The presented work reports on the solidification studies in two alloy systems: the niobium bearing γ-TiAl, relevant for the automotive and aero-engine applications, and aluminium rich Raney-Ni, precursor alloys for catalyses used in the chemical industry. The time-resolved observations of equilibrium liquid-solid phase transformations, as well as non-equilibrium solidification from the undercooled melt, are performed by combination of in situ structural studies using high-energy X-rays at a synchrotron source and the electromagnetic levitation technique. Containerless processing assured the contamination-free environment leading to high undercooling levels even at moderate cooling rates. For the critical part of the Ti-Al-Nb phase diagram an equilibrium involving the liquid phase is deduced from the phase transformations gathered on heating periods of levitation experiment. New experimental data on the partial liquidus and solidus surfaces are delivered as well as the information on the nature of the reactions along the univariant lines. These data provide a valuable contribution to the reassessment of the thermodynamic description. The primary phase selection as function of undercooling is studied in ternary Ti-Al-Nb alloys. The metastable formation of the cubic β phase within the primary solidification region of the hexagonal α phase is observed with increasing melt undercooling. Furthermore, the microstructure evolution of the β solidifying Ti-46Al-8Nb alloy discloses the transition to the thermal growth mode for ∆T>200−250 K, accompanied by complete solute trapping. Supplemented with the data on the solidification velocity determined as function of melt undercooling, this results are discussed within the local non-equilibrium model of the free dendrite growth. The in situ observations of the non-equilibrium solidification of the binary Al-Ni system give insight into multiple phase transformation sequence. The achieved undercooling levels up to 320 K for the aluminium alloys containing 18–31.5 at.% Ni did not alter the primary phase selection. However, during further cooling of L+Al3Ni2 semisolid samples the peritectic formation of a metastable decagonal quasicrystalline phase is observed providing a critical undercooling below the peritectic temperature of Al3Ni phase is reached. On further cooling the metastable phase subsequently transforms into the equilibrium Al3Ni. A similar solidification pathways are expected for the Raney-Ni alloys produced by gas atomisation, where the associated high cooling rates allowed to retain the metastable phase at room temperature.

Wetting and phase transitions play a very important role our daily life. Molecularly thin films of long-chain alkanes at solid/vapour interfaces (e.g. C30H62 on silicon wafers) are very good model systems for studying the relation between wetting behaviour and (bulk) phase transitions. Immediately above the bulk melting temperature the alkanes wet partially the surface (drops). In this temperature range the substrate surface is covered with a molecularly thin ordered, solid-like alkane film ("surface freezing"). Thus, the alkane melt wets its own solid only partially which is a quite rare phenomenon in nature. The thesis treats about how the alkane melt wets its own solid surface above and below the bulk melting temperature and about the corresponding melting and solidification processes.<br> Liquid alkane drops can be undercooled to few degrees below the bulk melting temperature without immediate solidification. This undercooling behaviour is quite frequent and theoretical quite well understood. In some cases, slightly undercooled drops start to build two-dimensional solid terraces without bulk solidification. The terraces grow radially from the liquid drops on the substrate surface. They consist of few molecular layers with the thickness multiple of all-trans length of the molecule. By analyzing the terrace growth process one can find that, both below and above the melting point, the entire substrate surface is covered with a thin film of mobile alkane molecules. The presence of this film explains how the solid terrace growth is feeded: the alkane molecules flow through it from the undercooled drops to the periphery of the terrace.<br> The study shows for the first time the coexistence of a molecularly thin film ("precursor") with partially wetting bulk phase. The formation and growth of the terraces is observed only in a small temperature interval in which the 2D nucleation of terraces is more likely than the bulk solidification. The nucleation mechanisms for 2D solidification are also analyzed in this work. More surprising is the terrace behaviour above bulk the melting temperature. The terraces can be slightly overheated before they melt. The melting does not occur all over the surface as a single event; instead small drops form at the terrace edge. Subsequently these drops move on the surface "eating" the solid terraces on their way. By this they grow in size leaving behind paths from were the material was collected. Both overheating and droplet movement can be explained by the fact that the alkane melt wets only partially its own solid. For the first time, these results explicitly confirm the supposed connection between the absence of overheating in solid and "surface melting": the solids usually start to melt without an energetic barrier from the surface at temperatures below the bulk melting point. Accordingly, the surface freezing of alkanes give rise of an energetic barrier which leads to overheating. / Sowohl Benetzung als auch Phasenübergänge spielen eine sehr wichtige Rolle im täglichen Leben. Molekular dünne Filme langkettiger Alkane an Festkörper/Gas-Grenzflächen (z. B. C30H62 an Silizium-Waferoberflächen) sind sehr gute Modellsysteme um die Wechselbeziehung zwischen Benetzungsverhalten und (Volumen-)Phasenübergängen zu untersuchen. In einem Temperaturbereich knapp oberhalb der Volumenschmelztemperatur benetzt die Alkanschmelze die Substratoberfläche nur partiell (Alkantropfen). In diesem Temperaturbereich ist die Substratoberfläche mit einer molekular dünnen, festkörperartig geordneten Alkanschicht bedeckt ("Oberflächengefrieren" ). Die Alkanschmelze benetzt also die eigene Festkörperoberfläche nur partiell, ein in der Natur ziemlich seltenes Phänomen. Die Dissertation beschäftigt sich damit wie die Alkanschmelze ihre eigene Festkörperoberfläche über und unter dem Volumenschmelzpunkt benetzt und mit den entsprechenden Vorgängen beim Schmelzen bzw. Erstarren. Flüssige Alkantropfen lassen sich einige Grad unter ihren Schmelzpunkt unterkühlen ohne sich sofort zu verfestigen. Dieses "Unterkühlungsverhalten" ist üblich und es ist theoretisch qualitativ gut verstanden. Allerdings beobachtet man bei den Alkanen bei leichter Unterkühlung statt einer eventuellen Volumenverfestigung oft die Ausbildung von zweidimensionalen Terrassen aus erstarrtem Alkanen. Die Terrassen wachsen auf der Substratoberfläche radial aus den flüssigen Tropfen. Sie bestehen aus wenigen Alkanlagen mit jeweils der Dicke einer Moleküllänge. Die Analyse der Terrassen-Wachstumsprozesse zeigt, dass die gesamte Substratoberfläche einschliesslich der Terrassen sowohl oberhalb als auch unterhalb der Volumenschmelztemperatur mit einer dünnen Schicht mobiler Alkanmoleküle bedeckt ist. Durch diese Schicht fliessen bei Unterkühlung die Alkane vom unterkühlten Tropfen zur Terrassenkante und liefern den Nachschub für deren Wachstum. Die Untersuchungen zeigen damit erstmalig die Koexistenz eines molekular dünnen Films ("Precursor") mit einer partiell benetzenden Volumenphase. Die Entstehung und das Wachstum der Terrassen wird nur in einem engen Temperaturfenster beobachtet in dem die Keimbildung zweidimensionaler Terrassen wahrscheinlicher ist als die dreidimensionale Volumenverfestigung. Auch dieses Keimbildungsverhalten wird in der Dissertation genauer analysiert. Noch erstaunlicher als das Terrassenwachstum, d. h. das Verfestigungsverhalten ist das Schmelzverhalten der Terrassen. Sie lassen sich bis zu einer gewissen Temperatur überhitzen bevor sie schmelzen! Weiterhin findet bei genügender Überhitzung das Schmelzen nicht gleichzeitig überall statt sondern es entstehen zuerst kleine Alkantropfen an den Terrassenrändern. Diese bewegen sich dann über die Substratoberfläche und "fressen" sich durch die festen Terrassen. Dabei wachsen sie weil sie das geschmolzene Material aufnehmen und hinterlassen eine alkanfreie Spur. Sowohl die Überhitzung als auch die Tropfenbewegung lassen sich damit erklären dass die flüssige Alkanschmelze ihren eigenen Festkörper nur partiell benetzt. Die Ergebnisse bestätigen erstmals explizit den seit vielen Jahrzehnten vermuteten Zusammenhang zwischen der üblicherweise nicht beobachtbaren Überhitzung von Festkörpern und Oberflächenschmelzen: Festkörper beginnen normalerweise ohne Energiebarriere von der Oberfläche an zu schmelzen. Entsprechend bildet das Oberflächengefrieren der Alkane eine Energiebarriere und erlaubt damit deren Überhitzen.

The presented work reports on the solidification studies in two alloy systems: the niobium bearing γ-TiAl, relevant for the automotive and aero-engine applications, and aluminium rich Raney-Ni, precursor alloys for catalyses used in the chemical industry. The time-resolved observations of equilibrium liquid-solid phase transformations, as well as non-equilibrium solidification from the undercooled melt, are performed by combination of in situ structural studies using high-energy X-rays at a synchrotron source and the electromagnetic levitation technique. Containerless processing assured the contamination-free environment leading to high undercooling levels even at moderate cooling rates. For the critical part of the Ti-Al-Nb phase diagram an equilibrium involving the liquid phase is deduced from the phase transformations gathered on heating periods of levitation experiment. New experimental data on the partial liquidus and solidus surfaces are delivered as well as the information on the nature of the reactions along the univariant lines. These data provide a valuable contribution to the reassessment of the thermodynamic description. The primary phase selection as function of undercooling is studied in ternary Ti-Al-Nb alloys. The metastable formation of the cubic β phase within the primary solidification region of the hexagonal α phase is observed with increasing melt undercooling. Furthermore, the microstructure evolution of the β solidifying Ti-46Al-8Nb alloy discloses the transition to the thermal growth mode for ∆T>200−250 K, accompanied by complete solute trapping. Supplemented with the data on the solidification velocity determined as function of melt undercooling, this results are discussed within the local non-equilibrium model of the free dendrite growth. The in situ observations of the non-equilibrium solidification of the binary Al-Ni system give insight into multiple phase transformation sequence. The achieved undercooling levels up to 320 K for the aluminium alloys containing 18–31.5 at.% Ni did not alter the primary phase selection. However, during further cooling of L+Al3Ni2 semisolid samples the peritectic formation of a metastable decagonal quasicrystalline phase is observed providing a critical undercooling below the peritectic temperature of Al3Ni phase is reached. On further cooling the metastable phase subsequently transforms into the equilibrium Al3Ni. A similar solidification pathways are expected for the Raney-Ni alloys produced by gas atomisation, where the associated high cooling rates allowed to retain the metastable phase at room temperature.

High-entropy alloys (HEAs) have attracted significant interest in the materials science community over the last 15 years. At the first moment, what caught the attention was the fact that these alloys tend to form solid solutions at room temperature, despite being composed of multiple elements in equiatomic or near-equiatomic concentrations. It was initially concluded that the configurational entropy plays a key role in the stabilization of the solid solutions. Later studies revealed the importance of lattice strain enthalpies, enthalpies of mixing, structural mismatch of constituents, and kinetics in phase formation/stability. The study presented in this thesis was branched into three major parts, all related to understanding phase formation, stability, or metastability in this class of alloys. The first part deals with developing an empirical method to predict single-phase solid solution formation in multi-principal element alloys. The second, which makes the core of this thesis, are non-equilibrium solidification studies of CrFeNi and CoCrNi medium-entropy alloys, and CoCrFeNi, Al0.3CoCrFeNi, and NbTiVZr high-entropy alloys. The last part is devoted to understanding the thermophysical properties of CrFeNi, CoCrNi, and CoCrFeNi medium- and high-entropy alloys. An empirical approach, based on the theoretical elastic-strain energy, has been developed to predict the phase formation and its stability for complex concentrated alloys. The conclusiveness of this approach is compared with the traditional empirical rules based on the atomic-size mismatch, enthalpy of mixing, and valence-electron concentration for a database of 235 alloys. The proposed “elastic-strain energy vs. valence-electron concentration” criterion shows an improved ability to distinguish between single-phase solid solutions, mixtures of solid solutions, and intermetallic phases when compared to the available empirical rules used to date. The criterion is especially strong for alloys that precipitate the μ phase. The elastic-strain-energy parameter can be combined with other known parameters, such as those noted above, to establish new criteria which can help in designing novel complex concentrated alloys with the on-demand combination of mechanical properties. The solidification behavior of the CoCrFeNi high-entropy alloy and the ternary CrFeNi and CoCrNi medium-entropy suballoys has been studied in situ using high-speed video-camera and synchrotron X-ray diffraction (XRD) on electromagnetically levitated samples at Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden) and German Synchrotron DESY, Hamburg. In all alloys, the formation of a primary metastable body-centered cubic bcc phase was observed if the melt was sufficiently undercooled. The delay time for the onset of the nucleation of the stable face-centered cubic fcc phase, occurring within bcc crystals, is inversely proportional to the melt undercooling. The experimental findings agree with the stable and metastable phase equilibria for the (CoCrNi)-Fe section. Crystal-growth velocities for the CrFeNi, CoCrNi, and CoCrFeNi medium- and high-entropy alloys, extracted from the high-speed video sequences in the present study, are comparable to the literature data for Fe-rich Fe-Ni and Fe-Cr-Ni alloys, evidencing the same crystallization kinetics. The effect of melt undercooling on the microstructure of solidified samples is analyzed and discussed in the thesis. To understand the effect of Al addition on the non-equilibrium solidification behavior of the equiatomic CoCrFeNi alloy, the Al0.3CoCrFeNi HEA has been studied. While the quaternary alloy melt could be significantly undercooled, this was not possible in the five-component alloy. Therefore, the investigations on phase formation, crystal growth, and microstructural evolution were confined to the low undercooling regime. In situ XRD measurements revealed that the liquid crystallized into a fcc single-phase solid solution at this undercooling level. However, ex situ XRD revealed the precipitation of the ordered L12 phase for a sample solidified with ΔT = 30 K. Crystal growth velocities are shown to be smaller than in the CoCrFeNi, CrFeNi, and CoCrNi alloys; nonetheless, they are in the same order of magnitude. Spontaneous grain refinement, without the formation of crystal twins, is observed at low undercooling of ΔT = 70 K, which could be explained by the dendrite tip radius dependence on melt undercooling. In situ studies of the equiatomic NbTiVZr refractory high-entropy alloys revealed the effect of processing conditions on the high-temperature phase formation. When the melt was undercooled over 80 K, it crystallized as a bcc single-phase solid solution despite solute partitioning between the dendritic and interdendritic regions. When the sample was solidified from the semisolid state, it resulted in the formation of two additional bcc phases at the interdendritic regions. The crystal growth velocity, as estimated from the high-speed videos, showed pronounced sluggish kinetics: it is 1 to 2 orders of magnitude smaller compared to literature data of other medium and high-entropy alloys. The study of the linear expansion coefficient α and heat capacity at constant pressure 𝐶𝑝 of the equiatomic CoCrFeNi and the medium-entropy CrFeNi and CoCrNi alloys revealed an anomalous behavior with S-shaped curves in the temperature range of 700 – 950 K. The anomalous behavior is shown to be reversible as it occurred during the first and second heating. However, a minimum is only observed on the first heating, while in the second heating a sudden increase of both the α and 𝐶𝑝 occurs at the temperature of the onset of the minima in the first heating. Magnetic moment measurements as a function of temperature showed that the observed anomaly is not associated with the Curie temperature. Consideration of the structural and microstructural evaluation discards a first-order phase transformation or recrystallization as probable causes, at least for the CoCrFeNi and CoCrNi alloys. Based on literature evidence, the anomalies in the temperature dependences of the linear expansion coefficient and heat capacity are believed to be caused by a chemical short-range order transition known as the K-state effect. However, to reveal the exact nature of this phenomenon, further experimental and theoretical studies are required, which is outside the frame of the present work.:Abstract ....................................................................................................................... I Kurzfassung .............................................................................................................. IV Chapter 1: Motivation and Fundamentals .................................................................. 1 1.1 Introduction .......................................................................................................... 1 1.2 The high-entropy alloy (HEA) design concept ...................................................... 4 1.3 Empirical rules of phase formation for HEAs ....................................................... 6 1.4 Calculation of phase diagrams of HEAs ............................................................. 18 1.5 The core effects of HEAs ................................................................................... 20 1.5.1 Lattice distortion .............................................................................................. 20 1.5.2 Sluggish diffusion ............................................................................................ 22 1.5.3 Cocktail effect................................................................................................... 23 1.6 Mechanical properties ........................................................................................ 24 1.6.1 Lightweight high-entropy alloys ....................................................................... 24 1.6.2 Overcoming the strength-ductility tradeoff ...................................................... 26 1.6.3 Cryogenic high-entropy alloys ......................................................................... 28 1.6.4 Refractory high-entropy alloys ........................................................................ 30 1.7 Functional properties .......................................................................................... 33 1.7.1 Soft magnetic properties ................................................................................. 33 1.7.2 Magnetocaloric properties ............................................................................... 35 1.7.3 Hydrogen storage ............................................................................................ 36 Chapter 2: Experimental .......................................................................................... 38 2.1 Sample preparation ............................................................................................ 38 2.2 Electromagnetic levitation .................................................................................. 40 2.3 In situ X-ray diffraction ........................................................................................ 43 2.4 Microstructural and structural analysis ............................................................... 44 2.5 Thermal analysis ................................................................................................ 45 2.6 Dilatometry ......................................................................................................... 45 2.7 Magnetic moment ............................................................................................... 46 2.8 Heat treatment ................................................................................................... 46 Chapter 3: In situ study of non-equilibrium solidification of CoCrFeNi high-entropy alloy and CrFeNi and CoCrNi ternary suballoys ...................................................... 47 3.1 Introduction ........................................................................................................ 47 3.2 Results ............................................................................................................... 48 3.2.1 In situ synchrotron X-ray diffraction ................................................................. 48 3.2.2 High-speed video imaging ............................................................................... 52 3.2.3 Microstructure of the solidified samples .......................................................... 62 3.3 Discussion .......................................................................................................... 64 3.3.1 bcc-fcc nucleation and growth competition ..................................................... 64 3.3.2. Crystal growth kinetics ................................................................................... 68 3.3.3. Microstructural evolution ................................................................................ 70 Chapter 4: The effect of Al addition to the CoCrFeNi alloy on the non-equilibrium solidification behaviour.............................................................................................. 72 4.1 Introduction ........................................................................................................ 72 4.2 Results and Discussion ...................................................................................... 73 Chapter 5: Non-equilibrium solidification of the NbTiVZr refractory high-entropy alloy ................................................................................................................................. 84 5.1 Introduction ........................................................................................................ 84 5.2 Results ............................................................................................................... 85 5.2.1 In situ synchrotron X-ray diffraction ................................................................. 85 5.2.2 Room temperature synchrotron X-ray diffraction ............................................ 88 5.2.3 High-speed video imaging ............................................................................... 89 5.2.4 Microstructure and structure analysis ............................................................. 91 5.3 Discussion .......................................................................................................... 94 5.3.1 Phase formation upon solidification ................................................................ 94 5.3.2 Crystal growth kinetics .................................................................................... 98 5.3.3 Structural and microstructural features............................................................ 99 Chapter 6: Solid-state thermophysical properties of CrFeNi, CoCrNi, and CoCrFeNi medium- and high-entropy alloys ........................................................................... 101 6.1 Introduction ...................................................................................................... 101 6.2 Results ............................................................................................................. 102 6.3 Discussion ........................................................................................................ 106 6.3.1 Thermophysical properties ............................................................................ 106 6.3.2 Short-range order in medium- and high-entropy alloys ................................. 109 Chapter 7: Summary ............................................................................................... 111 7.1 Empirical rule of phase formation of complex concentrated alloys ................... 111 7.2 Non-equilibrium solidification of medium- and high-entropy alloys ................... 111 7.3 Thermophysical properties of the medium- and high-entropy alloys ................ 113 Chapter 8: Outlook ................................................................................................. 115 Appendix 1 .............................................................................................................. 117 Appendix 2 ............................................................................................................. 123 Appendix 3 ............................................................................................................. 133 Appendix 4 ............................................................................................................. 134 References.............................................................................................................. 140 Acknowledgments .................................................................................................. 164 List of publications .................................................................................................. 166 Erklärung ......................................................................................................................... 167

The European legislation prohibits the use of lead containing solders in Europe. However, lead free solders have a higher melting point (typical 20%) and their mechanical characteristics are worse. Additional problems are aging and adhesion of the solder on the electronic circuits. Thus, research activities must focus on the optimization of the properties of Sn-Ag-Cu based lead free solders chosen by the industry. Two main objectives are treated in this work. In the center of the first one is the study of curious hysteresis effects of metallic cadmium-antimony alloys after thermal cycles by measuring electronic transport phenomena (thermoelectric power and electrical resistivity). The second objective, within the framework of “cotutelle” between the universities of Metz and of Chemnitz and supported by COST531, is to study more specifically lead free solders. A welding must well conduct electricity and well conduct and dissipate heat. In Metz, we determined the electrical conductivity, the thermoelectric power and the thermal conductivity of various lead free solders (Sn-Ag-Cu, Sn-Cu, Sn-Ag, Sn-Sb) as well in the liquid as well in the solid state. The results have been compared to classical lead-tin (Pb-Sn) solders. In Chemnitz we measured the surface tension, the interfacial tension and the density of lead free solders. We also measured the viscosity of these solders without and with additives, in particular nickel. These properties were related to the industrial problems of wettability and spreadability. Lastly, we solidified alloys under various conditions. We observed undercooling. We developed a technique of mixture of nanocristalline powder with lead free solders "to sow" the liquid bath in order to obtain "different" solids which were examined using optical and electron microscopy. / Die europäische Gesetzgebung verbietet die Benutzung von Lötmitteln, die Blei enthalten. Bleilose Lote haben aber einen höheren Schmelzpunkt (typisch 20%) und ihre mechanischen Eigenschaften sind schlechter. Zusätzliche Probleme sind das Alterungsverhalten und das Haftvermögen des Lots an den Leiterbahnen. Daher müssen sich Forschungsaktivitäten auf die Optimierung der Eigenschaften von bleifreien Sn-Ag-Cu (SAC) Loten konzentrieren, die von der Industrie gewählt wurden. Zwei Hauptgebiete werden in dieser Arbeit bearbeitet. Im Zentrum des Ersten stehen seltsame Hysterese-Effekte von metallischen Kadmium- Antimon Legierungen bei thermischen Zyklen, wobei Transporteigenschaften wie die thermoelektrische Kraft und der elektrische Widerstand untersucht werden. Die zweite Aktivität, die in einer Kooperation der Universitäten Metz und Chemnitz (cotutelle) bearbeitet und die durch COST531 unterstützt wird, besteht in der detaillierten Erforschung des Lötprozesses ohne Blei. Eine Lötverbindung muß den Strom gut führen und die Wärme gut ableiten. In Metz haben wir die elektrische Leitfähigkeit, die thermoelektrische Kraft und das Wärmeleitvermögen bestimmt für verschiedene bleilose Lote (Sn-Ag-Cu, Sn-Cu, Sn-Ag, Sn-Sb), sowohl im flüssigen als auch festen Zustand. Die Ergebnisse wurden mit dem klassischen bleihaltigen Lötzinn (Sn-Pb) verglichen. In Chemnitz haben wir die Oberflächen- und Grenzflächenspannung und die Dichte bleifreier Lote gemessen. Ebenfalls wurde die Viskosität dieser Lote ohne und mit Zusätzen (insbesondere Nickel) gemessen. Diese Eigenschaften wurden in Beziehung gesetzt zu den industriellen Problemen der Benetzbarkeit und des Fließverhaltens. Schließlich haben wir Legierungen unter verschiedenen Bedingungen verfestigt. Wir haben Unterkühlung beobachtet. Wir haben eine Technik entwickelt, basierend auf einer Mischung von Lot mit Pulver. Durch "Einsäen" von Nanokristallen in das flüssige Bad erhielten wir "verschiedene" Festkörper, die mit optischer und Elektronenmikroskopie untersucht wurden.

The European legislation prohibits the use of lead containing solders in Europe. However, lead free solders have a higher melting point (typical 20%) and their mechanical characteristics are worse. Additional problems are aging and adhesion of the solder on the electronic circuits. Thus, research activities must focus on the optimization of the properties of Sn-Ag-Cu based lead free solders chosen by the industry. Two main objectives are treated in this work. In the center of the first one is the study of curious hysteresis effects of metallic cadmium-antimony alloys after thermal cycles by measuring electronic transport phenomena (thermoelectric power and electrical resistivity). The second objective, within the framework of “cotutelle” between the universities of Metz and of Chemnitz and supported by COST531, is to study more specifically lead free solders. A welding must well conduct electricity and well conduct and dissipate heat. In Metz, we determined the electrical conductivity, the thermoelectric power and the thermal conductivity of various lead free solders (Sn-Ag-Cu, Sn-Cu, Sn-Ag, Sn-Sb) as well in the liquid as well in the solid state. The results have been compared to classical lead-tin (Pb-Sn) solders. In Chemnitz we measured the surface tension, the interfacial tension and the density of lead free solders. We also measured the viscosity of these solders without and with additives, in particular nickel. These properties were related to the industrial problems of wettability and spreadability. Lastly, we solidified alloys under various conditions. We observed undercooling. We developed a technique of mixture of nanocristalline powder with lead free solders "to sow" the liquid bath in order to obtain "different" solids which were examined using optical and electron microscopy. / Die europäische Gesetzgebung verbietet die Benutzung von Lötmitteln, die Blei enthalten. Bleilose Lote haben aber einen höheren Schmelzpunkt (typisch 20%) und ihre mechanischen Eigenschaften sind schlechter. Zusätzliche Probleme sind das Alterungsverhalten und das Haftvermögen des Lots an den Leiterbahnen. Daher müssen sich Forschungsaktivitäten auf die Optimierung der Eigenschaften von bleifreien Sn-Ag-Cu (SAC) Loten konzentrieren, die von der Industrie gewählt wurden. Zwei Hauptgebiete werden in dieser Arbeit bearbeitet. Im Zentrum des Ersten stehen seltsame Hysterese-Effekte von metallischen Kadmium- Antimon Legierungen bei thermischen Zyklen, wobei Transporteigenschaften wie die thermoelektrische Kraft und der elektrische Widerstand untersucht werden. Die zweite Aktivität, die in einer Kooperation der Universitäten Metz und Chemnitz (cotutelle) bearbeitet und die durch COST531 unterstützt wird, besteht in der detaillierten Erforschung des Lötprozesses ohne Blei. Eine Lötverbindung muß den Strom gut führen und die Wärme gut ableiten. In Metz haben wir die elektrische Leitfähigkeit, die thermoelektrische Kraft und das Wärmeleitvermögen bestimmt für verschiedene bleilose Lote (Sn-Ag-Cu, Sn-Cu, Sn-Ag, Sn-Sb), sowohl im flüssigen als auch festen Zustand. Die Ergebnisse wurden mit dem klassischen bleihaltigen Lötzinn (Sn-Pb) verglichen. In Chemnitz haben wir die Oberflächen- und Grenzflächenspannung und die Dichte bleifreier Lote gemessen. Ebenfalls wurde die Viskosität dieser Lote ohne und mit Zusätzen (insbesondere Nickel) gemessen. Diese Eigenschaften wurden in Beziehung gesetzt zu den industriellen Problemen der Benetzbarkeit und des Fließverhaltens. Schließlich haben wir Legierungen unter verschiedenen Bedingungen verfestigt. Wir haben Unterkühlung beobachtet. Wir haben eine Technik entwickelt, basierend auf einer Mischung von Lot mit Pulver. Durch "Einsäen" von Nanokristallen in das flüssige Bad erhielten wir "verschiedene" Festkörper, die mit optischer und Elektronenmikroskopie untersucht wurden.