K. J. Hollis, B. D. Bartram, Los Alamos National Laboratory, Los Alamos, NM
Plasma spray forming ceramic components on a mandrel provides a way of net shape forming of difficult to machine materials. In addition, the structure of plasma sprayed ceramics contains fine porosity that improves strain accommodation as compared to sintered ceramics. However, plasma spray forming causes complex stress states in materials that may lead to cracking during spraying or during separation from the mandrel. Monitoring surface temperatures by infrared videography and controlling deposit surface temperature by directed cooling can be used to minimize thermal gradients and minimize part cracking. Control of thermal stresses is also necessary for proper separation of the sprayed part from the mandrel. Details of the plasma spray forming of yttrium oxide crucibles show how temperature monitoring, directed cooling, and robot manipulation are used to produce a crack free crucible.
Summary: This presentation explains the process for spray forming yttrium oxide crucibles used for molten metal processing. Control of stresses by infrared videography, directed cooling, and spray trajectory selection allow the production of crack free crucibles.