Scratch Response Research Articles

Augmenting microstructure and tribological performance of wire arc additive manufactured PH13-8Mo stainless steel via TiC/TiB2 nano-particles incorporation

This study aimed to investigate the effect of TiC and TiB2 nano-inoculants addition on the microstructure and tribological behavior of PH13-8Mo stainless steel processed through wire arc additive manufacturing (WAAM). The incorporation of TiC/TiB2 inoculants demonstrated notable efficiency in mitigating the anisotropic wear and scratch response and enhancing wear resistance observed in the as-printed state. This improvement was ascribed to the refinement of the grain structure, disruption of the columnar structure, and increased content of the retained austenite. Notably, TiB2 inoculation exhibited superior grain refinement and achieved the highest hardness. However, the TiC-inoculated condition demonstrated the best wear resistance, attributed to its excellent combination of hardness and fracture resistance, and a higher contribution of strain-induced martensite transformation during wear testing. Additionally, the implementation of post-printing solutionizing and aging treatment was found to improve the scratch and wear resistance of the alloy, attributed to the formation of nano-sized β-NiAl precipitates. The main wear mechanism observed involved oxidation wear, adhesive wear, and three-body abrasive wear. The findings of this study highlight the significant potential of incorporating ceramic-based nano-particles for improving the wear resistance of WAAM PH13-8Mo components, particularly in demanding applications like injection molding dies where superior abrasion resistance is paramount.

Modification of Microstructural and Surface-Mechanical Properties of Nickel-Coated Copper by Ultrasonic Shot Peening with Emphasis on Scratch Response

Modification of Microstructural and Surface-Mechanical Properties of Nickel-Coated Copper by Ultrasonic Shot Peening with Emphasis on Scratch Response

Effect of grain boundary on scratch behavior of polycrystalline copper

The anisotropy in the elastoplastic response of crystalline solids influences substantially their scratch resistance at the microscale. While grain boundaries typically act as obstacles to the motion of dislocations at the grain level, the scratch behavior in the vicinity of the grain boundary is influenced by other factors such as crystallographic orientation and pile-up topography. We performed a systematic set of nano-scratch simulations using the mechanism-based strain gradient crystal plasticity to study the evolution of scratch force and depth near grain boundaries. To validate our model, we conducted a nano-scratch test on a polycrystalline copper sample and compared the scratch depth profile for a specific grain boundary with the simulated result, where a good qualitative agreement was achieved. Our simulations showed that the scratch depth, force, and hardness vary between the corresponding values for the individual constitutive grains, and the variation decreases by reducing the grain size. Additionally, we analyzed the scratch response in terms of the pile-up topography and subsurface stresses and distinguished different regimes when the indenter approaches and scratches across the boundary. Our findings offer a new direction to optimize the scratch resistance of polycrystalline metals by tailoring the size and orientation of grains near the surface. Additionally, it introduces scratching as a robust material characterization method.

Scratch Response of Hollow Cathode Radiofrequency Plasma-Nitrided and Sintered 316L Austenitic Stainless Steel

Low-temperature plasma nitriding is a thermochemical surface treatment that promotes surface hardening and wear resistance enhancement without compromising the corrosion resistance of sintered austenitic stainless steels. Hollow cathode radiofrequency (RF) plasma nitriding was conducted to evaluate the influence of the working pressure and nitriding time on the microstructure and thickness of the nitrided layers. A group of samples of sintered 316L austenitic stainless steel were plasma-nitrided at 400 °C for 4 h, varying the working pressure from 160 to 25 Pa, and the other group was treated at the same temperature, varying the nitriding time (2 h and 4 h) while keeping the pressure at 25 Pa. A higher pressure resulted in a thinner, non-homogeneous nitrided layer with an edge effect. Regardless of the nitriding duration, the lowest pressure (25 Pa) promoted the formation of a homogenously nitrided layer composed of nitrogen-expanded austenite that was free of iron or chromium nitride and harder and more scratching-wear-resistant than the soft steel substrate.

Environmental influences on induction of itching and scratching using immersive virtual reality

Chronic itching is a serious and uncomfortable condition. The scratch response might result in a vicious cycle of alternating itching and scratching. To develop psychological interventions for people suffering from chronic itching and to break the vicious itch-scratching-itch cycle, it is important to elucidate which environmental factors trigger itch sensations. Virtual reality (VR) techniques provide a useful tool to examine specific content characteristics in a three-dimensional (3D VR) environment and their influences on itch sensations and scratching behaviour. This article describes two experiments in which we focused on the effects of environmental information on itching and scratching behaviour. Additionally, in the second experiment, we examined the influence of having a chronic skin condition on sensitivity to itch induction. We found evidence for the importance of the content of audio–visual materials for the effectiveness in inducing feelings of itch in the observers. In both experiments, we observed significantly higher levels of perceived itch in the itch-inducing conditions than in the control condition. Moreover, the results showed that elevated levels of perceived itch were associated with an increase in scratching behaviours, which was especially salient in the contagious itch condition, in which perceived itch was accompanied by a significant increase in the number of scratches. Experiment 2 additionally showed increased perceived itch levels in participants who reported having a chronic skin condition, reflecting higher sensitivity to itch-inducing audio–visual stimuli in this group than in participants without a chronic skin condition. Based on the results we concluded that directing attention towards itch- or scratch aspects of related information in the environment and to the consequences for one’s own skin are effective tools to induce itch sensations and scratching behaviour. This knowledge provides tools for developing novel strategies in advising and treating people suffering from chronic itching and breaking the vicious itch-scratching-itch cycle.

Thermal and tribo-mechanical properties of high-performance poly(etheretherketone)/reduced graphene oxide nanocomposite coatings prepared by electrophoretic deposition

The thermal stability and degradation, near-to-surface mechanical properties, and scratch resistance and damage mechanism of poly(etheretherketone) (PEEK)/reduced graphene oxide (RGO) nanocomposite coatings are analyzed and discussed in terms of their nanosheet content and microstructure. Although RGO modified the thermal stability and degradation of the polymeric matrix, for instance, by slightly reducing the onset degradation temperature, its addition was not a limiting factor in the PEEK processing. Respecting the microstructural features induced by the nanosheets, the nanocomposite coatings were found to exhibit (i) a partially exfoliated and large-scale co-continuous morphology related to RGO nanosheets whose basal planes were mainly aligned with the coating surface, (ii) a dendritic morphology of PEEK domains related to transcrystallinity, (iii) and irregular domains associated with the deposition of PEEK particles wrapped by the nanosheets. The changes provoked by RGO in the morphology and PEEK crystalline phase influenced the near-to-surface mechanical properties, scratch resistance, and scratch damage mechanism of the nanocomposite coatings. Within this context, the interlayer strength between the nanosheets in the large-scale co-continuous morphology and PEEK transcrystallinity had an important effect. Furthermore, the random-bumpy surface texture formed by the irregular PEEK domains together with the conformal cracking damage mechanism was decisive in the scratch response of the PEEK/RGO nanocomposite coatings. The comprehensive characterization carried out in this work concludes that PEEK/RGO electrophoretic coatings are suitable for a variety of applications requiring tribo-mechanical resistance.Graphical

On the size effect in scratch and wear response of single crystalline copper

Indentation hardness is a well-known material parameter for determining the resistance of a material to deformation. It is however known that indentation hardness alone cannot fully characterize anisotropic material strength in particular for single crystalline materials. Recently, it is shown that scratch hardness is a more suitable material property to characterize the wear response of crystalline materials. In this study, we use the mechanism-based strain gradient crystal plasticity to explore the size effect in the scratch behavior of single crystalline copper. Our simulations picture strong size effects in the scratch hardness value and pile-up magnitude. Interestingly, it shows that the degree and nature of size-dependency for these two parameters varies significantly and oppositely by the scratch direction. For instance, while [001] direction shows the highest degree of size effect in scratch hardness, it presents the lowest pile-up size effect. This opposite effect is explained in terms of the contribution of different slip systems to dislocation resistance and work hardening. We also show that scratch hardness, which takes into account both the size effect and crystallographic direction dependence, is an appropriate material property for wear characterization.

Effect of heat treatment on microstructure and tribological performance of PH 13-8Mo stainless steel fabricated via wire arc additive manufacturing

The scratch and reciprocating sliding wear response of a PH 13-8Mo stainless steel fabricated by wire arc additive manufacturing (WAAM) are investigated after different cycles of post-printing heat treatments and correlated with the microstructure and mechanical properties. The performed heat treatment cycles comprised of solutionizing for 1 h at 1050 °C followed by an aging cycle for 4 h at 400 °C, 500 °C, and 600 °C. The optimum aging temperature was found to be at 500 °C under which hardness, scratch, and wear resistance were maximum and the coefficient of friction was minimum due to removal of determinantal δ-ferrite phase from the as-printed microstructure and the attained precipitation hardening through the formation of coherent nano-scale β-NiAl precipitates. The employed heat treatment was effective in eliminating the anisotropic scratch and wear response in the as-printed part arising from its anisotropic microstructure. The overall wear micro-mechanisms were similar for as-printed and heat-treated conditions with ploughing during scratch test, and adhesive, oxidative, and three body abrasive wear mechanism during the reciprocating sliding wear test. The results showed that WAAM-produced PH 13-8Mo parts have great potential to be an alternative to their wrought counterparts for wear resistance demanding applications.

Scratch and corrosion behaviour study of electroless Ni-B reinforced with ultrasonicated nano TiO2

The present investigation is a study into the scratch and corrosion response of as-coated Ni-B-TiO2 as compared to the as-deposited Ni-B coatings. Ultrasonicated nano TiO2 particles were used to reinforce electroless Ni-B coatings. The presence of hard nano TiO2 particles improved the scratch hardness of the Nickel-Boron-TiO2 coatings. During the scratch test for an applied load of 20 N, the Nickel-Boron-TiO2 coating showed a decrease of 42 % in scratch width as compared to the Ni-B coatings. Corrosion behavior also showed remarkable improvement with the addition of nanoparticles. As compared to the Nickel-Boron coatings, the corrosion potential Ecorr improved by 5 % while the corrosion current density Icorr showed a 1.5-fold decrease for Ni-B- TiO2 coatings. The double-layer capacitance Cdl which is a qualitative indicator of the porosities present in the coatings was nearly halved with the addition of TiO2 nanoparticles. The specimen underwent SEM analysis for the morphological study and scratch testing to determine the scratch hardness and corrosion behaviour to identify the electrochemical response to a corrosive environment.

Scratch responses of ductile materials by instrumented scratch with a spherical indenter under progressive load

Scratch responses of ductile materials by instrumented scratch with a spherical indenter under progressive load

Testing length-scale considerations in mechanical characterization of WC-Co hardmetal produced via binder jetting 3D printing

The extreme versatility of additive manufacturing (AM) as processing technology results in “AMed pieces” with intrinsic characteristics linked to the shaping route followed, which are also key for defining mechanical integrity. The latter requires validation by measuring the mechanical properties, at both macroscopic (global) and microscopic (local) levels; and thus, consideration of specific testing length-scale aspects. This work aims to study the correlation between microstructure and mechanical properties for a WC-12%wt.Co hardmetal grade produced via binder jetting 3D printing (BJT) and subsequent sintering. In doing so, macro- and micro- Vickers hardness as well as scratch tests, using different loads and indenter tips, are conducted. It is found that studied samples processed by means of BJT exhibit a microstructure consisting of a relatively wide carbide size distribution, including a significant volume fraction (higher than 15%) of carbides larger than 3 μm. This is a direct consequence of the relatively high sintering temperature needed for getting full dense specimens, when manufactured following this AM route. Meanwhile, mechanical properties are found to be isotropic, with hardness and scratch resistance values falling within ranges of those expected for hardmetals with similar binder content and mean carbide grain size. Very interesting, length-scale effects on testing are observed in terms of dispersion of measured hardness value as applied load decreases. These findings, together with similar ones linked to length-scale influence on scratch response, point out that effective selection of mechanical testing parameters become critical for studying and understanding phenomena such as elastic/plastic and deformation/fracture transitions in AMed hardmetals.

Mechanisms of pruritus in cholestasis: understanding and treating the itch.

Pruritus in cholestatic liver diseases can be a major burden and dramatically impair the quality of life of those affected. Here, we provide an update on the latest insights into the molecular pathogenesis of and novel therapeutic approaches for cholestasis-associated itch. Endogenous and exogenous small-molecule pruritogen candidates bind to their receptors on unmyelinated itch C-fibres in the skin. Candidate pruritogens in cholestasis include certain lysophospholipids and sulfated progesterone metabolites, among others, whereas total bile acid or bilirubin conjugates seem unlikely to have a dominant role in the pathogenesis of cholestasis-associated pruritus. Transmission of itch signals via primary, secondary and tertiary itch neurons to the postcentral gyrus and activation of scratch responses offer various targets for therapeutic intervention. At present, evidence-based treatment options for pruritus in fibrosing cholangiopathies, such as primary biliary cholangitis and primary sclerosing cholangitis, are the peroxisome proliferator-associated receptor (PPAR) agonist bezafibrate and the pregnane X receptor (PXR) agonist rifampicin. In pruritus of intrahepatic cholestasis of pregnancy, ursodeoxycholic acid is recommended and might be supported in the third trimester by rifampicin if needed. Alternatively, non-absorbable anion exchange resins, such as cholestyramine, can be administered, albeit with poor trial evidence. Liver transplantation for intolerable refractory pruritus has become an extremely rare therapeutic strategy.

Effects of Dopants on Scratch Responses of Diamond-Like Carbon Films by Rockwell C Diamond Indenter

Effects of Dopants on Scratch Responses of Diamond-Like Carbon Films by Rockwell C Diamond Indenter

Extraction of the plastic properties of metallic materials from scratch tests using deep learning

Powered by machine learning and computer technology, neural networks have opened new paths for solving engineering problems. In this paper, the plastic parameters, i.e., the yield stress and strain hardening index, of metallic materials are extracted from scratch tests using deep learning methods. Using a dataset generated by finite element simulations, three network models, i.e., the classical multi-output multi-layer perceptron (MLP), a single-target approach (ST-MLP) and the parameter sharing-based deep network (DMTR), are adopted to determine the relationship between scratch responses and plastic parameters. According to the test dataset results, the DMTR performs better than the MLP and ST-MLP. The trained DMTR is verified by comparing the plastic parameters of 18CrNiMo7-6 alloy steel, 304 stainless steel, and brass obtained from scratch tests with those under tension. This work is expected to provide an alternative method for determining the plastic parameters of metallic materials.

Generalized resistance to pruritogen-induced scratching in the C3H/HeJ strain.

Previously the effect of the pruritogens, such as histamine and chloroquine, was tested in 11 inbred mouse strains, and this study aimed to identify resistant and sensitive strains, consistent with the observation that underlies the large variability in human populations. In the present study, we used the low responder C3H/HeJ (C3H) and the more sensitive C57BL/6J (C57) strain to find out if resistance and sensitivity to develop pruritus is restricted to only histamine and chloroquine or extends to other known pruritogens as well. We tested five additional commonly known pruritogens. We established dose-response relationships by injecting four concentrations of the pruritogens in the range of 0.3, 1, 3, and ten-fold in the nuchal fold. Then we assessed the scratching behavior for 30 min after injection with an automated custom-designed device based on the bilateral implantation of mini-magnets in the hind paws and on single cages placed within a magnetic coil. We found that the resistance to pruritogens is a general phenotype of the C3H strain and extends to all pruritogens tested, including not only histamine and chloroquine, but also endothelin, trypsin, 5-HT (serotonin), the short peptide SLIGRL, and Lysophosphatidic acid (LPA). C57 was more sensitive to all pruritogens and, in contrast to C3H, dose-response relationships were evident for some of the pruritogens. In general, comparable peak scratch responses were observed for the 0.3-fold concentrations of the pruritogens in C57 whereas C3H required at least the ten-fold concentration and still displayed only between 5 and 33% of the scratch responses observed in C57 for the respective pruritogen. The general resistance to pruritogens and the low level of scratching behavior found in the C3H strain is an interesting trait and represents a model for the study of the heritability of itch. It is accompanied in C3H with a higher sensitivity in assays of nociception.

On the anisotropic scratching behavior of single crystalline copper at nanoscale

Anisotropic material behavior raises some difficulties in characterizing and predicting the wear response of crystalline materials. A systematic set of nano-scratch crystal plasticity finite element simulations and experiments is performed to study the effect of crystal orientation and scratching direction on the wear resistance of single crystalline copper. Our results show that the scratching profile and wear volume are significantly influenced by the crystallographic orientation and scratching direction, suggesting a considerable anisotropy in the scratch response of crystalline copper. Quantifying the wear volume using Archard’s wear law shows that this anisotropy results in an orientation and scratching direction dependent wear coefficient. Alternatively, it is shown that a unique wear coefficient can be obtained for crystalline materials when one uses the scratching hardness in Archard’s wear law. This new finding may help to unify discrepant experimental and numerical wear observations and to advance physics-based wear laws without empirical coefficients.

Tailoring the scratch adhesion strength and wear performance of TiNiN nanocomposite coatings by optimising substrate bias voltage during cathodic arc evaporation

The tribological properties of TiN-based coatings can be substantially influenced by the choice of substrate bias employed during physical vapor deposition. However, the effects of applied substrate bias voltages during cathodic arc evaporation on to the scratch adhesion strength and wear resistance of TiNiN coatings have not been previously studied. In this present work, a series of TiNiN coatings were fabricated onto tool steel (M2) substrates using the cathodic arc evaporation method by applying a range of bias voltages to the substrate. The aim of this study is to investigate the scratch response and wear performance of these coatings along with an investigation of the deformation mechanisms in operation during scratch and wear tests. The best scratch adhesion strength (i.e., greater LC1, LC2 and CPRs values) was noted for the coating prepared at a bias voltage of −100 V, which was ascribed to the synergistic responses arising from superior mechanical properties, the influence of a high compressive residual stress and a fine, equiaxed nanocomposite structure, that acted to promote effective resistance against cohesive and adhesive failure. Further, the failure mechanisms under progressive loading conditions were also investigated through observation of the complex crack patterns generated, compressive residual stress values and the coatings' hierarchical design. An approximately 85 % enhancement in wear resistance for these TiNiN coatings was achieved as the bias voltage was increased from 0 V to −100 V. This −100 V coating exhibited the highest values of H/Er (>0.1) and We (>60 %), as well as the highest Ni concentration (~ 4 at.%).

GPR15L is an epithelial inflammation-derived pruritogen.

Itch is an unpleasant sensation that often accompanies chronic dermatological conditions. Although many of the itch receptors and the neural pathways underlying this sensation are known, the identity of endogenous ligands is still not fully appreciated. Using an unbiased bioinformatic approach, we identified GPR15L as a candidate pruritogen whose expression is robustly up-regulated in psoriasis and atopic dermatitis. Although GPR15L was previously shown to be a cognate ligand of the receptor GPR15, expressed in dermal T cells, here we show that it also contributes to pruritogenesis by activating Mas-related G protein–coupled receptors (MRGPRs). GPR15L can selectively stimulate mouse dorsal root ganglion neurons that express Mrgpra3 and evokes intense itch responses. GPR15L causes mast cell degranulation through stimulation of MRGPRX2 and Mrgprb2. Genetic disruption of GPR15L expression attenuates scratch responses in a mouse model of psoriasis. Our study reveals unrecognized features of GRP15L, showing that it is a potent itch-inducing agent.

Motor-like Tics are Mediated by CB2 Cannabinoid Receptor-dependent and Independent Mechanisms Associated with Age and Sex

Δ9-Tetrahydrocannabinol (Δ9-THC) inhibits tics in individuals with Tourette syndrome (TS). Δ9-THC has similar affinities for CB1/CB2 cannabinoid receptors. However, the effect of HU-308, a selective CB2 receptor agonist, on repetitive behaviors has not been investigated. The effects of 2,5-dimethoxy-4-iodoamphetamine (DOI)-induced motor-like tics and Δ9-THC were studied with gene analysis. The effects of HU-308 on head twitch response (HTR), ear scratch response (ESR), and grooming behavior were compared between wildtype and CB2 receptor knockout (CB2−/−) mice, and in the presence/absence of DOI or SR141716A, a CB1 receptor antagonist/inverse agonist. The frequency of DOI-induced repetitive behaviors was higher in CB2−/− than in wildtype mice. HU-308 increased DOI-induced ESR and grooming behavior in adult CB2−/− mice. In juveniles, HU-308 inhibited HTR and ESR in the presence of DOI and SR141716A. HU-308 and beta-caryophyllene significantly increased HTR. In the left prefrontal cortex, DOI increased transcript expression of the CB2 receptor and GPR55, but reduced fatty acid amide hydrolase (FAAH) and α/β-hydrolase domain-containing 6 (ABHD6) expression levels. CB2 receptors are required to reduce 5-HT2A/2C-induced tics in adults. HU-308 has an off-target effect which increases 5-HT2A/2C-induced motor-like tics in adult female mice. The increased HTR in juveniles induced by selective CB2 receptor agonists suggests that stimulation of the CB2 receptor may generate motor tics in children. Sex differences suggest that the CB2 receptor may contribute to the prevalence of TS in boys. The 5-HT2A/2C-induced reduction in endocannabinoid catabolic enzyme expression level may explain the increased endocannabinoids’ levels in patients with TS.

Influence of substrate bias on the scratch, wear and indentation response of TiSiN nanocomposite coatings

TiSiN coatings were synthesised onto AISI M42 tool steel substrates via closed field unbalanced magnetron sputtering ion plating , using bias voltages of −40 and −50 V. The aim of this study is to investigate the underlying deformation mechanisms of TiSiN coatings, prepared at two different substrate bias voltages, following scratching, wear and indentation tests . A graded columnar microstructure evolved in these coatings. A hardness value of ~30.2 GPa was determined in the coating prepared at the lower bias voltage (i.e., −40 V), which was correlated to the fine nanocomposite structure and the presence of a high compressive residual stress. Of note, for the coating deposited at −40 V enhanced scratch adhesion strength , i.e., higher critical loads (L c1 and L c2 ) against cohesive and adhesive failure were determined with the higher H/E r and H 3 /E r 2 values. The improved scratch resistance was ascribed to the hierarchical structure that hindered crack propagation in the TiSiN coatings during progressive loading. An approximately 21% decrease in wear rate was obtained at the lower bias voltage, which was attributed to the slightly lower Si concentration (~8.3 at.%) and, in turn, higher hardness. Deformation behaviour under indentation loading was dominated by shear sliding along the columnar grain boundaries. • ~20% increase in L c1 was found in the TiSiN coating with the lower Si content. • The scratch resistance was enhanced by the coating's hierarchical structure. • ~21% reduction in wear rate was achieved in the coating with the lower Si content. • Indentation deformation was governed by columnar shear sliding.