B. Mikulowski

Wetting and bonding strength in Al/Al2O3 system

Abstract Experimental results are presented on the investigation of the correlation between wetting and bonding properties in Al/Al 2 O 3 couples. Applying the sessile drop method the wettability of alumina substrates by molten Al was investigated at temperatures from 953–1373 K under a dynamic vacuum of 0.2 mPa. A special procedure to study shear strength of metal–ceramic joints using the sessile drop samples has been elaborated. The results clearly indicate that the shear strength of Al/Al 2 O 3 joints strongly depends on wetting properties in Al/Al 2 O 3 system, i.e. the lower the contact angle Θ , the higher the value of interfacial shear strength.

Evolution of strength and structure during SPD processing of Ti–45Nb alloys: experiments and simulations

A β-phase Ti–45Nb alloy was processed by several severe plastic deformation (SPD) methods as high-pressure torsion, cold rolling and folding, and hydrostatic extrusion to enhance its strength by achieving an ultrafine grained structure without affecting the Young’s modulus being close to that of bone material. Mechanical properties during processing were monitored by direct torque and Vickers hardness measurements, while the micro-/nano-structural evolution was investigated by transmission electron microscopy and X-ray line profile analysis. Simulations of both mechanical and micro-/nano-structural data were performed on the basis of the SPD work-hardening model by Zehetbauer. The simulations not only found a good agreement with the deformation-specific evolution of strength and density of individual dislocations but also well reflected mesoscopic structural quantities such as the sizes of cell/grain interiors and walls without introducing additional fitting parameters.

Texture Evolution of Magnesium Single Crystals Deformed by High-Pressure Torsion

Single crystals of technical purity Magnesium (99.8 wt.%) of initial orientations [ ] 2 1 10 and [ ] 2 2 11 were subjected to HPT deformation at room temperature up to strains of 10. The microstructural evolution has been analyzed by X-ray microtexture investigations and by in-situ stress-strain measurements. The results can be described in terms of shear arising from HPT deformation and - with higher strains - in terms of recrystallization. In crystals with hard orientation[ ] 2 2 11 , these features occur at smaller strains than in crystals with soft orientation [ ] 2 1 10 , i.e. with higher symmetry. In general, the observed textures and strength variations are much stronger than those reported for fcc HPT deformed metals.

Oscillatory Structure of the Zn-Cu-Ti Single Crystals

Structures obtained during Zn-Cu-Ti single crystal growth by the Bridgman method were investigated. The alloys of composition Zn-Cu0.1wt.%-Ti0.1wt.% were used for single crystals growth, which were produced at rate in the range of 1.8mm/h to 16mm/h. The Zn-Cu-Ti alloys were characterized by multiphase structure; in the solute-hardened matrix by Cu atoms exists a needle-shaped intermetallic phase Zn16Ti. The strong anisotropy of the hexagonal structure gives a significant influence on a second phase distribution in the matrix volume. In the range of the low growth rates (from 1.8mm/h to 10mm/h) oscillatory structures were observed. That effect vanished at the growth rates higher than 10mm/h. The observed oscillatory structures were characterized by existing periodic layers rich in the intermetallic phase of Zn16Ti interlaid with pure matrix (alpha phase Zn with Cu solute).

Influence of silicon on the wetting-bond strength-structure relationship in the AlSi11/Al2O3 joints

The subject of the work was to study the effect of Si alloying addition to the aluminum on the bond strength properties, wettability, and structure of interface in the AlSi11/Al2O3 joints. Taking advantage of the sessile drop method, the wetting of alumina substrates by liquid AlSi11 alloy or Al was studied. The sessile drop tests were carried out in the temperature range between 1023 and 1223 K, under a vacuum of 0.2 mPa for 30 or 120 minutes of contact. The shear strength results demonstrated significant improvement of shear strength of AlSi11/Al2O3 joints due to the application of silicon as an alloying addition to aluminum. Microstructural investigations of interface indicated that the silicon crystals were formed at the AlSi11/Al2O3 interface, which influenced the strengthening of these joints. A conclusion could be drawn, that the interface structure influenced the increase of the shear strength of AlSi11/Al2O3 joints.

Control of the Single Crystal Reinforcement by the Intermetallic Compound Layers

. An improvement of the Brody & Flemings theory has been proposed to study not only the solute segregation but the solute redistribution during the single crystal growth as well. The redistribution is treated as a phenomenon superposed upon the segregation phenomenon. The crystal growth has been performed by the closed Bridgman system with a constant growth rate and an imposed temperature gradient. A hypo-eutectic Zn-Ti alloy has been subjected to oriented growth and precipitation of the Zn-16Ti intermetallic compound was observed. The precipitates have been placed as some layers distributed within the single crystal with a constant spacing. Some data from the Zn-Ti binary phase diagram was introduced into the theory to show possibility of the control the phenomenon of the reinforcement by precipitation during a single crystal growth.

Effects of recrystallization on texture, microstructure and mechanical properties in HPT-deformed pure Mg

Mg of purity 99.8 wt% was deformed by High Pressure-Torsion at hydrostatic pressures 1 to 4 GPa and RT, up to plastic shear strains of 120. X-ray texture analysis showed up deviations from expected shear texture, which increased with increasing shear strain and hydrostatic pressure. According to TEM and SEM investigations these deviations can be understood in terms of recrystallization. The current paper aimed at the differences of the recrystallization processes which occur during HPT deformation and unloading (dynamic recrystallization, DRX), and those after deformation (static recrystallization, SRX). For this purpose, two sorts of samples were investigated: (i) such being stored at RT immediately after HPT deformation, and (ii) such being stored at 77 K immediately after HPT deformation, and stored at RT for a minimum and constant time needed for preparation. The results show that SRX brings the texture closer to the ideal shear texture and to higher strength values, but to smaller ductilities than DRX does. The mechanical properties can be attributed to changes of texture rather than to those of grain size.