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Gaseous nitriding of binary Ni-Cr solid-solution alloys was studied at 1125°C over the range 1 to 6000 bar of N2-pressure. At the specified temperature the nitriding response of the Ni-Cr alloys depends on the Cr-content in the initial alloy and activity (fugacity) of nitrogen at the gas/metal interface. Transition from cubic d-CrN to hexagonal ß-Cr2N precipitation occurs within the reaction zone after nitrogenization at 1125°C under nitrogen pressure 100-6000 bar when chromium content in the initial alloy is 28 at. % or higher. It was found that a ternary phase, p (Cr12.8Ni7.2N4.0) is formed inside the Ni32Cr alloy upon cooling in nitrogen after nitriding at 1125°C and 1 bar of N2. Experimental evidence is presented that p-phase is involved in peritectoid relations with ß-Cr2N and ?-(Ni-Cr) solid solution. It was also demonstrated that nitriding behaviour of the Ni-Cr alloy can be rationalized using pertinent phase diagram information, but, in some cases, effect of mechanical stresses induced upon the internal precipitation can vitiate this prediction. [ABSTRACT FROM AUTHOR]

Evolution of the reaction zone on the nanoscale has been studied in bi- and multilayered Co/a-Si as well as in trilayered Co/a-CoSi/a-Si and Co/CoSi/a-Si thin film diffusion couples. The kinetics of the phase boundary movement during solid state reaction has been followed with special interest of the initial stage of the diffusion, i.e. effects happening on the nanoscale (short time, short distance). The interfacial reactions have been investigated in situ by synchrotron radiation. The formed phases were also characterized by transmission electron microscopy and resistance measurements. The effect of phase nucleation and shift of phase boundaries have been separated in order to determine the “pure” growth kinetics of the crystalline CoSi and Co2Si product phases at the very early stages. Deviations have been found from the traditional diffusion controlled parabolic phase growth. Computer simulations based on a kinetic mean field model illustrated that the diffusion asymmetry (large difference in diffusion coefficients of the materials in contact) may offer a plausible explanations for this. [ABSTRACT FROM AUTHOR]

It will be shown, in the framework of a general statistical (atomistic) treatment, that segregation inhibited grain coarsening in binary nanocrystalline alloys can be described by analytical expressions, if the effect can be attained with highly saturated grain boundaries. Relatively simple relations describing the temperature dependence of the stabilized grain-boundary fraction will be derived. The validity conditions of the relation proposed very recently by R. Kirchheim [Acta Mater. 50, 413 (2002)] are also analyzed. Our conclusions are compared with experimental results and the reliability of the few experimental data, known at present, will be discussed as well. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Potassium halogenthiophosphates K6PS5Br and K6PS5Cl as well as halogen-free K7PS6 compound were synthesized using the two-step technique from elemental substances as well as potassium halides. The elemental composition of the obtained samples was determined using energy-dispersive X-ray spectroscopy. Raman spectra of K6PS5Br and K6PS5Cl show themselves to be much similar to those of chemically related Cu6PS5Br and Cu6PS5Cl argyrodite crystals. The much richer spectra of K6PS5Br and K6PS5Cl as well as K7PS6, however, reveal that their structure most likely differs from the cubic structure of Cu6PS5Br and Cu6PS5Cl argyrodites. [ABSTRACT FROM AUTHOR]

Patterning processes in amorphous Se and $$\hbox {As}_{20}\hbox {Se}_{80}$$ films at short electron beam pulses (from 200 ns to 100 ms) were studied for the first time. The surface reliefs occurring as after-pulses effects were recorded and analysed. Giant hillock formation was detected at about $$200\,\upmu \hbox {s}$$ pulses while very small changes in surface morphology were observed at other pulse durations. The obtained data indicate that the strong increase in e-beam sensitivity of mechanical response (giant surface hillock formation) at about $$200\,\upmu \hbox {s}$$ is due to some resonance effect. A qualitative description is given, relating these times to the characteristic generation and relaxation time of the defects in these materials, which illuminates the process of e-beam induced structural rearrangement. The measurement has been performed at room temperature and at $$-120\,^{\circ }\hbox {C}$$ and only a 20% change in the maximal pattern height has been detected. [ABSTRACT FROM AUTHOR]

Interdiffusion experiments were performed between different Ni–Al two-phase alloys. A method is given to estimate the tracer diffusion coefficient of one of the constituents in a binary alloy knowing the tracer diffusion coefficient of the other species. The procedure is based on the so-called Darken-Manning analysis. The tracer diffusion coefficient of Al was determined in this way in Ni3Al:DAl*=5.05×10−7−1.117×10−7+2.28×10−6exp−243±16 KJ/mol/RTm2/sm2/sOur results are compared with others available in the literature. The values for the self diffusivity of Al calculated from interdiffusion experiments give consistent result. All these measurements support the theory that diffusion of the minor element occurs through a vacancy mechanism in Ni3Al. [Copyright &y& Elsevier]

Radio-tracer diffusion measurements of 63Ni have been performed in Ni75AlxGe25−x ternary intermetallic compounds at various temperatures. The tracer diffusivity was found to depend exponentially on the Ge content of the alloy. These compounds are ordered with the L12 structure, where the Ni atom diffusion proceeds mainly via Ni sublattice site jumps. The change of the diffusivity can be attributed to the change in vacancy concentration on the Ni sublattice as well as to the composition dependence of the saddle-point energy of the diffusion jumps. [ABSTRACT FROM AUTHOR]