Thick deposits were produced from pure Al powder of three different sieve sizes using cold spraying at the same process parameters. The in-plane mechanical and fracture properties of the deposits were investigated using bending of small specimens in four specimen orientations. It was shown that increasing the Al particle size by approximately 50% and 100% leads to small, but statistically significant differences of yield strength. Further, the increase in the powder particle size led to higher fracture toughness K IC but lower fatigue crack growth threshold ΔK thr . This can be attributed to two different fracture mechanisms in the cold sprayed deposits. A trans-particular fracture in the near-threshold fatigue regime is controlled by the microstructure and work hardening of the particles. At higher cyclic loads and in quasi-static regime, the particle decohesion and the resulting crack path determine the fracture behavior instead. However, the observed effect of particle size was rather small, much smaller than the effect of spray process parameters observed in the previous research.

Anisotropy of stress-strain behavior, fracture toughness, and fatigue crack growth rate was studied for Inconel 738LC alloy built by the Dynamic Metal Deposition technique (3DMD, a high-speed Directed Energy Deposition technique). The measured quasi-static properties, i.e. stress-strain and fracture toughness showed only subtle anisotropy, with no more than 10% differences found for different orientations. The fatigue crack growth rate was influenced by the specimen orientation more significantly (30% for fatigue crack growth threshold, up to 90% for Paris exponent and coefficient). This pilot study attributes the anisotropy of fatigue crack growth properties to material texture and the columnar grain geometry resulting from directional solidification. The obtained testing results indicate that 3DMD technology can produce materials with good mechanical and fracture properties even from materials considered as non-weldable such as In 738LC. The study provides a solid experimental base for further investigation of the fatigue crack growth mechanism relation to the material texture in 3DMD In 738LC.

The aim of this work is to study the effects of the titanium plasma spray (TPS) coating process on the fatigue resistance of a titanium-6Al-4V substrate. The combination of TPS processes and Ti alloy substrate is widely applied on components intended for cementless total hip replacement (THR). In order to understand the coating process mechanism behind the implants’ fatigue resistance decrease, one air-developed coating (Ti-APS) and one controlled atmosphere developed coating (Ti-CAPS) were considered. The effects of the most representative parameters of the plasma spray process on the fatigue resistance were analysed: the sandblasting process, the plasma and the coating powder. Fatigue resistance studies were performed by means of rotating bending fatigue testing. After fatigue failure specimens underwent morphological analyses both on the primary crack surface and on the cross-sectional area complemented by of the metallographic analyses of the coating. The titanium substrate fatigue resistance decreased after being blasted with direct relationship with the grain size. Ti-CAPS process showed a relatively limited further influence on the fatigue resistance reduction with respect to only sandblasted samples. By contrary a remarkable fatigue limit decreased was seen for Ti-APS coated samples against Ti-CAPS and simply sandblasted samples. The experiment pointed out the critical importance of cracks oxidation as a fatigue failure driving factor.

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.

Tungsten heavy alloy (WHA) of W-Ni composition was deposited from a blend of standard thermal spray powders using a radio frequency inductively coupled plasma torch in a protective atmosphere. The coating contained a fully developed WHA structure, i.e., spherical W particles embedded in a Ni-rich matrix. Bending tensile strength R m , bending yield strength R p,0.2 , and elastic modulus were measured and compared with W-Ni-Co references fabricated by sintered and quenched (SQ) and forged and annealed (FA) powder metallurgy (PM) processes. The fatigue and fracture properties of the plasma spray deposits are comparable with those of the SQ-PM reference material, but inferior to those of the FA-PM reference. The results of various property tests are presented and analyzed in the paper.

Fatigue crack growth in self-standing plasma sprayed tungsten and molybdenum beams with artificially introduced notches subjected to pure bending was studied. Beams width, thickness and length was 4 mm, 3 mm and 32 mm respectively. Fatigue crack length was measured using the differential compliance method and fatigue crack growth rate was established as a function of stress intensity factor. Unusual crack opening under compressive loading part of the cycle was detected. Fractographic analysis revealed the respective crack formation mechanisms. At low crack propagation rates, the fatigue crack growth takes place by intergranular splat fracture and splat decohesion for Mo coating. In W coating, intergranular splat fracture and void interconnection formed the fatigue crack. Frequently, the crack deflected from the notch plane being attracted to stress concentrators formed by porosity. At higher values of the stress intensity factor, the splat intergranular cracking become more common and the crack propagated more perpendicularly to the specimen surface.

Cold spray is a technology with great potential for additive manufacturing applications. Due to the high levels of plastic deformation experienced by the powder during the coating process, any deposit will require heat treatment post-spraying to improve ductility and fatigue strength. In extreme cases, the residual stresses from coating can cause delamination or compromise the bond strength when subsequent cold spray layers are deposited. This work details the use of a commercial CO 2 laser cutter to perform a surface heat treatment on single lines of cold sprayed aluminium, to relieve residual stresses. The effect of laser power and traverse speed on material hardness is quantified, and compared with as sprayed deposits. The results shown in this work demonstrate the potential for in-process heat treatment to reduce post-processing time and improve coating quality by reducing residual stresses.

In this study, pure Al coatings were deposited on ZK60-T5 Mg alloy substrates via in-situ shot-peening assisted cold spray in order to study the effect of the Al coating on fatigue behavior of coated samples. Fatigue behavior of the coated and un-coated samples has been investigated through experimental tests. The size and shape distribution of powders, microstructural characteristics of coatings and fractography of fatigue test samples have been studied using scanning electron microscopy. The average microhardness of pure Al coating is higher than 70 HV50. In order to obtain the fatigue S-N diagram for each set, coated and un-coated samples have been tested in a load-controlled condition. The tension-compression fatigue experiments reveal that the fatigue property of ZK60-T5 alloy coated with pure Al coatings has significantly deteriorated compared with un-coated samples.

Our previous experiments with low-cost steel substrates confirmed that individual steps of conventional thermal barrier coating (TBC) deposition may influence fatigue properties of the coated samples differently. In this study, testing was carried out for TBC samples deposited on industrially more relevant Hastelloy X substrates. Samples were tested after each step of TBC deposition process: as-received (non-coated), grit-blasted, bond-coated (NiCoCrAlY) and bondcoated + top-coated (yttria-stabilized zirconia - YSZ). Conventional atmospheric plasma spraying (APS) with gas stabilized plasma torch was used for deposition of both bond coat and top coat. In addition, for one half of the samples, bond coat was prepared by consecutive combination of HVAF (High Velocity Air Fuel) and APS processes. Samples were tested both in as-sprayed condition and after 100 hours annealing at 980 °C, which simulated in-service conditions. Obtained results showed that different fatigue performance may be expected for various stages of the TBC deposition as well as due to the variation of the deposition process and sample temperature history.

Automotive, aerospace, and energy applications demand for reliable coating systems to enhance the operating efficiency and the lifetime of processes, machines, and components. HVOF sprayed WC-CoCr coatings are commonly used, especially for wear resistant applications. Due to their high hardness and adapted corrosion resistance WC-CoCr coatings show perfect preconditions for highly stressed tribological systems. However, dynamic loads, caused by vibrations, alternating temperatures or cycling are challenging issues. Fatigue cracking and delamination can occur, resulting in fatal damage of the coated component. Therefore, crack and fatigue resistant high performance coatings are needed. In this research work, the influence of the substrate pre- and post-treatment (grit-blasting and micro-finishing) on the fatigue behavior of warm sprayed WC-CoCr is investigated. It was determined that the fatigue behavior of the applied coating can be improved by micro-finishing. The smooth surface structure results in a low interface roughness. This significantly reduces notching effects under load and enhances the fatigue strength of the specimen.

A390 alloy is a hypereutectic aluminum alloy with attractive mechanical properties at high temperature, good wear resistance and appropriate thermal properties making it challenging candidate material for automotive and aerospace applications. Currently, this alloy is widely used in automotive industry engine components production. In case of engine blocks, fatigue strength and wear resistance are the main cause of failure. Generally, the surface properties of aluminum alloys, in particular as hardness and wear resistance concerns, are insufficient to fulfill some requirements. Nowadays, there is an increasing interest toward the study and the development of innovative protective coatings suitable to enhance the wear resistance of such alloys. The goal of this paper is to develop appropriate protective coatings for A390 aluminum alloy enhancing its wear resistance. The study has been carried out to characterize the morphological, mechanical and wear resistance properties.

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.

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.

Surface state plays an important role in particle bonding and formation of the first layer of coatings in thermal spraying. From a chemical aspect as well as a mechanical point of view, in all cases, the substrate surface needs to be optimized to promote the adhesion of the sprayed particles and then the coating. In order to control such parameters, several works have been conducted to avoid drawbacks on sensitive materials. This study aims at developing a laser surface texturation before the spraying process to improve the coating adherence. According to the laser parameters, different surface morphologies (hole diameters, surface roughness, hole depth, etc.) can be developed. The surface material morphologies were characterised by SEM and bond strength was evaluated through ASTM C633 pull tests. This approach has been applied on the system Al 2017 / NiAl and demonstrates a high influence of the laser treatment. However, the thermal effect induced during the laser-matter interaction has to be controlled to avoid negative effects of the substrate properties particularly tribological properties. In this case, a study of the effect of the conventional processes and texturing process on the fatigue properties of substrate were studied.

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.

In this paper, as part of a systematic study on the rolling contact fatigue of HVOF-sprayed hardmetal coatings, the behavior of WC-17%Co coatings on hardened and nonhardened substrates is compared. To obtain a meaningful assessment, the coatings were applied to roller specimens made from soft as well as case-hardened MnCr steel. Two coating thicknesses were used with the expectation that maximum stress will occur in the substrate, in one case, and in the other case, in the coating. Test results show that the durability of HVOF-sprayed WC-Co is significantly better on nonhardened (soft) substrates and that the limiting factor for endurable Hertz pressure is the fatigue strength of the coating.

Nanostructured and conventional Alumina–13wt.% Titania powders were thermally sprayed using air plasma spray(APS) process. Scanning electron microscopy (SEM) was used to examine the morphology of the agglomerated powders and the cross section of the alumina-titania coatings. The microstructure and phase composition of the coatings were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM).The fatigue and mechanical properties of the coatings were investigated. SEM analyses were also carried out on the fracture surfaces of fatigue-tested samples to assess the mechanisms of deformations. The experimental data indicated that the nanostructured coated samples exhibited higher stiffness, hardness, and fatigue strength compared to the conventional coated samples.

Air plasma sprayed thermal barrier coatings, which reduce the temperature in the underlying substrate material, are an essential requirement for the hot section components of an industrial gas turbine. For TBC systems, the adherence of the top coating is one of the most important parameter for the durability of TBC system. In this work, the thermal fatigue behaviour of an air plasma sprayed thermal barrier coating was investigated. In addition, the residual interfacial strength was also evaluated by means of the 4-point bending test. From the measurement of the AE signals during the thermal fatigue tests, micro-cracking occurred in each cooling stage of the thermal fatigue cycles and then such damage depends on the number of thermal cycle. In addition, TGO grew at the interface with the exposed time at elevated temperature (the time dependent damage). Thermal barrier coating undergoes both time dependent damage and cycle dependent one under thermal fatigue condition. The life of thermal cycle with high temperature dwell time is shorter than not only that of isothermal exposure but also that of thermal cycle without dwell time.

Gas atomized feedstock particles of an Al-13Co-26Ce alloy system were sprayed using the Cold Spray deposition technique. The microstructures of the coatings produced are examined and the mechanical characteristics, in particular the bending fatigue and the bond strength, of the Al-Co-Ce coatings are reported. The results show that the Al-Co-Ce coating improved the fatigue behavior of AA 2024-T3 specimens when compared to uncoated and Al clad specimens. During the bond strength tests, the bonding agent failed and no delamination of the coating from the substrate occurred. The microstructural features of the feedstock powder were also found in the coatings. The coatings contained amorphous and crystalline phase contents similar to the ones found in the feedstock powder. It is suggested that the increase in the fatigue properties can be attributed to the residual compressive stresses induced in the coatings and to the high adhesion strength of the coatings to the substrates.