Engineering topics
Publications and source records attributed to Siemers, P. A..
Physical and mechanical properties were determined for plasma-sprayed MgO- or Y2O3-stabilized ZrO2 thermal barrier coatings. Properties were determined for the ceramic coating in both the freestanding condition and as-bonded to a metal substrate. The properties of the NiCrAlY bond coating were also investigated.
The effects of coating TBC on a CF6-50 stage 2 high-pressure turbine blade were analyzed with respect to changes in the mean bulk temperature, cooling air requirements, and high-cycle fatigue. Localized spallation was found to have a possible deleterious effect on low-cycle fatigue life. New blade design concepts were developed to take optimum advantage of TBCs. Process and material development work and rig evaluations were undertaken which identified the most promising combination as ZrO2 containing 8 w/o Y2O3 applied by air plasma spray onto a Ni22Cr-10Al-1Y bond layer. The bond layer was applied by a low-pressure, high-velocity plasma spray process onto the base alloy. During the initial startup cycles the blades experienced localized leading edge spallation caused by foreign objects.
The thermal expansion of GeSe has been studied above room temperature up to the melting point of 670 plus or minus 5 C by X-ray diffraction techniques using a 190 mm Unicam high temperature camera. The thermal expansion of the crystallographic axes is linear with a distinct change in the expansion coefficients for all axes above 400 C. The relative changes in the axes indicate a rearrangement of the structure towards cubic symmetry with increasing temperature. The transformation of GeSe from the orthorhombic to a normal NaCl-type structure is observed at 651 plus or minus 5 C. The lattice parameter of the cubic form of GeSe is a 0 ? 5.730 plus or minus 0.003 A at 656 C. The GeSe lattice remains cubic up to the melting point.