Anisotropy of stress-strain behavior, fracture toughness, and fatigue crack growth rate of Ti6Al4V deposited by cold spray using nitrogen was studied. For that, flat deposits were tested with stress acting in the in-plane directions and tubular deposits were tested in the out-of-plane stress directions. In all tests, unified small-size specimens were used. It was shown that for the in-plane stress, the deposits can be considered isotropic, whereas the out-of-plane stress led to significantly lower values of the measured properties. The obtained results were related to fractography and microstructural analysis. While a combination of trans-particle and inter-particle fracture determined the fatigue properties in the near-threshold regime, at higher loads, inter-particle fracture was dominant. It was also shown that the different particle-to-stress orientations influenced the resulting fatigue and static properties.

The fracture toughness of pure Al, Cu, Ni, and Ti deposited by cold spraying was investigated to gain a better understanding of the damage process and quantify material performance. Rectangular specimens of self-standing deposits with fatigue pre-cracks were tested in three-point bending. KIC values were obtained from J-R curves and stress-strain curves were plotted. The cold-sprayed deposits exhibited significantly lower fracture toughness than the same wrought materials, and fractographic analysis revealed either ductile or cleavage intergranular fracture as the major failure mode.

In this work, hot isostatic pressing (HIP) is used to reduce interior defects, adjust the microstructure, and improve the tensile properties of cold-sprayed Ti6Al4V. Optical microscope and X-ray tomography were used to characterize pore morphologies and porosity evolution. XCT reconstructions show that fully dense Ti6Al4V alloy with an equiaxed microstructure were achieved. Tensile testing shows that strength and ductility were improved as well because of enhanced diffusion and resultant metallurgical bonding.

This study evaluates the influence of shot peening on the fatigue life of cold spray aluminum alloy 6082 coatings. A pneumatic blast machine with standard steel shot was used to peen both uncoated and coated substrates. Six test groups representing different treatment protocols were characterized in terms of residual stress, roughness, and rotating bending fatigue. The results show that the best fatigue performance is obtained by intense shot peening prior to cold spraying. Post-treatment shot peening, in contrast, had a detrimental effect as a large portion of the kinetic energy is absorbed in the coating, resulting in surface damage rather than further work hardening.

The fatigue performance of conventional structural steel with an applied thermal barrier coating (TBC) was evaluated via cyclic bending. Tests were carried out for as-received and grit-blasted substrates as well as for samples with thermally sprayed bond coats and topcoats. Failure mechanisms were identified and changes in fatigue resistance were assessed based on results obtained for different loading amplitudes supplemented by fractographic analysis.

A magnesium coating with a low porosity and high microhardness was elaborated using cold spraying. However at present, a poor bonding strength between the coating and substrate limits its application. This paper aims at improving the bonding strength between the coating and substrate using substrate preheating. Aluminum substrates were heated to 100, 200 and 300°C respectively by a flame prior to cold spraying. The results show that substrate preheating can significantly increase the bonding strength. The bonding strength increased from 3.3±0.8 MPa to 11.6±0.5 MPa when the substrate temperature increased from room-temperature to 200°C. The fracture analyses show that the coating fracture occurred within the coating when the substrate was preheated at 200°C.

Adhesion/cohesion testing represents one of the most common methods for benchmarking and optimization of thermal spray coatings. However, due to the inhomogeneous coating microstructure, such testing may be quite troublesome. In this study, adhesion/cohesion strength of representative metallic and ceramic coatings deposited by Water Stabilized Plasma (WSP) spraying was evaluated by different methods, namely Tensile Adhesion Test (TAT), newly utilized pin test and Tubular Coating Tensile (TCT) test. Combination of various methods enabled the evaluation of the splat bonding quality in different loading modes. Limitations and benefits of each method for testing of WSP coatings are demonstrated. Dominating failure micromechanisms were determined by supplementary fractographic analysis.

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.

The aim of this study is to quantify the pore network architecture of thick zirconia coatings deposited by suspension plasma spraying of nano-sized particles. It is shown by FESEM fractography that the coatings exhibit a granular structure with a lamellar layer at the substrate interface and that the average void diameter is orders of magnitude smaller than the resolution of conventional SEM systems.

Plasma sprayed chromium oxides coatings have been widely applied in anilox rolls and pump seal for many years. This paper is researching the effect of nanostructured Cr 2 O 3 5SiO 2 3TiO 2 composite powder preparation when adding nano-size SiO 2 and TiO 2 powder in Cr 2 O 3 powder, to prepare for through spray drying, high temperature sintering and flame density. The microstructure of powder and plasma sprayed coating are analyzed by SEM and XRD, compared with pure Cr 2 O 3 powder and METCO 136F powder. The Microhardness of the coatings are measured by 402MVA TM Vickers hardness tester. Fracture test is used to analysis the ductility of coatings, and the fracture appearance is analyzed by SEM. The result indicates that the mechanical behaviors of nanostructured Cr 2 O 3 5SiO 2 3TiO 2 coating has better performance in the nature of hardness and ductility.

An earlier study reported an investigation of the mechanical properties of cold sprayed aluminum and the effect of annealing on those properties. In that study, cold spray coatings approximately one centimeter thick were prepared using three different feedstock powders: Valimet H-10, Valimet H-20, and Brodmann Flomaster. ASTM E8 tensile specimens were machined from these coatings. Each material was tested in two conditions: as-sprayed and after a 300°C, 22 hour air anneal. The as-sprayed material showed a high ultimate strength and low ductility, < 1% elongation. The annealed samples showed a reduction in the ultimate strength but a dramatic increase in ductility, up to 10% elongation. Microstructural examinations and fractography clearly showed a change in the fracture mechanism between the as-sprayed and annealed material, but insufficient data was available to conclusively explain the ductility increase at that time. Since then, Kikuchi mapping of the Valimet H-10 material in the as-sprayed and annealed conditions has been conducted. Kikuchi mapping allows indexing of grains, identification of grain boundaries, and phase identification using backscattered diffraction patterns in an SEM. The data shows that significant recrystallization within the splats upon annealing has occurred. No significant crystal growth across splat boundaries is observed. The data demonstrate that the mechanism of ductility increase in annealed cold spray deposits is recrystallization of the base aluminum material.

Coatings deposited by thermal spraying are widely used for applications where enhanced resistance to wear is a crucial factor. In this work we focused on HVOF and plasma sprayed WC-Co, NiCrSiB, Cr 3 C 2 -NiCr, AISI 316L and Cr 2 O 3 coatings. The materials were examined by wet slurry abrasion tests, microhardness and roughness measurements. Systematic fractographic analysis in SEM was devoted to determine the main failure mechanisms of selected coatings. The WC-Co coating exhibited the lowest wear rate while 316L coating exhibited the highest wear rate. The plasma sprayed Cr 2 O 3 coating exhibited wear rate higher than HVOF sprayed cermet coatings but lower than metal coating. In most cases it was found that the higher microhardness, the higher is the wear resistance of the coating. The most favorable microstructure was found to be a mixture of hard particles dispersed in tough metal matrix. Matrix-like structure and internal splat microstructure were the main factors controlling the wear resistance of the investigated HVOF and WSP coatings.

This paper investigates the adhesion of thermally sprayed ceramic particles on metal substrates. Two aluminum oxide powders are applied to nickel-oxide coated steel substrates by detonation and vacuum plasma spraying. SEM and XRD fracture analysis is used to examine the ceramic-metal interface and the morphology of fracture surfaces. In all test samples, failure occurs in the alumina, not at the interlayer boundary, indicating a high level of adhesion between the ceramic and nickel oxide layers. Paper includes a German-language abstract.

Alumina matrix composites reinforced with metal thin wire (Inconel-600) were successfully fabricated by plasma spray forming. The atmospheric plasma sprayed matrix layers and wire layers arranged by filament-winding technique were piled up alternately. Though the matrix and the wire were partially bonded only on the side which sprayed particles came flying to, a solid structure was obtained by this technique. Spraying in one direction perpendicular to the substrate made peculiar V-shape pores around the wires, but tilting the torch was effective to reduce the pores. The flexural strength of composite did not increase in spite of some crack deflections on the fracture surface. Owing to the wire pullout, however, the composite exhibited a remarkably higher apparent fracture energy than that of monolithic alumina ceramics.