scholarly journals Effects of Annealing on Enthalpy Recovery and Nanomechanical Behaviors of a La-Based Bulk Metallic Glass

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 579
Author(s):  
Ting Shi ◽  
Lanping Huang ◽  
Song Li
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Structural Relaxation ◽  
Supercooled Liquid ◽  
Supercooled Liquid Region ◽  
Liquid Region ◽  
Nanoindentation Measurement

Structural relaxation and nanomechanical behaviors of La65Al14Ni5Co5Cu9.2Ag1.8 bulk metallic glass (BMG) with a low glass transition temperature during annealing have been investigated by calorimetry and nanoindentation measurement. The enthalpy release of this metallic glass is deduced by annealing near glass transition. When annealed below glass transition temperature for 5 min, the recovered enthalpy increases with annealing temperature and reaches the maximum value at 403 K. After annealed in supercooled liquid region, the recovered enthalpy obviously decreases. For a given annealing at 393 K, the relaxation behaviors of La-based BMG can be well described by the Kohlrausch-Williams-Watts (KWW) function. The hardness, Young’s modulus, and serrated flow are sensitive to structural relaxation of this metallic glass, which can be well explained by the theory of solid-like region and liquid-like region. The decrease of ductility and the enhancement of homogeneity can be ascribed to the transformation from liquid-like region into solid-like region and the reduction of the shear transition zone (STZ).

Hot pressing and characterizations of mechanically alloyed Zr52Al6Ni8Cu14W20 glassy powders.

2006 ◽  
Vol 21 (4) ◽  
pp. 976-987 ◽  
Author(s):  
M. Sherif El-Eskandarany ◽  
A. Inoue
Keyword(s):  
Solid Solution ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Supercooled Liquid ◽  
Supercooled Liquid Region ◽  
Solution Phase ◽  
Solid Solution Phase ◽  
Liquid Region ◽  
Gradual Change

Low-energy ball milling technique was successfully used to synthesis new glassy Zr52Al6Ni8Cu14W20 multicomponent alloy powders using mechanical alloying method. During the intermediate stage of milling the atoms of Zr, Al, Ni, and Cu migrated and diffused into the W lattice to form a body-centered cubic solid solution phase. As the milling time increases, the obtained metastable powders are subsequently subjected to continuous defects and lattice imperfections that lead to a gradual change in the free energy so that solid solution phase transformed to another metastable phase (glassy). The glassy powders that were obtained after 720 ks milling are fully amorphous and have spherical-like morphology with an average particle size of 0.60 μm in diameter. The synthetic glassy Zr52Al6Ni8Cu14W20 alloy powder, which exhibits a glass transition temperature of 811 K, crystallizes at a high temperature (884 K) through a single sharp exothermic peak with an enthalpy change of crystallization of −5.48 kJ/mol. Whereas the supercooled liquid region before crystallization of the obtained glassy powders is 73 K, the reduced glass transition temperature (ratio between Tg and liquidus temperatures) was found to be 0.46. The fabricated glassy powders were consequently hot-pressed into bulk samples in an argon gas atmosphere at several temperatures with a pressure of 936 MPa. The samples that were consolidated within the temperature of the supercooled liquid region are fully dense, with relative density above ∼99.82%, and maintain their original homogeneous glassy structure. They have high Vickers microhardness values in the range between 8.46 and 8.62 GPa. They also show very high fracture strength (2.13 GPa) with an extraordinary high Young's modulus of 138 GPa. Neither yielding stress, nor plastic strain could be detected for this glassy alloy, the elastic strain of which is 1.47%.

Influence of Structural Relaxation on Compressive Plasticity of Zr64.13Cu15.75Ni10.12Al10 Bulk Metallic Glass

2014 ◽  
Vol 910 ◽  
pp. 48-52 ◽  
Author(s):  
Jian Sheng Gu ◽  
Hui Feng Bo
Keyword(s):  
Differential Scanning Calorimetry ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Free Volume ◽  
Structural Relaxation ◽  
Isothermal Annealing ◽  
Scanning Calorimetry

Structural relaxation through isothermal annealing below the glass transition temperature was conducted on a Zr64.13Cu15.75Ni10.12Al10bulk metallic glass. Differential scanning calorimetry was used to quantify enthalpy differences between the as-cast and relaxed samples, which were then related to average free volume differences. The influence of structural relaxation on plasticity was examined. While the free volume decreasement can be clearly observed between the as-cast and relaxed samples, structural relaxation is not accompanied by severe embrittlement.

Solid-state synthesis of new glassy Co65Ti20W15 alloy powders and subsequent densification into a fully dense bulk glass

2005 ◽  
Vol 20 (10) ◽  
pp. 2845-2853 ◽  
Author(s):  
M. Sherif El-Eskandarany ◽  
M. Omori ◽  
A. Inoue
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Glassy Alloy ◽  
Supercooled Liquid ◽  
High Energy ◽  
Supercooled Liquid Region ◽  
Exothermic Peak ◽  
Liquid Region ◽  
Plasma Sintering

The mechanical alloying method was used to synthesize a single glassy phase of Co65Ti20W15 alloy powders, using a high-energy ball mill. The glass transition temperature of the end-product, which was obtained after 173 ks of milling time, lies at 786 K, whereas the crystallization takes place at 878 K through a single sharp exothermic peak with an enthalpy change of crystallization of −4.37 kJ/mol. The reduced glass transition temperature was found to be 0.51. This glassy alloy powders exhibit a very large supercooled liquid region (92 K) for a ternary metallic system. The spark plasma sintering method was used to consolidate the glassy powders under an argon gas atmosphere at 843 K with a pressure of 19.6–38.2 MPa. The sample that was consolidated within 180 s maintains its chemically homogeneous glassy structure with a relative density of above 99.6%. Neither the supercooled liquid region nor crystallization temperature was affected by such a rapid consolidation procedure. Thus, the thermal stability of the bulk glassy sample is almost identical with the original glassy powders. The Vickers microhardness of the bulk glassy Co65Ti20W15 reveals high values, ranging between 8.69 and 8.83 GPa. The fabricated bulk glassy alloy shows high compressive strength of 2.44 GPa with a Young’s modulus of 176.81 GPa. Neither yielding stress, nor plastic strain could be detected for this glassy alloy, which its elastic strain is 1.33%.

Mechanically induced solid-state reaction for synthesizing glassy Co75Ti25 soft magnet alloy powders with a wide supercooled liquid region

2002 ◽  
Vol 17 (9) ◽  
pp. 2447-2456 ◽  
Author(s):  
M. Sherif El-Eskandarany ◽  
Wei Zhang ◽  
A. Inoue
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Ball Milling ◽  
Glassy Phase ◽  
Glassy Alloy ◽  
Supercooled Liquid ◽  
High Energy ◽  
Supercooled Liquid Region ◽  
Liquid Region

A single phase of glassy Co75Ti25 alloy powders was synthesized by high-energy ball milling the elemental powders at room temperature, using the mechanical alloying method. The final product of the glassy alloy, which is obtained after ball milling for 86 ks, exhibits soft magnetic properties with polarization and coercivity values of 0.67 T and 2.98 kA/m, respectively. This binary glassy alloy, in which its glass transition temperature (Tg) lies at a rather high temperature (833 K), transforms into face-centered-cubic Co3Ti (ordered phase) at 889 K through a single sharp exothermic reaction with an enthalpy change of crystallization (ΔHx) of −2.35 kJ/mol. The supercooled liquid region before crystallization ΔTx of the synthesized glassy powders shows an extraordinary high value (56 K) for a metallic binary system. The reduced glass transition temperature [ratio between Tg and liquidus temperatures, Tl (Tg/Tl)] was 0.56. We also demonstrated postannealing experiments of the mechanically deformed Co/Ti multilayered composite powders. The results show that annealing of the powders at 710 K leads to the formation of a glassy phase (thermally enhanced glass formation reaction). Its heat formation was measured directly and found to be −0.56 kJ/mol. The similarity in the crystallization and magnetization behaviors between the two classes of as-annealed and as-mechanically alloyed glassy powders implies the formation of the same glassy phase.

Elastic Properties of Cu-Based Bulk Metallic Glass around Glass Transition Temperature

2007 ◽  
Vol 539-543 ◽  
pp. 1932-1936 ◽  
Author(s):  
R. Tarumi ◽  
H. Ogi ◽  
M. Hirao ◽  
T. Ichitsubo ◽  
Eiichiro Matsubara ◽  
...  
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Acoustic Resonance ◽  
Supercooled Liquid ◽  
Elastic Behavior ◽  
Linear Temperature Dependence ◽  
Linear Temperature

Temperature dependent elastic constants Cij(T) of Cu60Hf30Ti10 bulk metallic glass (BMG) have been investigated in a MHz frequency range using electromagnetic acoustic resonance (EMAR) up to 823 K. At room temperature, the BMG showed high Poisson’s ratio ν arising from low shear modulus G compared with that of constitutive crystalline elements. With increasing temperature, G showed usual linear temperature dependence while it suddenly drops around glass transition temperature, Tg. Within a framework of quasiharmonic approximation, Grüneisen parameter γ around Tg is estimated to be 10. This extremely large γ indicates the high anhramonicity of long wavelength limit acoustic mode phonon in the supercooled liquid state. The unusual elastic behavior can be interpreted on the basis of heterogeneous microstructure.

Microstructure and Microhardness in Current Annealed Fe65.5Cr4Mo4Ga4P12C5B5.5 Bulk Metallic Glass

2007 ◽  
Vol 555 ◽  
pp. 521-526 ◽  
Author(s):  
N. Mitrović ◽  
B. Čukić ◽  
Branka Jordović ◽  
Stefan Roth ◽  
M. Stoica
Keyword(s):  
Thermal Stability ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Amorphous State ◽  
Supercooled Liquid ◽  
Supercooled Liquid Region ◽  
Nominal Composition ◽  
Liquid Region ◽  
Scanning Calorimetry

The rods of Fe-based bulk metallic glasses with the nominal composition Fe65.5Cr4Mo4Ga4P12C5B5.5 were cast by melt injection into 1.5 and 1.8 mm diameter copper molds. The thermal stability, microstructure and crystallization behavior were investigated by differential scanning calorimetry, optical micrography and X-ray diffraction, respectively. The wide supercooled liquid region between crystallization temperature (Tx) and glass transition temperature (Tg) in the as-cast state Tx=Tx-Tg=60 K, as well as the high value of reduced glass transition temperature Trg=Tg/Tl=0.567 (Tl is liquidus temperature) approves enhanced thermal stability of the alloy against crystallization. In the as-cast “XRD-amorphous” state, microhardness HV1=742 was observed. Multistep current annealing thermal treatments were performed for structural relaxation. After applying high enough heating power per square area (PS ≥ 6 W/cm2), intensive crystallization of the samples characterized by appearance of several iron-metalloid compounds (Fe5C2, Fe3Ga4, Fe63Mo37 and Mo12Fe22C10) was observed. The microstructure changes after crystallization bring about differences in the microhardness values. The areas of still present amorphous matrix are with increased value HV1=876, but a remarkable decrease to HV1=323 was observed in precipitated crystallized zone that propagate along inner part of cylinders.

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