[en] Nanometre-sized freestanding alloy particles of B2-ordered AuCd with an average composition of Au₅₀Cd₅₀ (at.%) were synthesized by a wet-chemical process. The thermoelastic transformation behaviour with respect to particle size was investigated by means of calorimetry, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The martensitic transformation start temperature, M_s, of nanometre-sized AuCd particles was determined to about 49 K and thus drastically lowered compared to AuCd bulk alloys. The lowering of the transformation temperatures is discussed on the basis of the obtained calorimetric data regarding the following two aspects: firstly, a reduction in the thermodynamic equilibrium temperature, T₀, and secondly, a suppression of the martensite formation due to the absence of pre-existing nucleation sites in the small AuCd particles. Moreover, it is demonstrated that due to a coarsening of the nanometre-sized alloy particles during a heat treatment, the martensitic transformation was shifted towards ambient temperature

[en] Highlights: • Fast scanning calorimeter calibration with position dependence. • Calibration of fast scanning calorimeter during cooling. • Quantitative determination of nucleation rates by treating the undercooling as stochastic parameter - Abstract: Accurate thermal analyzes and calorimetry measurements depend on careful calibration measurements. For conventional differential scanning calorimeters (DSC) the calibration procedure is well known. The melting point of different pure metals is measured and compared with literature data to adjust the temperature reading of the calorimeter. Likewise, the measured melting enthalpies of standard reference substances serve for enthalpy calibration. Yet for fast chip calorimetry, new procedures need to be established. For the medium-area and large-area calorimeter chips, this procedure needs to be modified, because the calibration behavior depends on the position of the sample on the measurement area. Additionally, a way to calibrate the calorimeter for measurements performed during cooling will also be shown. For this second aspect, the athermal and diffusionless martensitic phase transformation of Ni_4_9_._9–Ti_5_0_._1 at% was used. The well-calibrated sensor chips are ideally suited to perform nucleation rate density analyzes based on a statistical approach. Here, the nucleation rate densities of micron-sized pure Sn droplets that had been coated with a non-catalytic coating have been determined by experimental analysis of the statistical variance of the undercooling response

[en] Mechanical alloying via high pressure torsion (HPT) is studied for the immiscible Cu-Ta system. Stacks of alternating 25 µm thick sheets of pure Cu and Ta were subjected to HPT processing at a pressure of 4 GPa for 10, 30, 50, 100 and 150 revolutions, respectively. The effect of subsequent heat treatment on the phase composition and microstructure evolution of Cu/Ta and pure Cu or pure Ta foil stacks is examined by X-ray diffraction, scanning and transmission electron microscopy and microhardness measurements. The HPT processing of the Cu/Ta assembly by 150 revolutions is shown to produce a mixture of ultrafine grains corresponding to a Cu-16% Ta solid solution with embedded nano-scaled Ta-rich particles and almost pure Ta grains. The microstructure reveals a superior thermal stability and remains fine-grained even after annealing at 1000 °C for 1 h. HPT deformation of pure Cu stacks results in formation of a mixture of pure Cu and CuO, presumably due to availability of numerous interfaces in the assembly, with the existence of the copper mono-oxide being verified by X-ray measurements.

[en] The defect accumulation, thermal expansion, microhardness and microstructure are investigated for severely plastically deformed technically pure Al (Al-base alloy of the 1050 series) as a function of initial state and post-deformation annealing treatments. Coarse grained as-cast and heat-treated states are deformed via high-pressure torsion. The excess volume release upon subsequent annealing is measured by dilatometry employing a constant heating rate and two characteristic sub-stages are revealed. The corresponding microstructure changes are further investigated by transmission electron microscopy. A strong impact of the initial state on the microstructure and the properties of ultrafine grained Al is established. The dilatometric length changes of ultrafine grained Al under annealing are related to the formation of Fe-rich precipitates as well as to the annihilation of deformation-induced defects.

[en] The melting behaviour of small crystalline solid particles has attracted the interest of many researchers. In the present work, an alloy of Al-4 at % In with nanoparticles of Indium embedded in an Aluminium matrix was synthesized by rapid quenching using the melt-spinning technique. The melting point and freezing behaviour of the embedded nanoparticles were investigated using differential scanning calorimetry and transmission electron microscopy (TEM) including high resolution transmission electron microscopy (HRTEM). DSC experiments showed broad melting and crystallization peaks. The crystallization temperature of the embedded particles shifted to remarkable low temperature. The microstructure exhibited a homogeneous distribution of facetted In particles embedded in the Al-matrix. Analyses of HRTEM images were done to analyse the topology of the heterophase interfaces between Al and In in detail. The results are discussed with respect of the impact of the mismatch accommodation of interfaces on the thermodynamics of nanoscale systems.

[en] Tungsten oxide (WO₃) is a suitable material for gas sensing applications relying on the change of conductivity by adsorped molecules. Regular arrays of nanotubes provide a large surface area and promise very high sensitivity. This work presents the production of such nanotube arrays with the potential of tuning the surface area by sol-gel-deposition of WO₃ in porous alumina membranes (PAM) from the precursors tungsten hexachloride (WCl₆) and acetylacetone (C₅H₈O₂). Dimensions and composition of the nanotubes are characterized by SEM and EDX, their sensing properties for CO and NO₂ will be investigated.

[en] The thermodynamics of nanoscaled systems have drawn considerable scientific attention due to the strong influence of the particle size and shape. In the present work, nanoparticles of indium embedded in an aluminum matrix were processed by rapid quenching using the melt-spinning technique. The as-processed samples were analyzed using conventional and analytical transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). TEM data revealed isolated and mainly spherical nanoparticles of indium with a size in the range of 20 to 300 nm. Indium particles in aluminum grains are equiaxed, whereas particles at aluminum grain boundaries show elongation. Analytical TEM showed neither a notable concentration of indium in the aluminum matrix nor a concentration gradient at the interfaces of the particles. By DSC experiments using a wide range of different constant heating and cooling rates, broad melting and crystallization peaks were observed. A slight reduction of the melting temperature of the embedded particles in comparison to the bulk indium is detected, whereas the crystallization temperature shifts to remarkable low temperatures. Upon thermal cycling, the melting as well as the crystallization temperatures of the nanoparticles reduces and the peak shape changes clearly.

[en] Metallic glasses are still an attractive object of investigation in the field of materials physics due to their outstanding mechanical properties. Hardness and yield strength exceed the values of their crystalline counterpart by far, but the applicability of metallic glasses is limited by the lack of considerable plasticity. Stress localization and the associated shear softening strongly weaken the structure, thus leading to the formation of shear bands. The structure of shear bands is still far from being understood. Due to their extreme sensitiveness to the free volume localization, the diffusion measurements by the radiotracer technique can bring further insight into the structural modifications of shear bands with respect to the amorphous matrix as well as to the conditions of slip during plastic straining. Here, we present the results of diffusion as well as relaxation experiments in HPT-deformed Zr-based bulk metallic glass.

[en] Nanoscale Bi particles embedded in a Zn matrix were obtained by casting and melt-spinning, resulting in quenching rate-dependent sizes and shapes. With decreasing Bi particle size, an increasing aspect ratio was observed. Due to high resolution transmission electron microscopy performed for different orientations of the nanoparticles and the matrix, the three-dimensional shape and the respective crystallographic orientations of the Bi nanoparticles as well as the orientation relationship with the matrix have been evaluated. It is suggested that the size-dependence of the nanoparticle morphologies has a strong impact on their thermal stabilities thus affecting the size dependence of the melting temperature

[en] In order to contribute to an atomistic understanding of the interfacial structure and processes during amorphization and nanocrystallization, the present work deals with studies of interfacial free volumes by means of positron-annihilation-spectroscopy. In addition to positron lifetime spectroscopy, coincident Doppler broadening of the positron-electron annihilation photons is applied as novel technique for studying the chemistry of interfaces. To study the amorphization process, pure foils of Cu and Zr with a nominal composition of Cu₆₀Zr₄₀ were mechanically intermixed by cold rolling. Starting from the constituent pure metals, a nanoscale multilayer structure of elemental layers and amorphous interlayers develops in an intermediate state of folding and rolling, where free volumes with a Zr-rich environment occur that are presumably located in the hetero-interfaces between the various layers or in grain boundaries of the Cu-layers. To analyze the nanocrystallization reaction that occurs in marginal glass formers, pure foils of Al and Sm with a composition of Al₉₂Sm₈ were produced by the abovementioned synthesis route. Specific modifications of free volumes and their chemical environment could be observed for various strain levels