Previous own works revealed that novel partially amorphous Fe-based alloys have a combination of proper-ties that are beneficial for the application in liquid hydrogen (LH2) tanks, viz low thermal diffusivity, little porosity, and good adhesion. The influence of cryogenic temperatures or hydrogen on coating tensile strength, on the other hand, has not been investigated yet for this material. However, this is crucial for the long-term durability of the coatings under hydrogen and other alternative fuels. Thus, in this work, tubular coating tensile (TCT) tests were performed at room temperature and cryogenic temperatures. In addition, hydrogen charging was carried out to identify a possible regime that is sufficient for TCT tests under the influence of hydrogen. Subsequently, the fracture surfaces were evaluated analytically, optically and profilometrically. Under cryogenic conditions, a significant increase in tensile strength and a finer structure of the fracture surfaces was observed.

The piezoresistivity of flame-sprayed NiCoCrAlTaY on an electrically insulated surface of a steel substrate was investigated through cyclic extension and compression cycles between 0 and 0.4 mm for 1000 cycles and uniaxial tensile test. The sprayed NiCoCrAlTaY was in grid form with grid thickness of 3 mm and grid length of 30 mm while the electrical insulation was fabricated by flame spraying alumina on the surface of the steel. During mechanical loading, instantaneous electrical resistance measurements were conducted to evaluate the corresponding relative resistance change. Images of the loaded samples were captured for strain calculations through Digital Image Correlation (DIC) technique. After consolidation of the pores within the coating, the behavior of the flame-sprayed NiCoCrAlTaY was consistent and linear within the cyclic compression and extension limits, with strain values of approximately -1000 με and +1700 με, respectively. The coating had a consistent and steady maximum relative resistance change of approximately 5% within both limits. The tensile test revealed that the coating has two gauge factors due to the bi-linearity of the plot of relative resistance change against strain. The progression of damage within the coating layers was analyzed from its piezoresistive response and through back-scattered scanning electron microscopy images. Based on the results, the nickel alloy showed high piezoresistive sensitivity for the duration of the loading cycles, with little or no damage to the coating layers. These results suggest that the flame-sprayed nickel alloy coating has great potential as a surface damage detection sensor.

This paper presents the results of two metals coatings, molybdenum and tantalum, prepared by Controlled Atmosphere Plasma Spray (CAPS) onto Al 6061 substrates that were thermal cycled to calculate the effective coating modulus. Traditional uniaxial tensile testing samples were prepared from thicker duplicate coatings for comparison, as well as to measure thermal expansion properties and oxygen and nitrogen content. The molybdenum samples cut from thicker coatings were un-able to be tensile tested due to their fragility. Thermal cycle testing of molybdenum on an Al 6061 substrate was found to have a modulus approximately 18 to 19% of literature values for bulk molybdenum using the bi-layer beam thermal cycling method. Additionally, non-linear modulus behaviour was observed in the molybdenum sample when enough thermal strain was induced to shift the coating from a compressive to tensile stress state. The tantalum coating was found to have a modulus approximately 42 to 46% of literature values for bulk tantalum using the bi-layer thermal cycling method. Traditional tensile testing measured a modulus approximately 44 to 46% of bulk, which shows good agreement between the two methods and supports that the bi-layer thermal cycling method is valid for plasma sprayed refractory metal coatings.

In this work, advanced Al/diamond wear-resistance composites were fabricated by solid-state cold spray additive manufacturing using core-shell-structured diamond powders. Based on the experimental results and thorough discussion, it is found that core-shell-structured diamond powders were much easier to deposit than pure Al by cold spray, showing great potentials as feedstock for cold spraying. The deposition mechanism of the Al/diamond composites were dominated by the true metallic bonding between Al matrix and Cu layer, which is different from other conventual cold sprayed metal matrix composites. Tensile tests indicated that the tensile strength of the Al/diamond composites can be higher than cold sprayed pure Al. In addition, the Al/diamond composites had super wear-resistance performance. The wear rate was reduced by 17.8 times for the N 4-1 composite and by 37.5 times for the N 1-1 composite as compared with cold sprayed Al/Al 2 O 3 composite.

The cold spray deposition mechanism of Ultra-High Molecular Weight Polyethylene (UHMWPE) requires a detailed understanding of strain rate sensitivity of UHMWPE. The yield and flow in UHMWPE are complex and sophisticated compared to metals due to their dependency on time, temperature, strain, strain-rate and the history of the processing. In this research work, powder-sintered UHMWPE of 10.5 Mg/mol was subjected to various strain-rates ranging from 10-2 s-1 to 103 s-1 via low compression strain-rate testing and Split Hopkinson Pressure Bar testing (SHPB). The experimental true stress-strain curves in compression of a sintered UHMWPE at pre-yield, yield point, and post-yield were analyzed. The pre-yield and yield point region, 10.5 Mg/mol UHMWPE exhibited an increase in the tangent modulus and the yield stress with an increase in strain rate. Further, the post-yield phenomenon in UHMWPE shows no apparent post-yield softening and shows an increase in the strain hardening with an increase in the strain-rate. The curves at increasingly higher strain rates showed an increasingly pronounced bi-linearity to its flow behavior with the rate of hardening increasing above 10~15% strain. Under the domain tested, the strain rate dependence for UHMWPE can be depicted by a logarithmic fit.

The present work summarizes the most important results of a research project dealing with the comprehensive!! investigation of the bonding mechanisms between cold sprayed Al coatings and various poly- and monocrystalline ceramic substrates (Al 2 O 3 , AlN, Si 3 N 4 , SiC, MgF 2 ). Due to their exceptional combination of properties, metallized ceramics are gaining more and more importance for a wide variety of applications, especially in electronic engineering. Cold spraying provides a quick, flexible and cost-effective one-step process to apply metallic coatings on ceramic surfaces. However, since most of the existing cold spray-related publications focus on metallic substrates, only very little is known about the bonding mechanisms acting between cold sprayed metals and ceramic substrates. In this paper, the essential factors influencing the bonding strength in such composites are identified. Besides mechanical tensile strength testing, a thorough analysis of the coatings and especially the metal/ceramic interfaces was conducted by means of HRTEM, FFT, STEM, EDX, EELS, XRD and EBSD. The influence of substrate material, substrate temperature and particle size is evaluated with regard to the observed bonding behavior. The results suggest that, apart from mechanical interlocking, the adhesion of cold sprayed metallic coatings on ceramics is based on a complex interplay of different mechanisms such as quasi-adiabatic shearing, static recrystallization as well as heteroepitaxial growth.

Adhesion strength is one of the most important characteristics when discussing the reliability of a cold spray. A focused ion beam (FIB) was used to conduct ultra-micro tensile tests for micro-scale adhesive strength evaluations of high-pressure type cold-sprayed copper deposition on an aluminum substrate. It was also used to determine the essential factor of adhesion strength and the coating formation mechanism. The micro-scale local adhesion strength of cold-sprayed copper deposits on an aluminum substrate was successfully evaluated by FIB microtensile tests. The average local adhesion strength of this deposit was 223 MPa. The variations in adhesion strength between deposit and substrate were smaller than the interfacial strength of cold-sprayed deposits. This was caused by the repeated collision of these subsequent particles.

Measuring the cohesive strength of thermally sprayed coatings is relatively difficult matter, which can be accessed in many directions. This issue is nowadays solved by use of Scratch test method. This method is not completely sufficient for the cohesive strength testing because the coating is under load of combined stresses during the Scratch test. The reason to develop this method was need for exact measurement of tensile cohesion toughness of thermally sprayed coatings, which could provide results as close to a classic tensile test as possible. Another reason for development of this method was the impossibility of direct comparison with results obtained by other methods. Tested coatings were prepared using HP / HVOF (Stellite 6, NiCrBSi, CrC-NiCr and Hastelloy C-276). These coatings were selected as commonly used in commercial sector and on because of rising customer demand for ability to provide such coating characteristics. The tested coatings were evaluated in terms of cohesive strength (method based on tensile strength test). Final fractures were evaluated by scanning electron microscopy and EDS analysis. As expected higher cohesive strength showed metallic coatings with top results of coating Stellite 6. Carbide coatings showed approximately third of the cohesion strength in comparison with metal based coating.

Effect of plasma spraying parameter on the strain of plasma sprayed YSZ coatings is investigated by changing the spraying power and spraying distance. The porosity is measured through using image processing method. The strain of coatings is calculated and characterized through using the digital image correlation (DIC) software system. It can be found that the porosity of YSZ coatings increases with the increment of spraying distance and the decrement of spraying power. The strain on the far field of the cracking tip shows a fluctuation tendency when the tensile forces increase. The slope of strain-force is related with the coating porosity. DIC method can be used to characterize the coating deformation in 2-dimension.

In this study, acoustic emission sensing is used to monitor interfacial cracking in thermal barrier coatings during uniaxial tensile adhesion testing. The TBCs consist of a ZrO 2 topcoat and a NiCrAl bond coat, both of which are applied by atmospheric plasma spraying. Tensile testing was performed to failure and the resulting fracture surfaces were examined by SEM and XRD analysis. Experimental results show that cracks usually initiate in the ceramic layer then propagate toward the metallic-ceramic interface where failure occurs. Finite element simulations were also conducted, confirming the experimental findings.

This work assesses the effects of defects in thermally sprayed chromia via multiscale modeling and imaging techniques. Defect distributions in coating samples are identified by way of image processing and synthetic 3D microstructures are generated from extracted statistical information. The properties of the microstructures are determined by subjecting them to simulated tensile testing, and the significance of different types of defects is evaluated through defect-containing coating models. The approach is able to handle complex defect morphologies, including pore, crack, and splat boundary clusters, making it a versatile tool for assessing the influence of defects on component performance.

This paper describes the development of detonation-sprayed aluminum-matrix composite coatings reinforced with boron carbide. The goal is to achieve a homogeneous coating structure with low porosity, low oxide content, and high concentration of embedded carbides. Tensile tests of various types were conducted and different stages of deformation were analyzed using micro computed tomography, a 3D imaging technique that reveals the formation of cracks in real time.

The adhesion of plasma-sprayed coating is to a large extent controlled by the cleanness and roughness of the surface on which the coating is deposited. So, most of the plasma spray procedures involve surface pretreatment by grit-blasting to adapt the roughness of the surface to the size of the impacting particles. This preparation process brings about compressive stresses that make it inappropriate for thin substrates. The present works aims to elaborate a ceramic coating on a thin metal substrate with a smooth surface. The coating system is intended for use in a generation–IV nuclear energy system. It must exhibit a good adhesion between the ceramic topcoat (about 0.5-mm thick) and the smooth metal substrate (1-mm thick) to meet the specifications of the application. Our approach has consisted in depositing the ceramic layer on a few micrometers thick ceramic layer made by suspension spraying. We have observed the interface between both ceramic layers by transmission electronic microscope and studied the adhesion of the nanostructured layer by the Vickers Indentation Cracking technique and that of the coating system by tensile test.

The pin test and stress analysis by FEM were performed for erosion-resistant thermal sprayed coatings, and characteristic of interfacial strength between sprayed coating and substrate was assessed. As a result, the (Kcr) was not affected with specimen size and uniformly converges in spite of the eccentricity of pin.

In Warm Spraying (WS), the temperature of the combustion flame is reduced and controlled by injecting nitrogen gas into the combustion flame before the injection of spray powders. Thus, temperatures of spray particles are kept under their melting points with moderately heated and thermally softened states. As compared to HVOF-spraying, the oxidation of particles can be significantly suppressed due to lower deposition temperatures, whereas, as compared to cold spraying, the degree of particle deformation upon impact can be enhanced by attaining higher particle temperatures. In the present study, Ti, Cu, and Al coatings were fabricated by WS under various nitrogen flow rates. The mechanical properties of the coatings were evaluated by tubular coating tensile (TCT) and micro flat tensile (MFT) tests. For the lower impact temperature regime, the coatings became denser and the ultimate strengths of Ti or Cu coatings increased reaching a maximum by decreasing the nitrogen flow rates. A further decrease of nitrogen flow rates and reaching the upper temperature regime reduced the coating strength. These results clearly demonstrate how particle temperatures affect the microstructures and mechanical properties of WS coatings and that optimum spray conditions have to be balanced between softening and oxidation by adjusting particle temperatures.

Biomedical Ti-coatings were deposited on Ti-substrates by the microplasma wire spraying method. The influence of different factors of the wire spraying process on sizes of the particles produced as a result of atomisation of the wire melt by the microplasma jet, as well as the deposition efficiency were determined by using multifactorial experimental design. Linear regression models were developed, showing the effect of the most significant process parameters (current, plasma gas flow rate, wire feed speed) on formation of a jet of the spraying Ti-particles, structure and properties of the Ti-coatings. Establishing the possibility of controlling macroporosity of the Ti-coatings in microplasma wire spraying and correspondence of the Ti-coatings bond strength in tensile and shear tests to the ISO 13779-2 and ASTM C633 requirements, as well as data of the Ti-coatings “in-vivo” tests proved the efficiency of using them for manufacture of various-purpose endoprostheses (hip joint, dental, etc.).

The goal of this research group is to homogenize properties of three-cathode plasma sprayed coatings on basis of numerical simulations and advanced diagnostics. Results of the first project phase as well as an outlook to future work are presented. A numerical model for investigation of plasma flow in the free jet, produced by three-cathode torch was developed. Modelling results are verified by plasma diagnostics (Computer Tomography). In order to include particle shrinking effects, coating formation simulation is accomplished by a newly developed model, based on Computational Fluid Dynamics coupled with the Finite Element method, whereat diagnostics carried out in the fields of particle diagnostics. During the next phase of the project, the investigation of the plasma free jet and particle injection by advanced diagnostics and simulation respectively is scheduled. In a subsequent stage the transition from conventional particles to suspensions will be considered. Coating formation simulations are scaled up to dimensions of macroscopic tensile tests. By combining these overarching investigations, appropriate process parameters for homogenized coatings will be obtained.

Cold spraying has a high potential for building up thick coatings or structures, like for rapid prototyping or production of free-standing parts. This method is particularly interesting for high strength materials that are difficult to process or to shape, e.g. Titanium for special applications in aviation industries. In this contribution, the two major challenges are addressed: (I) optimizing mechanical properties by systematic variation of process parameters, and (ii) evaluating the influence of the spray angle with respect to complex geometries as requested by aviation industry. While in the past, high quality titanium coatings were only achieved using Helium as process gas, Nitrogen is used in this study to reduce costs. High deposition efficiencies of more than 95 % can be obtained and the coatings show very low porosities as well as high tensile strength of over 480 MPa. The influence of process conditions on the mechanical properties is discussed on the basis of coating microstructures, Micro Flat Tensile (MFT) and Tubular Coating Tensile tests (TCT-test).

This is the first of two papers concerning the intrinsic mechanical properties of arc-sprayed WC-FeCSiMn coatings. In part 1 the elastic and plastic forming behavior of the layers are investigated by indentation, bending and tensile tests. They were performed on coated mild steel substrates as well as freestanding as-sprayed samples with different geometries. Considering the coatings microstructure, element and pore distribution, as well as the local microhardness the results of the indentation, bending, and tensile tests were evaluated. The critical role of pores and inhomogeneities within the sprayed coating was examined in detail. Micro- and macrocracking were investigated by SEM after the indentation and tensile tests. In-situ surface observation by optical 3D-microscopy was used to study the onset of cracking during the 3-point bending test.

Hydroxyapatite (HA) is preferred for its ability to interact with living bone, resulting in improvements of implant fixation and faster bone healing. In this study, a small amount of silicon dioxide (~ 2wt%) was introduced into HA slurry which was subsequently spray-dried into powder. A silicon modified HA coating was then deposited onto Ti-6Al-4V alloy substrates by atmospheric plasma spraying technology. Scanning electron microscopy (SEM), X-ray diffraction and X-ray photoelectron spectrometry, and Raman spectrometry were employed to investigate the surface chemistry that would directly influence bone forming cell proliferation. Additionally, the adhesive bonding strength of the as-sprayed coatings were specified measured using a universal testing system. The fracture surfaces after tensile test were also investigated by SEM.