Comprehensive Study of the Influence of the Bonding Temperature and Contact Pressure Regimes during Diffusion Bonding on the Deformation and Mechanical Properties of AISI 304

Process parameters for diffusion bonding are temperature, dwell time, and contact pressure. Temperature and contact pressure have opposite effects on deformation. The effect of temperature on deformation was investigated in steps of 20 K from 1015 to 1135 °C. Contact pressure and dwell time were 16 MPa and 4 h, respectively. The deformation increase steadily with temperature. Yield strength and tensile strength decrease slightly with temperature, which is attributed to grain growth. The elongation-at-fracture values are 100–105%. For 925 to 995 °C, values for elongation at fracture decrease. It was investigated if comparable mechanical properties can be obtained at a temperature of 850 °C only. Experiments with higher constant contact pressures were supplemented by tests with superimposed short load peaks. Similar and higher values for the yield strength were achieved. A correlation of yield strength, tensile strengths and elongation-at-fracture values with contact pressure and contact pressure regime was found. The values for elongation at fracture are significantly lower than those for higher temperatures. This even applies to parameter sets at different temperatures, leading to almost identical deformations. Reduced elongation-at-fracture values at 850 °C are attributed to microscopically small defects in the bonding plane and to notch effects

Highly Molybdenum-Alloyed Materials Hastelloy BC-1 (2.4708) and B3 (2.4600): Diffusion Bonding Experiments and Evaluation of both Mechanical Behavior and Corrosion Resistance in Hot 70% Sulfuric Acid

Sulfuric acid is a widely used raw material in the chemical industry. Its corrosive effect on materials varies considerably, depending on impurities, temperature and water content. This is an issue for micro process apparatuses with thin walls. Such devices are often joint by diffusion bonding what may alter materials properties due to high temperatures and long dwell times. In this paper, two high molybdenum alloys, namely Hastelloy B3 and BC-1, were investigated. Diffusion bonding tests were performed at different temperatures. Tensile tests were carried out for different material conditions, to determine the change in mechanical strength and elongation at fracture values. The fracture behavior of both alloys was ductile and the fracture surfaces showed dimple structure. For diffusion bonded samples, weak spots or rather non-bonded areas were found. These obviously caused the onset of material failure and thus, degradation of mechanical properties. Tensile samples, aged in 70% sulfuric acid at 100 °C for 1000 h showed local corrosion attacks at the grain boundaries at the circumferential surfaces and joining planes—for Hastelloy B3 more pronounced than for Hastelloy BC-1. Accordingly, a further decrease of stress and elongation at fracture values was observed. However, 0.2% yield strength used for dimensioning components are found to be reasonable. As conclusion, at least Hastelloy BC-1 reveals both good mechanical properties and an excellent corrosion resistance, regardless of the heat treatment. This is a significant advance compared to the results obtained from a previously research project on four different alloys

Influence of Laser Welding Speed on the Morphology and Phases Occurring in Spray-Compacted Hypereutectic Al-Si-Alloys

Normally, the weldability of aluminum alloys is ruled by the temperature range of solidification of an alloy according to its composition by the formation of hot cracks due to thermal shrinkage. However, for materials at nonequilibrium conditions, advantage can be taken by multiple phase formation, leading to an annihilation of temperature stress at the microscopic scale, preventing hot cracks even for alloys with extreme melting range. In this paper, several spray-compacted hypereutectic aluminum alloys were laser welded. Besides different silicon contents, additional alloying elements like copper, iron and nickel were present in some alloys, affecting the microstructure. The microstructure was investigated at the delivery state of spray-compacted material as well as for a wide range of welding speeds ranging from 0.5 to 10 m/min, respectively. The impact of speed on phase composition and morphology was studied at different disequilibrium solidification conditions. At high welding velocity, a close-meshed network of eutectic Al-Si-composition was observed, whereas the matrix is filled with nearly pure aluminum, helping to diminish the thermal stress during accelerated solidification. Primary solidified silicon was found, however, containing considerable amounts of aluminum, which was not expected from phase diagrams obtained at the thermodynamic equilibrium. View Full-Tex

Zebrafish Pou5f1-dependent transcriptional networks in temporal control of early development

Time-resolved transcriptome analysis of early pou5f1 mutant zebrafish embryos identified groups of developmental regulators, including SoxB1 genes, that depend on Pou5f1 activity, and a large cluster of differentiation genes which are prematurely expressed.Pou5f1 represses differentiation genes indirectly via activation of germlayer-specific transcriptional repressor genes, including her3, which may mediate in part Pou5f1-dependent repression of neural genes.A dynamic mathematical model is established for Pou5f1 and SoxB1 activity-dependent temporal behaviour of downstream transcriptional regulatory networks. The model predicts that Pou5f1-dependent increase in SoxB1 activity significantly contributes to developmental timing in the early gastrula.Comparison to mouse Pou5f1/Oct4 reveals evolutionary conserved targets. We show that Pou5f1 developmental function is also conserved by demonstrating rescue of Pou5f1 mutant zebrafish embryos by mouse POU5F1/OCT4

The Laccase Engineering Database: a classification and analysis system for laccases and related multicopper oxidases

Laccases and their homologues form the protein superfamily of multicopper oxidases (MCO). They catalyze the oxidation of many, particularly phenolic substances, and, besides playing an important role in many cellular activities, are of interest in biotechnological applications. The Laccase Engineering Database (LccED, http://www.lcced.uni-stuttgart.de) was designed to serve as a tool for a systematic sequence-based classification and analysis of the diverse multicopper oxidase protein family. More than 2200 proteins were classified into 11 superfamilies and 56 homologous families. For each family, the LccED provides multiple sequence alignments, phylogenetic trees and family-specific HMM profiles. The integration of structures for 14 different proteins allows a comprehensive comparison of sequences and structures to derive biochemical properties. Among the families, the distribution of the proteins regarding different kingdoms was investigated. The database was applied to perform a comprehensive analysis by MCO- and laccase-specific patterns