Equation of state of solids from high-pressure isotherm

A new variant of the method of finding the equation of state in the Mie–Grüneisen form is presented. It is based only on high-pressure isotherms of solids. Using this procedure, the semiempirical equation of state and shock adiabats of solids may be found at high pressures and high temperatures. The method is tested on periclase MgO within the range of shock pressures up to 300–500 GPa.     

Formation and properties of rocksalt-type AlN and implications for high pressure phase relations in the system Si–Al–O–N

Pressure-dependent thermodynamic properties of the ambient and high pressure phases of aluminum nitride (w-AlN and rs-AlN) were calculated from first principles in order to determine their phase boundary in the p? T phase diagram. These predictions were checked by static HP/HT experiments, using a multianvil press and an Al/N/H precursor with low decomposition temperature as educt. The experimental data show that at temperatures between 1000 and 2000 K, the boundary line between the two phases is situated between 11 and 12 GPa, which is ～1.3 GPa lower than the theoretical result and generally lower than previously assumed. The hardness of rs-AlN – measured for the first time – is ～30 GPa (Knoop indenter at loads of 25–50 g), twice as hard as w-AlN. Shock wave recovery experiments on nano w-AlN allowed testing of the chemical and thermal stability of rs-AlN, and determination of its infrared absorption and ²⁷Al NMR data. The shock wave technique will eventually enable the synthesis of larger amounts of rs-AlN, making it available for technological use. Finally, implications on the high pressure stability of phases in the Si–Al–O–N system are discussed in the light of thermoelastic properties of AlN.     

Numerical solution for curved crack problem in elastic half-plane using hypersingular integral equation

A hypersingular integral equation for the curved crack problems of an elastic half-plane is introduced. Formulation of the equation is based on the usage of a modified complex potential. The potential is generally expressed in the form of a Cauchy-type integral. The modified complex potential is composed of the principal part and the complementary part. The principal part of the complex potential is actually equivalent to the original complex potential for the curved crack in an infinite plate. The role of the complementary part is to eliminate the boundary traction along the boundary of the half-plane caused by the principal part. From the assumed boundary traction condition, a hypersingular integral equation is obtained for the curved crack problems of an elastic half-plane. The curve length coordinate method is used to obtain a final solution. Several numerical examples are presented that prove the efficiency of the suggested method.     

Unusual nucleation and growth of γ′ iron nitride upon nitriding Fe–4.75 at.% Al alloy

The influence of substitutionally dissolved Al in ferritic Fe–4.75 at.% Al alloy on the nucleation and growth of γ′ iron nitride (Fe₄N_{1? x} ) was investigated upon nitriding in NH₃/H₂ gas mixtures. The nitrided specimens were characterised employing optical microscopy, scanning electron microscopy, transmission electron microscopy, electron probe microanalysis and X-ray diffraction. As compared to the nitriding of pure ferrite (α-Fe), where a layer of γ′ develops at the surface, upon nitriding ferritic Fe–4.75 at.% Al an unusual morphology of γ′ plates develops at the surface, which plates deeply penetrate the substrate. In the diffusion zone, nano-sized precipitates of γ′ and of metastable, cubic (NaCl-type) AlN occur, having, with the ferrite matrix, a Nishiyama–Wassermann orientation relationship and a Bain orientation relationship, respectively. The γ′ plates contain a high density of stacking faults and fine ε iron nitride (Fe₂N_{1? z} ) precipitates, although the formation of ε iron nitride is not expected for the employed nitriding parameters. On the basis of dedicated nitriding experiments it is shown that the unusual microstructural development is a consequence of the negligible solubility of Al in γ′ and the obstructed precipitation of the thermodynamically stable, hexagonal (wurtzite-type) AlN in ferrite.     

On the absence of shear cracking and grain boundary cavitation in secondary tensile regions of Ti–6Al–4V–0.1B alloy during hot (α + β)-compression

Deformation instabilities, such as shear cracking and grain boundary cavitation, which are observed in the secondary tensile region of Ti–6Al–4V alloy during compressive deformation in the (α?+?β)-phase field, do not form in Ti–6Al–4V–0.1B alloy when processed under the same conditions. This has been attributed to the microstructural modifications, e.g. the absence of grain boundary α and adjacent grain boundary retained β layers and a lower proportion of 90^o-misoriented α-colonies that occur with boron addition.     

Formation of Composites in the System of Organic Europium Complexes–Silica

Lanthanide doped sol–gel glasses are an attractive type of luminescent material which can be processed at ambient temperatures. However, it is very difficult to obtain a uniform distribution of the complexes in glass materials because of their strong tendency to cluster formation. This problem can be solved by covalently linking of lanthanide complexes to silica matrix. In our work such materials were obtained by the sol–gel method of hydrolysis and polycondensation of tetramethoxysilane with europium complexes containing trimethoxysilyl groups. For this purpose we synthesized a novel ligand — (N-3-trimethoxysilylpropyl)-N′-1,10-phenanthroline-5-yl-thiocarbamide — and corresponding complexes [Eu(tta)₃phen′]Cl₃ and [Eu(pta)₃phen′]Cl₃. Our approach enabled us to simplify the synthetic procedure. A number of uniform samples showing intense luminescence have been obtained and the concentration dependence of their luminescence has been studied.     

Sliding Wear Studies on Aluminium–Copper Composites

Metal–metal composites are prepared by dispersing copper particulates in an aluminium matrix using stir-cast technique. Behaviour of the same is compared with the alloy having similar composition. Wear behaviour of the alloy in the cast condition is superior to the homogenized condition, though cast structure exhibit low hardness compared to the other. This is attributed to the easy crack propagation along the CuAl₂ precipitates in the homogenized condition, compared to the grain boundary in the as-cast structure. Wear properties of the resultant composite are superior to the alloy. Effect of particulate composition is studied by varying the copper concentration between 5 and 15 wt%. Composites with high copper content exhibit better wear resistance than the dilute ones, which is attributed to the increased hardness due to large population of intermetallics.