Scratch Adhesion Research Articles

Adhesion and dynamic impact wear of nanocomposite TiC-based coatings prepared by DCMS and HiPIMS

Nanocomposite nc-TiC/a-C:H coatings exhibit a unique combination of mechanical properties such as high hardness, and low friction and wear. These physical and mechanical properties make those coatings attractive for application in industry. However, the properties of the whole coating/substrate system such as adhesion of the coating to substrate and its response on repeated impact loading known such as dynamic impact wear are also important for industrial applications. Thus, this paper is focused on the adhesion and the dynamic impact wear of nc-TiC/a-C:H coatings prepared by the hybrid PVD-PECVD process. Two series of nc-TiC/a-C:H coatings with a different amount of carbon were deposited onto commonly used industrial cemented tungsten carbide substrates using DC magnetron sputtering (DCMS) and the high power impulse magnetron sputtering (HiPIMS) of a titanium target in argon and acetylene mixture atmosphere. Both series of coatings were analysed using a scratch test and dynamic impact tester with an impact load of 600 N. The HiPIMS prepared coatings exhibited lower thickness and lower thicknesses of the Ti adhesive interlayers between the substrates and coatings than the DCMS prepared coatings. Thus, the adhesion and the impact wear of both series were discussed separately. These properties were discussed with respect to the coating microstructure, phase composition and mechanical properties such as the hardness H, the effective elastic modulus E, and the H/E and H3/E2 ratios. The scratch adhesion of coatings depended on the H3/E2 ratio and coating microstructure, hardness and surface roughness. The impact wear of the nc-TiC/a-C:H coatings depended on the H/E ratio and coating microstructure.

Effects of hard TiN under layer on mechanical properties and wear characteristics of TiN-WSx composite coating

Effect of hard TiN underlayer on mechanical and wear characteristics of TiN-WSx composite coating was studied. A mono layer TiN coating was also incorporated in the study as a reference. The coatings were synthesized with pulsed magnetron sputtering process. Structural properties were investigated with field emission scanning electron microscopy, energy dispersive spectroscopy, grazing incidence x-ray diffraction; mechanical properties with scratch adhesion test, nanoindentation test and finally tribological properties were studied with pin-on-disc test. TiN underlayer resulted in a more compact morphology of top TiN-WSx hard-lubricious layer. WS2 phase with (002) orientation coexisted with crystalline TiN for TiN-WSx composite both with and without hard TiN underlayer. Scratch test revealed 35% increase in critical load of adhesion for TiN-WSx/TiN dual layer structure as compared to TiN monolayer. Brittle flaking of TiN along edges of scratch track also became negligible for dual layer coating owing to presence to soft WSx as well as presence of hard under layer which hindered substrate deformation during scratching. Low hardness of TiN-WSx as compared to TiN, partially recovered owing to addition of hard TiN underlayer. The dual layer coating also exhibited significantly low coefficient of friction of approximately 0.25–0.3 relative to 0.7–0.8 for TiN. The hard TiN underlayer reduced ploughing of top TiN-WSx composite layer. This in turn, resulted in low wear loss and subsequently less accumulation of wear debris at the leading edge of the counterbody.

Inhibition of HIF-1a-mediated TLR4 activation decreases apoptosis and promotes angiogenesis of placental microvascular endothelial cells during severe pre-eclampsia pathogenesis

ObjectiveHypoxia-induced factor 1a (HIF-1a) and Toll-like receptor 4 (TLR4) are involved in pre-eclampsia (PE) pathogenesis. However, little is known about their relationships. This study aimed to investigate the interaction of HIF-1a and TLR4 in PE pathogenesis. MethodsThe expression of HIF-1a and TLR4 were analyzed by qRT-PCR. Celluar PE model was established by hypoxia/reoxygenation treatment of human placental microvascular endothelial cells (hPMEC). Cell proliferation, apoptosis, invasion and migration were analyzed by CCK-8, flow cytometry, Transwell and scratch adhesion test, respectively. Angiogenesis was performed by tube formation, Ang-1 in culture supernatant was analyzed by ELISA. ResultsHIF-1a and TLR4 expression were significantly elevated in placental tissues from early-onset and late-onset severe pre-eclampsia patients compared with control, with increased Bax, TRIF and PUMA, and decreased Bcl-2 and VEGFA; Down-regulation of HIF-1a expression decreased TLR4 expression, promoted proliferation, invasion, migration and angiogenesis but suppressed apoptosis in cellular model. In addition, silencing HIF-1a and TAK232 treatment synergically promoted some more proliferation, invasion, migration and angiogenesis but suppressed apoptosis in cellular model. ConclusionHIF-1a could promote hPMEC apoptosis by regulating TLR4 expression during PE pathogenesis.

Corn oil based poly(urethane-ether-amide)/fumed silica nanocomposite coatings for anticorrosion application

Poly(urethane-ether-amide) (PUIEtA) nanocomposite coatings on mild steel were prepared by using corn oil, isosorbide and isophorone diisocynate and fumed silica. The syntheses steps were confirmed by FTIR, 1H NMR and 13C NMR spectroscopy techniques. The morphology of PUIEtA nanocomposite coating was studied by SEM-EDX, that confirmed the presence of nanosilica and thermal behavior was studied by DSC/TGA analysis. The anticorrosion performance of PUIEtA coating systems on mild steel, exposed to 3.5 wt% NaCl solution, was evaluated using electrochemical impedance spectroscopy. Scratch hardness, pencil hardness, adhesion, and bending test were performed in order to investigate the performance of nanocomposite coating on mild steel substrate. It was found that PUIEtA-fumed silica nanocomposite coating could provide much better protection than PUIEtA. PUIEtA-3 nanocomposite coating can be safely used up to 200 °C.

Dihydrodiosgenin inhibits endothelial cell-derived factor VIII and platelet-mediated hepatocellular carcinoma metastasis.

Background: Our previous studies have demonstrated that diosgenin and diosgenin derivatives exhibit excellent antithrombotic activity via regulating platelet function and coagulation factor level. Platelets and blood coagulation system are highly associated with tumor hematogenous metastasis. Therefore, the purpose of this study was to evaluate whether dihydrodiosgenin (dydio) mediated-platelet inhibition or coagulation factor level modulation is involved in hepatocellular carcinoma cell (HCC) metastasis.Methods: Cell viability was examined by MTT and colony formation assays. Platelet aggregation text and morphology were used to assess dydio’s role on tumor cell-induced platelet activation (TCIPA). Scratch assay, adhesion assay and Western blot were used to evaluate dydio’s role on platelet-mediated metastasis. Western blot and fluorescence detection were performed to clarify dydio's role on endothelial cell (EC) function. The mice lung metastasis model was constructed to investigated dydio’s function on coagulation factor and platelet-mediated metastasis.Results: This study found that pretreatment with dydio caused a significant inhibition of TCIPA. Platelets exposed to dydio significantly inhibited their adhesion to tumor cells, meanwhile, releasates of platelets that pretreated with dydio led to diminished cancer cell proliferation and migration along with the increase of epithelial markers E-cadherin and loss of mesenchymal phenotype. Additionally, ECs pretreated with dydio suppressed factor VIII (FVIII) level which in turn restrained the activation of platelets and the adhesion of cancer cells or platelets to ECs. Interestingly, our study demonstrated that FVIII could promote HCC proliferation. In vivo study revealed that mice intragastrical (i.g.) administration with dydio significantly inhibited the lung metastasis of hepal-6 cells which is highly correlated with the altered platelet function and coagulation level.Conclusion: Taken together, these results demonstrated that dydio altered platelet function and coagulation FVIII level, resulting in decreased metastatic potential of HCC. Thus, our study reveals that dydio exerts novel mechanisms of antitumor action beside its direct antitumor activity.

Scratch response and tribological behaviour of CrAlNiN coatings deposited by closed field unbalanced magnetron sputtering system

CrAlNiN coatings were deposited on M2 tool steels using closed-field unbalanced magnetron sputtering. The coating microstructure transformed from coarse columnar grains to fine equiaxed grains with increasing Ni content, which was accompanied by a general decrease in both hardness (H) and elastic modulus (Er) values. The scratch tests showed both scratch toughness and adhesion strength were improved for coatings with higher ratios of H/Er and H3/Er2, whereby higher critical loads (LC1 and LC2) are required to initiate cohesive and adhesive failure. For the coatings with coarser columnar grains, the improved scratch toughness may be ascribed to tortuous crack deflection patterns. Improved wear resistance was found in the columnar grained coatings, which also exhibited the higher H/Er and H3/Er2 values. The inferior wear resistance in the equiaxed grained coatings was suggested to arise from these coatings being more susceptible to grain pull-out processes during abrasive sliding. The wear debris composed of tribo-oxides serving as additional capacity for load bearing via re-distribution of the applied stress. This was believed to boost the wear resistance of the coatings.

Measure and evaluate the hardness of the electrodeposited Nickel-Phosphorous (Ni-P) thin film coating on carbon steel alloy for automotive applications

In this research work, the electrodeposition of Nickel-Phosphorous (Ni-P) coating on carbon steel alloy for higher surface hardness has been investigated. Nickel phosphorus (Ni–P) with 11–12 wt% phosphorous was electrodeposited onto AISI 1045 steel substrate with direct current and solutions of phosphorous and phosphoric acid, nickel sulphate and nickel chloride. The effect of current density as a plating parameter was investigated. It appeared that by increasing the current density by 50, 100 and 150 mA/cm2 it is possible to obtain greater phosphorous content in Ni-P alloy coating. FESEM, XRD, EDS, scratch adhesion and micro hardness methods were employed to investigate the surface morphology, micro structure, composition and mechanical characteristics of Ni-P alloy coating. The structure became amorphous when the P content ranged from 11 to 12 wt%. Ni–P alloys with different phosphorous content were exposed to heat treatment at 300, 400 and 500 °C for 1 h in a hot air oven. The changes in mechanical characteristics were investigated.

Adhesion of PVD and CVD hard coatings as an essential parameter that determines the durability of coated tools

Purpose: The work is connected with the current trend related to the modification of tool surfaces with PVD and CVD methods through the deposition of coatings to increase their durability. The research results of coated tools tests that are carried out in industrial conditions are presented in details. Design/methodology/approach: Structure, chemical and phase composition investigations related to the mechanical and tribological properties of coatings produced on tool substrates and analysis of the results are included. Investigations of the properties of deposited coatings on the following tool materials were made: high speed steels, hot work tool steel, sintered carbides and SiAlON tool ceramics. Findings: Interpretation of production tests results of coated tools and an analysis of the wear mechanisms of tool blades in relation to the properties of coatings and their adhesion, in particular characterized in the scratch test, were described. Research limitations/implications: Adhesion scratch test cannot be the only and final method of such evaluation. For example a direct comparison of the results of the scratch tests of coatings is possible when adhesion is being examined of different coatings yet on the same type of the substrate. Practical implications: Based on the adhesion test results using the scratch test, the suitability of the coatings produced on the cutting tools can be quickly assessed. Originality/value: It was sought those parameters which characterize the properties of coatings, ones which would permit to effectively/practically assess the performance of tools with coatings produced, with an exclusion or limitation of long-term and expensive durability tests of tools that are carried out in industrial conditions.

Therapy of Prostate Cancer by Nanoyam Polysaccharide

We evaluated the effect and mechanism of yam polysaccharide on the proliferation of the prostatic cancer cell line and tumor-bearing mice. The effect of nanoyam polysaccharide on prostatic cancer cell line PC-3 was measured using the scratch adhesion test and flow cytometry. The growth effect induced by nanoyam polysaccharide was detected with the CCK-8 test. The levels of caspase-3 protein were determined with Western blot. In our data, nanoyam polysaccharide presented inhibitory effect on the proliferation of PC-3. The scratch adhesion test showed that the rate of wound healing in the intervention group was significantly lower than that in the control group (p<0.05). Flow cytometry assay showed that, after treatment with nanoyam polysaccharide, the apoptosis rate in the intervention group was significantly lower than that in the control group (45.8%±2.6%, 25.8%±3.1%; p<0.05). Western blot assay showed upregulated levels of caspase-3 in the intervention group, compared to the control group (p<0.05). Our results suggested that nanoyam polysaccharide strongly suppressed the growth of prostatic cancer by inducing the overexpression of caspase-3 and may be a potent anticancer strategy.

Mechanical behavior of PVD coatings deposited on ADI

ABSTRACT In this work, the mechanical behavior of the coated ADI system is studied. For this purpose, single layer Ti and bilayer Ti/TiN and TiAl/TiAlN coatings, with different thicknesses, were deposited by the PVD technique of cathodic arc deposition on high strength ADI substrates using industrial and experimental devices. The characterization of the coatings includes the measurement of the layer thicknesses by the spherical abrasion method, the determination of existing phases and residual stresses by x-ray diffraction and the evaluation of the surface topography using a stylus profilometer. The analysis of the mechanical properties of the coatings comprises the measurement of the surface hardness by micro indentation tests and the evaluation of the scratch resistance. The scratch tests were performed on a scratch tester equipped with a Rockwell indenter. A progressive load from 1 to 100 N, a load rate of 99 N/min, a speed of 5 mm/min and a scratch length of 5 mm were employed. The influence of the coatings characteristics on the scratch resistance of the coated samples and the friction coefficients obtained are evaluated. The results show that Ti coated samples had tensile residual stresses, the lowest surface hardness and the lowest critical loads for scratch adhesion strength. The samples coated with Ti/TiN and TiAl/TiAlN had highly compressive residual stresses and the highest critical loads, while the hardness was higher for TiAl/TiAlN. On the other hand, the evolution of the friction coefficient was similar for all the coated samples.

Desert sand cemented by bio-magnesium ammonium phosphate cement and its microscopic properties

Loose desert sand grains can be cemented through the microbially-induced magnesium ammonium phosphate sediment into sandstone. Ammonia and ammonium were produced by Sporosarcina-Pasteurii hydrolyzing urea and effectively became environmentally friendly magnesium ammonium phosphate in the presence of HPO42− ions (hydrogen phosphate). This a new kind of the bio-cement based on Sporosarcina-Pasteurii, and the bio-phosphate mineral has cementation. The chemical components of the bio-sandstone were mainly MgNH4PO4(H2O)6 (struvite) and quartz, as discovered through X-ray diffraction (XRD) analysis. The internal micro-structure of the desert sand was observed by scanning electron microscopy (SEM), and its morphology was of irregular spheres with a size in the range of 100–300 µm. SEM images of the bio-sandstones showed the morphology of the cementation products as irregular flakes. The average hardness of two bio-sandstones cemented by spraying 1 and 3 times with cementation solution was 4.4 and 12.3, respectively. The evolution law of the micro-structure for the bio-sandstone cemented by spraying 3 times with cementation solution was revealed by the X-ray computed tomography (XRCT) technique. Maximum defect volume and average porosity of the bio-sandstone was 134 mm3 and 18.39%, respectively. Interface binding forces between the bio-cement and smooth sheet glass (SiO2) were determined with WS-2005 coating adhesion scratch tester, which was 3.69 ± 1.02 N.

Electrophoretic deposition of graphene oxide on NiTi alloy for corrosion prevention

Graphene oxide (GO) coating was prepared on the surface of a NiTi shape-memory alloy via a simple and practical electrophoretic deposition method from an aqueous suspension containing GO at low temperatures. The coating was characterized by field emission scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. The adhesion force and stabilization of the GO coating were analyzed by using a coating adhesion scratch testing system. The surface of the GO-coated NiTi exhibited hydrophilicity with a water contact angle of 17.6°. Moreover, the corrosion resistance of NiTi alloy was evaluated by a potentiodynamic polarization test in Hank's solution. The potentiodynamic polarization curves revealed that GO-coated NiTi demonstrated a more positive corrosion potential (Ecorr, −107 mV) than bare NiTi (Ecorr, −186 mV), and the corrosion current density (Icorr) decreased by approximately two orders of magnitude. The improved corrosion resistance and hydrophilicity of NiTi coated with GO compared with those of bare NiTi were mainly attributed to the GO coating.

Corrosion resistance and tribological behavior of WS2-Ti coatings by Ti cathode power changes in magnetron co-sputtering

Titanium-doped tungsten disulfide thin films (WS2-Ti) were deposited using a DC magnetron co-sputtering on AISI 304 stainless steel and silicon substrates. Different Ti cathode power densities between 0 and 1.25 W/cm2 were used for coating deposition. Energy-dispersive spectroscopy evidenced an increase in Ti percentage at the expense of W, as well as a sulfur deficiency. Raman spectroscopy was used to identify bands corresponding to W-S for undoped WS2. As the material was doped, changes in crystalline structure caused W-S main bands to separate. Scratch adhesion testing showed that Ti percentage increased along with the critical load (Lc). Furthermore, adhesive failure type changed from plastic to elastic. Finally, corrosion resistance analysis using electrochemical impedance spectroscopy (EIS) showed that, at high Ti concentrations, corrosion resistance was enhanced as Ti facilitates coating densification and generates a protective layer.

Characterization and Quick Screening Methodology of Novel Alloys for Biomedical Applications Using Filtered Cathodic Vacuum Arc Deposited Thin Film

Ti-based amorphous alloys containing no harmful elements are desired. However, many Ti-based amorphous alloys contain toxic elements such as Al, Ni, V and Be. The presence of toxic elements within amorphous alloys is a concern when they are intended for use as a biomaterial. This problem has steered many researchers toward the development of Ti-based amorphous alloys without toxic elements. Our novel amorphous alloys were developed based on this principle. A series of Ti44Zr10Pd10Cu6+xCo23-xTa7 (x = 0, 4, 8) amorphous alloys were developed for biomedical application. A series of protocol tests were performed to check for biocompatibility and potential use of the novel alloys in humans. First, alloy ingots were alloyed by induction melting and then cast into copper molds. The cast rod was then used as the plasma cathode in a filtered cathodic vacuum arc deposition chamber to coat the 25-nm amorphous alloy thin film on the cover glass slides. These coated cover glass slides were then examined for biocompatibility. Cell proliferation and cell differentiation were investigated using Methylthiazol Tetrazolium assay test and by alkaline phosphatase assay on osteoblast like cells (SaOS-2), respectively. Field emission scanning electron microscopy was performed to evaluate the thin film surface characteristics. The thickness of thin film was analyzed using a Stylus profilometer. An adhesion scratch test was administered to evaluate the thin film adhesive strength and indirect hardness comparison. Electron Dispersive X-ray Spectrometry was performed to study the elemental composition. Lastly, a medical grade Ti-6Al-4V alloy was studied in parallel as a control material. Results indicated that all investigated Ti-based amorphous alloys were non-cytotoxic and were comparable to the Ti-6AL-4V. They also demonstrated an ability to support differentiation of osteoblast like cells. The adhesion and the hardness of the thin films on the substrates were superior to that of Ti-6Al-4V. The results suggested that the novel alloys in this study could be potentially utilized in biomedical applications.

TiN Films Deposited on Uranium by High Power Pulsed Magnetron Sputtering under Low Temperature.

Depleted uranium (DU) is oxidized readily due to its chemical activities, which limits its applications in nuclear industry. TiN film has been applied widely due to its good mechanical properties and its excellent corrosion resistance. In this work, TiN protection films were deposited on DU by direct current magnetron sputtering (DCMS) and high power pulsed magnetron sputtering (HPPMS), respectively. The surface morphology and microstructures were investigated by atomic force microscope (AFM), scanning electron microscopy (SEM), and grazing incidence X-ray diffraction (GIXRD). The hardness and Young’s modulus were determined by nano-Indenter. The wear behavior and adhesion was analyzed by pin-on-disc tests and scratch adhesion tests and the corrosion resistance was evaluated by electrochemical measurements. The results show that the TiN films that were deposited by HPPMS outperformed TiN film deposited by DCMS, with improvements on surface roughness, mechanical properties, wear behavior, adhesion strength, and corrosion resistance, thanks to its much denser columnar grain growth structure and preferred orientation of (111) plane with the lowest strain energy. Besides, the process of Ti interlayer deposition by HPPMS can enhance the film properties to an extent as compared to DCMS, which is attributed to the enhanced ion bombardment during the HPPMS.

Thickness Characterization Toolbox for Transparent Protective Coatings on Polymer Substrates.

The thickness characterization of transparent protective coatings on functional, transparent materials is often problematic. In this paper, a toolbox to determine the thicknesses of a transparent coating on functional window films is presented. The toolbox consists of a combination of secondary ion mass spectrometry and profilometry and can be transferred to other transparent polymeric materials. A coating was deposited on designed model samples, which were characterized with cross-sectional views in transmission and in scanning/transmission electron microscopy and ellipsometry. The toolbox was then used to assess the thicknesses of the protective coatings on the pilot-scale window films. This coating was synthesized using straightforward sol-gel alkoxide chemistry. The kinetics of the condensation are studied in order to obtain a precursor that allows fast drying and complete condensation after simple heat treatment. The shelf life of this precursor solution was investigated in order to verify its accordance to industrial requirements. Deposition was performed successfully at low temperatures below 100 °C, which makes deposition on polymeric foils possible. By using roll-to-roll coating, the findings of this paper are easily transferrable to industrial scale. The coating was tested for scratch resistance and adhesion. Values for the emissivity (ε) of the films were recorded to justify the use of the films obtained as infrared reflective window films. In this work, it is shown that the toolbox measures similar thicknesses to those measured by electron microscopy and can be used to set a required thickness for protective coatings.

Effects of scratch tests on the adhesive and cohesive properties of borided Inconel 718 superalloy

New results about the scratch adhesion resistance of nickel boride layer on Inconel 718 superalloy were estimated in the present study. The nickel boride layer was developed on the surface of Inconel 718 superalloy by means of the powder-pack boriding process conducted at 1173K with 2, 4, and 6h of exposure. The microstructure of the nickel boride layer was analyzed from optical microscopy, X-ray diffraction and energy dispersive spectroscopy (EDS). Furthermore, and before the scratch tests, indentation properties of the nickel boride layers such as hardness, Young's modulus, and the distribution of residual stresses were evaluated using Berkovich nanoidentation tests applying a constant load (50mN) across the diffusion layers. The scratch tests were performed over the surface of the nickel boride layer-substrate systems using a Rockwell-C diamond indenter with a continuously increasing normal force from 1 to 80N, whereas the behavior of the coefficient of friction and the residual depth as a function of the scratch length were monitored during the tests. For the determination of the critical loads, the combination of acoustic emission signal with microscopic observations of the worn tracks were used; the critical loads were estimated at which the layer cracks (cohesive failure) or is detached (adhesive failure) and they explained according to the mechanical properties of the nickel boride layer-substrate system. For all the set of experimental conditions, the presence of three types of failure mechanisms over the worn tracks were detected, while the results showed that the critical loads increase with enhancing nickel boride layer thickness.

Structure and properties of hydrophobic CeO2−x coatings synthesized by reactive magnetron sputtering for biomedical applications

Cerium oxide coatings were synthesized onto Si wafers by reactive magnetron sputtering in an Ar + O2 gas mixture. The argon gas flow rate was varied from 35 to 15 sccm with a concurrent change in oxygen gas flow rate from 0 to 20 sccm. The influence of increasing the oxygen flow rate on the composition, microstructure, mechanical properties and scratch adhesion behavior, along with surface morphology and hydrophobic response of the coatings were investigated. X-ray photoelectron spectroscopy (XPS) analysis revealed the existence of Ce4+ and Ce3+ species in the coatings with decreasing Ce3+ species as the oxygen flow rate increased, which is in accordance with grazing incidence X-ray diffraction (GI-XRD) results. GI-XRD analysis also showed a strongly preferred (111) orientation in all of the coatings. Moreover, the CeO2 (111) peak became broader as the oxygen flow rate increased, indicative of a reduction in grain size, which was also noticeable from high resolution TEM analysis. The mechanical properties of the coatings improved, along with the scratch resistance of the coatings, owing to the increase in elastic strain to failure (H/E) and plastic deformation resistance (H3/E2). A marginal increase in surface roughness (Ra) was noticed, which was accompanied by reduction in surface energy leading to an increase in hydrophobic performance of the coatings in the presence of both water and a 0.9 wt% NaCl solution.

Characterization of Al2O3/ZrO2 composite coatings deposited on Zr-2.5Nb alloy by plasma electrolytic oxidation

Plasma electrolytic oxidation (PEO) process was employed in a galvanostatic regime on Zr-2.5Nb alloy in NaAlO2 aqueous electrolyte solutions within a concentration gradient of 5–30 g/L in order to produce Al2O3/ZrO2 composite coatings. The composition and microstructure of the oxide layers were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). Vickers microhardness, scratch adhesion and potentiodynamic polarization measurements were used to assess the mechanical and electrochemical properties of the PEO coatings. The experimental findings suggest a strong correlation between the electrolyte concentration and the coating layers. By increasing the concentration of NaAlO2 in the electrolyte solution, significantly increased tetragonal crystal structure, particle size, hardness, adhesion strength and corrosion resistance occur with pore size decrease. Best values for the hard and adherent coating were ∼1500 HV and ∼60 N critical load. The corrosion current densities for the plasma electrolytic oxidized samples are lower than the black oxide coated Zr alloy.

Study of the structure, properties, scratch resistance and deformation behaviour of graded Cr-CrN-Cr(1-x)AlxN coatings

An in-depth investigation of the structure, properties, scratch adhesion characteristics of graded Cr-CrN-Cr(1-x)AlxN coatings synthesized onto M42 steel substrates using closed – field unbalanced magnetron sputtering (CFUBMS) was carried out. Advanced microscopy (scanning and transmission electron microscopy), focused ion beam (FIB) imaging, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and micro–scratch tests was used to investigate the microstructure, mechanical properties and scratch performance as a function of Al content. FIB and TEM investigations revealed that the coatings exhibited a distinct structure; i.e., an adhesive Cr layer, a CrN transition layer and a graded CrAlN top layer with a face centered cubic (FCC) B1 structure. A columnar morphology was exhibited by the coatings and the dimensions of the columnar grains decreased with increasing Al content. Residual stress measurements, obtained from the XRD – sin2ψ method, revealed increasing compressive stresses with increasing Al content. Furthermore, nanoindentation tests showed an increase in mechanical properties, fracture toughness index (H/E) and plastic deformation resistance (H3/E2) as the Al content increased, accompanied by a decrease in the critical load, LC, during scratch testing implying a decrease in scratch toughness.