A thermogravimetric study of the oxidative growth of Al2O3/Al alloy composites

1991 ◽  
Vol 6 (9) ◽  
pp. 1982-1995 ◽  
Author(s):  
K.C. Vlach ◽  
O. Salas ◽  
H. Ni ◽  
V. Jayaram ◽  
C.G. Levi ◽  
...  
Keyword(s):  
Surface Layer ◽  
Volume Fraction ◽  
Alloy Layer ◽  
Al Alloy ◽  
Near Surface ◽  
Bulk Growth ◽  
Continuous Formation ◽  
Metal Volume ◽  
Si Content ◽  
Metal Volume Fraction

The oxidation of liquid Al–Mg–Si alloys at 900–1400 °C was studied by thermogravimetric analysis (TGA). The development of a semi-protective surface layer of MgO/MgAl2O4 allows the continuous formation of an Al2O3-matrix composite containing an interpenetrating network of metal microchannels at 1000–1350 °C. An initial incubation period precedes bulk oxidation, wherein Al2O3 grows from a near-surface alloy layer by reaction of oxygen supplied by the dissolution of the surface oxides and Al supplied from a bulk alloy reservoir through the microchannel network. The typical oxidation rate during bulk growth displays an initial acceleration followed by a parabolic deceleration in a regime apparently limited by Al transport to the near-surface layer. Both regimes may be influenced by the Si content in this layer, which rises due to preferential Al and Mg oxidation. The growth rates increase with temperature to a maximum at ∼1300 °C, with a nominal activation energy of 270 kJ/mole for an Al−2.85 wt. % Mg−5.4 wt. % Si alloy in O2 at furnace temperatures of 1000–1300 °C. An oscillatory rate regime observed at 1000–1075 °C resulted in a banded structure of varying Al2O3-to-metal volume fraction.

Scaling of Complex Conductivity for A Percolating Metal-Insulator Composite with Inter granular Tunneling Above and Below the Superconducting Transition

1995 ◽  
Vol 411 ◽  
Author(s):  
D. S. Mclachlan ◽  
A. B. Pakhomov ◽  
I. I. Oblachova ◽  
F. Brouers ◽  
A. Sarychev
Keyword(s):  
Volume Fraction ◽  
Frequency Dispersion ◽  
Scaling Theory ◽  
Complex Conductivity ◽  
Superconducting Transition ◽  
Percolation Transition ◽  
Metal Insulator ◽  
Metal Volume ◽  
Metal Volume Fraction ◽  
Composite Samples

ABSTRACTThe complex conductivity was measured on 3d granular NbC-KCI composite samples at varying metal volume fraction p, frequency ω and temperature above and below the superconductivity critical Tc. The observed frequency dispersion is anomalous in that it is not in accord with the scaling theory of percolation transition. The results are compared with a recently developed scaling theory, which takes both intercluster tunneling and intercluster capacitance into account. The experimental estimates for the new critical exponents are in reasonable agreement with the theory. The very low value of the crossover frequency can also be understood. We also present the data showing the dispersion of the complex conductivity well below the superconducting transition Tc of NbC.

Microstructure and Oxidation of a Cast Nickel Aluminide Alloy

2002 ◽  
Vol 753 ◽  
Author(s):  
D. Y. Lee ◽  
M. L. Santella ◽  
I. M. Anderson ◽  
G. M. Pharr
Keyword(s):  
Nickel Aluminide ◽  
Volume Fraction ◽  
Surface Region ◽  
Oxidation Products ◽  
Al Alloy ◽  
X Ray Diffraction ◽  
Multivariate Statistical ◽  
Near Surface ◽  
X Ray ◽  
Spectrum Imaging

ABSTRACTSpecimens of the cast Ni3Al alloy IC221M were annealed in air at 900°C to examine the effects of oxidation and thermal aging on the microstructure. The alloy is comprised of a dendritically solidified γ-γ′ matrix containing γ+Ni5Zr eutectic colonies in the interdendritic regions. Microstructures of aged specimens were examined by optical microscopy and energy dispersive X-ray (EDX) spectrum imaging in the scanning electron microscope (SEM). Two primary changes in the microstructures were observed: (1) there is considerable homogenization of the cast microstructures with aging, and (2) the volume fraction of the γ+Ni5Zr eutectic decreases. Oxidation products were identified using x-ray diffraction and EDX spectrum imaging with multivariate statistical analysis (MSA). During the initial stages of oxidation, the first surface oxide to form is mostly NiO with small amounts of Cr2O3, ZrO2, NiCr2O4, and θ-Al2O3. Initially, oxidation occurs primarily in the interdendritic regions due to microsegregation of alloying elements during casting. With further aging, a continuous film of α-Al2O3 forms immediately beneath the surface that eventually evolves into a double layer of α-Al2O3 and NiAl2O4. Although these oxides are constrained to the near surface region, others penetrate to greater depths facilitated by oxidation of the γ+Ni5Zr eutectic colonies. These oxides appear in the microstructure as long, thin spikes of ZrO2 surrounded by a thin sheath of Al2O3.

scholarly journals Physical Nature of Strengthening Mechanisms During Extremely Long-Term Operation of Rails

2021 ◽  
pp. 33-39
Author(s):  
Yu.F. Ivanov ◽  
A.A. Yuriev ◽  
V.E. Kormyshev ◽  
X. Chen ◽  
V.B. Kosterev ◽  
...  
Keyword(s):  
Surface Layer ◽  
Relative Content ◽  
Formation Mechanisms ◽  
Strengthening Mechanisms ◽  
Near Surface ◽  
Term Operation ◽  
Rail Head ◽  
Metal Volume ◽  
Lamellar Pearlite

The quantitative estimation of strengthening mechanisms of rails’ surface layer is carried out on the basis of regularities and formation mechanisms of structure-phase states revealed by the methods of modern physical materials science. It is performed at different depths of the rail head along the central axis and fillet of differentially quenched 100-meter rails after the extremely long-term operation (gross passed tonnage of 1411 mln tons). A long-term operation of rails is accompanied by the formation of structural constituent gradient consisting of a regular change in the relative content of lamellar pearlite, fractured pearlite, the structure of ferrite-carbide mixture, scalar, and excess dislocation density along the cross-section of the rail head. As the distance to the rail fillet surface decreases, the relative content of metal volume with lamellar pearlite decreases. However, the relative content of metal volume with the presence of the fractured pearlite structure and ferrite-carbide mixture increases. The contributions caused by the matrix lattice friction, intraphase boundaries, dislocation substructure, presence of carbide particles, internal stress fields, solid-solution strengthening, pearlite component of steel structure are estimated. It is shown that the main mechanism of strengthening in the surface layer is due to the interaction of moving dislocations with low-angle boundaries of nanometer dimensional fragments and subgrains. The main dislocation strengthening mechanism in a near-surface layer at a depth of 2-10 mm is due to the interaction of moving dislocations with immobile ones.

Simulation of Stiffness and Thermal Conductivity of Ordered Metal Microstructure Reinforced Polymer Composite Interposer

2013 ◽  
Vol 663 ◽  
pp. 326-330 ◽  
Author(s):  
Ming Wang ◽  
Ping Cheng ◽  
Yan Wang ◽  
Hong Wang ◽  
Gui Fu Ding
Keyword(s):  
Thermal Conductivity ◽  
Polymer Composite ◽  
Volume Fraction ◽  
Pure Polymer ◽  
Reinforced Polymer ◽  
Metal Volume ◽  
The One ◽  
Metal Microstructure ◽  
Triangular Model ◽  
Metal Volume Fraction

An interposer model based on ordered metal microstructure reinforced polymer composite was established using ANSYS software. The shape of metal microstructure includes quadrilateral, hexagon and triangle. The stiffness and thermal conductivity of composite interposer was calculated and discussed. Simulation results show that the stiffness of the metal microstructure-reinforced polymer composite interposer increases with augmenting the volume fraction of metal compared with the pure polymer. For the composite with metal volume fraction of 65%, the stiffness of the triangular composite interposer is 3.12 times that of the pure polymer interposer. The thermal conductivity of the hexagonal model is the best, while the one of quadrilateral and triangular model is similar. For the composite with the metal volume fraction of 65%, the thermal conductivity of the triangular composite interposer is 3.42 times that of the pure polymer interposer. Therefore, metal microstructure can effectively improve the performance of the pure polymer interposer.

Effective Thermal Conductivity of Phase Change Material-Based Composites for High Heat Flux Electronic Cooling

2020 ◽  
Author(s):  
Ayushman Singh ◽  
Srikanth Rangarajan ◽  
Leila Choobineh ◽  
Bahgat Sammakia
Keyword(s):  
Thermal Conductivity ◽  
Phase Change ◽  
Effective Thermal Conductivity ◽  
Phase Change Material ◽  
Heat Sink ◽  
Volume Fraction ◽  
Electronic Cooling ◽  
Metal Volume ◽  
Metal Volume Fraction ◽  
Change Material

Abstract This work presents a simplified approach to optimally designing a heat sink with metallic thermal conductivity enhancers infiltrated with phase change material for electronic cooling. In present study, thermal conductivity enhancers are in the form of a honeycomb structure. A benchmarked two-dimensional computational fluid dynamics model was employed to investigate the thermal performance of the phase change material-metallic thermal conductivity enhancer composite heat sinks. Metallic thermal conductivity enhancers are often used in conjunction with phase change material to enhance the conductivity of the composite heat sink. Under constrained heat sink volume, the higher volume fraction of thermal conductivity enhancers improves the effective thermal conductivity of the composite, while it reduces the amount of latent heat storage simultaneously. The present work arrives at the optimal design of heat sink for electronic cooling by resolving the stated tradeoff. In this study, the total volume of the heat sink and the interfacial heat transfer area between the phase change material and thermal conductivity enhancers are constrained for all design points. Furthermore, assuming conduction-dominated heat transfer, an effective numerical model that solves the single energy equation with the effective properties of the phase change material- metallic thermal conductivity enhancer composite has been developed. The temperature gradient-time history is compared and matched for both the models to arrive at the accurate effective thermal conductivity value. The relationship of effective thermal conductivity as a function of metal volume fraction and thermal conductivity of metallic thermal conductivity enhancer is obtained. The figure of merit (FOM) is used to define the balance between effective thermal conductivity and energy storage capacity. The FOM is maximized to find the optimal volume fraction for the present design. The results from the study reveals that there exists an optimal metal volume fraction that maximizes the thermal performance of the composite.

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