Volume 92, Issue 7

Life cycles of materials are analysed in a systematic manner as a six-stage process. It starts with primary or secondary raw materials and ends with recycling or deposition of waste. The purpose of the industrial process is the transformation of matter into materials from which useful goods are produced. The complete cycle can be described as a sequence of man-made transformations with defined changes in entropy and energy. Entropy is the measure for any type of disorder. Changes in entropy are due to separation (mining, purification: negative entropy), ordering (consolidation, construction: negative entropy) or disordering (mixing, crushing: positive entropy). Sustainability comprises undesired, irreversible changes of our environment. It can be regarded as an inverse function of the raise in entropy. We have to distinguish entropy with respect to matter, energy and information. In our context, entropy changes due to different distributions of matter are of primary importance. Sustainability implies that increases in entropy due to industrial activities must be balanced, as much as possible, by extraterrestrial negative entropy. This requires the evaluation and comparison of entropy efficiency for the production of goods with defined useful properties.

The stable and supercooled melts as well as the crystalline phases of Ga, In, Sn, Pb, and Bi have been investigated in the age –momentum correlation (AMOC) positron annihilation facility at the Stuttgart pelletron. The comparison of the lineshape parameter S, characterizing the momentum distribution of the annihilating electron –positron pairs, and of the mean positron lifetime with measurements of the positron diffusivity confirms in considerable detail the ‘polaron’ model of positrons in metallic melts developed earlier. The quantitative analysis of the data provides us with valuable information on the structure of the melts. E. g., in the investigated melts the existence of an appreciable concentration of ‘free volumes’ comparable in size with the atomic volume can be excluded. It is shown that this is in accord with earlier deductions from self-diffusivity measurements. An interesting but hitherto incompletely understood correlation between the entropy of fusion and the absence of trapping of positrons by vacancies in thermal equilibrium is pointed out.

The paper summarizes the recent studies on the diffusive mass transport accompanying the discontinuous precipitation (DP). The studies were performed by applying a local characterization of the kinetics of the DP reaction. In order to accomplish this, a technique of the analytical electron microscopy was used to measure the solute concentration profiles left behind the moving reaction front of single cells. Such an approach, combined with the information on the local values of the lamella thickness and growth rate of the cell, enabled for the first time the determination of local values of the grain boundary diffusivity in the systems Al–Zn, Ni–Sn, Cu–In, Ni–In and Co–Al. The obtained values were comparable to those resulting from the use of the global treatment of the diffusion problem for the DP reaction and the data on the radiotracer diffusion along stationary grain boundaries. This clearly indicates that there is no difference in the rate of diffusion along stationary and moving grain boundaries.

When 316 L stainless steel specimens are compressed to 30% and annealed at 1300 °C, primary recrystallization rapidly occurs and grains grow normally during further annealing treatment. Thus by annealing for various periods at 1300 °C, specimens with varying average sizes with identical normalized grain size distributions are obtained. When these specimens are heat-treated again at temperatures below 1150 °C, abnormal grain growth (AGG) occurs depending critically on the initial grain size.With decreasing initial grain size, AGG begins earlier during the heat-treatment, and if the initial grain size is large, only slow grain growth occurs without any distinct AGG for periods up to 48 and 96 h. It is observed that AGG occurs by faster growth of large grains with their velocities expected to increase nonlinearly with the driving force arising from the size difference. Because the AGG structure develops gradually, there is not really a well defined incubation time. With the same initial grain size the initiation ofAGGis slower at lower temperatures. A step heat-treatment experiment shows that if there are large grains embedded in the matrix of fine grains, they can grow abnormally under the condition where no AGG occurs with a narrow grain size distribution. The extremely slow grain growth with initially large average grain sizes is attributed to the low grain boundary velocity limited by the boundary step nucleation or growth. It is proposed that the same boundary step mechanism is qualitatively consistent with abnormal growth of the large grains with singular grain boundaries at low temperatures.

The kinetics of W grain growth during liquid-phase sintering (LPS) of W-15 – 25 wt.% Cu nanocomposite powder compacts was investigated in terms of microstructural development as well as theWatom diffusion process in liquid Cu. It was found that W grains grew rapidly while maintaining a round shape during LPS at 1623 K, being inversely proportional to the Cu matrix contents. This indicates that the diffusion-controlled Ostwald ripening (DOR) mechanism dominates the growth process in W–Cu nanocomposites. The result of this investigation on the kinetics of W grain growth definitely identifies the occurrence of DOR growth. Namely, the time exponent of the growth equation was close to the value of 3 and the kinetic constant forWgrain growth decreased with decreasing volume fraction of the W solid phase. This is basically due to the fact that the increase of a liquid matrix lengthens the diffusion path, as a result decreasing the growth rate. The diffusivity of the W atoms in liquid copper was calculated from the growth kinetics to be lower within an order of magnitude than the self-diffusion of the liquid atoms. The presence of Watom solubility in liquid Cu, as well as atom diffusivity, is thought to be responsible for diffusion-controlled growth of W grains during LPS of W–Cu nanocomposite powder.

The contact flattening between grains has long been considered to be the densification mechanism during liquidphase sintering. Recently, however, we proposed pore filling as being the major mechanism. In this investigation, we critically examine the two densification mechanisms by calculating their contributions to the sintering. The calculation shows that the contact flattening can be operative at the early stage for systems with a dihedral angle of zero degrees. However, its contribution to grain shape change and compact shrinkage is insignificant compared with that of the grain growth. A consideration of microstructures in real systems further suggests that the contribution of contact flattening is much less than the calculated value and is negligible from the beginning of the liquid-phase sintering. In fact, pore filling, which is induced by grain growth, appears to be essentially the only densification mechanism. An exemplified calculation of densification kinetics by pore filling is also presented and its implication discussed.

A metastable Al 90 Fe 10 (at.%) alloy, composed of a supersaturated solid solution of face-centred cubic (fcc) Al(Fe) and an amorphous phase matrix, was prepared by mechanical alloying of a mixture of Al and Fe elemental blends. The thermally induced microstructural evolution in the dual phase alloy was characterized by X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and magnetothermal analysis. On continuous heating two stages of solid state phase transformation occurred: (i) a polymorphous crystallization of the amorphous phase to a metastable crystalline Al 6 Fe that structurally stabilizes over a temperature range of about 200 K, and (ii) a eutectoid decomposition of the crystalline Al 6 Fe into the equilibrium phases of Al 13 Fe 4 and fcc Al(Fe). Thermodynamic and kinetic analyses of the observed phase transformation processes were given. The formation of the dual phase alloy in the as-milled state and the phase transitions can be illustrated by a hypothetical free energy diagram, implying the dual phase structure facilitates the polymorphous crystallization of Al 6 Fe.

Discrete element modeling (DEM) was applied for simulating the powder packing dynamics during electrophoretic deposition of electrostatically stabilized ZrO 2 (powder size 1 μm) and tape casting of BaTiO 3 (powder size 0.3 μm) stabilized by polymer adsorption. The results indicate that a transition zone of ordering is supposed to exist ahead of the growth front of the solid sediment during electrophoretic deposition. Local variation of the shear rate in the tape casting process with increasing distance from the blade gives rise for the generation of particle clusters under low shear, and cluster disintegration (shear thinning) under high shear conditions. Thus, DEM simulation provides a detailed insight into local variations of particle interaction processes during consolidation which can be used for optimization of the shaping process of colloidal ceramic powder suspensions.

For the investigation of structural relaxation near the glass transition quasistatic creep after-effect measurements have been performed on the alloy Zr 65 Cu 17:5 Ni 10 Al 7:5 which shows a large stability above the glass temperature T g . By a separation of anelastic local atomic rearrangements and viscous long-range diffusion processes the thermal activation parameters of both processes could be determined from Arrhenius diagrams. Below T g = 606 K an activation enthalpy of 2.1 eV and above T g an activation enthalpy of 5.6 eV has been determined. For a quantitative description of these relaxation phenomena a new dynamic model is developed which takes into account the continuous formation and annihilation of relaxation centers near T g . From measurements of the internal friction after rapid temperature changes it could be shown that extended relaxation centers present above T g become instable below T g and are split up by diffusion processes above 585 K, however, disappear spontaneously below 580 K.

Thermodynamic modeling has been developed to explain the apparent stability of an intergranular amorphous phase in the liquid-phase sintered ceramic. The basic postulate has been to consider such a grain boundary phase as a separate phase of the system. An analytic form of the Gibbs energy functions recently derived for amorphous silicates has been taken to describe this boundary phase. A derived equilibrium condition conforming with the construction of parallel tangents to Gibbs energy functions has been used to estimate the compositions of the bulk and of the boundary phase. The microstructure of liquid-phase sintered β-SiAlON ceramic has been ascertained in this way. This model supports the existence of amorphous boundary phases as thermodynamically stable and provides a relation between their amount and the composition of the sinter additives in agreement with the experimental evidence.

The model system Me/(100) SrTiO 3 (Me: Pd, Pt, Cu, Ni, Cr, Mo, Nb, and Al) was used to show that there exists a simple correlation between the formation of particular epitaxial orientations, the lattice mismatch between metal and SrTiO 3 , and the oxygen affinity of the metal. The growth of the metal films on the (100) SrTiO 3 surface was studied by reflection high-energy electron diffraction. Most metals (Pd, Pt, Ni, Nb and Al) grew with the following epitaxial orientation relationship on the SrTiO 3 : (100) SrTiO 3 | | (100) Me, [001] SrTiO 3 | | [001] Me. A second epitaxial orientation relationship was detected for Cr and Mo: (100) SrTiO 3 | | (100) Cr, Mo, [001] SrTiO 3 | | [011] Cr, Mo. For Mo, this orientation was detected only at very high growth temperatures. For each of the epitaxial orientation relationships, the substrate and film planes of four fold symmetry were parallel. Besides the second epitaxial orientation relationship, a third epitaxial orientation relationship was detected for Mo at growth temperatures below 900 K: (100) SrTiO 3 | | (110) Mo, [001] SrTiO 3 | | [001] Mo. In contrast to all other metals under investigation, Cu grew with a (111) fiber texture on the (100) SrTiO 3 surface. The appearance of the first two epitaxial orientation relationships can be interpreted with a simple relationship between the metals’ oxygen affinities and the lattice mismatches with SrTiO 3 . This relationship can be used for other metals to predict epitaxy on the (100) SrTiO 3 surface.

A combined approach of high-resolution transmission electron microscopy and electron energy-loss near-edge structure studies was employed to determine the atomic structure and bonding mechanisms at Cu/Al 2 O 3 interfaces in dependence on the α-Al 2 O 3 substrate orientation. The investigated specimens were prepared by molecular beam epitaxy using ultrahigh vacuum conditions, which led to atomically abrupt interfaces. The results show that intermetallic Cu–Al bonds occur at the investigated Cu/ (112̅0)Al 2 O 3 interface, while ionic-covalent bonding contributions are observed at the Cu/(0001)Al 2 O 3 interface. The interfacial microstructure of diffusion-bonded Cu/ (0001)Al 2 O 3 samples was changed by annealing treatments under various oxygen partial pressures. Annealing resulted in the formation of a CuAlO 2 reaction phase at the interface between Cu and Al 2 O 3 .

High-resolution electron microscopy in connection with electron energy filtered microscopy is used for evidencing the precipitation of free C clusters in polysiloxanes and polycarbosilanes, responsible for the hardening and luminescence of these classes of inorganic polymers after ion irradiation. While during irradiation with 3 MeV Au ions randomly distributed carbon clusters are formed, in the case of irradiation with 100 MeVAu ions, the carbon clusters are aligned along tubular ion tracks without forming continuous wires. Contrary to observations in some other polymers and semiconductors, no tubular voids or crystallization of amorphous SiC were found. It is concluded that in both cases the carbon precipitation is due to a solid state transformation induced by electronic excitations.

Fast cooling leads to the formation of metastable phase equilibria in the Al-rich part of the Al –Nd –Ni system. The metastability is characterized by a suppressed formation of the ternary τ 1 phase. The stable Al –La – Ni system is similar to the Al –Nd– Ni system but without the existence of a τ 1 phase. For comparison, this system is investigated. The results are represented as isopleths, liquidus surface projections, and reaction schemes. A fine-grain ternary eutectic morphology with enhanced hardness can be produced by rapid cooling in both ternary systems; the ideal chemical composition of this morphology depends on the cooling rate.

The Al-rich parts of the Al-Nd and Al-Nd-Ni systems were investigated by thermal and magnetothermal analysis, microstructure, and X-ray analysis. The results are represented as isopleths, isothermal sections, liquidus surface projections, and a reaction scheme.

An isothermal section of the phase diagram for the system Pr– Pd–O at 1223 K has been established by equilibration of samples representing 13 different compositions, and phase identification after quenching by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive analysis of X-rays (EDX). The binary oxide PdO was not stable at 1223 K. Three oxide phases were stable along the binary Pr– O; Pr 2 O 3 , Pr 7 O 12 and a phase of variable composition between these two oxides designated as σ . Two ternary oxides Pr 4 PdO 7 and Pr 2 Pd 2 O 5 were identified and their crystal structures were determined. Liquid alloy, the intermetallic compounds PrPd, Pr 3 Pd 4 , PrPd 3 , PrPd 5 , and Pd-rich solid solution (Pd s.s. ) were found to be in equilibrium with Pr 2 O 3 . Based on the phase relations, two solid-state cells were designed to measure the Gibbs energies of formation of the two ternary oxides. An advanced version of the solid-state cell incorporating a buffer electrode was used for high temperature thermodynamic measurements. The function of the buffer electrode, placed between reference and working electrodes, was to absorb the electrochemical flux of the mobile species through the solid electrolyte caused by trace electronic conductivity. The buffer electrode prevented polarization of the measuring electrode and ensured accurate data. Yttria-stabilized zirconia was used as the solid electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode. Electromotive force measurements, conducted in the temperature range 925 – 1400 K, indicated the presence of a third ternary oxide Pr 2 PdO 4 , stable below 1150 ± 9 K. Additional solid state cells were designed to study this compound. The standard Gibbs energy of formation of the interoxide compounds from their component binary oxides Pr 2 O 3 and PdO can be represented by the following equations: Pr4PdO7:Δf(ox)Go/J⋅mol−1=−43 540+0.74 T(±150)Pr2PdO4:Δf(ox)Go/J⋅mol−1=−38 805+1.91 T(±120)Pr2Pd2O5:Δf(ox)Go/J⋅mol−1=−68 640+1.28T(±270) $$\eqalign{ & {\rm{P}}{{\rm{r}}_4}{\rm{Pd}}{{\rm{O}}_7}:{{\rm{\Delta }}_{{\rm{f}}\left( {{\rm{ox}}} \right)}}{G^{\rm{o}}}{\rm{/J}} \cdot {\rm{mo}}{{\rm{l}}^{ - 1}} = - 43\,540 + 0.74\,T\left( { \pm 150} \right) \cr & {\rm{P}}{{\rm{r}}_2}{\rm{Pd}}{{\rm{O}}_4}:{{\rm{\Delta }}_{{\rm{f}}\left( {{\rm{ox}}} \right)}}{G^{\rm{o}}}{\rm{/J}} \cdot {\rm{mo}}{{\rm{l}}^{ - 1}} = - 38\,805 + 1.91\,T\left( { \pm 120} \right) \cr & {\rm{P}}{{\rm{r}}_2}{\rm{P}}{{\rm{d}}_2}{{\rm{O}}_5}:{{\rm{\Delta }}_{{\rm{f}}\left( {{\rm{ox}}} \right)}}{G^{\rm{o}}}{\rm{/J}} \cdot {\rm{mo}}{{\rm{l}}^{ - 1}} = - 68\,640 + 1.28T\left( { \pm 270} \right) \cr} $$ Crystallographic data for all three ternary oxides have been determined based on the thermodynamic information, isobaric phase diagrams and isothermal chemical potential diagrams for the system Pr–Pd –O are developed.

New solder alloys are being developed for electronic assemblies as replacements for traditional Pb-containing solder materials as a result of international pressure to remove Pb from the waste stream. In the transition period from Pb-containing to Pb-free solder alloys, component leads and copper interconnections on circuit board will continue to be pre-tinned with a Pb-containing solder to improve solderability. Phase equilibria information is needed for the evaluation of candidate Pb-free solder alloys in terms of their melting behavior and of the possible effects of Pb-contamination on manufacturing and reliability. The CALPHAD method of phase equilibria calculation using thermodynamic descriptions from databases provides a powerful tool for obtaining such information. The reliability of the calculation, however, depends on the quality of the thermodynamic descriptions of the individual phases. Criteria for the evaluation of these descriptions and the available thermodynamic databases are discussed. The effect of Pb-contamination on four solder alloys is analyzed.

Thermodynamic and phase diagram experimental data relevant to the Zr–O binary system have been assessed. A set of Gibbs energy functions describing the phases in this system is presented. The adjustable parameters of the models are obtained by least-squares fit to the experimental data. The liquid phase is described by Hillert’s partially ionic liquid model. The interstitial solid solution model is applied to the metallic zirconium solid solutions bZr and αZr. The ordering αZr is described by a three-sublattice model with Bragg-Williams treatment of ordering. The two modifications of the zirconium dioxide, αZrO 2 and bZrO 2 , are modelled as stoichiometric phases. The modification cZrO 2 is described by the Wagner-Schottky model expressed in the compound-energy formalism. The gas phase is treated as an ideal solution of the species Zr, Zr 2 ,O 1 , O 2 , O 3 , ZrO and ZrO 2 . The calculated phase diagrams and values for the thermodynamic properties are compared with experimental data.

Two-phase zirconia/porous alumina layered composites with a variety of microstructures and good damage tolerance have been fabricated. The flatness of the layer microstructure can be controlled by deformation processing in the green state when the constituent ceramic powders are suspended in a fluid medium. Mismatch in deformation resistance leads to flow localization creating wavy layers without long-range coherence. Repeated folding and pressing further allows large deformation strains to accumulate and thin layers to be obtained. Under flexural loading, very high nominal strains can be sustained by successive layer fracture and delamination at the alumina-to-zirconia interface. Compared to conventional flat-layer laminates, these composites are attractive in view of their relative processing ease and their good mechanical performance.

The key issues for thermal barrier coating (TBC) development are high temperature capability and durability under thermal cyclic conditions as experienced in the hot section of gas turbines. Due to the complexity of the system and the interaction of the constituents, performance improvements require a systems approach. However, there are issues closely related to the ceramic top coating and the bond coat, respectively. Reduced thermal conductivity, sintering, and stresses within the ceramic coating are addressed in the paper as well as factors affecting failure of the TBC by spallation. The latter is primarily governed by the formation and growth of the thermally grown oxide scale and therefore related to the bond coat. A strategy for lifetime assessment of TBCs is discussed.

Strength data of brittle materials have a large scatter. Therefore, probabilistic methods have been developed for designing with brittle materials. In general, a Weibull-type strength distribution function is determined by strength testing of a sample of about 30 specimens. This function is then used to predict a tolerable load level for a high component’s reliability. Curved structures in Weibull plots are often attributed to special features of the strength distribution function, e. g. to a threshold strength for failure or to bi- and multimodal flaw distributions. For such strength distributions the usual extrapolation is impossible. By means of Monte Carlo simulations it is shown that on the basis of small samples (containing around 30 experiments) real structures in strength distributions can hardly be distinguished from artefacts arising from the statistical nature of the data. On the basis of a small sample it is also not possible to decide whether a distribution is of a Weibull-type or any other distribution. Requirements for the determination of strength distribution functions and possible problems are discussed. Safe data extrapolations are possible if the flaw size distribution, which causes the strength distribution, is known. This knowledge can be acquired by testing a sample containing several subsamples with specimens of different size.

Since their introduction, contact materials based on Ag– SnO 2 have been significantly improved with respect to their applicability and their performance. Only recently, however, have the manufacturers embarked upon optimizing the microstructure of these materials, e. g., determining the optimal particle size, improving homogeneity, or tailoring of the phase arrangement, rather than solely modifying the material’s composition. The intent of this paper is to describe a process for the production of composite powders for electric contacts, the versatility of which allows the modification of all three parameters: particle size, homogeneity, and phase arrangement. Results are presented on a new generation of Ag–SnO 2 –In 2 O 3 contact materials that were manufactured with this process.

A new possibility in tailoring microstructures and properties of silicon nitride ceramics is demonstrated by the use of fine b-Si 3 N 4 powders. Fine powders were produced by a plasmachemical synthesis and by crystallisation of amorphous Si 3 N 4 in the presence of an oxide nitride liquid. A wide range of microstructures can be obtained depending on sintering and powder characteristics. At low sintering temperatures microstructures consisting of nanosized, equiaxed grains were obtained, whereas at high temperatures or long sintering times microstructures consisting of fine needle like grains were formed. Microstructural analysis revealed a high anisotropic grain growth of the b grains in the fine grained materials.

The electrochemical behavior of Ni-based SOFC anodes with different microstructures was studied. The anodes consisted either of a Ni gauze, a Ni pattern, a Ni paste, or a Ni –YSZ cermet. According to electrochemical impedance spectroscopy (EIS) measurements, the anodes are dominated by two main processes. The high frequency process decreases exponentially with an applied overpotential and is thermally activated with an activation energy of around 1 eV. The process could be attributed to the adsorption of hydrogen including charge transfer. The low frequency impedance arc arises only under a high overpotential applied between the working and the reference anode. The impedance of this process increases the higher the overpotential and is thermally activated with an activation energy of 0.5 eV. This process is assigned to the desorption of water.

The atomic transport processes which could cause degradation mechanisms in Cu interconnects are described. The influence of interconnect line width, barrier type and anneal process on the microstructure and reliability of the inlaid Cu lines are discussed. Grain size and texture measurements have been performed at blanket films and at arrays of Cu lines using advanced analytical techniques. The median grain size decreases with decreasing line width, and it can be influenced by heat treatments. The crystallographic texture is predominantly {111} out-of-plane with sidewall-oriented grains in narrow Cu lines. The grains have an in-plane preferred orientation with the 〈110〉 direction parallel to the sidewall normal. The Cu texture is influenced by barrier structure and thickness.

The thermal stability of Co(2 nm)/Cu(2 nm) multilayers, which exhibit the giant magnetoresistance (GMR) effect, has been investigated both experimentally and theoretically. Conventional and analytical transmission electron microscopy, Auger spectroscopy and X-ray analysis revealed changes of the composition on the nanometer scale, the phase morphology as well as the grain structure of multilayers which arise during annealing up to 740 °C. Above an annealing temperature of 300 °C, the onset of grain coarsening accompanied by a transition from a 〈111〉 to a 〈100〉 texture is observed. Moreover, a sharpening of the Co/Cu phase boundaries occurs during annealing up to 600 °C. Transmission electron microscopy observations revealed the coalescence of adjacent Co layers at 600 °C, and a complete disintegration of the layer morphology at 740 °C. Thermally induced changes of the phase morphology were also analysed by means of Monte Carlo simulations. With the assumption that the multilayer decomposition starts by a formation of Cu bridges through Co layers at grain boundaries, simulations of the subsequent evolution of the phase morphology showed a recession of Co layers near grain boundaries which can lead to the localised fusion of adjacent Co layers as well as to a Co and Cu layer thickness coarsening.

Nanometer-sized secondary hardening carbides are the most relevant microstructural constituents regarding the properties of tool steels. Due to their extreme fineness, direct inspection by microscopy is difficult and time consuming despite the progress recently achieved, e. g. by energy filtering transmission electron microscopy. Indirect methods are therefore additionally employed to obtain more detailed information on the processes taking place. Differential scanning calorimetry and in-situ hot hardness testing are demonstrated as powerful methods for the determination of kinetic data. In combination with results from a recently developed tensile specimen and test procedure for hard materials with low ductility, more detailed conclusions can be drawn on the effects of secondary hardening carbides on the strength and the thermal stability.

A simulation procedure to predict local deformation and properties in deep drawing and other sheet forming processes has been developed, and model experiments were performed to verify the predicted local strain after various ways and degrees of deformation. A strip of aluminium alloy sheet was pulled through a gap between a die and a punch, and bent around a rounded edge and bent back again. Local strains in a cross section of the sheet were estimated from hardness values measured before and after bending by using the hardness – strain relationship obtained for the alloy from tests carried out in tension and compression and with alternating deformation. The finite element (FE) model using ABAQUS was adjusted to the experimental set-up as closely as possible. The agreement between predictions and experiments is in the range of experimental scatter and the general trends are excellently reproduced. However, the precision of hardness measurements is not high enough to check the reliability of the numerical predictions in detail.

Al 2 O 3 –TiAl and Al 2 O 3 -containing refractory Ni- and Fealloy composites have been fabricated by reactive in situ infiltration of TiO 2 and metal oxide/metal compacts loaded with large-sized (> 5 lm) Al particles. When the compacts were heated to ignition temperature (∼ 900 °C) under pressure, thermal explosion with temperatures > 2000 °C took place leading to fully dense composites. These were characterized by X-ray diffraction, scanning and transmission electron microscopy, and atomic force microscopy. Fracture strengths and toughnesses of 47 vol.% Al 2 O 3 –TiAl were 650 MPa and 6.4 MPapm, of 26 vol.% Al 2 O 3 -containing Fe-based alloys were 1100 MPa and 18 MPapm, and those of 12 vol.% Al 2 O 3 -containing Ni-base alloys were 1450 MPa and 23 MPapm, respectively.

The microstructure of AlN ceramics, which were pressureless sintered with CaO and CaF 2 as additives, was modified via an annealing process. The thermal conductivity of these samples was measured and correlated with the microstructure changes. The influence of the microstructural elements, especially content and distribution of secondary phases, is described and quantitatively related to mixture models from literature for a full understanding of the relationships between microstructure, impurity content and thermal conductivity. The main result of the investigation is that the microstructural influence on thermal conductivity is limited to at maximum 41 W/m · K. The increase of the intrinsic thermal conductivity, due to loss of impurities especially oxygen during the beginning of the annealing process, is the main effect influencing thermal conductivity of sintered samples.