This study demonstrates the use of bulge testing to evaluate fuel plates for high-performance nuclear reactors. Uranium-molybdenum alloy substrates were plasma sprayed with zirconium and clad between aluminum sheets by hot isostatic pressing. The coated-and-clad samples were cut into disks, the top cladding was thinned, and a small hole was milled through the bottom cladding. The samples were then placed in a pressure cell and a syringe pump was used to inject distilled water through the hole in the bottom Al sheet. Two cameras measured bulge height while fluid pressure was simultaneously recorded. Test results show that all failures occurred at the plasma-sprayed Zr/U-Mo interface rather than the HIP-bonded Zr/Al interface. It is also shown that the use of transferred arc (TA) cleaning prior to spraying improves both failure pressure and initiation fracture toughness, especially under high ac current. TA cleaning facilitates the formation of strong diffusion bonds by removing oxide from the substrate and increasing interface temperature.

The standard technique for applying zirconium (Zr) to uranium (U) is roll bonding, where a thin foil of Zr is placed on each side of a U plate which is then encased in steel and rolled at high temperatures. This study evaluates an alternative approach in which Zr layers are plasma sprayed on U and then clad with aluminum (Al) by hot isostatic pressing. The interface region between the Zr and Al is examined by SEM, revealing a reaction layer consisting of Al, Zr, and Si. SEM images show good conformance between the Al sheet and Zr surface along with the presence of Al in the porous Zr. Initial test results indicate that increased interface roughness and Al penetration into the plasma-sprayed Zr have the potential to improve bond strength by impeding crack propagation in the reaction layer.

The future production of low enriched uranium nuclear fuel for test reactors requires a well-adhered diffusion barrier coating of zirconium (Zr) on the uranium/molybdenum (U-Mo) alloy fuel. In this study, the interfacial bond between plasma sprayed Zr coatings and U-Mo fuel has been characterized for localized bond strength by microcantilever beam testing. Test results have revealed the effect of specific flaws such as cracks and pores on the bond strength of interfaces with a sampling area of approximately 20 µm 2 . TEM examination has shown the Zr/U-Mo interface to contain rows of very fine grains (5-30 nm) with the Zr in contact with UO 2 . Bond strengths of plasma sprayed samples have been measured that are similar to those of diffusion-bonded samples showing the potential for plasma sprayed Zr coatings to have high bond strength.

The exceptional properties of beryllium (Be) including low density and high elastic modulus, make it the material of choice in many defense and aerospace applications. However, health hazards associated with Be material handling limit the applications that are suited for its use. Innovative solutions that enable continued use of Be in critical applications while addressing worker health concerns are highly desirable. Plasma Transferred Arc solid freeform fabrication is being evaluated as a Be fabrication technique for civilian and military space based components. Initial experiments producing beryllium deposits are reported here. Deposit shape, microstructure and mechanical properties are reported.

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.

Transferred-arc cleaning and roughening as discussed in the patent by Muhlberger is often used as a surface preparation method prior to low pressure plasma spray (LPPS) deposition of coatings. In this article, electrically transmitted arc cleaning is investigated as a precision cleaning method for thin films lubricating substrates as well as traditional cleaning and roughening for LPPS. A Box-Behnken reaction surface construction test is carried out with variation of the chamber pressure, the substrate distance and the torch current taking into account the transferred arc voltage, the voltage fluctuation, the current, the emitted light, and the surface cleanliness. The results of the analysis show the effect of the various independent quantities on the measured responses. Different stages in the cleaning process are determined by their sample cleanliness, their voltage level, their voltage fluctuation, their emitted light and their rate of erosion. Paper includes a German-language abstract.