Interfacial Indentation Test Research Articles

Quantitative evaluation of interfacial adhesion between steel reinforcements and self-compacting concretes, in steel/concrete composites, by indentation tests

ABSTRACTTo ensure reinforced concrete bars applications in more severe loading conditions, the contact between the steel bar and concrete must be strongly adhesive. This adhesion constitutes an important property for the use of reinforced concrete. That is why many techniques were developed with the aim of determining this property. Adhesion can be easily found out by standard pull-out test machine. However, in this work, the adhesion was measured for the first time using Interfacial Indentation test. In this work, given the lack of results obtained using the interfacial indentation test in the literature so that we can compare our results with, the alone alternative found is to compare them with those of the pull out test. Using reinforcing bars, adhesion was measured using Self Compacting Concrete (SCC) and Normal Vibrated Concrete (NVC) specimens. The impact of water-to-binder ratio variations and concrete type on steel bar/concrete adhesion has been the incentive of the present study. As a main conclusion, interfacial indentation test can be more properly represent the actual steel/concrete interface adhesion compared to the pull-out test which is a more global test.

Interfacial Indentation Test for the Study of Reinforcement bar/concrete matrix Adhesion i n High Performance Self Compacting Concretes

Interfacial Indentation Test for the Study of Reinforcement bar/concrete matrix Adhesion i n High Performance Self Compacting Concretes

Interface bonding of NiCrAlY coating on laser modified H13 tool steel surface

Bonding strength of thermal spray coatings depends on the interfacial adhesion between bond coat and substrate material. In this paper, NiCrAlY (Ni-164/211 Ni22 %Cr10 %Al1.0 %Y) coatings were developed on laser modified H13 tool steel surface using atmospheric plasma spray (APS). Different laser peak power, Pp, and duty cycle, DC, were investigated in order to improve the mechanical properties of H13 tool steel surface. The APS spraying parameters setting for coatings were set constant. The coating microstructure near the interface was analyzed using IM7000 inverted optical microscope. Interface bonding of NiCrAlY was investigated by interfacial indentation test (IIT) method using MMT-X7 Matsuzawa Hardness Tester Machine with Vickers indenter. Diffusion of atoms along NiCrAlY coating, laser modified and substrate layers was investigated by energy-dispersive X-ray spectroscopy (EDXS) using Hitachi Tabletop Microscope TM3030 Plus. Based on IIT method results, average interfacial toughness, Kavg, for reference sample was 2.15 MPa m1/2 compared to sample L1 range of Kavg from 6.02 to 6.96 MPa m1/2 and sample L2 range of Kavg from 2.47 to 3.46 MPa m1/2. Hence, according to Kavg, sample L1 has the highest interface bonding and is being laser modified at lower laser peak power, Pp, and higher duty cycle, DC, prior to coating. The EDXS analysis indicated the presence of Fe in the NiCrAlY coating layer and increased Ni and Cr composition in the laser modified layer. Atomic diffusion occurred in both coating and laser modified layers involved in Fe, Ni and Cr elements. These findings introduce enhancement of coating system by substrate surface modification to allow atomic diffusion.

Effect of Grinding on the Residual Stress and Adhesion Strength of HVOF Thermally Sprayed WC–10Co–4Cr Coating

In carbide cermet coatings, such as WC–Co–Cr, the surface roughness of the sprayed workpiece is much more than the acceptable values for various industrial demands. Thus, the surface of the carbide cermet coatings is to be ground appropriately to obtain suitable surface finish. However, the grinding may change the properties of coating. In this study, effects of the grinding process on the porosity content, residual stress, microhardness, and adhesion and cohesion strength of the high-velocity oxy-fuel WC–10Co–4Cr coatings are investigated. For this purpose, the grinding experiments have been performed on a surface grinder using a diamond wheel (resin bond) under different grinding parameters, such as table feed rate, cutting speed, and depth of cut. The investigations of residual stress state and adhesion properties were carried out using the X-ray diffraction and interfacial indentation test methods, respectively. The results indicated that the coating's porosity content increased after grinding due to the mechanical loading of coating by diamond grits of the grinding wheel. On the other hand, adhesion and cohesion strength and microhardness of the coating were improved after grinding. This can be interpreted by the residual stress state of the coating samples.

Effect of Powder Injection on the Interfacial Fracture Toughness of Plasma-Sprayed Zirconia

Adhesive strength of the plasma-sprayed thermal barrier coating is one of the most important parameters which influence their durability and reliability during service. While many methods exist to measure the adhesive strength, in general, they require cumbersome and time-consuming specimen preparation. Furthermore, considerations of the adhesion strength from the point-of-view of fracture toughness or for that matter, their systematic correlation to both processing variances are limited. Consequently, there is an opportunity to both simplify the measurement procedure and establish correlations among methods and linkages between processing parameters and interfacial fracture toughness. In this paper, we report results on adhesion strength of plasma-sprayed yttria-stabilized zirconia (YSZ) coating on aluminum substrates based on both interfacial indentation test (to measure interfacial fracture toughness) and the modified tensile adhesive test. Carrier gas flow for powder injection into the plasma torch was systematically varied to introduce variances in particle melting with concomitant impact on the measured adhesive strength. The results indicate the correlation between the particle melting index and the measured interfacial fracture toughness.

Plastic Deformation in an Amorphous Ni-P Coating

An experimental and numerical investigation of the hardness and associated plastic deformation in as-deposited and as-annealed nickel-phosphorus (Ni-P) coatings was conducted. In addition to the indentation-deformation behavior, the deformation morphology underneath the indenter was examined. The yield strength extracted from the indentation data is as high as 5.6 GPa, indicating pressure-sensitive plasticity. Results show that the as-deposited Ni-P coating was deformed appreciably through the shear-band mechanism with semicircular and radial shear-band morphologies. From the incremental loading-unloading cyclic experiments, the phenomena on hardening and recovery, which have scarcely been recognized in amorphous materials at room temperature, were observed in the amorphous coating using instrumented nanoindentation. A numerical simulation of the interfacial indentation test between the Ni-P coating and the substrate reveals the pileup and shear bands of the Ni-P coating that were observed during the indentation tests.

Microstructure, Adhesion and Wear of Plasma Sprayed AlSi-SiC Composite Coatings

Al-12.5 wt% Si alloy powder with 15 wt% SiCp was mechanically alloyed (MA) using attrition mill in purified nitrogen atmosphere. The MA processed powder was found to have nano grain size and uniform distribution of SiCp in the AlSi matrix. This MA processed powder was used for atmospheric plasma spraying (APS) for varying distances and currents densities. The coatings obtained were studied by image analyzer, SEM and XRD. Microhardness and wear rate of the coatings were evaluated using Vickers indenter and pin on disk type tribometer, respectively. Adhesion strength of the coatings was measured by interfacial indentation test. The results showed that these coatings have uniform distribution of reinforced SiC particles in the nano crystalline matrix, low porosity (1% - 2%), low wear rates and improved adhe-sion strength. It was also observed that by increasing current density of APS, the adhesive strength increased.

Interfacial indentation test of FeB/Fe2B coatings

The present study uses interfacial indentation testing to estimate the adhesion of the FeB/Fe2B coating formed on the surface of borided AISI 316 steel. This technique creates and propagates a crack along the FeB/Fe2B interface and defines the apparent fracture toughness, which can then be related to the adhesion and mechanical support of the aforementioned interface. The boriding process was performed on the surface of AISI 316 steel by means of the powder-pack method at temperatures of 1123, 1173, 1223 and 1273K with 2, 4, 6, 8 and 10h for each temperature. The Young's modulus for each surface layer was obtained by Knoop microindentation at a constant indentation load. Vickers microindentation fracture technique was used to generate microcracks at the FeB/Fe2B interface with varying indentation loads. The applied load, Young's modulus, hardness, and lateral crack lengths generated from the corners of the indentations, along with the depth of the FeB layer, were used to determine the apparent fracture toughness and adhesion of the FeB/Fe2B interface. The apparent fracture toughness of the FeB/Fe2B interface varied between 3.56 and 4.45MPa m. Finally, the intensity of residual stress at the FeB/Fe2B interface was estimated as a function of the FeB layer thickness.

The adhesion strength and indentation toughness of plasma-sprayed yttria stabilized zirconia coatings

In this work, yttria stabilized zirconia (YSZ) coatings were deposited by atmospheric plasma spray (APS) technique under various powder feed rates and spray distances. The microstructure and phase analysis were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Tensile adhesion test (TAT) and interfacial indentation test (IIT) methods were used to evaluate adhesion of coatings. The effect of spray parameters on the coatings adhesion as well as its toughness was investigated. The obtained results revealed that with increasing powder feed rate and spray distance, adhesion of the coatings reaches to a maximum and then reduces. Interfacial toughness values change in the same manner. Adhesion/toughness behaviors of the YSZ coatings were related to microstructural characteristics including the volume fraction and size of pores and unmelted particles.

The interfacial indentation test to determine adhesion and residual stresses in NiCr VPS coatings

The interfacial indentation test allows determining the interface toughness of a coating obtained by thermal spraying. During this test, a Vickers indentation is carried out on a cross-section of the sample. A crack is initiated and propagated along the interface. An analytical model allows defining an interface toughness representing the coating adhesion. The objective of this study is to compare this test with other tests (tensile adhesive test, shear test) and to specify its applicability. The residual stresses are also estimated by two different methods. Their influence on adherence is discussed in a third part. Those experiments were conducted on NiCr 80-20 VPS coatings with different thicknesses and roughnesses. In particular, it is shown that the interfacial indentation test is the most universal one and that compressive residual stresses improve coating adhesion.

Adhesion tests for thermal spray coatings: correlation of bond strength and interfacial toughness

In this paper, experiments for determining the adhesion properties have been performed using two test methods; tensile adhesive test which is widely used in industry and interfacial indentation test still under development in research laboratories. Therefore, only few experimental data on the accuracy of the methods and on the potential in an industrial context are available. For that reason, dissimilar coating–substrate combinations covering different ranges of type of thermal spray coating–substrate systems were tested. Ceramic (Al2O3) and metallic (80Ni–20Cr) coatings were deposited by flame spraying system with two different thicknesses on titanium alloy and steel substrates exhibiting each two distinct roughness levels. The distinguished coating properties include the interfacial toughness and adhesive strength. The impacts of interfacial roughness and the thickness of the coating on the adhesion were conducted, and some adhesion tendency was also observed. Typical bond strength values measured were from 40 up to 100 MPa, and the interfacial toughness obtained from 1 to 4 MPa m0·5. The correlation of tensile adhesive strength and interfacial toughness has been discussed.

Interfacial indentation test and adhesive fracture characteristics of plasma sprayed cermet Cr 3C 2/Ni–Cr coatings

Thermal spraying is often used to create coatings protecting parts against physico-chemical aggressions or improving superficial mechanical properties. It involves several problems because of the high temperatures of the process: cracks, porosity, coating adhesion. The authors use Vickers interfacial indentation test to characterize adhesive fracture between substrates and coatings. From the Lawn’s relation two curves: load/crack length ratio ( P/C 3/2) vs crack length ( C 1/2) and ln P vs ln C are drawn for varying loads. They allow the determination of the type of residual stress, a coating fracture “toughness”/residual stress ratio ( K C/ σ r) characterizing interfacial behavior and may lead, in some cases, to residual stress σ r. Influence of superficial remelting by CO 2 laser of cermet coating Cr 3C 2/Ni–Cr deposited on NiCrAlY covered steel and of annealing of Cr 3C 2/Ni–Cr coated cast iron are then studied. Possibility of reducing residual stress is shown at the same time as the interest of both approaches.

Interfacial indentation and shear tests to determine the adhesion of thermal spray coatings

Adhesion is one of the most important parameters which influences the development of thermal spray coatings. Therefore, the level of adhesion should be known for a given application. Apart from the standardized Tensile Adhesive Test (TAT), more than 80 methods are reported to measure the coating adhesion. Most of them are energy consuming in terms of time, cost and equipment. Moreover, they do not fulfil the necessary requirements of accuracy, confidence and representation of the real delamination process observed in service. To address this problem, the interfacial indentation test is used here to initiate and propagate a crack at the interface between the substrate and the coating. Studying the extension of the crack, an interfacial toughness is defined and deduced analytically from the experimental results. The new shear test, developed in the frame of the EU-CRAFT-project “Shear Test for Thermally Sprayed Coatings”, is also employed to assess the coating adhesion. Both tests are compared to the standardized TAT for various spraying systems, materials, substrate roughness and coating thickness. Advantages and disadvantages of the three tests are discussed. Correlations between the tests results obtained for different coating–substrate combinations are presented and general trends are described.

A numerical fracture analysis of a stationary semi-circular interface crack during interfacial indentation test

The aim of this work is to investigate the fracture behavior of a stationary crack lying along the interface in a coated system during interfacial indentation test. One traditional 3D numerical model and one cohesive element numerical model have been made to study the Vickers indentation test process. A crack-block approach is applied to generate 3D meshes containing the crack front along the interface. The stress intensity factors and the energy release rates ( G) on the crack front are computed. The fracture mode mixity is also presented. It is found that the near surface propagation of the crack can be prevented during loading due to compressive stresses. It may occur during unloading due to residual stresses resulting from plastic strain.

Adhesion Evaluation of Plasma Sprayed Coatings Using Piecewise Linear Regression Analysis

The critical load for adhesion of 75%WC-Co + 25%Ni alloy plasma sprayed coatings was evaluated by an interfacial indentation test. A statistical analysis—piecewise linear regression—was used to estimate the critical load PC and its confidence interval. It was determined that a post heat treatment increases the practical adhesion load of plasma sprayed coatings. This increase was attributed to interdiffusion mechanisms verified at the interface between the coating and substrate.

Optimisation d’un revêtement cermet Ni-Cr/Cr3C2 par refusion laser superficielle

Plasma spraying is often used to create coatings protecting parts against physical and chemical agression or improving superficial mechanical properties. The projection of ceramic or cermet coatings involves several problems because of the high temperatures of the process : cracks, porosity, coating adhesion, residual stress.The authors study the optimization of cermet coating Cr3 C2 /Ni-Cr (deposited on NiCrAlY covered steel) using a superficial remelting by laser. The treatment is realized under nitrogen as protection gas (pressure: 0.4 bar) with a CO2 non focused laser beam (diameter: 0.8 mm). The variable parameters are the laser power (80-410 W), the scanning velocity (0.5-7 m/min) and the overlap rate (0-100%). The microstructural and the mechanical studies are consistent and clarify the influence of the treatment parameters.It is shown that the cermet microstructure is refined and homogenized by the laser treatment. The cracks and porosity are reduced. There is not any segregation phenomenon.The scanning velocity acts upon the coating hardness and leads to a hardness gradient increasing with the velocity value. The final coating thickness depends too on the velocity.The adhesion between steel and coating is determined by interfacial indentation test; the decohesion occurs at cermet / NiCrAlY interface. A coating fracture toughness / residual stress ratio (K1C /σr ) is introduced. It is characteristic of the interfacial behaviour and it allows treatments grading. The residual (tensile) stress is never relaxed.The optimum laser treatments in that study are: medium laser power (212 W), medium overlap rate (50%). The scanning velocity depends on the desired hardness or mechanical properties.