Marcus Hopfeld

In-situ synthesis of Y2W3O12 within a Co-based superalloy powder mixture

Abstract In this work, the synthesis of the negative thermal expansion ceramic Y2W3O12 within a Co-based superalloy was analyzed in detail. On the basis of thermal analysis of the synthesis from the feedstock powders Y2O3 and WO3 further experiments were conducted. Thermal behavior and stability of different mixtures of the powders Y2O3, WO3 and the Co-based superalloy were investigated. The qualitative and quantitative results of the synthesis separately and within the superalloy are presented as achieved by energy dispersive X-ray analysis, X-ray powder diffraction, differential thermal analysis and thermal gravimetric analysis. It was found that the synthesis of yttrium tungstate inside the Co-based superalloy is possible with a defined temperature program and a simple basic production process of powder mixtures.

Ultrasonic response of a piezoelectric aluminum nitride film deposited on silicon

ABSTRACT An aluminum nitride (AlN) thick film for ultrasonic transduction was deposited on a silicon wafer by magnetron sputtering. A columnar structure with uniform elemental depth profiles with 40 at.% to 60 at.% (Al-N) concentrations and with a c-axis preferential orientation was observed by X-ray diffraction. The ultrasonic response of the Al/AlN/Si overmoded resonator was characterized from 1.24 MHz to 2 GHz using a vector network analyzer. The time domain transform and the gate features of the vector network analyzer were used to characterize the AlN thick film capabilities in the time and frequency domains. The results show that the obtained resonator operates over a broad frequency range with a central frequency at approximately 930 MHz and a 738 MHz bandwidth at -6 dB. The results were compared with those obtained from a one-dimensional simulation to highlight and predict the AlN response features. A comparison was performed to validate the experimental measurements and to validate the circuit modeling. Overall agreement between the experiment values and the simulation was observed.

Model switch experiments for determining the evolution of contact resistance of electrical contacts in contactors

As a first step in a long-term planned cooperation between the TU Ilmenau and several industry partners a model switch was developed and constructed in order to investigate the influence of different aspects affecting the evolution of contact resistance during the lifetime of electrical contacts in low voltage contactors. The device permits, besides the variation of different geometrical and kinetic parameters, the determination of the contact resistance by different contact closing forces. Several material analysis methods, such as laser surface profilometry, light microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were applied to Ag/Ni10 contacts before and after experimental series with breaking AC-arcs according to IEC 60947. Important information regarding surface structure, chemical composition and formed crystalline phases of the surface contact materials and ambient materials were obtained. The main characteristics of the model switch and some results of the first experiments are presented in this paper.