Mechanical Softening Research Articles

Structure-Reactivity Relationships in a Small Library of Imine-Type Dynamic Covalent Materials: Determination of Rate and Equilibrium Constants Enables Model Prediction and Validation of a Unique Mechanical Softening in Dynamic Hydrogels.

The development of next generation soft and recyclable materials prominently features dynamic (reversible) chemistries such as host-guest, supramolecular, and dynamic covalent. Dynamic systems enable injectability, reprocessability, and time-dependent mechanical properties. These properties arise from the inherent relationship between the rate and equilibrium constants (RECs) of molecular junctions (cross-links) and the resulting macroscopic behavior of dynamic networks. However, few examples explicitly measure RECs while exploring this connection between molecular and material properties, particularly for polymeric hydrogel systems. Here we use dynamic covalent imine formation to study how single-point compositional changes in NH2-terminated nucleophiles affect binding constants and resulting hydrogel mechanical properties. We explored both model small molecule studies and model polymeric macromers, and found >3-decade change in RECs. Leveraging established relationships in the literature, we then developed a simple model to describe the cross-linking equilibrium and predict changes in hydrogel mechanical properties. Interestingly, we observed that a narrow ≈2-decade range of Keq's determine the bound fraction of imines. Our model allowed us to uncover a regime where adding cross-linker before saturation can decrease the cross-link density of a hydrogel. We then demonstrated the veracity of this predicted behavior experimentally. Notably this emergent behavior is not accounted for in covalent hydrogel theory. This study expands upon structure-reactivity relationships for imine formation, highlighting how quantitative determination of RECs facilitates predicting macroscopic behavior. Furthermore, while the present study focuses on dynamic covalent imine formation, the underlying principles of this work are applicable to the general bottom-up design of soft and recyclable dynamic materials.

Correlation analysis of feedstock flowability and temperature for laser-based powder bed fusion of polymers

PurposeFor additive manufacturing (AM) through laser-based powder bed fusion of polymers (PBF-LB/P), accurate characterization of powder flowability is vital for achieving high-quality parts. However, accurately characterizing feedstock flowability presents challenges because of a lack of consensus on which tests to perform and the diverse forces and mechanisms involved. This study aims to undertake a thorough investigation into the flowability of eight feedstock materials for PBF-LB/P at different temperatures using various techniques.Design/methodology/approachFor ambient temperature assessments, established metrics such as avalanche angle and Hausner ratio, along with the approximated flow function coefficient (FFCapp), are used. The study then focuses on the influence of elevated temperatures representative of in-process conditions. FFCapp and differential scanning calorimetry (DSC) are performed and analyzed, followed by a correlation analysis as a holistic approach to identify key aspects for flowability. Furthermore, two feedstock materials are compared with a previous study to connect the present findings to PBF-LB/P processing.FindingsThe study revealed intrinsic material properties such as mechanical softening near the melting point to become significant. This partially explains why certain powders with poor ambient temperature flowability are consistently demonstrated to produce high-quality parts. FFCapp and thermal characterization through DSC are identified as critical metrics for optimizing feedstock material characteristics across temperature ranges.Originality/valuePrevious studies emphasized specific characterizations of feedstock material at ambient temperature, presented a limited materials selection or focused on metrics such as shape factors. In contrast, this study addresses a partially understood aspect by examining the critical role of temperature in governing feedstock material flowability. It advocates for the inclusion of temperature variables in flowability analyses to closely resemble the PBF-LB/P process, which can be applied to material design, selection and process optimization.

The effect of chemical doping on the lithiation processes of the crystalline Si anode ‒ A first-principles study.

We employed first-principles calculations to investigate the effect of chemical doping on the lithiation kinetics and dynamic properties of the c-Si anode. Our abinitio molecular dynamics simulations reveal that phosphorous/arsenic doping can greatly enhance the lithiation kinetics of c-Si, whereas boron doping is unable to produce such an improvement. Our calculations also show that boron doping could enhance Li insertion into c-Si, but phosphorous/arsenic doping tends to increase the insertion energy of Li ions. Although the migration energy barriers of Li ions may slightly increase (decrease) in the boron-(phosphorus-/arsenic-)doped c-Si, these changes were only effective within the range of the nearest-neighbor distance from dopants. Furthermore, it was found that the phosphorus-/arsenic-doped Si can be more ductile and can more easily undergo plastic deformation upon lithiation, while the c-Si matrix becomes more brittle and stiffer when doped with boron. Our simulation results also demonstrate that phosphorous- and arsenic-doping can effectively speed up the Li-induced structural amorphization of c-Si while boron doping appears to severely slow it down. These findings unambiguously indicate that the induced mechanical softening of the c-Si bond network can be the primary factor that leads to the enhanced lithiation kinetics in the n-type doped c-Si anodes.

High-Temperature Resistance of Anchorage System for Carbon Fiber-Reinforced Polymer Composite Cable-A Review.

Unidirectional carbon fiber-reinforced polymer (CFRP) may exhibit significant mechanical softening in the transverse direction at an elevated temperature. While significant transverse compressive stress exists on CFRP due to the clamping force from anchorage, a CFRP cable may exhibit anchorage failure when suffering an accidental fire disaster. The high-temperature resistance of a CFRP cable anchorage is critical, and clarifying the performance deterioration and failure mechanism of a CFRP cable anchorage system at elevated temperature is fundamental for clarifying its fire resistance. This paper reviews the current research status of the high-temperature resistance of CFRP cable anchorage systems from two aspects, including the high-temperature resistance of the comprising materials and the anchorage system. The reviews on the high-temperature properties of the comprising materials are summarized from two aspects. Firstly, the mechanical performance degradation of bonding epoxy resin at elevated temperatures and the effect of a filler on its mechanical-thermal properties are analyzed. Secondly, the mechanical performances of CFRP composites at elevated temperatures are summarized, with consideration of the stress state of the CFRP cable under the constraint of an anchorage device. The reviews on the high-temperature resistance of the anchorage system also include two aspects. Firstly, the temperature field solution method for the anchorage system is summarized and discussed. Secondly, the current research status of the anchorage performance at elevated temperatures is also summarized and discussed. Based on these reviews, the research shortage of the high-temperature resistance of CFRP cable anchorage systems is summarized, and further research is recommended.

Softening of the hypertriton transverse momentum spectrum in heavy-ion collisions

Understanding the properties of hypernuclei helps to constrain the interaction between hyperon and nucleon, which is known to play an essential role in determining the properties of neutron stars. Experimental measurements have suggested that the hypertriton (HΛ3), the lightest hypernucleus, exhibits a halo structure with a deuteron core encircled by a Λ hyperon at a distance of about 10 fm. This large Λ−d distance in HΛ3 wave function is found to cause a suppressed HΛ3 yield and a softening of its transverse momentum (pT) spectrum in relativistic heavy-ion collisions. Within the coalescence model based on nucleons and Λ hyperons from a microscopic hybrid hydro model with a hadronic afterburner for nuclear cluster production in Pb-Pb collisions at sNN= 5.02 TeV, we show how this softening of the hypertriton pT spectrum appears and leads to a smaller mean pT for HΛ3 than for helium-3 (3He). The latter is opposite to the predictions from the blast-wave model which assumes that HΛ3 and 3He are thermally produced at the kinetic freeze-out of heavy-ion collisions. The discovered quantum mechanical softening of the (anti-)hypertriton spectrum can be experimentally tested in relativistic heavy-ion collisions at different collision energies and centralities and used to obtain valuable insights to the mechanisms for light (hyper-)nuclei production in these collisions.

Fabrication of biopolyethylene-based biocomposites with coffee ground waste: Effect of polyethylene-graft-maleic anhydride

The production of plastic products from non-renewable raw materials, such as petroleum, damages the environment. Consequently, biocomposites have aroused interest from industry and researchers due to their ecologically correct characteristics, mainly because they come from renewable sources. Therefore, this study aimed to produce biopolyethylene/coffee ground waste (BioPE/CGW) biocomposites and analyze the impact of CGW and polyethylene-graft-maleic anhydride (PE-g-MA) on BioPE. The biocomposites were prepared in a co-rotational twin-screw extruder equipped with a side feeder to feed the CGW. The materials were subsequently injection molded to produce the impact, tensile, and HDT samples. The temperature profiles used during extrusion and injection were between 170 and 180°C. The BioPE and biocomposites were investigated for the vibrational (Infrared Spectroscopy - FTIR), thermal (differential scanning calorimetry), mechanical (tensile, impact, and hardness), thermomechanical (heat deflection temperature (HDT) and Vicat softening temperature (VST)), and morphological (scanning electron microscopy (SEM)) properties. The compatibilizer improved the interface between phases, promoting mechanical and thermomechanical improvements in the biocomposites. PE-g-MA promoted increments in tensile strength and elastic modulus of up to 38% and 25% in the BioPE/CGW30 and an increase of 44% in the elastic modulus compared to BioPE. The thermomechanical investigations showed that HDT increased by 8.8 and 3.3°C and VST increased by 2.5 and 6.6°C compared to BioPE and the BioPE/CGW30, respectively. Biocomposites from renewable and biodegradable sources align with a sustainable development concept.

Microstructural and micromechanical characterization of Cr diffusion barrier in ATR irradiated U-10Zr metallic fuel

Chromium (Cr) has been recognized as a promising diffusion barrier candidate to mitigate the Fuel Cladding Chemical Interaction (FCCI) failure in metallic fuels for sodium-cooled fast reactor. This paper, for the first time, conducted an in-depth post-irradiation examination of the microstructure and composition evolution, and micromechanics of the Cr diffusion barrier in U-10Zr fuel/HT9 cladding irradiated in the Advanced Test Reactor (ATR) to 8.7% burnup at an averaged Peak Inner Cladding Temperature of 540–550 °C. Transmission Electron Microscope (TEM) characterization confirmed the preferential intergranular diffusion of Zr and U in the Cr diffusion barrier, suggesting that grain boundaries served as fast path for the diffusion of Zr and U into the Cr diffusion barrier. The interaction zone is dominated by nano crystalline α-ZrCr2 Laves phase. Despite the interaction, there is no microcracks being observed in the preserved Cr diffusion barrier and HT9 cladding, serving as a good barrier to mitigate FCCI under the studied in-reactor irradiation conditions. High density cavities in uniform distribution are observed inside Cr grains, nano particles contains Cr, Mn, and O are confirmed by Electron Energy Loss Spectroscopy (EELS) analysis. However, it is unclear whether the cavities will become an issue to the barrier integrity at higher burnup. In-situ Scanning Electron Microscopy (SEM) micro-tensile testing uncovered mechanical softening in the HT9 cladding nearing the Cr diffusion barrier, possibly due to the coarsening of lath structure and carbides precipitates.

The prospects of applying ionic modification of nitride coatings to high temperature corrosion processes in the oil and gas industry

The use of ion modification methods associated with high-dose irradiation with low-energy ions is one of the promising ways to increase the resistance of materials to external influences, including high-temperature corrosion. The process of ionic modification involves creating a near-surface layer of material with a high dislocation density due to implantation effects. This inhibits destructive processes caused by corrosive oxidation or mechanical influences. In this work, using the ion modification method to improve the resistance to high temperature corrosion, the authors modified nitride coatings of the order of 500 nm thick. The main purpose of using the ion modification method was to increase the strength characteristics of nitride coatings against high-temperature corrosion, as well as to reduce the effects of coating degradation to mechanical softening and wear after corrosion tests. In the course of the studies, it was found that the use of low-energy irradiation with O2+ ions (40 keV) leads to an increase in the stability of strength characteristics during high-temperature corrosion (with prolonged heating in an oxygen-containing environment at a temperature 700 °C), as well as a decrease in wear in comparison with unmodified nitride coatings applied to the surface of 316L steel. The promise of these studies lies in the development of new methods for modifying steel structures, which will improve the efficiency of resistance to corrosion and mechanical damage, as well as increase the wear resistance of the surface under external mechanical influences. The possibility of increasing stability due to deformation inclusions caused by implantation makes it possible to increase corrosion resistance by increasing the resistance of materials to high-temperature oxidation.

Cross-scale mechanical softening of Marcellus shale induced by CO2-water–rock interactions using nanoindentation and accurate grain-based modeling

Mechanical softening behaviors of shale in CO2-water–rock interaction are critical for shale gas exploitation and CO2 sequestration. This work investigated the cross-scale mechanical softening of shale triggered by CO2-water–rock interaction. Initially, the mechanical softening of shale following 30 d of exposure to CO2 and water was assessed at the rock-forming mineral scale using nanoindentation. The mechanical alterations of rock-forming minerals, including quartz, muscovite, chlorite, and kaolinite, were analyzed and compared. Subsequently, an accurate grain-based modeling (AGBM) was proposed to upscale the nanoindentation results. Numerical models were generated based on the real microstructure of shale derived from TESCAN integrated minerals analyzer (TIMA) digital images. Mechanical parameters of shale minerals determined by nanoindentation served as input material properties for AGBMs. Finally, numerical simulations of uniaxial compression tests were conducted to investigate the impact of mineral softening on the macroscopic Young’s modulus and uniaxial compressive strength (UCS) of shale. The results present direct evidence of shale mineral softening during CO2-water–rock interaction and explore its influence on the upscale mechanical properties of shale. This paper offers a microscopic perspective for comprehending CO2-water-shale interactions and contributes to the development of a cross-scale mechanical model for shale.

Thermo-mechanical aging of carbon-black reinforced styrene-butadiene rubber under cyclic-loading

PurposeThe research aims to investigate the impact of thermo-mechanical aging on SBR under cyclic-loading. By conducting experimental analyses and developing a 3D finite element analysis (FEA) model, it seeks to understand chemical and physical changes during aging processes. This research provides insights into nonlinear mechanical behavior, stress softening and microstructural alterations in SBR compounds, improving material performance and guiding future strategies.Design/methodology/approachThis study combines experimental analyses, including cyclic tensile loading, attenuated total reflection (ATR), spectroscopy and energy-dispersive X-ray spectroscopy (EDS) line scans, to investigate the effects of thermo-mechanical aging (TMA) on carbon-black (CB) reinforced styrene-butadiene rubber (SBR). It employs a 3D FEA model using the Abaqus/Implicit code to comprehend the nonlinear behavior and stress softening response, offering a holistic understanding of aging processes and mechanical behavior under cyclic-loading.FindingsThis study reveals significant insights into SBR behavior during thermo-mechanical aging. Findings include surface roughness variations, chemical alterations and microstructural changes. Notably, a partial recovery of stiffness was observed as a function of CB volume fraction. The developed 3D FEA model accurately depicts nonlinear behavior, stress softening and strain fields around CB particles in unstressed states, predicting hysteresis and energy dissipation in aged SBRs.Originality/valueThis research offers novel insights by comprehensively investigating the impact of thermo-mechanical aging on CB-reinforced-SBR. The fusion of experimental techniques with FEA simulations reveals time-dependent mechanical behavior and microstructural changes in SBR materials. The model serves as a valuable tool for predicting material responses under various conditions, advancing the design and engineering of SBR-based products across industries.

Mechanical softening of CuX alloys at elevated temperatures studied via high temperature scanning indentation

The thermal stability and temperature dependent hardness of ultrafine-grained Cu-alloys CuSn5 and CuZn5 after high pressure torsion are investigated using the high temperature scanning indentation (HTSI) method. Fast indentations are carried out during thermal cycling of the samples (heating-holding-cooling) to measure hardness and strain rate sensitivity as a function of temperature and time. The microstructures after each thermal cycle are investigated to characterize the coarsening behaviour of both alloys.Results show that the thermal stability of the tested alloys can be expressed in terms of several temperature regimes: A fully stable regime, a transient regime in which growth of individual grains occurs, and finally a regime in which the microstructure is fully coarsened. The onset of grain growth is accompanied by high strain rate sensitivity on the order of 0.2–0.3. Furthermore, the obtained hardness and strain rate sensitivity values are in good agreement with continuous stiffness measurement (CSM) and strain rate jump (SRJ) experiments. This highlights the applicability of the HTSI method to the characterization of the thermomechanical properties of ultrafine-grained alloys.

Strain engineering of the mechanical properties of two-dimensional WS2.

Tuning the physical properties of two-dimensional (2D) materials is crucial for their successful integration into advanced applications. While strain engineering demonstrated an efficient means to modulate the electrical and optical properties of 2D materials, tuning their mechanical properties has not been carried out. Here we applied compressive strain through the buckling metrology to 2D tungsten disulfide (WS2), which demonstrated mechanical softening manifested by the reduction of its effective Young's modulus. Raman modes analysis of the strained WS2 also showed strain-dependent vibrational modes softening and revealed its Grüneisen parameter (γ E2g = 0.29) and its shear deformation potential (β E2g = 0.56) - both are similar to the values of other 2D materials. In parallel, we conducted a molecular dynamic simulation that confirmed the validity of continuum mechanics modeling in the nanoscale and revealed that due to sequential atomic-scale buckling events in compressed WS2, it shows a mechanical softening. Therefore, by tuning the mechanical properties of WS2 we shed light on its fundamental physics, thus making it an attractive candidate material for high-end applications, such as tunable sensors and flexible optoelectronic devices.

Flexoelectric and electrostatic effects on mechanical properties of CuInP2S6

Ferroelectric polarization is crucial to the development of modern electronic devices. The mechanical properties of ferroelectric materials are however interlinked with its polarization through piezoelectricity and flexoelectricity, as uniform and non-uniform mechanical deformation can bring about changes of polarization. While the mechanical properties of ferroelectric domains and domain walls of conventional ferroelectric oxides have been investigated widely, the mechanical properties of two-dimensional ferroelectrics (van der Waals ferroelectrics) have barely been studied, although they have drawn significant attention due to the need for miniaturization in new-generation low-energy nanoelectronics. Here, we report on variations in mechanical properties of copper indium thiophosphate (CuInP2S6, CIPS), which shows mechanical softening at 180° domain walls, and we discuss flexoelectric and electrostatic effects on the elastic modulus of its ferroelectric domains. In addition, an inhomogeneous mechanical response in mixed-phase CuInP2S6-In4/3P2S6 heterostructures has also been observed. The ferroelectric CuInP2S6 phase appears to be stiffer than the non-polar In4/3P2S6 phase, while the phase boundaries between the two phases, interestingly, display the lowest elastic modulus. Our findings provide new insight into the mechanical properties of two-dimensional ferroelectrics, which may inspire further investigation and applications of these materials.

In situ characterization of thermomechanically loaded solution strengthened, nanocrystalline nickel alloys

Nanocrystalline (NC) Ni-40Cu and Ni-40Cu-0.6P (at.%) alloys were mechanically loaded in tension at ambient (23 °C) and elevated (150 °C) temperatures with the deformed nanostructure captured by in situ transmission electron microscopy coupled with digital image correlation for data mining high strain regions prior to catastrophic failure. The addition of the P provided grain boundary partitioning that stabilized the NC structure under both loading cases, which was not found to be the case for the binary alloy. While mechanical strength softening was observed in each of the alloys upon thermomechanical loading, the retention of strength was substantially higher in the ternary alloy than its binary counterpart. Digital image correlation was found to be a useful means for image mining to identify different regions where failure mechanisms were initiated. Intergranular failure was observed as the dominant failure mechanism in all specimens with the binary alloy revealing a coarser fracture profile as compared to a finer fracture profile in the ternary alloy. Atomistic simulations are used to understand P solute strengthening of the grain boundaries against this fracture failure mode.

The maximum-strain and strain-interval dependences of microstructural evolution underneath the Mullins effect

In situ small-angle neutron scattering (SANS) and constitutive model were combined to investigate silica filled deuterated silicone rubber (SFdSR) under strain rise path at strain rate of 0.001 s−1, with strain intervals from 0.1 to 1. It was found that, (i) The non-linear behaviors are sensitive to strain interval, cycle - number, and maximum strain, etc. (ii) SANS suggests that the cyclic orientation-relaxation of bound rubber can cause accumulative fatigue. (iii) The orientation of bound rubber tH/tV − 1 decreases from 9.9 to 3.6 with increasing the strain intervals from 0.1 to 1 for the same macroscopic maximum strain 3.0. Interestingly, the mechanical response softening (Es) and recovery hysteresis (Erh), the evolution of bound rubber, and the constitutive analysis consistently suggests a strain threshold of 1.5. Accordingly, the roles of matrix, interface, and filler networks as well as their interactions on the origin of the Mullins effect were discussed.

Effects of structure and strain rate on deformation mechanism of twin lamellar Al0.3CoCrFeNi alloys

Lamellar twined materials display simultaneous ultrahigh strength and high ductility, which is attributed to the interaction between twin boundaries and dislocation. However, deformation at the atomic level is rarely seen in experiments. To study the deformation properties and mechanical behavior of the lamellar twined Al0.3CoCrFeNi high-entropy alloys (HEA) sample, we applied the uniaxial tension by employing molecular dynamics (MD) simulations. The impact of various twin inclination angles, twin boundary spacing (TBS), and strain rates are investigated. The mechanical softening as the increasing TBS from 4a to 12a was observed, which corresponds to Hall – Petch relationship. The yield strength of the medium inclination angle (450, 600) records the minimum value with all various TBS due to the elastic energy being easier released. The strain-hardening phenomenon appears at these angles. The sample with an inclination angle perpendicular to the tension loading axis (900) displays the highest stress value. The shrinking migration twin has been observed in 00, 150, and 300 twin inclination angles. The migration and disappearance of initial TBs lead to grains being reoriented into the same orientation at 450 and 600. With twin orientations of 750 and 900, the TB is no longer as crisp and straight as the initial TB under the tension process. An extensive dislocation process occurs at higher strain values, and their interaction with TB leads to establishing the shear band. After that, twin boundaries within the shear band are almost destroyed. Besides, the results also indicate that the flow stress, ultimate strength, and Young's modulus rise with the rising strain rate and decreasing temperature.

Significant mechanical softening of copper under coupled electric and magnetic stimuli

The mechanical reliability of metallic components is vital for the stable operation of electrical equipment, especially for those used in ultra-high voltage transmission and electromagnetic launching, where metallic materials inevitably suffer from high-density current and strong magnetic field. However, little has been known about the mechanical behavior of metals under the electric-magnetic coupling stimuli. Here, by performing quantitative electromechanical tests under the built-in magnetic field inside transmission electron microscope, we found that copper, one of most commonly used conductive metals, can be significantly softened by the coupled electrical-magnetic stimuli, manifested as notable yield strength drop by five-times and obvious creep deformation at room temperature. A plausible mechanism behind the unusual softening, local-Lorentz-force-assisted dislocations depinning, has been proposed. Our results shed new light on understanding the deformation-induced failure of metals served in electromagnetic environments, and also inspire a new mechanical processing way for reshaping metals at much lower loads and temperatures.

Ultrasonic-promoted defect activation and structural rejuvenation in a La-based metallic glass

Ultrasonic-assistant rejuvenation in a La-based metallic glass was demonstrated by means of nanoindentation for the first time. A more pronounced nanoindentation creep behavior along with mechanical softening was detected. It is proposed to be associated with the activation of flow defects with long characteristic relaxation time at a low loading rate and short characteristic relaxation time at a high loading rate during anelastic deformation process based on the Maxwell-Voigt model. Such rejuvenation behavior also leads to an unstable plastic flow and a relatively low energy barrier for atomic diffusion during the fast growth process of crystalline phases accompanied with the reduced glass transition and crystallization temperatures. Our studies might provide insights into the microscopic deformation mechanism of glassy materials, which could help in seeking the novel applications of amorphous alloys such as ultrasonic-assistant cold joining or molding.

On the thermal and mechanical properties of Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O across the high-entropy to entropy-stabilized transition

As various property studies continue to emerge on high entropy and entropy-stabilized ceramics, we seek a further understanding of the property changes across the phase boundary between “high-entropy” and “entropy-stabilized” phases. The thermal and mechanical properties of bulk ceramic entropy stabilized oxide composition Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O are investigated across this critical transition temperature via the transient plane-source method, temperature-dependent x-ray diffraction, and nano-indentation. The thermal conductivity remains constant within uncertainty across the multi-to-single phase transition at a value of ≈2.5 W/mK, while the linear coefficient of thermal expansion increases nearly 24% from 10.8 to 14.1 × 10−6 K−1. Mechanical softening is also observed across the transition.

Grinding Temperature and Surface Integrity of Quenched Automotive Transmission Gear during the Form Grinding Process.

Grinding burn is an undesired defect in gear machining, and a white layer is an indication of severe burn that is detrimental to gear surface performance. In this work, the influence of grinding parameters on the thickness of the white layer during form grinding of quenched transmission gear was investigated, and the microstructure evolution and mechanism of severe burn formation were analyzed. The grinding temperature increased with the grinding depth and grinding speed, with the highest level of ~290 °C. The thickness of the white layer exceeded 100 μm when the grinding depth was 0.03 mm, and the top layer was a plastic deformation layer followed by a fine-grained martensite layer. Coarse-grained acicular martensite was found at the interface between the white layer and softened dark layer. The mechanical effect and thermal softening mainly contributed to the formation of white layer stratification. The ground surface topography showed several scratches and typical grooves; when grinding depth increased to 0.03 mm, the grinding surface roughness Sa was relatively high and reached up to ~0.60 μm, mainly owing to severe plastic deformation under grinding wheel extrusion and the thermal effect.