Abstract Cold spray deposition is being investigated for mitigation of chloride-induced stress corrosion cracking (CISCC) in dry cask storage systems (DCSS) for spent nuclear fuel. Welded regions of austenitic stainless-steel canisters in DCSS are under tensile stress and susceptible to environmental chloride corrosion, which can potentially lead to the formation of CISCC. The low thermal input and high throughput nature of cold spraying make it a viable repair and mitigation option for managing potential CISCC. Cold spray coatings are under compressive stress and act as a barrier in Cl-rich environments. Characterization data including microstructure, hardness, and corrosion resistance are presented for cold spray coatings on stainless steel substrates.

Abstract Metals often require coatings with wear resistant metals like ceramics or WC-Co for applications in mechanical engineering. Due to the different classes of materials of substrate and coating in these systems, the mechanisms of adhesion available are mainly mechanical interlocking bonding. In this paper a process is described, which makes use of these bonding mechanisms to apply mainly WC-Co coatings by a thermal sprayed process (HVOF). In order to assess the adhesive strength of the coatings a fracture mechanical test was developed. Furthermore it is shown that some reliable and numerical effective local energy method (crack closure integral method), which offer special advantages for mixed-mode fracture analysis of inhomogeneous materials, like WC-Co coated metals, work well successful. This is done by the finite element analysis of a modified compact tension specimen, the MOCH- specimen. In addition to that, the adhesive strength of the WC-Co layers is optimized by a variation the parameter of the thermal spray process. The results show different criteria of failure, as there is premature crack propagation depending on spread parameters and the damaging of the composite material accompanied by low energy release rates and low adhesive strength. Paper text in German.

Abstract Fracture mechanical properties of metallic, thermally sprayed layers made of NiCr, NiCrAlY, molybdenum, and NiCrBSi were characterized using an indentation process close to the edge, known as edge chipping. Thermally sprayed layers were assessed according to their relative fracture toughness. The indentation took place in a vacuum chamber of a scanning electron microscope, which enables positioning in the micrometer range and in-situ observation of crack growth. The evaluation of preliminary indentation tests on a choice of thermally sprayed nickel based alloys failed for different indenter geometriy in most cases due to the porosity and the plasticity of the coating material avoiding a defined crack formation and propagation even at very high loads. Scaling down from macroscopic dimension to the micro range is feasible for edge chipping. It can be applied on coatings considering the anisotropic properties parallel and perpendicular to the substrate surface. Paper includes a German-language abstract.

Abstract Methodology to evaluate the adhesive strength between the MCrAlY alloy coating film and the Ni-base superalloy substrate was studied and proposed. By employing the double cantilever beam specimens which were taken from the CoNiCrAlY alloy coated Ni-base superalloy, the fatigue crack propagation tests along the interface were carried out. Through the work particular attention was given to the threshold level to the fatigue crack propagation along the interface as a measure to represent the adhesive strength, based on fracture mechanics approach. The effects of temperature, the surface finishing of the substrate and the long term thermal aging on the adhesive strength were also investigated.

Abstract This paper describes the development of an online process control system for spraying thick thermal barrier coatings as part of a Brite Euram research project. In addition to the evaluation of the substrate temperature, a system for acoustic emission analysis for particle impact and for controlling crack propagation is developed. The procedure, the problems overcome, and the results obtained are described. Paper includes a German-language abstract.

Abstract Fatigue properties of the Al 2 O3 plasma-sprayed SUS316L stainless steel rod specimens coated on different spraying conditions have been studied in a physiological saline solution (0.9 % NaCl solution) to evaluate the potential of surgical implant application. Fatigue tests were conducted in push-pull loading at the stress ratio of R = -1, and frequency of 2 Hz. Microstructure related with fatigue damage was examined by SEM and TEM. The fatigue strength of Al 2 O 3 plasma-sprayed metals significantly depended on spraying conditions: the effects of spraying on fatigue strength decreased with increasing the applied stress amplitude. As-blasted specimens were higher in fatigue strength than Al2O3 plasma-sprayed specimens. It was found that the plasma spraying had significant effects on fatigue crack growth behavior in the early stage of crack propagation. Fatigue cracks preferentially originated from dents that had been caused on the substrata metal surface subjected to grit-blasting. These results are discussed with both the compressive residual stresses due to the grit blasting which was carried out prior to plasma spraying and the corrosion-resistance of the alumina deposit.

Abstract The porous microstructure of plasma-sprayed deposits prepared from gray-alumina feedstock and from two different yttria-stabilized zirconia (YSZ) feedstocks were studied as a function of spray distance. For each material, the behavior of the two major void systems—intralamellar cracks and interlamellar pores—was investigated. The results offer the first proof that the quantity and the character of the porosity in these materials can be controlled independently by selecting the appropriate processing protocols.