Metallurgical operations at elevated temperatures, such as those that involve solidification and/or mechanical deformation, can be critically influenced by the thermal stresses and strains that result from expansion and contraction of the material as a function of temperature. With the increasing use of computer-based process models for these operations, there arises a greater need for quantitative data on the thermal expansion coefficient of the relevant alloy at the temperatures involved. After briefly reviewing some existing sources of data for this property, the various techniques for its measurement at elevated temperatures are then described. These include mechanical dilatometry, optical imaging and interference systems, x-ray diffraction methods and electrical pulse heating techniques. Finally the implications, for process modelling, of the available data and measurement techniques are discussed.

https://iopscience.iop.org/article/10.1088/0957-0233/12/3/201/pdf

A review of measurement techniques for the thermal expansion coefficient of metals and alloys at elevated temperatures

Due to economical demands to further increase the efficiency of production processes, it is essential to exploit the full potential of wear resistant hard coatings. This is, however, possible only if the coating microstructure and properties are well characterized. Thus, in the present work, recently suggested advanced characterization techniques for coatings are reviewed. The application of atom probe tomography, electron backscatter diffraction and synchrotron X-ray nanodiffraction enables previously unrevealed insights in their chemical composition, microstructure and crystallographic structure. For the determination of mechanical and tribological properties at elevated temperatures, high-temperature nanoindentation and high-temperature ball-on-disk tests in combination with in-situ measurement techniques are discussed. Utilization of micromechanical tests for coatings provides information about their fracture toughness and rupture strength. High-temperature X-ray diffraction and biaxial stress temperature measurements for the determination of the coefficient of thermal expansion are compared. The thermal conductivity as well as the specific heat capacity of coatings can be studied using the 3- ω technique, time domain thermoreflectance and differential scanning calorimetry. The introduced portfolio of characterization techniques enables the determination of a complementary microstructural, mechanical and thermo-physical fingerprint of wear resistant hard coatings, which allows to understand the complex structure–property relations in these materials and subsequently to further improve their performance.

Advanced characterization methods for wear resistant hard coatings: A review on recent progress

Review—Investigation and Review of the Thermal, Mechanical, Electrical, Optical, and Structural Properties of Atomic Layer Deposited High-k Dielectrics: Beryllium Oxide, Aluminum Oxide, Hafnium Oxide, and Aluminum Nitride John T. Gaskins,a Patrick E. Hopkins,a,b,c,z Devin R. Merrill,d,e Sage R. Bauers,d Erik Hadland,d David C. Johnson,d,z Donghyi Koh,e,f Jung Hwan Yum,f Sanjay Banerjee,f,∗ Bradley J. Nordell,g Michelle M. Paquette,g Anthony N. Caruso,g William A. Lanford,h Patrick Henry,e Liza Ross,e Han Li,e Liyi Li,e Marc French,e Antonio M. Rudolph,e and Sean W. Kinge,∗,z

https://iopscience.iop.org/article/10.1149/2.0091710jss/pdf

Review—Investigation and Review of the Thermal, Mechanical, Electrical, Optical, and Structural Properties of Atomic Layer Deposited High-k Dielectrics: Beryllium Oxide, Aluminum Oxide, Hafnium Oxide, and Aluminum Nitride

A coated cutting tool that has a rake face and a flank face with a cutting edge at the juncture of the rake and flanks faces, a substrate, and a coating bonded to the substrate The coating has a coating scheme that includes a layer of a Group IVB metal-aluminum alloy applied by physical vapor deposition, and a layer of alumina applied by physical vapor deposition to the layer of the Group IVB metal-aluminum alloy

Coated cutting tool

The metastable forms of aluminum oxide that exist in the range of 300–800°C are characterized; differences in the microstructures of homogeneous γ-, η-, and χ-Al2O3 are demonstrated; and the acid-base properties of the above modifications are compared. The catalytic properties of aluminum oxide in ethanol dehydration and propionitrile ammonolysis were studied. It was found that an increased surface concentration of Lewis acid sites, including strong acid sites (ν(CO) = 2237 cm−1), is required for preparing an effective catalyst for the dehydration of ethanol, whereas the rate of propionitrile conversion increased proportionally to the surface concentration of Bronsted acid sites. γ-Aluminum oxide was used to prepare catalysts for carbon monoxide oxidation. It was found that the supporting of Pd on γ-Al2O3 did not change the support structure. Palladium on the surface of γ-Al2O3-550 (T
 calcin = 550°C, S
 BET = 300 m2/g) occurred as single particles (2–3 nm) and aggregates (∼100 nm). The single particles were almost completely covered with a layer of aluminum oxide to form core-shell structures. According to XPS data, they were in atypical states (BE(Pd 3d
 5/2) = 336.0 and 338.0 eV), which were not reduced by hydrogen in the range of 15–450°C and were resistant to the action of the reaction mixture. Palladium on the surface of γ-Al2O3-800 (S
 BET = 160 m2/g) was in the states Pd0 and PdO, which are typical of Pd/Al2O3, and the proportions of these states can change under the action of the reaction mixture. An increase in the T
 calcin of the Pd/Al2O3(800)-450 catalyst from 450 to 800 → 1000 → 1200°C led to the agglomeration of palladium particles and to an increase in the temperature of 50% CO conversion from 145 to 152 → 169 → 189°C, respectively. α-Aluminum oxide was used in the preparation of an effective Mn-Bi-O/α-Al2O3 supported catalyst for the synthesis of nitrous oxide by the oxidation of ammonia with oxygen: the NH3 conversion was 95–97% at 84.4% N2O selectivity.

Aluminum Oxide and Systems Based on It: Properties and Applications

In this work, the thermal expansion of κ -Al 2 O 3 has been characterised using high temperature X-ray diffraction of κ -Al 2 O 3 powder obtained from crushed chemical vapour deposited κ -Al 2 O 3 coatings. The lattice parameters, volume, thermal linear and volume expansion coefficients have been determined in the range 23 to 840 °C. It was found that κ -Al 2 O 3 expands anisotropically, the expansion being about equal along the b - and c -axis, while it is significantly lower along the a -axis. Compared with α -Al 2 O 3 , the expansion is slightly lower along c κ than along c α , similar along b κ and a α , while it is significantly lower along a κ than along a α . The expansion data imply that all aluminium ions in κ-Al 2 O 3 are not ordered in a hexagonal mesh as in α -Al 2 O 3 , but are ordered in lines along the a -axis.

Determination of the thermal expansion of κ-Al2O3 by high temperature XRD

X-ray powder diffraction data for κ-Al2O3

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Determination of the thermal expansion of κ-Al2O3 by high temperature XRD

X-ray powder diffraction data for κ-Al2O3