Pit Size Research Articles

Electrochemical behavior of 2205 duplex stainless steel in simulated solution containing high concentration Cl− and saturated CO2 at different temperatures

2205 duplex stainless steel (DSS) has good corrosion resistance due to its typical duplex organization, but the increasingly harsh CO2-containing oil and gas environment leads to different degrees of corrosion, especially pitting corrosion, which seriously threatens the safety and reliability of oil and gas development. In this paper, the effect of temperature on the corrosion behavior of 2205 DSS in a simulated solution containing 100 g/L Cl− and saturated CO2 was investigated with immersion tests and electrochemical tests and combined with characterization techniques such as laser confocal microscopy and X-ray photoelectron spectroscopy. The results show that the average critical pitting temperature of 2205 DSS was 66.9 °C. When the temperature was higher than 66.9 °C, the pitting breakdown potential, passivation interval, and self-corrosion potential decreased, while the dimensional passivation current density increased, and the pitting sensitivity was enhanced. With a further increase in temperature, the capacitive arc radius of 2205 DSS decreased, the film resistance and charge transfer resistance gradually decreased, the carrier density of the donor and acceptor in the product film layer with n + p bipolar characteristics also increased and the inner layer of the film with Cr oxide content decreased, while the outer layer with Fe oxide content increased, the dissolution of the film layer increased, the stability decreased, and the number and pore size of pits increased.

Controllable Droplet Sliding on a Smart Shape-Memory Slippery Surface.

Recently, slippery surfaces with controllable droplet sliding have aroused much attention in both fundamental research and realistic applications. However, for almost all existing surfaces, constant stimuli such as heat, light, magnetic field, etc., are indispensable. Herein, by constructing pit structures on a shape memory polymer and further infusing oil with low surface tension, we report a shape memory slippery surface that can overcome the above imperfection. Based on the shape memory performance, the surface can memorize a diverse pit size as the surface is stretched or recovered. With the variation of pit structure, the sliding performances for both water and organic liquid droplets can be reversibly adjusted between the rolling and pinning states. This work, based on the shape memory effect, reports smart droplet sliding control through regulating the surface microstructure, which not only provides a strategy for droplet sliding control, but also offers some ideas for designing novel intelligent slippery surfaces.

Mechanical Investigation of Carbon Steel under Strong Corrosion Effected by Corrosion Pits

This study investigated the effect of corrosion pits on the mechanical degradation of steel Q345 under strong acid corrosion. The experiment on a total of 27 steel Q345 specimens corroded by 36% industrial hydrochloric acid for 0 h, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, and 72 h, respectively, is conducted to study failure mode and stress-strain curves. After that, a noncontact topography scanner (DSX500) scanned geometric parameters of corrosion pits in steel Q345 to establish its mechanical degradation. The surface morphology and the corresponding degradation law of corroded steel are also revealed. In addition, the steel plastic fracture criterion taking into account equivalent plastic fracture strain and average stress triaxiality T is adopted to propose the uniform pit model. The analysis results show that the failure mode gradually changes from ductile to brittle. It is noted that the depth and relative size of the corrosion pit are the main factors affecting the increase of the maximum pit coefficient. Further, FEM based on uniform corrosion pits is found by the flexible damage evolution criterion. Its calculation results are entirely consistent with experimental results, indicating that this model can mirror the surface morphology of steel suffering strong corrosion, and simulated accurately stress flow law and necking failure of strong corrosion steel. The proposed criterion is validated with verification results and can provide good references for the design of steel bridges under strong corrosion.

The influence of corrosion pit–pit spacing on the pit‐to‐crack transition and fatigue lifetime

AbstractThe influence of separation distance between pre‐induced corrosion pits on both crack initiation and fatigue lifetimes is studied in an air environment by testing specimens containing pit pairs in the low‐stress, high cycle fatigue regime. The results of these tests are compared with equivalent tests with samples containing similar sized single pit. Within the scope of pit sizes and separation distances investigated, when the separation distance is below a threshold, decreasing the separation distance between pits leads to earlier onset of crack initiation and decreased fatigue lifetimes; this threshold being dependent on the applied stress and relative pit sizes. When the separation distance is above this threshold, multiple pits tend to behave independently of each other. The implication of the results from the viewpoint of structural integrity assessment of components containing flaws such as corrosion pits in close proximity is discussed.

Critical Role of Pits in Suppressing Li Dendrites Revealed by Continuum Mechanics Simulation and In Situ Experiment

Dendrite growth and surface pitting are critical factors hindering the development of ultra-high energy density rechargeable lithium battery. However, the mechanism of dendrite growth promoted by pits on the surface of lithium metal remains unclear. In this study, we propose a combination of continuum mechanics simulations and develop an in situ experimental observation device to investigate the effects of pit size, curvature of pit edge, overpotential, and lithium-ion concentration gradient on dendrite growth. Results show that a larger size and curvature of pits can reduce the deposition rate of lithium and dendrite morphology significantly. Larger overpotential can aggravate dendritic nucleation and thereby promotes dendrite growth. Uneven lithium-ion concentration gradient distribution significantly influences the direction of the dendrite growth and leads to the formation of branches. The lithium deposition behavior near the ideal pit predicted by continuum mechanics is consistent with that observed in the in situ experiments. These results lay the basis for future studies to determine the effect of the surface morphology of lithium metal electrodes on the electrodeposition stability and performance of lithium metal batteries.

Fatigue Life Assessment of Key Fatigue Details of the Corroded Weathering-Steel Anchor Boxes of a Cable-Stayed Bridge

In order to study the influence of corrosion on the fatigue life of weathering steel bridges, firstly the nominal stress method is employed to identify the key fatigue details of a typical weathering-steel anchor box of a cable-stayed bridge and then, a multi-scale refined finite-element model for the weathering-steel anchor box is established. The established fatigue-life assessment method for corroded weathering steel is extended to the multi-scale model, the remaining fatigue life for the fatigue details under corrosion are predicted, and the influence of the initial pit size on the fatigue life of weathering steel structures is analyzed. The research results show that corrosion pits can be equated to the introduction of initial cracks in the structure, and the remaining fatigue life for key fatigue details is calculated when the initial crack size is 1 mm, 2 mm, and 3 mm of the fatigue life when the initial crack size is 0 mm, with results of 20.3%, 12.7%, and 11.5%, respectively. Therefore, the research results show that the corrosion pits are equivalent to the introduction of initial cracks in the structure and, even if the initial crack size is small, the fatigue life of the structure is greatly reduced. The fatigue-life assessment method for corroded weathering-steel structures established in this paper is based on the finite element method and fracture mechanics, which offer universal applicability and generalizability and make up for the lack of a fatigue-life assessment method for corroded weathering-steel bridges in service.

Behavioral differences between pit-building antlions and wormlions suggest limits to convergent evolution.

Antlions and wormlions are distantly related insect taxa, both digging pits in loose soil and ambushing arthropod prey. Their hunting method, which is rare in the animal kingdom, is a clear example of convergent evolution. There is little research directly comparing the 2 pit-building taxa. Using the same experimental platform to investigate how they respond to biotic and abiotic environmental factors enables an examination of their convergence and its limits. We investigated the response of antlions and wormlions to 3 factors common in their daily life: disturbance to the pits, prey arrival, and conspecific competitors. Although both increased the pit size following disturbance, wormlions increased it faster than antlions. Antlions responded to prey faster than wormlions, but wormlions improved their response time over days. The most diverging response was toward conspecifics. Whereas antlions relocated their pits fast in response to increasing conspecific density, wormlions never relocated. We suggest explanations for the behavioral differences between the taxa. Our results imply that despite the similar hunting method of the 2 taxa they may differ greatly in their behavior, which in turn might have consequences for their habitat use and population dynamics.

Study of Size, Shape, and Etch pit formation in InAs/InP Droplet Epitaxy Quantum Dots

We investigated metal-organic vapor phase epitaxy grown droplet epitaxy (DE) and Stranski–Krastanov (SK) InAs/InP quantum dots (QDs) by cross-sectional scanning tunneling microscopy (X-STM). We present an atomic-scale comparison of structural characteristics of QDs grown by both growth methods proving that the DE yields more uniform and shape-symmetric QDs. Both DE and SKQDs are found to be truncated pyramid-shaped with a large and sharp top facet. We report the formation of localized etch pits for the first time in InAs/InP DEQDs with atomic resolution. We discuss the droplet etching mechanism in detail to understand the formation of etch pits underneath the DEQDs. A summary of the effect of etch pit size and position on fine structure splitting (FSS) is provided via the k · p theory. Finite element (FE) simulations are performed to fit the experimental outward relaxation and lattice constant profiles of the cleaved QDs. The composition of QDs is estimated to be pure InAs obtained by combining both FE simulations and X-STM results. The preferential formation of {136} and {122} side facets was observed for the DEQDs. The formation of a DE wetting layer from As-P surface exchange is compared with the standard SKQDs wetting layer. The detailed structural characterization performed in this work provides valuable feedback for further growth optimization to obtain QDs with even lower FSS for applications in quantum technology.

The dynamic changes of tracheary elements in an intraspecific quinoa (Chenopodium quinoa) graft

Vascular connection is key to successful graft. Little study has been devoted to the behavior of tracheary elements (TEs), the basic component of vascular bundles, during vascular connection between scion and rootstock. Here we report the structural changes of TEs at the graft interface between two quinoa cultivars, Qaidam White-1 (QW1) and Qaidam Red-1 (QR1). Our results showed that TEs in ungrafted plants developed following an ontogenetic sequence, i.e., the annular vessel, helical vessel, scalariform vessel, reticulate vessel, and pitted vessel. However, this process was greatly accelerated in grafted plants, resulting in quick developmental transition of TE wall patterning. At the early stage of intraspecific grafting (e.g., 5 days after grafting), the membrane-like cellular patches were heavily accumulated at the graft interface but quickly retreated within 2–4 days, suggesting an early emergency response to grafting. The TE length in both scion and rootstock was significantly shorter (more than 50% on average, nTE = 747) than the ungrafted plants in the same period. These short TEs were gradually integrated into a long, continuous conduit, thereby enabling the functional vasculature at the graft union. In addition, the pit size was gradually reduced, for example, for the surface area of outer pit aperture, from 12.73 ± 3.15 to 5.40 ± 0.30 μm2, or for the surface area of inner pit aperture, from 9.34 ± 3.33 to 1.96 ± 1.04 μm2, in 18 days (npits = 2830). Taken together, the morphological changes of TEs and cellular responses to grafting in the intraspecific grafts seemed to be conservative to other homografts and heterografts, implying that these behavioral changes are highly adaptive to the scion–rootstock interaction.

Characteristics of a Large-Scale Deep Foundation Pit Excavated by the Central-Island Technique in Chengdu Soft Clay

A large-scale foundation pit, 25,720 m2 (127 m × 213 m), was excavated to a depth of approximately 20 m by the central-island technique from 2012 to 2013 in Chengdu, China. This paper aims to comprehensively study the deformation behaviours of the foundation pit during excavation and investigate the primary factors affecting the deformation behaviour of the foundation pit. The deformation characteristics monitored during excavation included 1) horizontal column movement, 2) vertical column movement, 3) lateral column deflection, 4) internal stress in the column, 5) axial force in anchor cables, 6) ground settlement, and 7) artesian water levels. To further explore the pit sizes on the excavation behaviour, field data from another ten excavations in Chengdu were also included in the analysis. The results showed the maximum deflection of the column was mostly detected at the top of the column. The vertical column movement, δcu, undulates during excavation. After the desired depth was reached, the increase in the vertical column movement was negligible. The internal force in the anchor cable varied between 20–30 kN during the excavation and between 30–70 kN when the expected depth was excavated. A relatively small ground settlement in the studied excavation sites was observed due to the mudstone at the bottom of the excavation and the installation of anchor cables. In addition, it was noticed that the aspect ratio and excavation depth have a significant effect on the maximum deflection at the top of the column. This paper enriches the database and improves the understanding of the deformation behaviour of large-scale foundation pits during excavation.

The Transition from Short- to Long-Term Marine Corrosion of Carbon Steels: 1. Experimental Observations

This paper is concerned with developing an understanding of the transition between modes 1 and 2 of the bi-modal characteristic often observed for corrosion (mass) loss of many different alloys and in a variety of longer-term (years) exposure conditions. Corrosion losses and pit depth and size for carbon steels (0.01 wt%, 0.04 wt%, and 0.06 wt% C) immersed continuously in sheltered 20°C (av.) seawater, 30°C (constant) seawater, and 70°C (constant) distilled water environments are reported with observations at 14 d and 28 d intervals over 1.4 y. The data allow clear demonstration of bi-modal behavior and variability in mass loss much less than typical for unprotected environments. All cases showed significant development of pit depths and pit areas particularly later in mode 1, through the transition phase and into mode 2. Using established observations of pitting mechanisms, the development of pitting is interpreted as facilitating the reduction in pH at the corrosion interface that permits the cathodic reaction to change from oxygen reduction in mode 1 to hydrogen evolution in mode 2, consistent with longer-term predominantly anaerobic corrosion in the later part of the bi-modal model. The observations also shed some light on the relationship between pitting corrosion and what is conventionally referred to as uniform corrosion.

Are liming and pit size determining for tree species establishment in degraded areas by kaolin mining?

Mining contributes to the global economy on different scales and plays a fundamental role in the development of the goods and services sectors. However, the negative impacts caused by the activity are unavoidable, as they intensely degrade soil structures and modify landscapes. The use of native tree species has been effective in restoring the structure and functions of post-mining ecosystems in the Amazon. Thus, the objective of this work was to evaluate chemical indicators of soil quality, survival and initial growth of six tree species planted in degraded ecosystem by kaolin mining under the effects of liming in three pit volumes in the Eastern Amazon. The initial conditions indicated highly degraded soil, with acidic pH, low content of OM, P and K. Liming significantly reduced the level of toxic Al in the soil and provided Ca and Mg for the plants. Through Principal Component Analysis (PCA), we found that the two first components explained 69.30% of the variance of 13 functional indicators of soil quality. PC1 was positively correlated with Ca, Mg, K, SB, CEC and V% and negatively correlated with H+Al and Al saturation. Survival was higher than 80% for Clitoria fairchildiana in all treatments. Liming and pit volume were determining in growth, with high growth rates in height of Inga edulis, Inga cayennensis, Clitoria fairchildiana and Tachigali vulgaris. The species used in this study presented good initial development in restoring ecosystems after kaolin mining.

Improvement of spatial resolution of elemental imaging using laser ablation-ICP-mass spectrometry.

Laser ablation-ICP-mass spectrometer (LA-ICPMS) now becomes one of the most principal analytical technique for mapping analysis for major to trace elements in rocks, minerals, functional materials, or biological tissue samples. In this study, imaging analysis was conducted with coupling of small volume cell and off-set laser ablation protocol to improve the spatial resolution. Combination of newly designed small volume cell and in-torch gas mixing protocols provides faster washout time of the signals (about 0.8s for reducing 238U being one part in a hundred, 1% level). This is very important to improve the spatial resolution in a direction of laser scanning. Moreover, combination of small distances between the laser-line scan (laser pitch distance) and preferential and total ablation of only biological tissue samples placed on glass substrate results in laser ablation of smaller areas than the size of laser ablation pit (shaving ablation). With the shaving ablation, laser-line scanning with narrower-band width (e.g., 2µm) can be achieved even by the laser beam of 8µm diameter. To demonstrate the practical usage of the present technique, imaging analysis of Gd-ethylenediamine tetra-methylene phosphonic acid-doped mouse bone was conducted. Preferential distribution of Gd at the edge of the apatite cell was more clearly identified by the present technique. Combination of the shorter washout system setup and the shaving ablation protocol enables us to improve the spatial resolution of the elemental imaging obtained with the LA-ICPMS technique.

Dynamin 1 controls vesicle size and endocytosis at hippocampal synapses

Following calcium-triggered vesicle exocytosis, endocytosis regenerates vesicles to maintain exocytosis and thus synaptic transmission, which underlies neuronal circuit activities. Although most molecules involved in endocytosis have been identified, it remains rather poorly understood how endocytic machinery regulates vesicle size. Vesicle size, together with the transmitter concentration inside the vesicle, determines the amount of transmitter the vesicle can release, the quantal size, that may control the strength of synaptic transmission. Here, we report that, surprisingly, knockout of the GTPase dynamin 1, the most abundant brain dynamin isoform known to catalyze fission of the membrane pit's neck (the last step of endocytosis), not only significantly slowed endocytosis but also increased the synaptic vesicle diameter by as much as ∼40–64% at cultured hippocampal synapses. Furthermore, dynamin 1 knockout increased the size of membrane pits, the precursor for endocytic vesicle formation. These results suggest an important function of dynamin other than its well-known fission function – control of vesicle size at the pit formation stage.

Understanding the nature of passivation film formed during corrosion of Fe39Mn20Co20Cr15Si5Al1 high entropy alloy in 3.5 wt% NaCl solution

In metallic materials, the nature of passivation film plays an important role in governing corrosion behavior. The present work focuses on a detailed analysis of the passivation film characteristics of a transformation induced plasticity Fe39Mn20Co20Cr15Si5Al1 (at%) high entropy alloy (HEA) in 3.5 wt% NaCl solution at room temperature. The characteristics of the passivation film were assessed using a potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The microstructural analysis of the alloy achieved using electron backscattered diffraction revealed that it consisted of two different phases: γ phase (face-centred cubic crystal) and ε (hexagonal closed pack), with the area fraction of ε phase being 96.5%. The electrochemical experiments showed that the HEA maintained excellent uniform corrosion resistance but low pitting corrosion resistance. The scanning electron microscopy revealed deep pits covered with perforated layers, and the average pit size and pit depth was determined to be 202.8 µm and 168 µm, respectively. The EIS revealed a bilayer type of passivation film formations at different voltages. For the passivation film grown at −0.1 V, the upper layer film thickness was 2.08 nm and the inner layer film thickness was 3.14 nm. For the passivation film grown at −0.05 V, the upper and inner film thicknesses were 1.78 nm and 3.10 nm. The passivation film resistance was found to be one order of magnitude higher for the passivation films grown at −0.1 V and −0.05 V than that for the naturally grown passivation film. The XPS of the sample that corroded during the potentiodynamic polarization test revealed that the passive layer contained Fe, Mn, Co, Cr, Si, and O elements as metal oxides and hydroxides with Mn and Cr based chemical species present as dominant species. Their oxidation states were estimated to be present as Fe2+, Fe3+, Mn3+, Co2+, Cr3+, Si4+, O2-, and OH1- along with their corresponding metallic states. According to the proposed corrosion mechanism, a bilayer type of passivation film forms on the alloy. The film’s upper layer is rich in Mn and Cr and the inner layer is devoid of Mn and Cr. The detection of two particles in the same pit with two different chemical compositions seems to corroborate the formation of a bilayer passivation film and its chemical compositions.

Molten Barium Hydroxide as Defect Selective Drop Etchant for Dislocation Analysis on Aluminum Nitride Layers

In this article, the suitability of the etchants NaOH/KOH and Ba(OH)2 for defect etching of metalorganic vapour‐phase epitaxy (MOVPE) grown AlN layers with a MgO‐assisted “drop method” is compared. Defect selectivity for the new etchant Ba(OH)2 is confirmed by the local TEM analysis. Temperature dependence (420–500 °C) of etch pit sizes of a‐, mixed‐, and c‐type dislocations for both etchants are investigated by statistical evaluation of scanning electron microscopy (SEM) images. Additionally, the etch pit shape is analyzed for samples etched at 460 °C by atomic force microscopy (AFM) measurements. While a‐ and mixed‐type dislocations result in pits of comparable size and shape for both etchants, c‐type dislocations are already strongly etched with NaOH/KOH at low temperatures leading to over‐etching and MgO precipitation. Ba(OH)2, in contrast, generates smaller c‐type etch pits at low and medium etching temperatures and no MgO precipitates and is therefore preferable for drop etching.

The single-crystal diamond trap (SCDT): a new method to determine the composition of high-P\u2013T fluids

In view of recently reported discrepancies in mineral solubility results obtained with the classical diamond trap method, an alternative approach to quantify the composition of high P–T fluids was developed. In this approach the high P–T fluids are trapped in laser-drilled holes within single-crystal diamond plates and subsequently analyzed by LA–ICP–MS using the same pit size as the one that was used to drill the holes, which allows more rigorous testing of the data reproducibility than in the case of the classical diamond trap, where the fluid resides in a large, open network. To reduce the spikiness of the LA–ICP–MS signals and minimize element fractionation, the aqueous solution within the holes was allowed to evaporate, and the solid residue was melted to a glass. Because this results in the partial loss of the internal standard elements that are usually used for quantifying the LA–ICP–MS signals we developed a new quantification procedure that works without any internal standard in the fluid but instead uses the carbon signal produced by the epoxy that was filled into the holes after melting the precipitates. The new method was first tested on holes filled with epoxy resins doped with known amounts of chemicals, then on holes filled with known amounts of minerals that were subsequently melted, and finally on real high P–T mineral solubility experiments at 1.0 GPa and 700–900 °C in the quartz–H2O and olivine–enstatite–H2O systems, for which reliable reference data exist. In all 15 experiments the measured concentrations agree within 1–21% (avg. 13%) with the reference values. In contrast, four mineral solubility experiments that were performed at identical conditions with the classical diamond trap method returned concentrations that deviated by 7–56% (avg. 28%) from the reference value. Furthermore, a strong fractionation effect that has been observed during the ablation of albite + H2O in a classical diamond trap is efficiently prevented in our single-crystal diamond trap (SCDT) approach. On the downside, we observe significant mobility of alkalies during the melting step in our approach.

Pit Stability Predictions of Additively Manufactured SS316 Surfaces Using Finite Element Analysis

Stainless steels are susceptible to localized forms of corrosion attack, such as pitting. The size and lifetime of a nucleated pit can vary, depending on a critical potential or current density criterion, which determines if the pit repassivates or continues growing. This work uses finite element method (FEM) modeling to compare the critical pit radii predicted by thermodynamic and kinetic repassivation criteria. Experimental electrochemical boundary conditions are used to capture the active pit kinetics. Geometric and environmental parameters, such as the pit shape and size (analogous to additively manufactured lack-of-fusion pores), solution concentration, and water layer thickness were considered to assess their impact on the pit repassivation criterion. The critical pit radius (the transition point from stable growth to repassivation) predicted for a hemispherical pit was larger when using the repassivation potential (Erp) criteria, as opposed to the current density criteria (pit stability product). Including both the pit stability product and Erp into its calculations, the analytical maximum pit model predicted a critical radius two times more conservative than the FEA approach, under the conditions studied herein. The complex pits representing lack-of-fusion pores were shown to have minimal impact on the critical radius in atmospheric conditions.

Hydraulic Function Analysis of Conifer Xylem Based on a Model Incorporating Tracheids, Bordered Pits, and Cross-Field Pits

Wood has a highly complex and anisotropic structure. Its xylem characteristics are key in determining the hydraulic properties of plants to transport water efficiently and safely, as well as the permeability in the process of wood impregnation modification. Previous studies on the relationship between the xylem structure and hydraulic conductivity of conifer have mainly focused on tracheids and bordered pits, with only a few focusing on the conduction model of cross-field pits which connect tracheids and rays. This study takes the xylem structure of conifer as an example, drawing an analogy between water flow under tension and electric current, and extends the model to the tissue scale, including cross-field pits by establishing isometric scaling. The structure parameters were collected by scanning electron microscopy and transmission electron microscopy. The improved model can quantify the important hydraulic functional characteristics of xylem only by measuring the more easily obtained tracheid section size. Then, this model was applied to quantify the relationship between the xylem anatomical structure and hydraulic properties in the pine (Pinus sylvestris L. var. mongholica Litv.) and the spruce (Picea koraiensis Nakai), and also to evaluate the effects of the number and size of cross-field pits on xylem conduction. The results showed that the growth ring conduction value of the pine was more than twice that of the spruce for the two tree species with similar growth widths in this study. The tracheid wall resistance of the pine reflected the result of the interaction of the size and number of cross-field pits, in comparison, the wall resistance of the spruce was more sensitive to the number of cross-field pits. Finally, the calculation output of the new model was cross-validated with the literature, which verified the accuracy and effectiveness of the model. This study provides an effective and complete solution for xylem conductivity measurement and the study of wood ecophysiological diversity and processing.

Characteristics of acoustic signals emitted during millisecond laser-BK7 glass interaction

A microphone was used to study the characteristics of acoustic emission for millisecond laser-induced damage of BK7 glass. Different temporal and spectral distributions were obtained for the front and rear surface damage processes. The front surface damage was associated with the strong thermal melting process, and the size of the conical molten pit was strongly linked to the intense oscillating period of the acoustic signal. The effects of the detection distance and angle on the spectrum below 5 kHz, which were induced during the front surface damage process, were found to be associated with the distribution of the ejection expelled out of the molten pit. The results indicate that the detection of acoustic emission can be used as a real-time online method to obtain information on the millisecond laser-induced damage.