy powder exhibited similar thermal stability. No crystallization of the metallic glassy matrix was demonstrated during the spark plasma sintering process. The plastic ductility of the sintered Zr55Cu30Al10Ni5 glassy matrix composite was enhanced by adding the ZrO2 particulates into the metallic glassy alloy. The improvement was originated from the structural inhomogeneity caused by the micro particles inclusion. [doi:10.2320/matertrans.MJ200716]

Effect of ball-milling and shot-peening on Zr 55Al 10Ni 5Cu 30 alloys

Effect of ball-milling and shot-peening on a metallic glass Zr 55Al 10Ni 5Cu 30, which possesses a large supercooled liquid region, has been investigated by means of differential scanning calorimetry, x-ray diffractometry and transmission electron microscopy. Metallic glassy ribbons, powders and plates were prepared by melt-spinning, gas-atomizing and mold-clamp casting techniques, respectively. No structural changes were observed in both the ribbon and powder specimens by ball-milling for around 100 h; however, the powder specimens were crystallized by Fe contamination when they were ball-milled for 540 h. No structural evolution was also observed when the plate specimens were subjected to shot-peening, while crystallized plate specimens were easily amorphized by mild and short period shot-peening. These results imply high phase stability of the Zr 55Al 10Ni 5Cu 30 metallic glass against deformation.