Progressive Load Scratch Test Research Articles

Structural, Mechanical, and Optical Properties of Laminate-Type Thin Film SWCNT/SiOxNy Composites

The development of new encapsulating coatings for flexible solar cells (SCs) can help address the complex problem of the short lifespan of these devices, as well as optimize the technological process of their production. In this study, new laminate-type protective composite coatings were prepared using a silicon oxynitride thin-film matrix obtained by curing the pre-ceramic polymer perhydropolysilazane (PHPS) through two low-temperature methods: (i) thermal annealing at 180 °C and (ii) exposure to UV radiation at wavelengths of 185 and 254 nm. Single-walled carbon nanotubes (SWCNTs) were used as fillers via dry transfer, facilitating their horizontal orientation within the matrix. The optical, adhesive, and structural properties of the matrix films and SiOxNy/SWCNT composite coatings, along with their long-term stability, were studied using Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy, HR-SEM, spectral ellipsometry, and a progressive-load scratch test. In this work, the optical constants of PHPS-derived films were systematically studied for the first time. An antireflection effect was observed in the composites revealing their two-component nature associated with (i) the refractive index of the SiOxNy matrix film and (ii) the embedding of a SWCNT filler into the SiOxNy matrix. The curing method of PHPS was shown to significantly affect the resulting properties of the films. In addition to being used as protective multifunctional coatings for SCs, both SiOxNy/SWCNT composites and SiOxNy matrix films also function as broadband optical antireflective coatings. Furthermore, due to the very low friction coefficients observed in the mechanical tests, they show potential as scratch resistant coatings for mechanical applications.

Tribological and mechanical properties of ZrxNy films obtained by HiPIMS in DOMS mode

Maritime transportation represents one of the biggest industries worldwide. The functionality improvement of critical ship parts such as sea chest gratings could mean substantial impacts in fuel consumption reduction, larger lifetime span or reduction of non-indigenous sea species transportation. Since 2008, the ban imposed by the international maritime organization over polluting products, especially tributyltin, created the need to explore new sustainable and environmentally friendly alternatives. Multifunctional coatings have the potential to overcome this situation, creating highly tuneable materials able to combine properties according to the naval industry's needs. Zirconium nitride is known for its reliable mechanical and anti-corrosion properties, critical in a multifunctional coating used in the sea. In the present study, this material was obtained through high-power impulse magnetron sputtering technology in a reactive atmosphere (R-HiPIMS). SEM, EDS, AFM and XRD were used to assess the coatings. Also, the films’ mechanical properties and adhesion were assessed via nanoindentation and progressive load scratch tests, respectively. The pin-on-disk test was used to assess the coatings' tribological properties under dry and wet (3.5% wt. NaCl solution) conditions. The results demonstrate that the increase in hardness was directly influenced by the changes in the structure promoted by the nitrogen rise, from 16 GPa to 25 GPa, with a nitrogen increase in film composition from 47% to 54%. Besides, the tribological tests revealed the key role of an oxygen-rich tribolayer and surface roughness features (skewness and kurtosis) in keeping the film’s integrity. The ZrxNy films obtained by HiPIMS improved the mechanical and tribological properties compared to ZrN obtained by DCMS, opening new possibilities to be explored as a solution inside a multifunctional coating system.

Scratch behaviors of polyacrylate-based hard coatings on alternating multi-layered PMMA+PC substrates

In our previous work [1], the scratch behaviors of alternating multi-layered polymethyl methacrylate (PMMA)/polycarbonate (PC) laminates were studied. Generally, a hard coating layer must be introduced to the surface of PMMA + PC laminate to further enhance its hardness and scratch resistance. In this work, the same laminates used in our previous work were coated by a UV-cured polyacrylate hard layer, and the scratch behaviors and relating mechanisms of hard coating (HC) systems were investigated via both progressive normal load scratch test and pencil hardness test. Sliding counterfaces of two tests were stainless steel ball with a diameter of 1 mm and cylinder made of pencil core with a diameter of 2 mm, respectively. Length, width and thickness of test specimen were 150 mm, 33 mm and 1.6 mm, respectively. The effects of HC's thickness and substrate's hardness on scratch behaviors of HC systems were also included. In both scratch tests, experimental results demonstrated that scratch damages of HC systems were featured with dense periodic cracks. Finite element modeling (FEM) revealed that the formation of such crack types was attributed to the maximum principal stress perpendicular to crack propagation direction. Furthermore, it was found that the scratch resistances of HC systems were enhanced as thickness of HC or hardness of substrate increased, the mechanism behind which were found to be decreasing of the maximum principal stress and consequent delaying of crack formation as revealed through FEM.

Scratch resistance of cobalt boride layer subjected to a diffusion annealing process

This work studies the effect of a diffusion annealing process in cobalt boride layers by progressive load scratch (PLST) and multipass scratch (MPST) tests. First, a double-phase CoB/Co2B layer was formed on CoCrMo alloy at 1000 °C for 6 h. Next, a single-phase Co2B layer was obtained through a diffusion annealing process. The scratch tests were conducted with a progressive load from 5 to 150 N in PLST, whereas in MPST, up to 400 passes were applied with a subcritical load of 38 N. Conducting the diffusion annealing process significantly improved the scratch resistance; in PLST, the achieved layer avoided severe failure mechanisms and decreased residual depth by 60%. In MPST, friction was reduced and the volume loss decreased around 50%.

Scratch behavior and mechanical properties of alternating multi-layered PMMA/PC materials

Poly (methyl methacrylate) (PMMA)/polycarbonate (PC) laminates have been widely used as backboards for 5G cellphones where surface aesthetics are required. For this reason, the scratch behavior of the material is of particular interest. In the present work, the scratch behavior of alternating multi-layered PMMA/PC materials was studied by progressive normal load scratch tests and finite element modeling (FEM). The experimental results showed that interfacial delamination between the PMMA and PC layers occurred after the onset of scratch damage. The detailed delamination process and related mechanisms were revealed by FEM. It was found that interfacial delamination during scratching can be divided into three successive stages: delamination initiation, delamination expansion, and delamination propagation. All stages were revealed to be dominated by shearing mode (Mode II & III) crack propagation, while opening mode (Mode I) crack propagation was not involved. Furthermore, the mechanical results demonstrated a dramatic enhancement of ductility and toughness when the number of layers was increased.

Comparative investigation of scratch resistance and tribological performance of Ni–B–TiO2 composite coatings prepared by conventional and novel processing methods

Ni–B–TiO2 composite coatings were elaborated by conventional and novel methods. While the first one was designed using TiO2 powder, the second was prepared by adding TiO2 sol in the bath solution. A comparative study between both coatings was performed in terms of microstructure, adhesion strength and wear resistance. To achieve a systematic study, various characterization tests were carried out, including Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), microhardness test, progressive load scratch test, reciprocating sliding test and multi-pass scratch test. The results showed that the TiO2 structure (crystalline or amorphous) has extensively changed the microstructure of Ni–B matrix. Furthermore, it was proven that the novel process provided superior scratch response and better wear resistance of the Ni–B deposit since it offers a compact structure. Nevertheless, the traditional method yielded to porous one, thus leading to mediocre mechanical properties of the same coating.

Effect of nitriding pretreatment on adhesion and tribological properties of AlCrN coating

In this work, a gas nitriding pretreatment (iron nitrides layer) formed on the surface of 4140 steel is proposed to improve the adhesion and wear resistance of the AlCrN coatings deposited by arc cathodic PVD. AlCrN, FexN and AlCrN/FexN (duplex) systems were formed with total thicknesses of 3, 10 and 13 µm, respectively. Using spherical instrumented indentation, hardness more than 22 GPa were determined for the AlCrN-based coatings, meanwhile 10 GPa for the iron nitrides. The adhesion of the coatings were evaluated by progressive load scratch tests (PLST) where the duplex coating reduced the CoF and changed the failure mode from adhesive to cohesive for the AlCrN coating. The AlCrN/FexN coating exhibited the lowest specific wear rate and the severity of damage was reduced in multipass scratch wear tests (MPST). The duplex system presented the best adhesion and wear resistance.

The effects of TiO2 sol concentration on single- and multiple-scratch damage in electroplated Ni–B-TiO2 sol composite coating

The electrodeposited sol-enhanced Ni–B–TiO2 composite coatings were elaborated using a novel electroplating process. This coating was assessed in terms of tribological behavior and corrosion resistance. However, the adhesion strength of this coating has not been discussed so far. The aim of this study is to evaluate the adhesion behavior of this coating, considering different TiO2 sol concentration in the plating solution in order to predict its effectiveness and its sustainability when used in mineral crushing process. A progressive load scratch test and multi-pass scratch test were performed on coatings. The morphology of scratched surfaces was analyzed to identify the scratch failure mechanism. The results indicate that the addition of TiO2 sol significantly enhanced the deposit adhesion to the substrate compared to pure Ni–B coating. No spallation failure was observed on the sol-enhanced coatings after progressive load scratch test, contrary to Ni–B coating. Moreover, the multi-pass scratch test demonstrated that the improvement in adhesion strength depends strongly on the quantity of the TiO2 sol added to the plating solution. For the optimal concentration of TiO2 sol (25 ml/L), the sol-enhanced Ni–B–TiO2sol composite coating boasts the best adhesion strength. However, further increase in TiO2 sol concentration results in a deterioration of coating adhesion.

Friction and Damage Evolution of the Borided CoCrMo Alloy

Abstract In this study, friction and evolution of cohesive failures (cracks and spallations) in CoB/Co2B layers were analyzed. Thermochemical treatment was carried out at 950, 975, and 1000 °C during 6, 8, and 10 h of exposure time, respectively. The characterization techniques include scanning electron microscopy (SEM) for morphology inspection of layers and thickness measurement, X-ray diffraction for the investigation of phases formed, and instrumented indention to obtain hardness, Young’s modulus, and residual stresses. The practical adhesion of the boride layers was evaluated by a progressive load scratch test (PLST), and the critical loads of cracking, chipping, and spallation were calculated. Later, unidirectional multipass scratch tests (MPSTs) were performed by applying subcritical loads selected from the lower spallation load (54 N); these tests were conducted for a different number of scratch passes. The results show that the coefficient of friction (COF) and coating damage depend on the applied load, the number of passes, and coating thickness. In multipass scratch, the mechanical properties, residual stress state, and thickness play a significant role in the evolution of the coating damage that manifests in the form of cracks and cohesive spallations. Considering the scratch and multipass scratch results, it was found that the sample with 10 h of exposure time presents a better performance among the samples.

Measurement of Cohesion and Adhesion of Semiconducting Polymers by Scratch Testing: Effect of Side-Chain Length and Degree of Polymerization.

Most advantages of organic electronic materials are enabled by mechanical deformability, as flexible (and stretchable) devices made from these materials must be able to withstand roll-to-roll printing and survive mechanical insults from the external environment. Cohesion and adhesion are two properties that dictate the mechanical reliability of a flexible organic electronic device. In this paper, progressive-load scratch tests are used for the first time to correlate the cohesive and adhesive behavior of poly(3-alkylthiophenes) (P3ATs) with respect to two molecular parameters: length of the alkyl side chain and molecular weight. In contrast to metrological techniques based on buckling or pull testing of pseudofreestanding films, scratch tests reveal information about both the cohesive and adhesive properties of thin polymeric films from a single procedure. Our data show a decrease in cohesion and adhesion, that is, a decrease in overall mechanical robustness, with increasing length of the side chain. This behavior is likely due to increases in free volume and concomitant decreases in the glass transition temperature. In contrast, we observe increases in both the cohesion and adhesion with increasing molecular weight. This behavior is attributed to an increased density of entanglements with high molecular weight, which manifests as increased extensibility. These observations are consistent with the results of molecular dynamics simulations. Interestingly, the normal (applied) forces associated with cohesive and adhesive failure are directly proportional to the average degree of polymerization, as opposed to simply the molecular weight, as the length of the alkyl side chain increases the molecular weight without increasing the degree of polymerization.

Adhesion and mechanical properties of Ti films deposited by DC magnetron sputtering

Titanium films were deposited on AISI 316L stainless steel substrates by D.C. unbalanced magnetron sputtering, the substrate temperature and deposition time were changed. In this study, the structural characterization was conducted by scanning electronic microscopy (SEM), spectroscopic ellipsometry (SE), X-ray diffraction (XRD) and atomic force microscopy (AFM). Furthermore, mechanical properties were obtained by nanoindentation. Adhesion and wear behavior were evaluated through progressive load scratch test (PLST) and pin-on-disk test, respectively. Titanium films thicknesses within a range of 2.5–4.2μm were obtained, different XRD Ti peaks such as (002), (102) and (103) were identified. Values estimated for hardness were between 7.2 and 8.4GPa, and for Young's modulus they were 126–162GPa. Tensile cracks, compressive and gross spallation failure mechanisms were found with scratch tests. Preferred oriented sample only showed cracks, with a critical load of 2.6N, and exhibited a better wear ratio (~1.5×10−4), which is about two times better than substrate steel. This study provides evidence of how a preferred oriented Ti (002) film exhibits better hardness, adhesion and wear properties.

Multipass Scratch Behavior of Borided and Nitrided H13 Steel

AISI H13 steel was subjected to boriding and nitriding; its performance was evaluated by the progressive load scratch test, and then by the multipass scratch test (MPST), to evaluate the accumulated damage. Boriding and nitriding were carried out at a temperature of 800 and 580 °C, respectively, both treatments for 1 and 5 h of exposure time. In scratch test, a load range of 3-90 N was used for borides; a higher range (3-180 N) was chosen for nitrides. Critical loads (Lc) were estimated based on optical microscope observations of the scratch tracks. Failure mechanisms and residual depths were examined by scanning electronic microscope and optical profilometry. Finally, using fractions of Lc, MPST was applied on uncoated and coated samples, for 25, 50, 75 and 100 unidirectional scratch cycles. The coefficient of friction (COF) evolution was recorded and analyzed. A decrease in COF was observed as cycles go through; it was initially higher in uncoated sample; moreover, it was observed that normal load was determinant in its behavior, regardless of the treatment time. Nitrided samples exhibited less catastrophic failures over borided ones, also showed a better volume loss/load ratio performance, from 6 to 8 times better compared to borided samples.

Evaluation of scratch resistance of functionalized graphene oxide/polysiloxane nanocomposite coatings

Abstract Functionalized graphene oxide (FGO) was synthesized with 3-glycidoxy-propyl trimethoxy silane (GPTMS) and subsequently incorporated into polysiloxane coatings to improve the mechanical properties, especially scratch resistance, through the sol-gel and epoxy/amino curing reactions. The surface functionalization of graphene oxide (GO) was evidenced by TEM, FTIR and XPS. FGO was found to have better compatibility and establish stronger interface with polysiloxane matrix than GO based on the observed microstructures using OM and SEM. Nanoindentation, macro scratch and progressive load scratch tests were employed to assess the mechanical performance of FGO/polysiloxane nanocomposite coatings, demonstrating significant improvement in comparison with either the pure polysiloxane or the GO/polysiloxane coatings. A 40% enhancement on microhardness (233 MPa), 83% improvement of scratch resistance (1100 g) and 144% increase in 1st scratch critical normal load (4.88N) are achieved by addition of only 0.75 wt% of FGO. Furthermore, elastic recovery and scratch damage morphology were investigated to provide insight into scratch behavior and reinforcement mechanism.

Electrophoretic Deposition as a New Bioactive Glass Coating Process for Orthodontic Stainless Steel

This study investigated the surface modification of orthodontic stainless steel using electrophoretic deposition (EPD) of bioactive glass (BG). The BG coatings were characterized by spectrophotometry, scanning electron microscopy with energy dispersive X-ray spectrometry, and X-ray diffraction. The frictional properties were investigated using a progressive load scratch test. The remineralization ability of the etched dental enamel was studied according to the time-dependent mechanical properties of the enamel using a nano-indentation test. The EPD process using alternating current produced higher values in both reflectance and lightness. Additionally, the BG coating was thinner than that prepared using direct current, and was completely amorphous. All of the BG coatings displayed good interfacial adhesion, and Si and O were the major components. Most BG-coated specimens produced slightly higher frictional forces compared with non-coated specimens. The hardness and elastic modulus of etched enamel specimens immersed with most BG-coated specimens recovered significantly with increasing immersion time compared with the non-coated specimen, and significant acid-neutralization was observed for the BG-coated specimens. The surface modification technique using EPD and BG coating on orthodontic stainless steel may assist the development of new non-cytotoxic orthodontic metallic appliances having satisfactory appearance and remineralization ability.

Abrasive wear of multilayered/gradient CrAlSiN PVD coatings: Effect of interface roughness and of superficial flaws

PVD coatings have been used to improve the wear resistance of various tribological systems. In general, analytical models that describe the abrasive wear behaviour of ceramic materials do not take into account the presence of superficial flaws in ceramic coatings. Flaws are pores or protuberances present in the coating surface formed during the coating process. In this work, the percentage of superficial flaws was measured using optical microscopy and was correlated to the abrasive wear resistance of the investigated coatings. Two different coating designs were analyzed, multilayer and gradient. In both coating architectures, the chemical composition at the coating-substrate interface was kept constant at 75% of CrN and 25% AlSiN, and the CrN/AlSi ratio was varied throughout the coating thickness. The mechanical properties of the coatings were evaluated using Knoop microhardness tests and progressive load scratch tests. The presence of flaws in the coatings was connected to the substrate roughness values. Free-ball microabrasive wear tests were carried out using SiC abrasive slurry with a concentration of 20 wt%. Wear rates of the coatings increased linearly with e.Lc−3/4.H−1/2, where e was the superficial flaws fraction, Lc the critical load measured in the scratch tests and H the microhardness. The coating wear rates were intensified up to 72% by increasing the interface roughness. The wear rate of 2.6µm thickness coatings was about 120% higher than the 3.1µm thickness coatings. This work showed that the percentage of superficial flaws was a key parameter that affected the wear rate and critical load of the coating. This result was related to the fact that superficial flaws acted as stress concentration sites that raised the local stress leading to premature failure of the coating during the wear process. The combination of these techniques afforded a powerful tool with which to develop an efficient and reliable methodology for characterizing tribological coatings.

Tribological Properties of Magnetron Sputtered Amorphous Silicon Carbide and Silicon Carbonitride Coatings

The tribological properties of magnetron sputtered amorphous silicon carbide (a-SiC) and silicon carbonitride coatings (a-SiCN) with thickness of 2.2 and 3.4 µm were investigated. Samples were additionally annealed at temperature of 700°C or 900°C in air. Progressive load scratch tests were performed on the annealed samples as well as on the as deposited ones. An acoustic emission signal was detected during all tests using the sample holder with embedded sensor of our own design. Results indicate no change in wear resistance of SiCN sample after high temperature exposure up to 900°C, unlike in the tests of SiC coatings. Detection of acoustic emission generated during the scratch test proved to be a significant improvement for the coating evaluation.

Enhancing Mar and Abrasion Resistance of Acrylic Hard Coatings with Soft Base Layer

Mar and abrasion resistance were investigated by a progressive load scratch test and steel wool abrasion test, respectively. Two acrylic coating systems including trimethylolpropane triacrylate (TMPTA) and pentaerythritol triacrylate (PETA) were prepared. A soft base layer was introduced as an intermediate layer between two different types of top layer and poly (methyl methacrylate) (PMMA) substrate to demonstrate the effect of soft base layer on mar and abrasion resistance. Abrasion damage on the coating surface was found to be less severe, when the soft base layer was incorporated into the coating systems. The reduction in scratch coefficient of friction (SCOF) and surface roughness was also observed. The results suggested that mar and abrasion resistance was greatly influenced by the presence of soft base layer, although different top layers were used. Moreover, it was found that abrasion resistance was further improved as the thicker soft base layer was applied.

Graphene reinforced UV-curable epoxy resins: Design, manufacture and material performance

Abstract Graphene and its derivatives (graphene oxide, reduced graphene, functionalised graphene oxide, and functionalised reduced graphene oxide) are found to improve the mechanical properties of the polymers in which they are dispersed. In the present work, the potential of graphene and its derivatives in terms of their anti-scratch performance is thus investigated. In particular, graphene oxides, as-is graphene nano-platelets and reduced graphene oxides that were functionalised with amino-propyl triethoxy silane (APTES) were blended as reinforcing phases in UV curable epoxy coatings on polycarbonates, and the resulting performances were comparatively evaluated. Additionally, UV curable epoxy coatings covalently bonded to amino-functionalised silica-nanoparticles were studied. The experimental analyses involved FT-IR spectroscopy to study the chemical interactions that occurred among the different compounds in the investigated mixtures, progressive and constant load scratch tests and SEM images of the residual scratch patterns to evaluate the micro-mechanical response and scratch visibility of the coatings. APTES-functionalised reduced-graphene oxide was found to be able to reduce the scratch visibility, thus revealing its suitability to promote the effective anti-scratch properties of UV-curable bis cyclo-aliphatic epoxy resins deposited on polycarbonate.

Highly oriented microstructures and surface mechanical properties of polypropylene (PP) molded by ultra-high shear rate

Raman spectroscopy and wide-angle X-ray diffraction (WAXD) were used to evaluate microstructures, i.e. molecular orientation, crystalline orientation and the relative amount of β-phase crystal (K), near the surface of injection molded polypropylene (PP). It was found that highly ordered structure near the surface (0–30 μm) was formed when ultra-high injection speed (1000 mm/s or γ˙ = 1670s−1) was utilized. Subsequently, increase of relative amount of β-phase crystal near the surface was achieved. The relationship between the microstructures and surface mechanical properties measured by micro-cutting method and progressive load scratch tests was investigated. The highly oriented PP showed higher surface mechanical properties due to the increase in degree of molecular and crystalline orientation. The increased scratch properties were considered to be also affected by higher β-phase crystal content.

Scratch- and wear-resistant photoluminescent silicone epoxy coatings on floor tiles

Photoluminescent silicone epoxy resins were prepared by physical dispersion of SrAl2O4:Eu2+, Dy3+ pigments. The resin was deposited on ceramic tiles for flooring by automatic drawdown and left to harden at ambient conditions. Morphology of the coated tiles was measured by contact gage profilometry and field emission gun scanning electron microscopy. Mechanical response was investigated by pencil and cross-hatch scratch tests; depth-sensing indentation measurements were performed using Vickers and flat punch indenters. Tribological response of the coated tiles was measured by progressive and constant load scratch tests and dry sliding linearly reciprocating ball-on-flat tests, respectively. Intensity of photoluminescent radiations and the corresponding decay time were estimated by digital imaging. The photoluminescent coatings feature high hardness, scratch and wear endurance as well as good clarity. Being the resin designed for spontaneous drying and suitable for easy-to-automate and versatile deposition processes, it is the ideal candidate for the decoration of a large variety of substrates as well as for the repowering and/or retrofitting of previous installations.