2001, Völkl, Rainer, Fischer, Bernd, Lupton, David, Teschner, Roman

Platinum components are now very widely used in the manufacture and processing of glass. At first sight it is, therefore, surprising that finite element modelling (FEM) is seldom used in their design. The reason for this omission is to be found in the specific type of mechanical loading at high temperatures and the lack of appropriate mechanical property data for the structural materials. Using the example of a glass fibre bushing from an indirect melt fiberizing proeess, the paper will demonstrate the use of FEM to determine the stresses resulting from the hydrostatie pressure of the glass melt, the intrinsic weight of the bushing, the stresses caused by the forces applied to withdraw the fibres from the bushing, and the stresses induced by the inhomogeneous temperature distribution in the bushing. On the basis of these model calculations it was possible to localize regions of stress concentrations, to select an appropriate structural material and to modify the component design to reduce the stresses.

2018-8-30, Haas, Sebastian, Mosbacher, Mike, Senkov, Oleg N, Feuerbacher, Michael, Freudenberger, Jens, Gezgin, Senol, Völkl, Rainer, Glatzel, Uwe

We determined the entropy of high entropy alloys by investigating single-crystalline nickel and five high entropy alloys: two fcc-alloys, two bcc-alloys and one hcp-alloy. Since the configurational entropy of these single-phase alloys differs from alloys using a base element, it is important to quantify the entropy. Using differential scanning calorimetry, cp-measurements are carried out from −170 °C to the materials’ solidus temperatures TS. From these experiments, we determined the thermal entropy and compared it to the configurational entropy for each of the studied alloys. We applied the rule of mixture to predict molar heat capacities of the alloys at room temperature, which were in good agreement with the Dulong-Petit law. The molar heat capacity of the studied alloys was about three times the universal gas constant, hence the thermal entropy was the major contribution to total entropy. The configurational entropy, due to the chemical composition and number of components, contributes less on the absolute scale. Thermal entropy has approximately equal values for all alloys tested by DSC, while the crystal structure shows a small effect in their order. Finally, the contributions of entropy and enthalpy to the Gibbs free energy was calculated and examined and it was found that the stabilization of the solid solution phase in high entropy alloys was mostly caused by increased configurational entropy.