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.

In this work the Brazilian disc test technique is applied to mechanical characterization of cold-sprayed Cu-In-Ga deposits. The main advantage of the test is that the material can be tested in its end product form while naturally attending to the distribution of micro-structural phases and flaws by choosing an appropriate specimen size. The stress state of the test specimen can be obtained in analytical closed form and testing can be readily extended to obtain the stress-strain curve. While limited to low ductility materials the Brazilian disc test appears ideal for testing as-sprayed cold spray deposits due to their typically brittle nature.

This study investigates the mechanical response of plasma-sprayed ceramic coatings to different levels of mechanical and thermal loading. Test samples were subjected to four-point bending and thermal cycling loads. Nonlinear behavior and significant hysteresis were observed, indicative of inelastic phenomena. Previous tests were complemented by structural examinations and bonded-interface testing. Relevant structural features and possible mechanisms underlying this behavior are discussed.

Instrumented indentation is well-suited as a technique for probing mechanical behaviour of coatings; it requires minimal specimen preparation, can be performed multiple times on a single specimen, and can measure behaviour over various length scales, by recourse to appropriate indenter tip selection. However, the complex nature of the deformation fields under the tip, coupled with complex (e.g. anisotropy, nonlinearity) coating properties necessitates robust means of interpretation in order to extract stress-strain behaviour. Here we present a simple method, based on empirical work by Tabor, for converting coating indentation force-depth data to stress-strain curves. Using this method, results of indentation can thus be used to quantify mechanical behaviour of coatings deposited by different processes, and subjected to post-processing treatments, providing a powerful supplement to microstructural characterization. In addition, we show how anisotropic elasticity of coatings, measured via indentation, can qualitatively identify the existence of different microstructual features. Finally, we explore subsurface strain mapping as a technique to quantitatively compare elastoplastic behaviour of coatings to bulk, isotropic materials.

It is very important to clarify the characteristic deformation behaviors of thermal barrier coatings. Monotonic and cyclic deformation behaviors of thermal barrier coatings under uniaxial compressive loading were examined. Specimens of plasma-sprayed ZrO 2 -8%Y 2 O 3 and CoNiCrAlY were fabricated to test the coating materials independent of the substrates. The specimen was fabricated by dissolving out the substrate only at the region of gauge length. Thicknesses of the coatings were 300 μm. The stress-strain response was measured using the laser speckle strain / displacement gauge (SSDG). ZrO 2 -8%Y 2 O 3 coating showed the nonlinear stress-strain response with a considerably lower elastic modulus which value was about 10% of sintering ceramics. The coating was found to leave permanent strain by compressive loading: the compliance of the coating decreased by compressive loading. The compliance was also found to decrease furthermore by undergoing cyclic compressive load. On the contrary, CoNiCrAlY coating deposited by low pressure plasma spraying was found to show the stress-strain response with insignificant nonlinearity. The compliance of the stress-strain curve didn’t also decrease with increasing the number of compressive stress cycles. It was found that coating with many defects and pores showed stress-strain response with large nonlinearity.

This paper investigates the effect of HVOF thermally sprayed WC-Co coatings on the cyclic deformation of the aluminum alloy 2024-T4 and the steel SAE 12L14. Strain gages are glued on the specimen surface to measure the strain response after certain intervals of fatigue cycles. The strain is also measured during the fatigue test. A calibrated beam is used to apply the bending moment and the stress calculated using the flexural formula. The stress-strain curves for uncycled and cycled specimens are determined. The dynamic strains for the coated and uncoated specimens are also monitored during the fatigue test. Paper includes a German-language abstract.

Mechanical properties of WC-Co D-Gun coatings produced from various powders were determined by using a four-point bend test equipped with a special device for strain measurements. The MOR(Modulus of Rupture), elastic modulus, fracture strain and toughness were measured from stress-strain curves using the four-point bend tests. The fracture strength values were increased in the order of clad, sintered, agglomerated(no densification), blended and cast & crushed powder coatings. The Co content blended with WC-Co cermet powders significantly increased fracture strain values and decreased elastic modulus values. It was found that the type of powder more significantly influenced the mechanical properties of D-Gun coatings than the composition of powders. The toughness of thermal spray coatings was increased by using WC-Co powders (high MOR) blended with self-fluxing alloy powders (high fracture strain).