Mechanical and fatigue properties of cold sprayed (CS) Cu 20 Sn bell metal were tested in order to assess the potential applicability of the technology to repair impact areas of church bells. The CS bell metal was compared to its traditional cast counterparts, a fine-grained Cu 22 Sn bell metal seen in small bells, and a coarse-grained Cu 20 Sn seen in large bells. Similar to other CS metals, it was shown that both the strength as well as the fatigue crack growth rates at low loading are similar to the cast materials. The fracture toughness of the CS material was comparable with the finegrained Cu 22 Sn bell metal, while both were significantly lower than the coarse-grained Cu 20 Sn bell metal. The impact damage rate of the CS material determined by a periodic impact test was significantly higher than the (finegrained) cast material. Both materials showed a stabilized, very slow damage rate after the relatively fast initial crater formation. The results presented in this paper identify CS as a feasible restoration technology for church bells, and the introduced methodology presents a characterization method for quantitative description of bell metal impact damage.

Diamond-reinforced composites prepared by cold spray are emerging materials simultaneously featuring outstanding thermal conductivity and wear resistance. Their mechanical and fatigue properties relevant to perspective engineering applications were investigated using miniature bending specimens. Cold sprayed specimens with two different mass concentrations of diamond 20% and 50% in two metallic matrices (Al – lighter than diamond, Cu – heavier than diamond) were compared with the respective pure metal deposits. These pure metal coatings showed rather limited ductility. The diamond addition slightly improved ductility and fracture toughness of the Cu-based composites, having a small effect also on the fatigue crack growth resistance. In case of the Al composites, the ductility as well as fatigue crack growth resistance and fracture toughness have improved significantly. The static and fatigue failure mechanisms were fractographically analyzed and related to the microstructure of the coatings, observing that particle decohesion is the primary failure mechanism for both static and fatigue fracture.

Many applications of thermally sprayed coatings call for increased fatigue resistance of coated parts. Despite the intensive research in this area, the influence of coating on fatigue is still not completely understood. In this paper, the spatiotemporal localization of crack initiation and the dynamics of crack propagation are studied. The resonance bending fatigue test is employed to test flat specimens with both sides coated. Hastelloy-X substrates coated with classical TBC YSZ/NiCoCrAlY composites were tested. The strain distribution on the coating surface is evaluated by the digital image correlation method (DIC) through the whole duration of the fatigue test. Localization of crack initiation sites and the mode of crack propagation in the coated specimen are related to the observed resonance frequency. The individual phases of specimen degradation, i.e. the changes of material properties, crack initiation, and crack propagation are identified. The tested coatings strongly influenced the first two phases, the influence on the crack propagation was less significant.

This study investigates the development of fatigue failure in steel specimens coated by various spraying methods with and without grit blasting. Commercial titanium powder was deposited on structural steel substrates by low-pressure and portable cold spray as well as plasma and warm spray. Coating samples were subjected to strain-controlled cyclic bending, while monitoring resonant frequency as a measure of accumulated damage. A change in frequency of 4 Hz was chosen as the test-stop with the corresponding cycle count serving as the main indicator of fatigue life. Test results are presented in the paper along with explanations of fatigue mechanisms and process-related factors.

The effect of grit blasting exposure time on the adhesion of plasma sprayed Al 2 O 3 and 316L stainless steel coatings was studied in the present work. The steel substrates were grit blasted prior to the coating deposition. Two sets of substrates with exposure time of 1 and 4 seconds were prepared. Both types of coatings were deposited using Water Stabilized Plasma (WSP) torch. Adhesion strength was evaluated using standardized pulloff test. The obtained results showed a slight improvement in the adhesion strength for the blasting time of 4 s. Failure processes taking place in the coatings during the pull-off tests were described based on the detailed fractographic analysis.

This work investigates the influence of plasma-sprayed deposits on the fatigue life of coated specimens. Hydroxyapatite (HA) and TiO 2 were deposited on dog-bone shaped substrates under different spraying conditions while measuring in-flight particle temperature and velocity. The coated specimens were then subjected to cyclic bending with constant deflection and the number of cycles to failure was recorded. It was found that the higher the temperature and velocity of particles during spraying, the greater the improvement in fatigue life up to a maximum of 46% compared to uncoated samples.

Thermal spray is a flexible technique enabling deposition of wide choice of feedstock materials including ceramics, metals or the mixture of both. Various spray technologies are available, such as different types of thermal plasma methods, electric arc based methods, HVOF and other combustion methods. Obviously, the fatigue properties of coated bodies will differ based on the choice of feedstock material and on the spray technology used. Comparison was made of fatigue properties of bodies with Alumina, Ni-5wt%Al and composite coatings produced by gas and water stabilized plasma spray. It has been found, for instance, that Alumina coatings sprayed by water stabilized plasma torch (WSP) had substantially increased fatigue life times of specimens compared to specimens with coatings of the same feedstock deposited by the gas stabilized plasma torch. Measured fatigue data were related to a detailed structural characterization of the tested coatings. Obtained results are discussed with regard to our previous results obtained during fatigue tests of specimens with one-component coatings.

Fatigue behavior and Young’s modulus of plasma sprayed gray alumina on low-carbon steel substrates were investigated. The investigation of the properties of composite material “coating-substrate” included the measurements of microhardness profile, residual stress on the top of the coating and residual stress profile in substrate. Fatigue samples were periodically loaded as a cantilever beam on a special testing machine. Failed samples were observed in SEM to determine failure processes in the coating. The Young’s modulus of the coating was measured by the four-point bending method. Samples were tested both in tension and compression at low (300 N) and high (800 N) loads. Our experiments revealed that the average fatigue lives of coated specimens were nearly 2 times longer than those of the uncoated specimens. The Young’s modulus of the coating varied between 27 and 53 GPa with an average value of 43 GPa. Loading in tension caused decrease in Young’s modulus of the coating while loading in compression lead to increase in Young’s modulus. Increase in the lifetime of coated samples was likely due to compressive residual stresses in the substrate, originating from the spray process. Failure of the coating consisted of several processes, among which the most important are splat cracking, splat debonding and coalescence of cracks through the voids in the coating.