3D Digital Microscope Research Articles

Microscopic analyses of the effects of mechanical cleaning interventions on cut marks

In many cases, the study of archaeological fossil surfaces is not possible without prior intervention by conservation-restoration specialists. This is most notable in the required cleaning process that facilitates detailed analyses of osteological remains. This experimental study develops a methodology that can be used to evaluate the possible effects that mechanical cleaning applications and tools may have on the consequent study of cut marks. To confront these objectives, this study implements advanced 3D digital microscopy and statistical analyses to evaluate the before and after stages of mechanical cleaning processes of cut-marked bones. These techniques present a novel means of evaluating the degree of modification produced by mechanical cleaning processes. The obtained data allows for an initial assessment of the effects of conservation-restoration interventions on taphonomic analyses. The consequent conclusions advise caution on the use of some tools in mechanical cleaning, additionally supporting the need for interdisciplinary research in future archaeological research. Research of this nature is of great value to archaeology and palaeontology, presenting a new promising line of investigation for future research.

Using 3D digital microscopy and SEM-EDX for in-situ residue analysis: A multi-analytical contextual approach on experimental stone tools

Residue analysis is a sub-discipline in archaeology that uses a variety of techniques which can be useful for determining the function of prehistoric stone tools. Past experimental studies have revealed the non-diagnostic nature of residues under reflected light microscopy and the challenges of identifying them as plant or animal and assigning them to a specific origin (i.e. use-related vs incidental). Recently, new contextual approaches and analytical techniques have addressed these limitations. Prior studies have suggested that use-related and incidental residues can be identified on stone tool surfaces based on differences in distribution patterns. Location, residue frequency, and associations with other residues are often the main criteria used in these studies to distinguish use-related from incidental residues, while other contextual information such as directionality, aspects of crushing and smearing, or dispersion from the working edge are often ignored. Moreover, the integration of chemical information provided by other analytical techniques into these contextual approaches that address residue mapping has received little attention. In this study, we address these issues and combine contextual information recorded through 3D digital microscopy with elemental compositions obtained through SEM-EDX to better identify different animal and plant residues on experimental stone tools. Based on an experimental sample tested under outdoor field conditions, we show how identification issues in fresh undamaged residues are not only restricted to the ambiguity between different use-related remains, but also the ambiguity between the latter and incidental residues. We demonstrate the versatility of 3D DM in recording in-situ contextual information of fresh residues (distribution patterns, invasiveness, disposition of specific tissues indicating tool-use direction, and aspects of crushing and smearing) and how supporting this information with the elemental composition obtained through SEM-EDX and element maps can help to improve identification of ambiguous residues, both use-related and incidental. Although more experiments are needed, the multi-analytical contextual approach tested here provides an example of in-situ characterization of fresh undamaged residues in experimental tools that can be conducted before performing post-depositional experiments or using other analytical techniques and extraction protocols.

Cubic boron nitride wheel topography effects on phase transformation of maraging C250 steel and grinding surface quality

It is likely for the interaction between the cubic boron nitride grains on the working surface of grinding wheels and maraging C250 steel workpiece to cause phase transformation, thus reducing the material removal rates and affecting the quality of the workpiece surface generated during grinding. Up to now, there remain few studies focusing on the relationship between grinding wheel topography and phase transformation. In this study, an analysis was conducted of the effects that the topography of cubic boron nitride grinding wheel has on the distribution of phase transformation and the surface quality of maraging steel during grinding. The phase transformation diffraction curve was plotted based on the results of X-ray diffraction (XRD) analysis, and then, it was compared with the known data under different grinding wheel conditions. The topography of the cubic boron nitride grinding wheel was characterized using 3D digital microscope analysis, and the dynamic abrasive grit density coefficient λd for micro-grinding was proposed to clarify the effect of relevant parameters on phase transformation. The surface quality of grinding wheel and workpiece after grinding was analyzed, while the combination of different grinding wheel topography parameters and the process optimization scheme were proposed to achieve the optimal effect of grinding.

Volumetric Changes in Morse Taper Connections After Implant Placement in Dense Bone. In-Vitro Study.

The stability of the implant–abutment interface is crucial for the maintenance of the implant index integrity. Several factors are capable of inducing deformation in implant–abutment connection, such as the actual insertion of the implant into the bone. This study aimed to evaluate the deformations produced in the connection after the insertion of the implant. Ten implants with two different implant carriers (Type A: carrier attached to platform and Type B: carrier attached inside the index-connection) were placed in artificial Type II bone, and volumetric changes were evaluated for different connection features with a 3D digital microscope. ANOVA (analysis of variance), Wilcoxon, and Tukey HSD post-test were used for statistical comparisons. Type A implants presented deformation at the platform level (inner slot angles and slot width), but no volumetric changes were observed inside the connection. Type B implants presented deformation in three parameters inside the connection (outer channel length, coronal step width, and coronal step length). Within the limitations of this study, we can conclude that more deformation is expected at the internal connection when the implant carrier engages this area. The engagement area should be as far away as possible from the index connection.

Scratches and grazes: a detailed microscopic analysis of trampling phenomena.

Sedimentary abrasion and postdepositional damage to fossil remains are of great interest if considering the possible distortion they could produce in the archaeological and paleontological record. Since their discovery, natural agents such as trampling phenomena have been a topic of great taphonomic interest. Nevertheless, the majority of investigation into these traces has focused almost exclusively on their differentiation from other anthropic agents such as cut marks. In recent years, advances into bone surface modification analysis via geometric morphometrics have proven useful for in-depth characterization of different taphonomic traces; including cut, tooth and percussion marks. Through this, a preliminary study of trampling marks using advanced 3D digital microscopy was able to detect differences between what have since been known as scratch and graze marks. The present study expands from this, developing a more detailed analysis of these traces. Here, we use advanced data science techniques to provide a means of understanding trampling mark variations, contributing to our knowledge of site formation processes. Our results show how scratch and graze marks are a product of progressional decay and changes in cortical hardness, providing a new means of understanding taphonomic processes. LAY DESCRIPTION: The study of microscopic bone surface modifications in archaeology and palaeontology is of great importance, allowing for a detailed reconstruction of the formation of a site and providing a means of interpreting the fossil register. The damage that sedimentary abrasion can produce, however, is likely to distort and influence these studies, thus requiring a detailed understanding of the different traces that can be found on different materials. Here, we use advanced 3D digital microscopy and pattern recognition algorithms to analyse the different marks produced in different sedimentological contexts, also controlling for other variables such as the state of the bone when buried, the type of bone and the time exposed to these types of damages. Through this detailed microscopic analysis of these types of damages, we are able to conclude that morphological variations in trampling marks are product of the state of decay when the bones are buried.

Influence of Graphite/Graphene on the Tribological Behaviors of Self-Lubricating Fabric Composite.

Graphite/graphene particles were employed as functional fillers to modify hybrid polytetrafluoroethylene/polyisophthaloyl metaphenylene diamine (PTFE/Nomex) fabric-reinforced phenolic composites. The tribology behavior was investigated using a ball-on-disk wear tester, together with a 3D digital microscope. The graphite/graphene exhibits the synergetic effect from the results, which not only reduces the friction efficient but also improves the wear resistance of the composites. Moreover, the wear mechanisms were studied by the wear surface microstructure analysis. It is proposed that the synergetic effect includes mainly the positive rolling effect from the graphene and an improved load-carrying capacity brought by graphite. In addition, in order to obtain the optimized formulation to satisfy the bearing application, the influence of graphite and graphene content on the tribological property of the composites was studied in detail. On the basis of that, the application research was carried out on the bearing oscillating wear test, which will evaluate the engineering service life of the composite.

A Hybrid Geometric Morphometric Deep Learning Approach for Cut and Trampling Mark Classification

The concept of equifinality is currently one of the largest issues in taphonomy, frequently leading analysts to erroneously interpret the formation and functionality of archaeological and paleontological sites. An example of this equifinality can be found in the differentiation between anthropic cut marks and other traces on bone produced by natural agents, such as that of sedimentary abrasion and trampling. These issues are a key component in the understanding of early human evolution, yet frequently rely on qualitative features for their identification. Unfortunately, qualitative data is commonly susceptible to subjectivity, producing insecurity in research through analyst experience. The present study intends to confront these issues through a hybrid methodological approach. Here, we combine Geometric Morphometric data, 3D digital microscopy, and Deep Learning Neural Networks to provide a means of empirically classifying taphonomic traces on bone. Results obtained are able to reach over 95% classification, providing a possible means of overcoming taphonomic equifinality in the archaeological and paleontological register.

Use-wear experimental studies for differentiating flint tools processing bamboo from wood

Bamboo is widespread in south China and is one of the major organic resources in daily use through history due to its similar potential use value as wood. Due to the unfavourable preservation conditions and taphonomic alteration, the rare discovery of well-preserved organic remains from Palaeolithic sites means there is a lack of direct studies on the technology and behaviour of early prehistoric humans. Use-wear analysis has been proved as a reliable method to detect evidence left by working wood and bamboo on stone artefacts. This study aims to provide an experimental reference of use-wear features and patterns to identify and interpret the exploration of bamboo and wood resources in prehistory. In this experiment, 12 flint flakes were selected for processing bamboo stems and pine branches with working motions of whittling, sawing, and chopping. The results show that the use-wear features, including edge scarring, edge rounding, and polish, of bamboo-working and wood-working are distinctive. Edge scarring is closely related to the working motion, and moderate bright to very bright polish is a significant feature associated with bamboo-working. It is possible to distinguish wear traces caused by bamboo-working from those by wood-processing througha combination of low-power and high-power techniques under a 3D digital microscope.

Use-wear experimental studies for differentiating flint tools processing bamboo from wood

Bamboo is widespread in south China and is one of the major organic resources in daily use through history due to its similar potential use value as wood. Due to the unfavourable preservation conditions and taphonomic alteration, the rare discovery of well-preserved organic remains from Palaeolithic sites means there is a lack of direct studies on the technology and behaviour of early prehistoric humans. Use-wear analysis has been proved as a reliable method to detect evidence left by working wood and bamboo on stone artefacts. This study aims to provide an experimental reference of use-wear features and patterns to identify and interpret the exploration of bamboo and wood resources in prehistory. In this experiment, 12 flint flakes were selected for processing bamboo stems and pine branches with working motions of whittling, sawing, and chopping. The results show that the use-wear features, including edge scarring, edge rounding, and polish, of bamboo-working and wood-working are distinctive. Edge scarring is closely related to the working motion, and moderate bright to very bright polish is a significant feature associated with bamboo-working. It is possible to distinguish wear traces caused by bamboo-working from those by wood-processing througha combination of low-power and high-power techniques under a 3D digital microscope.

Beauty is skin deep: the skin tones of Vermeer\u2019s Girl with a Pearl Earring

The soft modelling of the skin tones in Vermeer’s Girl with a Pearl Earring (Mauritshuis) has been remarked upon by art historians, and is their main argument to date this painting to c. 1665. This paper describes the materials and techniques Vermeer used to accomplish the smooth flesh tones and facial features of the Girl, which were investigated as part of the 2018 Girl in the Spotlight research project. It combines macroscopic X-ray fluorescence imaging (MA-XRF), reflectance imaging spectroscopy (RIS), and 3D digital microscopy. Vermeer built up the face, beginning with distinct areas of light and dark. He then smoothly blended the final layers to create almost seamless transitions. The combination of advanced imaging techniques highlighted that Vermeer built the soft contour around her face by leaving a ‘gap’ between the background and the skin. It also revealed details that were otherwise not visible with the naked eye, such as the eyelashes. Macroscopic imaging was complemented by the study of paint cross-sections using: light microscopy, SEM–EDX, FIB-STEM, synchrotron radiation µ-XRPD and FTIR–ATR. Vermeer intentionally used different qualities or grades of lead white in the flesh paints, showing different hydrocerussite/cerussite ratios and particle sizes. Lead isotope analysis showed that the geographic source of lead, from which the different types of lead white were manufactured, was the same: the region of Peak District of Derbyshire, UK. Finally, cross-section analysis identified the formation of new lead species in the paints: lead soaps and palmierite (K2Pb(SO4)2), associated with the red lake.

A journey into the microstructure: Using a multifocal 3D digital light microscope to study archaeological artefacts retrieved from shipwrecks

The multifocal 3D digital light microscope (LM) is an advanced tool which allows the high resolution tracking of surface topographies, morphologies and colours, and offers real-time measurements of parameters such as length and roughness, as well as in-situ field microscopic scale documentation. The use of a multifocal digital LM, equipped with powerful software, is examined in the present work as a justified tool for the study of ancient objects retrieved from shipwrecks. For that purpose, various archaeological objects were studied with an advanced multifocal LM system, which included an improved light sensitivity sensor. The results were compared to other methods, such as XRF, SEM-EDS, Raman spectroscopy and XRD. The use of a multifocal digital LM offers a unique opportunity to relate between the macroscopic and microscopic levels of the surface with colours as they appear in daylight, and correspondingly, in many cases, to expose the manufacturing process of the object.

Comparison of three 3D scanning techniques for paintings, as applied to Vermeer\u2019s \u2018Girl with a Pearl Earring\u2019

A seventeenth-century canvas painting is usually comprised of varnish and (translucent) paint layers on a substrate. A viewer’s perception of a work of art can be affected by changes in and damages to these layers. Crack formation in the multi-layered stratigraphy of the painting is visible in the surface topology. Furthermore, the impact of mechanical abrasion, (photo)chemical processes and treatments can affect the topography of the surface and thereby its appearance. New technological advancements in non-invasive imaging allow for the documentation and visualisation of a painting’s 3D shape across larger segments or even the complete surface. In this manuscript we compare three 3D scanning techniques, which have been used to capture the surface topology of Girl with a Pearl Earring by Johannes Vermeer (c. 1665): a painting in the collection of the Mauritshuis, the Hague. These three techniques are: multi-scale optical coherence tomography, 3D scanning based on fringe-encoded stereo imaging (at two resolutions), and 3D digital microscopy. Additionally, scans were made of a reference target and compared to 3D data obtained with white-light confocal profilometry. The 3D data sets were aligned using a scale-invariant template matching algorithm, and compared on their ability to visualise topographical details of interest. Also the merits and limitations for the individual imaging techniques are discussed in-depth. We find that the 3D digital microscopy and the multi-scale optical coherence tomography offer the highest measurement accuracy and precision. However, the small field-of-view of these techniques, makes them relatively slow and thereby less viable solutions for capturing larger (areas of) paintings. For Girl with a Pearl Earring we find that the 3D data provides an unparalleled insight into the surface features of this painting, specifically related to ‘moating’ around impasto, the effects of paint consolidation in earlier restoration campaigns and aging, through visualisation of the crack pattern. Furthermore, the data sets provide a starting point for future documentation and monitoring of the surface topology changes over time. These scans were carried out as part of the research project ‘The Girl in the Spotlight’.

Fading into the background: the dark space surrounding Vermeer\u2019s Girl with a Pearl Earring

The background of Vermeer’s Girl with a Pearl Earring (c. 1665, Mauritshuis) has, until recently, been interpreted as a flat dark space. The painting was examined in 2018 as part of the research project The Girl in the Spotlight using a combination of micro- and macro-scale analytical techniques. The stratigraphy of the background was determined from samples mounted as cross-sections, and its material composition was analysed using electron microscopy and chromatographic techniques. The underlayer contains mainly charcoal black, and the glaze contains two organic colourants—indigo and weld—and a copper drier. Deterioration of the glaze has made features in the background difficult to discern with the naked eye. Complementary imaging techniques were able to visualise Vermeer’s signature, and the suggestion of folded fabric (possibly a curtain) on the right side of the painting. The distribution of the layer(s) in the background were imaged using: infrared reflectography (900–1100 nm), multi-scale optical coherence tomography scanning, macroscopic X-ray fluorescence and 3D digital microscopy. Vermeer applied the black underlayer vigorously with overlapping brushstrokes that varied in thickness. When he applied the glaze on top, it levelled out to make a smooth flat surface. The visual effect of the background contrasts the figure of the Girl and projects her forward in space, closer to the viewer.

Revealing the painterly technique beneath the surface of Vermeer\u2019s Girl with a Pearl Earring using macro- and microscale imaging

The initial steps that Johannes Vermeer took to create Girl with a Pearl Earring (c. 1665) are, partially or completely, hidden beneath the painted surface. Vermeer’s painting technique involved applying underlayers that vary in colour and thickness, on top of which he applied the upper paint layer(s). To investigate the painting’s genesis, the Girl was examined using non-invasive scientific imaging as part of the project The Girl in the Spotlight (2018). This was complemented by the re-examination of existing paint cross-sections using microscopic analytical techniques, including focused ion beam-scanning transmission electron microscopy (FIB-STEM). The weave of the canvas, visible in the X-radiograph, was examined using a new computer-assisted thread-level canvas analysis algorithm to measure the thread spacing and thread angles. The canvas was primed with a warm light grey ground, although probably not by Vermeer himself. The tinted ground provided neutral base tone upon which he began to lay in areas of light and shade in his composition, and some outlines around the figure. Multispectral infrared reflectography( MS-IRR) images in four spectral bands spanning the spectral range from 900 to 2500 nm were collected of the painting at high spatial resolution (50 µm/pixel). Visible 3D digital microscopy visualised the underlayers where Vermeer left them visible around the perimeter of the figure as a contour, and where the upper paint layers are thin. These infrared reflectograms and visible micrographs identified three distinct preparatory phases of Girl with a Pearl Earring: the ground, fine black outlines, and underlayers. Some pentimenti were also detected, including a change in the position of her ear. The combination of examination methods showed that the materials beneath the surface played an important role in establishing the three-dimensional space, fall of light, and the eventual colour in different areas of the painting.

Tribological Properties of New Developed Nano Boric Acid Suspended as Additive in Engine Oil

It is well known that nanoparticles affect the interaction between lubricants and surfaces with various chemical compositions and different chemical and physical properties. In recent years, nanoparticles have started to play more important roles as lubricant additives for their potential in wear, friction and emission reduction and improving lubrication and fuel economy. Although nanolubricants are frequently used for friction tests, little is known about stability and degree of dispersion of these nanoparticles in viscous liquids. Most of them are unstable, agglomerate or aggregate which sediment over time. Boric acid (H3BO3) has always been a very important material due to its broad range of applications such as in medicine, cosmetics, automotive industry, metallurgy and also for miscellaneous purposes in other areas. Literature survey showed that friction between automobile engine parts could be greatly reduced using microscopic particles of boric acid.This study involves the new invention of successful suspension of nano boric acid (BA) additive added into 5W-40 fully synthetic commercial lubricating oil. This invention is confidential and realized by Murat ÖZAYMAN from Tribor ARGE Co. in Teknopark of YILDIZ Technical University in Istanbul-TURKEY. The particle size of BA is determined with (Transmission Electron Microscopy) (TEM). Backscattering and transmittance profiles proved that nano boric acid (BA) particles were in suspension in commercial engine oil. Suspended BA in engine oil is applied between piston ring and cylinder liner system in order to investigate their effect on friction and wear under boundary lubricated conditions. Simulation and measurement of friction and wear were conducted using a reciprocating tribometer. Surface analysis were performed using 3D digital optical microscope, Field Emission Scanning Electron Microscope (FESEM)/X-Ray, X-ray photoelectron spectroscopy (XPS) and Atomic Force Microscopy (AFM). Boron (B) from BA is well detected, mixed with other elements of additives and protected the surface under boundary lubrication conditions. The results indicate that BA can considerably improve the tribological performance of a piston ring and cylinder liner system under lubricated conditions. It has found that the friction coefficient is reduced with nano boric acid (BA) suspended engine oil and protected the surface mostly on cylinder liner mixing with other additives.

Application of Suspended Nanoboric Acid as an Efficient Lubrication Additive in Engine Oil

Lubricants play a vital role in machine life and performance, reducing friction and wear and preventing component failure. Performance-enhancing additives are a vital part of today’s modern lubricants. In response to this need, this experimental work presents the development of the new suspended nanoboric acid (nBA) additive added in engine oil that can drastically lowered friction and wear.This is a new invention of nBA additive hold in suspension and added into 5W-40 fully synthetic commercial lubricating oil. This invention is confidential and realized by Tribor ARGE Co. in Teknopark of YILDIZ Technical University in Istanbul-TURKEY.The particle size of nBA is determined with (Transmission Electron Microscopy) (TEM). Turbiscan Tower Stability Analyzer results proved that nBA particles were in suspension in commercial engine oil. Suspended nBA in engine oil is applied between ball and disk system in order to investigate their effect on friction and wear under lubricated conditions. Simulation and measurement of friction and wear were conducted using a ball on disk reciprocating tribometer UMT-3. Surface analysis was performed using 3D digital optical microscope and surface roughness, Field Emission Scanning Electron Microscope (FESEM)/X-Ray and Atomic Force Microscopy (AFM). Boron (B) from nBA is well detected, mixed with other elements of additives and protected the surface under boundary lubrication conditions. The results indicate that nBA can considerably improve the tribological performance of a ball and disk pairs under lubricated conditions. It has found that the friction coefficient is reduced with nBA suspended engine oil and protected the surface on both ball and disk mixing with other additives.

Whitish haze, soapy globules: micro-analysis of degraded burmese paintings on zinc supports

Two Burmese oil paintings on zinc supports depicting portraits of royal families, dated to the early 20th century by Saya Aye and Saya Mya, showed interesting corrosion, efflorescence and soapy globules for analytical investigation prior to conservation for exhibition. The features and colours on the two paintings, one of which was in worse condition than the other, were obscured by a whitish haze. Paint rupture and losses due to corrosion of the zinc support were apparent. Using a combination of 3D digital microscopy, FTIR microscopy and SEM–EDS, the degradation, as well as the paint materials and artists’ techniques were analysed and discussed. Zinc soaps, oxalates, silicates, hydroxychlorides, carbonates, wax and mould characterized the haze. Interestingly, brown outlines in Aye’s painting appeared unusually dark. Upon analysis, this degradation phenomenon was attributed to micro-sized greenish soap globules that have developed around copper/zinc (brass) particles, causing the brown outlines to lose their intended luminosity. The other painting by Mya, in which the same brown outline was applied, did not show such formation of globules. Detection of oxalates in the corrosion of zinc support and brown outlines are discussed. This study shows the importance in understanding the artists’ materials and techniques, which have consequential effects to the degradation observed.

Analysis of kerf quality on ultrafast laser cutting of anode material for lithium-ion battery

The service performance of lithium-ion battery is greatly affected by the cutting quality of sandwich structure electrode materials. Based on the ultrafast laser cutting experimental system, the ultrafast laser cutting processing parameters of anode material were studied, the processing ability of ultrafast laser on anode material was preliminary showed by the maximum single-scan velocity. The depth, heat affected zone (HAZ) and delamination width of anode kerf were characterized by 3D digital microscope and scanning electron microscope (SEM). It is revealed that kerf depth is a piecewise function of laser power and the ultrafast laser cutting process of anode is dominated by the copper foil. Raman analysis of anode active material shows that the ordered graphite structure is partially damaged in the color-changed zone near kerf edge, providing insight into characterization of HAZ. Kerf characteristics indicate that HAZ and delamination were resulted from heat accumulation, while analysis of anode plasma spectra shows potential impacts of plasma thermal radiation on the defects of anode. When anode material was completely penetrated with single-scan laser exposure, the HAZ size and delamination width of anode material increase with laser power and pulse width. Delamination of anode was completely eliminated by multi-scan ultrafast laser cutting at low laser power and high scanning speed.

Experimental investigation on laser ablation of C/SiC composites subjected to supersonic airflow

Continuous wave laser ablation behavior of C/SiC composites subjected to supersonic airflow, as well as in static air environment, is investigated experimentally. Ablation morphology and microstructure of the ablation region are measured by 3D digital microscope system and profiling system, respectively. Effects of supersonic airflow on the ablation morphology and ablation rates of the C/SiC composite are analyzed. Experimental results indicate that the mechanical erosion by supersonic airflow increases the ablation rates and smoothens the ablation surface. Many carbon fibers are left at the edge of center region due to the cooling effect of the supersonic airflow. The laser ablation behavior of C/SiC composites in supersonic airflow is attributed to the combined effect of convective cooling and mechanical erosion.

Effect of a DC Stray Current on the Corrosion of X80 Pipeline Steel and the Cathodic Disbondment Behavior of the Protective 3PE Coating in 3.5% NaCl Solution

The influence of a direct current (DC) stray current on the corrosion and cathodic disbondment of X80 steel coated with a polyethylene (3PE) coating in 3.5% NaCl solution was studied by immersion experiments, electrochemical tests, three-dimensional microscopy, and a surface analysis. The results showed that the potential of the X80 steel sample shifts under the direct current. After 100A/m2 DC interference was applied, the potential of the sample in the anode region positively shifted from –0.68 to –0.43 V. At the same time, the sample in the cathode region negatively shifted to –1.45 V. Under the DC anode action, the X80 steel corrosion exhibited no passivation and followed Faraday’s law of electrolysis, in which the corrosion rate is proportional to the current density. Three-dimensional (3D) digital microscopy showed that, as the DC current increased, the depth of the corrosion pit also increased (gradually), indicating a higher corrosion degree. The sample in the cathode region only underwent a hydrogen evolution reaction, which caused cathodic disbondment of the coating. The stray current had a critical current density for the coating disbonding: the coating delamination area reached its maximum and then remained unchanged.