Substrate Specimens Research Articles

Very low pressure plasma sprayed yttria-stabilized zirconia coating using a low-energy plasma gun

In the present study, a more economical low-energy plasma source was used to perform a very low pressure plasma-spray (VLPPS) process. The plasma-jet properties were analyzed by means of optical emission spectroscopy (OES). Moreover, yttria-stabilized zirconia coating (YSZ) was elaborated by a F100 low-power plasma gun under working pressure of 1 mbar, and the substrate specimens were partially shadowed by a baffle-plate during plasma spraying for obtaining different coating microstructures. Based on the SEM observation, a column-like grain coating was deposited by pure vapor deposition at the shadowed region, whereas, in the unshadowed region, the coating exhibited a binary microstructure which was formed by a mixed deposition of melted particles and evaporated particles. The mechanical properties of the coating were also well under investigation.

Microstructural evolution and mechanical, and corrosion property evaluation of Cu–30Ni alloy formed by Direct Metal Deposition process

In the current investigation Cu–30Ni alloy was successfully laser deposited on a rolled C71500 plate substrate by Direct Metal Deposition technology. The microstructural investigation of the clad was performed using optical and scanning electron microscopy. The phase and crystal structure analysis was performed using X-ray diffraction technique and transmission electron microscopy. The microstructure consisted of columnar and equiaxed dendrites with face centered cubic crystal structure. The dendrites grew epitaxially from the substrate and layer and bead boundaries. Dendrites’ growth direction 〈0 0 1〉 and growth angle 60° was maintained in each layer. The average primary dendritic arm spacing at the bottom part of the layers was about 7.5 μm and average secondary dendritic arm spacing in the upper part of the layer varied between 2 μm and 4.5 μm. The lattice parameter of the identified phase was found to be longer than that reported in literature. The reported lattice parameters in literature are however from samples processed under equilibrium conditions. The microhardness of the clad was found to be less than the substrate but very consistent along the clad. Cu–30Ni clad specimen showed higher ultimate tensile strength but lower yield strength and percentage elongation as compared to the C71500 substrate. DMD Cu–30Ni clad/C71500 substrate specimen showed the worst mechanical properties. The corrosion resistance of the specimens was found to decrease in the order DMD Cu–30Ni clad, half-and-half DMD Cu–30Ni clad-C71500 substrate, and C71500 substrate.

Vibrational Characteristics and Young's Modulus of Stainless Steel Sheets Coated with some Inorganic Films

Young's modulus of coat films has been estimated by using the double-beam vibration-reed method. The 18-8 stainless steel (SUS304; JIS) sheets coated by some inorganic films were prepared by using the sputtering and CVD. The method are applied to estimate the modulus by using the fundamental mode resonant frequencies of coated substrate before and after deposition of the films. The resonant frequency of each sample was measured by shaking the sample, and the displacement response detected by the eddy current displacement sensor. The specimens include non-coated stainless, TiO2, CrN, TiN, and diamond-like carbon(DLC) coated sheets. The thickness of the coat films range from 0.4 to 3.5. The non-coated substrate specimen requires an adequate annealing corresponding to the thermal history of the film deposition. The measured resonant frequencies have some amplitude dependencies, therefore the frequencies were extrapolated to zero amplitude. The extrapolated frequencies, the modulus of the annealed substrate, density and the geometrical parameters were assigned to the formula of the resonant frequency for the double-beam. The measured modulus of SUS304 substrate, TiO2 and TiN films are smaller than bulk form. The measured modulus for the CrN film is larger than the one form the literature data. The modulus of DLC film falls onto the range of literatures.

Method of Estimated Unloading Curve for Evaluation of Interfacial Strength by Nanoindentation Test

A new evaluation method was proposed for the interfacial strength between a thin film and its substrate by nanoindenation test. In this method, the released energy due to a coating delamination is obtained by estimating the shapes of the unloading curve at the points just after and before delamination on the load-displacement curve. Shape of unloading curves can be assumed by obtaining the contact stiffness of thin films. To confirm the validity of the method, nanoindentation tests were conducted for polyimide (PI) coating / Si substrate specimens and the interfacial strength was evaluated. Three specimens that have different thickness were prepared. Contact stiffness of PI film bears a linear relationship with indentation load. Irrespective of the coating thickness, the values of the interfacial strengths converge. In addition, the values of strengths agree with the results obtained by the authors in the previous paper for the case that small scale yielding conditions are satisfied. For the case that indentation loading rate is high and the delamination occurs before the relaxation of film, it is necessary to measure the contact stiffness with each indentation loading rate.

A Study on Effect of Friction Coefficient on Failure Process of Film

Titanium substrate specimen was sputter-coated with SiC or CoCrNi-oxide thin film and the wear test was carried out by using a “ball-on-disk” testing machine. The semi-circular parallel cracks appeared on the film surface with the angles of 45 degree to the sliding direction of SiC ball and the delamination of film quickly occurred after cracking. In the same study we have discussed the reason of cracking and delamination in film by FEM [1], and made a special effort to the effect of friction coefficient on failure process of film in this paper. With the increase in friction coefficient the high-stress area of the maximum principal stress σ1 has the trend to move towards the central trail of back-contact-edge, while the positive minimum principal stress σ3 also appears at more extensive range, the higher friction coefficient causes the higher stresses and makes the cracking and delamination more easily, where the cracks can be initiated much more near the center trail.

Effect of thick DLC coating on fatigue behaviour of magnesium alloy in laboratory air and demineralised water

ABSTRACTRotating bending fatigue tests have been performed using Diamond‐like carbon (DLC) coated specimens of a wrought magnesium alloy, AZ80A, in laboratory air and demineralised water and the effect of DLC coating on fatigue and corrosion fatigue behaviour was studied. Three film thicknesses of 3.5 μm, 13 μm, and 25 μm (two‐layer film) were evaluated and particular attention was paid to the role of thick DLC coating. In laboratory air, the fatigue strengths of the DLC‐coated specimens were higher than that of the substrate specimen and increased with increasing film thickness. This was because hard DLC coating with good adhesion suppressed the crack initiation due to cracking of inclusions or cyclic slip deformation on the substrate surface. In demineralised water, the fatigue strength of the 3.5‐μm DLC‐coated specimen was the same as that of the substrate specimen due to the penetration of the water through pre‐existing film defects, while the 13‐μm and 25‐μm DLC‐coated specimens showed increased corrosion fatigue strength with increasing film thickness and also exhibited nearly the same fatigue strength as in laboratory air except for a few premature failed specimens, indicating a potential of thick DLC coating or two‐layer coating for complete improvement of corrosion fatigue strength in aqueous environments.

Underlayer dependence of microtexture, microstructure and magnetic properties of c-axis oriented strontium ferrite thin films

Strontium ferrite (SrM) thin films were prepared by dc magnetron sputtering system on thermally oxidized silicon wafer (SiO 2/Si), single-crystal sapphire with (00 l) orientation and single-crystal MgO with (111) orientation and the effect of Au and Pt underlayers on morphology and magnetic properties was studied. Experimental results revealed that with the application of underlayers, the crystallization temperature of SrM was reduced. Strontium ferrite thin films with uniaxial anisotropy were formed on all substrate specimens. Comparison of the results obtained on all thin films indicated that the maximum saturation magnetization and coercivity in the perpendicular direction were 0.377 T and 0.382 MAm − 1 , respectively, for thin films with Au underlayer and SiO 2/Si substrate.

Microstructure and oxidation resistance of magnetron-sputtered nanocrystalline NiCoCrAlY coatings on nickel-based superalloy

Nanocrystalline NiCoCrAlY coatings on GH3128 nickel-based superalloy were produced using DC magnetron sputter deposition with a composite target. The microstructure and morphology of coatings were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX) and atomic force microscopy (AFM). Isothermal-oxidation tests were performed at 1100 °C in air for 24 h. The results show that the magnetron-sputtered NiCoCrAlY coating possesses a polycrystalline austenitic structure (FCC) with lattice constant 0.359821 nm. The (2 2 0) is the preferred growth direction of the NiCoCrAlY coating and the coating grain size is about 70 nm. The isothermal-oxidation test results exhibit that the oxidation kinetics of substrate and coating specimens all basically follow the parabolic rate law. However, the weight gain rate constant of coating is only about one-fifth of that of substrate. The weight gain of NiCoCrAlY coated specimen is only 48.16% of the superalloy substrate specimen after the isothermal-oxidation test. The above results reveal that the magnetron-sputtered nanocrystalline NiCoCrAlY coating is quite effective to increase the high temperature oxidation resistance of GH3128 superalloy.

Microstructure and Properties of Active Screen Plasma Nitrided Duplex Stainless Steel

UNS S31803 duplex stainless steel (DSS) was nitrided using the active screen plasma nitriding (ASPN) technique at temperature ranging from 400 to 450°C. Microstructures and corrosion properties of the untreated substrate and AS plasma nitrided specimens were analyzed by means of X-ray diffractometry, scanning electron microscopy, microhardness measurement, anodic polarization test, and wear test using a ring-on-disc tester. The result shows that ASPN specimen surface nitrided at 420°C consisted of a dual phase nitrided layer of nitrogen expanded austenite (γN or S-phase) and expanded ferrite (αN), which considerably improved the hardness, wear, and corrosion property of the UNS S31803 duplex stainless steel. For ASPN specimens nitrided at 435°C or 450°C, precipitated nitrides of Fe3N, Fe4N and chromium nitride (CrN) appeared in the nitrided layer. The results showed that the wear and corrosion resistance of the specimen nitrided at 420°C for 10 h were exceedingly improved, and the specimen exhibited the least wear mass loss and corrosion current density.

Film Thickness Dependency of Interfacial Strength Evaluation for Thin Film Coating Structure by Nanoindentation Method

Nanoindentation tests were conducted for polyimide (PI) coating / Si substrate specimens and the energy release rates were evaluated as the interfacial strength. The energy release rate due to coating delamination was obtained from the load-displacement curve by the method proposed by Omiya et al. Three specimens that have different thickness and another kind of specimen which is the same as the thinnest coating but with an additional layer were prepared. The dependencies on the coating thickness and delamination propagation rate were investigated. The interfacial strength of the only thinnest coating case is underestimated, since small scale yielding conditions were not satisfied. The value of the interfacial strength between PI coating and Si substrate increases with increasing of the delamination propagation rate. The value becomes constant when the delamination propagation rate exceeds around 7.0×10-3 mm/s. By considering the unloading curve, the corrected evaluation method for interfacial strength was proposed. The interfacial strength evaluated by the corrected method converge for all specimens cases.

A Very Simple Method for Quickly Making Large Numbers of Measurements on Micrographs

Abstract It has been in the back of my mind to write this up for MT since I retired from a certain large computer company. Inasmuch as Paul's article above is a perfect lead-in, there is no time like the present. Our lab supported a semiconductor integrated circuit and a ceramic substrate manufacturing facility. We were continually required to measure circuit line widths on plan-view specimens and layer thicknesses on cross-section specimens for both semiconductor and ceramic substrate specimens and we were often asked to determine thin film grain size and ceramic raw material particle size data. A large number of measurements were required for each specimen to guarantee statistically sound data. We had image analysis software available that we used whenever we could, but often found that measuring things on a system using grey-level image analysis as input simply did not work. This is especially true for thin film grain size determination when using diffraction contrast TEM images for input.

Measuring metal substrate roughness with glow discharge optical emission spectrometry

AbstractAlthough there are many methods to evaluate metal surface roughness, it is difficult to detect the substrate roughness of coated samples. Depth profile analysis (DPA) is proposed as a new method for the substrate roughness measurement, and glow discharge optical emission spectrometry (GDOES) becomes a candidate in substrate roughness measuring instruments. With this method, the typical roughness parameters Ra (arithmetic mean of the absolute deviation values of the roughness profile) and Ry (maximum value of consecutive peak and valley heights of the roughness profile along the sampling length) can be easily obtained. The principle of this method is discussed and the formulasof the principle are deducted in this paper. Electrodeposited zinc coating on copper substrate specimens is used as an example to explain the measuring process. Copyright © 2007 John Wiley & Sons, Ltd.

Effect of a laser pre-quenched steel substrate surface on the crack driving force in a coating–steel substrate system

A mechanical model of a coating/laser pre-quenched steel substrate specimen with a crack oriented perpendicular to the interface between the coating and the hardened layer is developed to quantify the effects of the residual stress and hardness gradient on the crack driving force in terms of the J-integral. It is assumed that the crack tip is in the middle of the hardened layer of the pre-quenched steel substrate. Using a composite double cantilever beam model, analytical solutions can be derived, and these can be used to quantify the effects of the residual stress and the hardness gradient resulting from the pre-quenched steel substrate surface on the crack driving force. A numerical example is presented to investigate how the residual compressive stress, the coefficient linking microhardness and yield strength and the Young’s modulus ratio of the hardened layer to the coating influence the crack driving force for a given crack length.

Characterization of fretting wear behavior of Cu–Al coating on Ti–6Al–4V substrate

Fretting wear and fretting fatigue are two commonly observed material damages when two contacting bodies with a clamping load are under the oscillatory motion. In this study, fretting wear damage of Cu–Al coating on titanium alloy, Ti–6Al–4V substrate was investigated using the dissipated energy approach. Fretting tests were conducted with either no fatigue load or the maximum fatigue load of 300 MPa and stress ratio of 0.1 on the substrate (specimen). In order to investigate the effect of contact load and contact size, different pad sizes and contact loads were used in the tests. Accumulated dissipated energy versus wear volume data showed a linear relationship regardless of fatigue loading condition on specimen with the smaller pad size. However, two separate linear relationships were observed based on the fatigue loading condition with the larger pad size, such that a relatively more dissipated energy was required for a certain amount of wear with fatigue load on the specimen. The linear relationship between the accumulated dissipated energy and wear volume for both pad sizes extended from partial to gross slip regimes and was not affected by the applied contact load. Further, fretting tests with and without fatigue load resulted in different shapes of fretting loops when the larger pad size was used.

P055 極薄板SUS304鋼の疲労き裂進展特性に及ぼすTiNコーティングの影響(フェロー賞表彰対象ポスターセッション)

The objectives of this study are to examine the influence of coating on the characteristic of fatigue crack growth of the ultra thin sheet of austenite stainless steel SUS304. The side edge notched specimens with thickness of 0.05 mm were fatigue tested under constant tension-tension loading condition after the surface of specimens were coated with sputtered TiN film of 2.0 μm thick using various bias voltages V_B. Two kinds of SUS304 with rolling or with annealing were used as a tested material. The main conclusions are the following. The da/dN-ΔK relationships of coating specimen were affected by the stress condition, da/dN on high stress conditions were larger than that of the substrate specimen, but da/dN on low stress conditions were smaller than that of substrate specimen independent of the tested material. The influences of V_B on the da/dN-ΔK relationships were a little observed.

Evaluation of Adhesive Strength of Thermal-Sprayed Hydroxyapatite Coatings Using the LAser Shock Adhesion Test (LASAT)

The adhesive strength between a coating and a substrate is an important factor that characterizes the quality of thermally sprayed Hydroxyapatite (HA) coatings such as those for biomedical applications. In this study adhesive strength was evaluated by the LAser Shock Adhesion Test (LASAT) technique. LASAT was developed to be suitable for determining the coating-substrate adhesion. This study deals with hydroxyapatite coatings on Ti-based alloy substrate produced by atmospheric plasma spraying. In order to discuss the influence of the spray condition on adhesive strength, different types of specimens, i.e. from various powder feed rate spraying and different surface roughness, were LASATested. The results showed that the adhesive strength decreases with increasing number of impinging particles on a given area of surface in unit time. Furthermore, the adhesive strength tendency of low-roughness substrate specimens showed scatter. This tendency depends on the surface profile i.e. skewness value. Consequently, not only the height direction roughness parameter but also the wavelength of roughness, roughness morphological parameter and powder feed rate are important factors for the adhesion of the thermally sprayed HA coatings.

FATIGUE PROPERTIES OF HYBRID SURFACE MODIFIED SCM435H STEEL

In order to clarify the effects of nitriding and hybrid surface modification process combining nitriding and induction hardening on fatigue properties of SCM435H steel, high cycle fatigue tests were carried out with a rotational bending machine at room temperature. Observations of fracture surfaces and measurement of hardness and residual stress distributions were carried out to investigate the fracture mechanism. It was revealed that hybrid surface modification process generated a compressive residual stress field and hardened even at center of the specimen. Fatigue strength of hybrid surface modified specimens was much higher than that of substrate and nitrided specimens. This was because a transition of fracture mode from internal to surface fracture; fatigue fracture of nitrided specimens occurred at inside of the hardened layer, in the case of hybrid surface modified specimens, however, fatigue crack initiated at the surface of the specimen with higher hardness and higher compressive residual stress.

A non-uniform friction distribution model for partial slip fretting contact

In partial slip fretting contact, the coefficient of friction (CoF) is often assumed to be constant along the contact surface. The literature shows that the CoF is related to the relative slip, which varies in the slip region of a partial slip contact. This study develops a methodology to consider the effects of non-uniform CoF distribution in the slip region. Two cases were investigated. In the first case, the axial stress on the substrate (specimen) was absent, while the axial stress was present in the second case. In both cases, the CoF was assumed to be static, kept constant in the stick zone, and varied linearly in the slip region. A closed form solution was developed to determine the stick/slip region size and the equivalent constant CoF for the no-axial stress case, and it was supplemented with finite element analysis. In the second case, where an axial stress was applied on the specimen, the stick/slip region size and the equivalent constant CoF were determined by finite element analysis. The equivalent constant CoF with an axial stress was slightly greater than that without the axial stress due to the larger slip zone size. The stress state in the contact region based on the equivalent constant CoF was comparable to its counterpart from the linearly varying CoF case.

Relative Slip on Contact Surface under Partial Slip Fretting Fatigue Condition

Abstract: A combined experimental–numerical approach was utilized to characterize the relative slip along the contact surface and its features under the partial slip fretting fatigue condition. Relative displacements at two locations on the substrate (specimen) and fretting pad were measured in fretting fatigue tests. These measurements were then utilized to validate finite element analysis. Effects of the coefficient of friction on the relative slip and contact condition were investigated. The stress state along the contact surface was also investigated. Two contact geometries were analysed: cylinder‐on‐flat and flat‐on‐flat. There was no change in relative displacement between locations away from the contact surface because of the change in the coefficient of friction, while relative slip on the contact surface was affected by coefficient of friction. In addition, stick/slip sizes were affected by the change in coefficient of friction. Comparison between present and previous finite element models showed that stress state, as well as a critical plane‐based crack‐initiation parameter, was not much different between these approaches, while relative slip on the contact surface changed considerably.

Performance of thermal barrier coatings on γ-TiAl

The current development of new generation gamma titanium aluminides is expected to result in alloy chemistries and microstructures capable of operating at temperatures in excess of 850 °C. Under these conditions, environmental and thermal protection becomes a concern since oxidation might eventually limit the maximum service temperatures achievable. Therefore protective coatings are necessary to exploit the full potential of gamma titanium aluminides at moderately elevated temperatures; however, as yet no coating system tested has proven sufficient performance for long-term use in automotive and aerospace applications. Thermal barrier coatings (TBCs), typically applied to nickel-based alloys, offer the potential to increase the service temperature of components by lowering the metal surface temperature in combination with cooling systems. The paper is focussed on development of thermal barrier coatings for gamma titanium aluminides. Different coatings were used for oxidation protection and bond coat application. Substrate specimens were either pre-oxidized or coated with PVD-Al 2 O 3 , TiAl-CrYN, or diffusion aluminides. Yttria-stabilized zirconia TBCs were deposited applying electron-beam physical vapour deposition. Cyclic and quasi-isothermal oxidation tests were carried out at 900 °C in air. Post-oxidation analysis of the coating systems was performed using scanning electron microscopy with energy-dispersive X-ray spectroscopy. Zirconia top coats offer a promising thermal protection concept to be applied on γ-TiAl components. However, high oxidation resistance has to be supplied by protective coatings. Diffusion layers of the TiAl 3 aluminide provided excellent environmental protection because of the formation of a continuous alumina scale. No spallation of the thermal barrier coatings was observed on aluminized specimens during 1000 1-h cycles and 3000 h of cyclic and isothermal oxidation testing, respectively.