Horst R. Maier

Corrosion mechanisms of low porosity ZrO2 based materials during near net shape steel casting

Abstract One of the most promising refractory materials for application in near net shape steel casting technologies is zirconia. The corrosion resistance of zirconia based materials in contact with steel and aggressive high casting speed powders has been investigated in a specially designed device simulating operating conditions; the corrosion mechanisms have been illustrated.

Fine grained Mg-PSZ ceramics with titania and alumina or spinel additions for near net shape steel processing

Abstract Mg–PSZ materials exhibit high corrosion resistance in steel/slag-systems. Through special additions of TiO 2 and Al 2 O 3 or MgAl 2 O 4 special microstructures have been obtained by slip casting with improved thermal shock performance and corrosion resistance for applications in near net shape steel processing. The thermomechanical properties have been measured at room and at elevated temperatures up to 1450°C and the corrosion rates have been investigated in a specially designed device simulating real operating conditions of thin slab casting of steel. The thermal shock behaviour has been evaluated due to water quenching tests and measuring of the remaining four point bending strengths. In addition disc shapes have been shocked by the aid of an arc torch.

Modelling and numerical simulation of the electrical, mechanical, and thermal coupled behaviour of multilayer capacitors (MLCs)

Abstract The modelling of non-linear coupled material characteristics has been used for finite element simulations of the integral device behaviour and mechanical and electrical stress distributions of ceramic multilayer capacitors. A two-dimensional finite element model of standard X7R-type capacitors of different sizes soldered on a printed circuit board has been developed to calculate residual, joining as well as mechanical and electrical load stresses. This model includes the experimentally measured non-linear bias field dependencies of the electric and piezoelectric characteristics of the BaTiO 3 based dielectric material. The validation of the model is demonstrated by calculations of the failure probability of soldered capacitors in a four-point bending test under simultaneous electrical loading. The results allow a description and possible improvement of the short-time reliability under particular load cases.

Weibull analysis of soldered MLC under bending load stress

A two-dimensional numerical model of MLCs is used to calculate the overall stress distribution of soldered and bent MLCs. Together with bending measurements the stress distribution leads to the Weibull parameters of three different MLC sizes. The material dependent Weibull parameters have been found to be different for each size. One possible reason under investigation are size related residual stresses due to manufacturing which are neglected in the simulation. Residual stress measurements have been carried out at the surface of three different MLC sizes near their terminations. Compressive stresses with high stress gradients were found near the terminations. These gradients may influence the accuracy of the measurement. The measured stresses are not constant from MLC size to MLC size and influences the determination of the Weibull parameters. The residual stresses influence the reliability of MLCs and should therefore be considered in future simulations.

Rheology of Semi-Solid Steel Alloys at Temperatures up to 1500°C

The investigation of the flow behavior of semi-solid steel alloys poses a great challenge by reason of high operation temperatures and the need of ceramic components for the measuring system. A high-temperature Couette rheometer has been developed to analyze flow properties of semi-solid alloys up to temperatures of 1500°C. In the present work the alloy under investigation is X210CrW12. Differently performed experiments clearly show its shear-thinning and time-dependent flow properties with a yield stress. This flow behavior is modeled using a Herschel-Bulkley approach where the experimental results achieved serve to identify model parameters.