Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.

X-Ray Diffraction

http://liu.diva-portal.org/smash/get/diva2:303552/FULLTEXT01

The Mn+1AXn phases: Materials science and thin-film processing

The MAX phases are a group of layered ternary compounds with the general formula Mn+1AXn (M: early transition metal; A: group A element; X: C and/or N; n = 1–3), which combine some properties of metals, such as good electrical and thermal conductivity, machinability, low hardness, thermal shock resistance and damage tolerance, with those of ceramics, such as high elastic moduli, high temperature strength, and oxidation and corrosion resistance. The publication of papers on the MAX phases has shown an almost exponential increase in the past decade. The existence of further MAX phases has been reported or proposed. In addition to surveying this activity, the synthesis of MAX phases in the forms of bulk, films and powders is reviewed, together with their physical, mechanical and corrosion/oxidation properties. Recent research and development has revealed potential for the practical application of the MAX phases (particularly using the pressureless sintering and physical vapour deposition coating rout...

Progress in research and development on MAX phases: a family of layered ternary compounds

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Dislocations in solids

Layered ternary carbides contain alternative stacking of structural slabs in the unit cells. Many mechanical and structural features are inherited with respect to their binary carbide counterparts, and some novel properties also appear because of new chemical bonds and atomic coordination at the boundaries of different slabs. In this review, we highlight important recent achievements that focus on theoretical prediction, microstructure characterization preparation, and macroscopic properties of newly developed layered ternary transition-metal carbides. These results provide insights into understanding the relationship between the structure (including crystal structure, chemical bonding, and microstructure) and the properties of these layered ternary carbides and further highlight their technological applications as high-temperature and ultrahigh-temperature structural materials.

Recent Progress in Theoretical Prediction, Preparation, and Characterization of Layered Ternary Transition-Metal Carbides

The oxidation behavior of Zr2[Al(Si)]4C5 and Zr3[Al(Si)]4C6 in air has been investigated. The oxidation kinetics of bulk Zr2[Al(Si)]4C5 and Zr3[Al(Si)]4C6 at 900–1300 °C generally follow a parabolic law at a very short initial stage and then a linear law for a long period with the activation energy of 237.9 and 226.8 kJ/mol, respectively. The oxide scales have a duplex structure, consisting of mainly an outer porous layer of ZrO2, Al2O3, and aluminosilicate/mullite, and a thin inner compact layer of these oxides plus remaining carbon. The oxidation resistance of Zr2[Al(Si)]4C5 and Zr3[Al(Si)]4C6 has been improved compared with Zr2Al3C4, and is much better than ZrC due to larger fraction of protective oxidation products, Al2O3 and aluminosilicate/mullite.

Oxidation of Zr 2 (Al(Si)) 4 C 5 and Zr 3 (Al(Si)) 4 C 6 in air

The isothermal oxidation behavior of Zr2Al3C4 in the temperature range of 500 to 1000 °C for 20 h in air has been investigated. The oxidation kinetics follow a parabolic law at 600 to 800 °C and a linear law at higher temperatures. The activation energy is determined to be 167.4 and 201.2 kJ/mol at parabolic and linear stages, respectively. The oxide scales have a monolayer structure, which is a mixture of ZrO2 and Al2O3. As indicated by x-ray diffraction and Raman spectra, the scales formed at 500 to 700 °C are amorphous, and at higher temperatures are α-Al2O3 and t-ZrO2 nanocrystallites. The nonselective oxidation of Zr2Al3C4 can be attributed to the strong coupling between Al3C2 units and ZrC blocks in its structure, and the close oxygen affinity of Zr and Al.

Isothermal oxidation of bulk Zr2Al3C4 at 500 to 1000 °C in air

Studies were carried out on the microstructure and thermal stability of an ultrafine Al/Al2O3 composite with high strength and low density. Transmission electron microscopy indicated that Al2O3 shells remained undeformed below 550 degreesC, which limited grain growth of Al. Both transmission electron microscopy and x-ray diffraction analysis indicated that no obvious grain growth of Al with time occurred upon annealing at 620 degreesC. After almost all the alumina shells were destroyed following annealing at 620 degreesC, the Al2O3 fragments with various morphologies distributed in the material could still limit the migration of Al grain boundaries to increase the thermal stability of the material. After Al melted and resolidified, the grain sizes of Al were still about 200 run. The bulk composite sample showed good dimensional stability. Even if the Al grains melted, the network of Al2O3 fragments kept the sample from deforming due to the wetting of Al2O3 network with liquid Al.

Microstructure and thermal stability of an ultrafine Al/Al2O3 composite

The orientation relationship (OR) and the interfacial structure of the eutectic alpha-Nb(5)Si(3) and Nb solid solution (Nbss) lamellar microstructure were investigated by transmission electron microscopy (TEM). The OR between alpha-Nb(5)Si(3) and Nbss was determined as (002)(alpha)//(002)(Nb) and [310](alpha)//[110](Nb). In spite of the significant difference in crystal structure between alpha-Nb(5)Si(3) and Nbss, the interface was found to be semi-coherent with good matching. High-resolution TEM images of the alpha-Nb(5)Si(3)/Nbss interface are presented to describe the chemistry of the terminating plane of alpha-Nb(5)Si(3). The results revealed that a pure Nb layer not Si or mixed (Nb + Si) layer of the alpha-Nb(5)Si(3) phase was bonded to the Nb phase at the interface. A periodic array of edge-type misfit dislocations, with line direction [1 (1) over bar0](Nb) and Burgers vector 1/2[1 (1) over bar0](Nb), was observed at the interface.

Lianlong He

Papers

Oxidation of Zr 2 (Al(Si)) 4 C 5 and Zr 3 (Al(Si)) 4 C 6 in air

Isothermal oxidation of bulk Zr2Al3C4 at 500 to 1000 °C in air

Microstructure and thermal stability of an ultrafine Al/Al2O3 composite

Orientation relationship and interfacial structure between α-Nb5Si3 and Nb solid solution in the eutectic lamellar structure

Microstructure and grain boundary relaxation in ultrafine-grained Al/Al oxide composites