Laurent Cretegny

Experimental and numerical studies of microwave power redistribution during thermal runaway

Plasma-assisted heating of Al2O3 is used to study power redistribution during thermal runaway when two samples are simultaneously heated in a microwave cavity. It is observed that thermal runaway in one of the samples completely suppresses the power availability to the other, demonstrating that thermal runaway in one region of the cavity acts as a “sink” for microwave power. Similar effects were observed during localized thermal runaway in a spatially extended single sample. Experimental trends were explored numerically by calculating the temperature evolution T (t) when one of the samples undergoes thermal runaway. Numerical investigation qualitatively captures the essential feature that thermal instability in one sample rapidly decreases the temperature of the second sample in agreement with the experimental observation. Experimental and numerical results as well as practical implications are discussed in the context of microwave processing of materials.

Fracture and Fatigue of Niobium Silicide Alloys

The fracture and fatigue behavior of refractory metal silicide alloys/composites is significantly affected by the mechanical behavior of the refractory metal phase. This paper reviews some of the balance of properties obtained in the alloys/composites based on the Nb-Si system. Since some of the alloy/composite properties are dominated by the behavior of the refractory metal phase, the paper begins with a review of data on monolithic Nb and its alloys. This is followed by presentation of results obtained on Nb-Si alloys/composites and a comparison to behavior of some other high temperature systems.

The Effects of Substitutional Additions on Tensile Behavior of Nb-Silicide Based Composites

Nb-silicide based in-situ composites consist of a ductile Nb-based solid solution with high-strength silicides, and they show excellent promise for aircraft engine applications. The Nb-silicide controls the high-temperature tensile behavior of the composite, and the Nb solid solution controls the low and intermediate temperature capability. The aim of the present study was to understand the effects of substitutional elements on the room temperature tensile behavior and identify the principal microstructural features contributing to strengthening mechanisms.