Surface Integrity Research Articles

Observed global mean state changes modulating the collective influence of the tropical Atlantic and Indian oceans on ENSO

Abstract In the last decades, many efforts have been made to understand how different tropical oceanic basins are able to impact El Niño Southern Oscillation (ENSO). However, the collective connectivity among the tropical oceans and their associated influence on ENSO is less understood. Using a complex network methodology, the degree of collective connectivity among the tropical oceans is analyzed focusing on the detection of periods when the tropical basins collectively interact and Atlantic and Indian basins influence the equatorial Pacific sea surface temperatures (SST). The background state for the periods of strong collective connectivity is also investigated. Our results show a marked multidecadal variability in the tropical interbasin connection, with periods of stronger and weaker collective connectivity. These changes seem to be modulated by changes in the North Atlantic ocean mean state a decade in advance. In particular, strong connectivity occurs in periods with colder than average tropical north Atlantic surface ocean. Associated with this cooling an anomalous convergence of the vertical integral of total energy flux (VIEF) takes place over the tropical north-west Atlantic, associated with anomalous divergence of VIEF over the equatorial eastern Pacific. In turn, an anomalous zonal surface pressure gradient over the tropical Pacific weakens the trades over the western equatorial Pacific. Consequently, a shallower thermocline emerges over the western equatorial Pacific, which can enhance thermocline feedbacks, the triggering of ENSO events, and therefore, ENSO variability. By construction, our results put forward opposite conditions for periods of weak tropical basins connectivity. These results have important implications for seasonal to decadal predictions.

Analysis of Grindability and Surface Integrity in Creep−Feed Grinding of High−Strength Steels

Creep−feed grinding of high−strength steel is prone to excessive wheel wear and thermal damage defects, which seriously affects the service performance of parts. To solve the above−−mentioned issue, a creep−feed grinding test was carried out on high−strength steel using SG and CBN abrasive wheels. The grindability of high−strength steel was scrutinized in terms of grinding force, machining temperature and grinding specific energy. Moreover, the effects of operation parameters and grinder performances on the surface integrity of the workpiece such as surface morphology, roughness, residual stress and hardness were rigorously studied. The results indicate that, when the instantaneous high temperature in the grinding area reaches above the phase transition temperature of the steel, the local organization of the surface layer changes, leading to thermal damage defects in the components. The outstanding hardness and thermal conductivity of CBN abrasives are more productive in suppressing grinding burns than the high self−sharpening properties of SG grits and a more favorable machining response is achieved. The effects of thermal damage on the surface integrity of high−strength steel grinding are mainly in the form of oxidative discoloration, coating texture, hardness reduction and residual tensile stresses. Within the parameter range of this experiment, CBN grinding wheel reduces grinding specific energy by about 33% compared to SG grinding wheel and can control surface roughness below 0.8 µm. The weight of oxygen element in the burn−out workpiece accounts for 21%, and the thickness of the metamorphic layer is about 40 µm. The essential means of achieving burn−free grinding of high−strength steels is to reduce heat generation and enhance heat evacuation. The results obtained can provide technical guidance for high−quality processing of high−strength steel and precision manufacturing of high−end components.

Comparative performance evaluation and economic assessment between traditional and vibration assisted EDM during machining of Inconel 718

Nickel based superalloy, Inconel 718 offers extensive applications in aerospace and gas turbine industries because of its outstanding properties, enabling high performance in various critical components. Despite the wide application of electric discharge machining (EDM) for difficult-to-cut conductive materials, the process becomes less productive due to unstable arcing and inadequate debris flushing during machining, leading to reduced operational efficiency. This research focuses on comparative performance evaluation and economic assessment between conventional-EDM and vibration assisted EDM (VA-EDM) while machining Inconel 718 with copper electrode. The workpiece was excited to vibrate with low frequency by employing unbalanced mass attached in a rotary motor with the aim of enhancing EDM performance. Material removal rate MRR, surface integrity (surface crack density SCD, surface roughness Ra, white (recast) layer thickness WLT) and tool wear rate TWR are analyzed to determine machining performance in comprehensive analysis. The results of the performance comparison show that vibration assisted is superior to the conventional-EDM process concerning enhanced material removal rate, and surface morphology with minimum surface crack density, tool wear rate and white layer thickness. The mean value ratios for Ra EDM/ Ra VA-EDM, TWR EDM/ TWR VA-EDM, WLT EDM/ WLT VA-EDM, and SCD EDM/ SCD VA-EDM are 1.35, 1.52, 1.21, and 1.74, respectively. Additionally, the surface integrity was enhanced using vibration-assisted EDM because it (a) increases the plasma flushing efficiency and the gap pressure gradient; (b) raises the energy of electrically charged plasma particles; (c) increases the effective flow of dielectric in the gap; (d) minimizes the number of ineffective pulses (short-circuiting and arching) on the surface; and (e) improves the dielectric flushing conditions in sparking gap. According to the findings, the overall machining expenditure per part under VA-EDM in Indian rupees (INR) 534 is lowered by 8% than expenditure under conventional-EDM (INR 576.60). The outcomes of this research have the potential to benefit numerous industries that deal with difficult-to-cut materials.

Melanin depletion affects Aspergillus flavus conidial surface proteins, architecture, and virulence.

Melanin is an Aspergillus flavus cell wall component that provides chemical and physical protection to the organism. However, the molecular and biological mechanisms modulating melanin-mediated host-pathogen interaction in A. flavus keratitis are not well understood. This work aimed to compare the morphology, surface proteome profile, and virulence of melanized conidia (MC) and non-melanized conidia (NMC) of A. flavus. Kojic acid treatment inhibited melanin synthesis in A. flavus, and the conidial surface protein profile was significantly different in kojic acid-treated non-melanized conidia. Several cell wall-associated proteins and proteins responsible for oxidative stress, carbohydrate, and chitin metabolic pathways were found only in the formic acid extracts of NMC. Scanning electron microscopy (SEM) analysis showed the conidial surface morphology difference between the NMC and MC, indicating the role of melanin in the structural integrity of the conidial cell wall. The levels of calcofluor white staining efficiency were different, but there was no microscopic morphology difference in lactophenol cotton blue staining between MC and NMC. Evaluation of the virulence of MC and NMC in the Galleria mellonella model showed NMC was less virulent compared to MC. Our findings showed that the integrity of the conidial surface is controlled by the melanin layer. The alteration in the surface protein profile indicated that many surface proteins are masked by the melanin layer, and hence, melanin can modulate the host response by preventing the exposure of fungal proteins to the host immune defense system. The G. mellonella virulence assay also confirmed that the NMC were susceptible to host defense as in other Aspergillus pathogens. KEY POINTS: • l-DOPA melanin production was inhibited in A. flavus isolates by kojic acid, and for the first time, scanning electron microscopy (SEM) analysis revealed morphological differences between MC and NMC of A. flavus strains • Proteome profile of non-melanized conidia showed more conidial surface proteins and these proteins were mainly involved in the virulence, oxidative stress, and metabolism pathways • Non-melanized conidia of A. flavus strains were shown to be less virulent than melanised conidia in an in vivo virulence experiment with the G. melonella model.

Influence of superimposed pulse position in superimposed pulse current waveform on surface integrity in electrical discharge machining

Influence of superimposed pulse position in superimposed pulse current waveform on surface integrity in electrical discharge machining

The impact of successive laser shock peening on surface integrity and residual stress distribution of laser powder-bed fused stainless steel 316L

Abstract The utilization of laser shock peening (LSP) in laser powder bed fused (LPBF) stainless steel (SS) 316L components enhances the mechanical characteristics and operational lifespan of the product quality through a significant reduction of residual stress and a noticeable increase in roughness parameters. The key objective of the study is to analyze the influence of consecutive laser shock peening (LSP) without ablative coating and low pulse energy on the surface properties, residual stress distribution, and microhardness of samples produced by LPBF with SS316L material. The surface quality of the sample subjected to consecutive laser shock peening shows a slight deterioration in its condition. This can be attributed to the combined impact of ablative surface and surface damage resulting from the production of high-energy plasma. However, the implementation of successive LSP results in a distinctive enhancement of compressive residual stresses (CRS) that are evenly distributed throughout the central axis and sharp edges. In contrast, the as-built condition exhibits non-uniform stress magnitudes. CRS observed in each LSP iteration exhibits a notable increase, reaching a maximum magnitude of −389 MPa compared to the initial stress level of 165 MPa in the as-built sample. This enhancement can be attributed to the repetitive impact of shock waves on the surface, leading to the formation of plastic deformation. The refinement of surface grains and the presence of favorable residual stresses were proven by the utilization of x-ray diffraction (XRD) studies and the Cos α plot. The XRD investigation also indicated the absence of any newly formed phases or secondary phases. A significant enhancement in microhardness was observed, with an increase of 58.3% achieved after the third consecutive peening process. The successive LSP samples displayed a gradual improvement in electrochemical behavior. Though the amplitude parameters increased after LSP, the increase in wear rate was observed.

Evaluating the influence of various friction stir processing strategies on surface integrity of hybrid nanocomposite Al6061

To fundamentally investigate the influence of different friction stir processing (FSP) strategies, namely raster, spiral, and parallel in various passes on the surface integrity of hybrid aluminum nanocomposites reinforced by titanium oxide (TiO2), silicon carbide (SiC), and zirconium oxide (ZrO2) nanoparticles, various examinations were conducted. The surface integrity, comprising microstructural characterization, elemental composition, surface topography, roughness, waviness, and microhardness was studied by different analyses, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), optical microscopy (OM), atomic force microscopy (AFM), and Vickers microhardness machine in different zones. Results demonstrated that surface integrity and quality are dependent on the type of FSP strategy. SEM images revealed that a homogeneous distribution of the nanoparticles in the matrix is obtainable by the parallel and raster FSP strategies. Roughness and waviness measurements illustrated that the surface topography of the hybrid nanocomposite was symmetrical and improved by raster strategy and TiO2 + ZrO2 nanoparticle reinforcement. Furthermore, the two-pass FSP improved the arithmetic average surface value (Ra) such that the Ra of two passes decreased by 32.5% compared to a single one. The mean microhardness in the spiral, raster, and parallel pass strategies increased by ~ 45%, 37%, and 31%, respectively.

Nano-cutting mechanism of ion implantation-modified SiC: reducing subsurface damage expansion and abrasive wear.

This study utilized ion implantation to modify the material properties of silicon carbide (SiC) to mitigate subsurface damage during SiC machining. The paper analyzed the mechanism of hydrogen ion implantation on the machining performance of SiC at the atomic scale. A molecular dynamics model of nanoscale cutting of an ion-implanted SiC workpiece using a non-rigid regular tetrakaidecahedral diamond abrasive grain was established. The study investigated the effects of ion implantation on crystal structure phase transformation, dislocation nucleation, and defect structure evolution. Results showed ion implantation modification decreased the extension depth of amorphous structures in the subsurface layer, thereby enhancing the surface and subsurface integrity of the SiC workpiece. Additionally, dislocation extension length and volume within the lattice structure were lower in the ion-implanted workpiece compared to non-implanted ones. Phase transformation, compressive pressure, and cutting stress of the lattice in the shear region per unit volume were lower in the ion-implanted workpiece than the non-implanted one. Taking the diamond abrasive grain as the research subject, the mechanism of grain wear under ion implantation was explored. Grain expansion, compression, and atomic volumetric strain wear rate were higher in the non-implanted workpiece versus implanted ones. Under shear extrusion of the SiC workpiece, dangling bonds of atoms in the diamond grain were unstable, resulting in graphitization of the diamond structure at elevated temperatures. This study established a solid theoretical and practical foundation for realizing non-destructive machining at the atomic scale, encompassing both theoretical principles and practical applications.&#xD.

Friction tensor for an ellipsoid enclosed in a rarefied gas

This research renders calculations of rotranslational friction and diffusion tensors in a rarefied gas, considering both specular and diffuse reflection off ellipsoidal particles. Calculations were conducted in a spherical polar coordinate system, revealing the dynamic nature of these off-diagonal tensors. The tensor elements were determined analytically, intending to compute the surface integrals. All diagrams, and pictures of two-dimensional surfaces were obtained by the numerical integration process in MATLAB. Additionally, we performed calculations without using the time parameter and time derivatives in the relevant relations. Deviations from the state of spherical symmetry were observed in the results for an ellipsoid and show that the tensors are dynamic quantities. Therefore, it is necessary to provide average values. We established that the non-zero elements of the friction tensor for an ellipsoid represent the directions of linear momentum transfer. Also, the non-zero components of the diffusion tensor signify the extent of fluctuations in relevant momentum transfers in corresponding directions.

Effects of instant controlled pressure drop treatment combined with refractance window drying on infusion quality of made green tea.

The study aimed to determine the effects of instant controlled decompression of steam pressure, termed as ICPD (instant controlled pressure drop) on fresh tea leaves, when combined with refractance window drying (RWD) of rolled green teas during green tea manufacturing. The ICPD steam treatment pressure (TP; 0.1-0.3 MPa), treatment time (TT; 10-20 s) and refractance window drying temperature (RWDT; 70-90 °C) were used as the processing parameters for manufacturing of green tea. Response surface methodology was employed to enumerate the effects of ICPD process conditions and temperature of RWD on total phenolic content (TPC), total flavonoid content (TFC) and DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity of the green tea infusion. An optimum condition for green tea processing was found at TP 0.2 MPa, TT 20 s with RWDT at 70 °C. In comparison to made green tea manufactured without ICPD treatment, the ICPD treated green tea showed enhanced TPC, TFC and DPPH radical scavenging activity along with better colour and sensory attributes. The microstructural study of ICPD treated green tea samples showed more deformed cell surface integrity, larger stomatal pore size and cracks at the leaf surface in comparison with non-treated green tea sample. Present study reveals that an ICPD treatment at 0.2 MPa for 20 s can be used as an alternative to the traditional enzyme inactivation step of hot water treatment, for green tea leaves to improve the infusion quality in terms of increased levels of TPC and TFC and DPPH radical scavenging activity. © 2024 Society of Chemical Industry.

Investigation of the Machined Surface Integrity of WC-High-Entropy Alloy Cemented Carbide

A fine-grained WC-15wt%Al0.5CoCrFeNi cemented carbide was prepared through a vacuum and gas pressure sintering. For achieving high surface integrity, diamond wheel grinding serves as the primary molding process for the machining of WC cemented carbide. To reveal the influence of grinding on the surface integrity of fine-grained WC-HEA cemented carbide, studies were conducted on grinding force, surface microstructure, surface roughness, residual stress, microhardness, and bending strength. The morphological analysis of the ground surface indicated a transition in the material removal mechanism of WC-HEA cemented carbide from ductile removal to brittle removal, with brittle removal becoming predominant as the depth of grinding increases. With the increasing depth of grinding, the grinding force increases, and the grinding force increases while the surface roughness decreases. Correspondingly, there is an improvement in both hardness and bending strength. Additionally, grinding induces high residual compressive stress on the surface, with a maximum compressive stress of 1795 MPa. The bending strength of the material is found to be dependent on the residual stress.

Improving fatigue properties of normal direction ultrasonic vibration assisted face grinding Inconel 718 by regulating machined surface integrity

Fatigue properties are crucial for critical aero-engine components in extreme service environments, which are significantly affected by surface integrity (SI) indexes (especially surface topography, residual stress σ res, and microhardness) after machining processes. Normal-direction ultrasonic vibration-assisted face grinding (ND-UVAFG) has advantages in improving the machinability of Inconel 718, but there is a competitive relationship between higher compressive σ res and higher surface roughness R a in affecting fatigue strength. The lack of a quantitative relationship between multiple SI indexes and fatigue strength makes the indeterminacy of a regulatory strategy for improving fatigue properties. In this work, a model of fatigue strength (σ f)sur considering multiple SI indexes was developed. Then, high-cycle fatigue tests were carried out on Inconel 718 samples with different SI characteristics, and the influence of ND-UVAFG process parameters on SI was analyzed. Based on SI indexes data, the (σ f)sur distribution in the grinding surface layer for ND-UVAFG Inconel 718 samples was determined using the developed model, and then the fatigue crack initiation (FCI) sites were further predicted. The predicted FCI sites corresponded well with the experimental results, thereby verifying this model. A strategy for improving the fatigue life was proposed in this work, which was to transfer the fatigue source from the machined surface to the bulk material by controlling the SI indexes. Finally, a critical condition of SI indexes that FCI sites appeared on the surface or in bulk material was given by fitting the predicted results. According to the critical condition, an SI field where FCI sites appeared in the bulk material could be obtained. In this field, the fatigue life of Inconel 718 samples could be improved by approximately 140%.

Investigating the wear mechanism of TiAlN/TiN PVD coated WC inserts in end milling of Incoloy 925 under synergy of bio-degradable fatty acids and nano-metallic solid lubricant

Abstract Rapid tool wear in machining difficult-to-cut material is a significant challenge since it is related to tool cost, surface integrity of machined components, and power consumption. The reduction in tool wear may be accomplished by cutting fluids, especially in modern biodegradable fatty acids. Because of its high lubricity, coconut oil is the best choice for lubricating fatty acids. However, this oil has poor heat-transfer properties. Hence, to further improve its properties, Copper (Cu) nanoparticles (NPs), which have a high thermal conductivity to cost ratio compared to other nanoparticles in addition to anti-frictional and anti-wear properties (due to self-repairing properties caused by their low shear strength and easy deposition on contacting surfaces) have been dispersed in coconut oil which in turn nanolubricant (nanofluid). It is found that synthesized nano-lubricants perform better in thermo-physics and tribology than pure coconut oil. Further, research has been carried out on the combined effects of coconut oil and 0.3 Vol% Cu-NPs on Incoloy 925's end milling performance and tool wear mechanism (viz., coating delamination, adhesion, abrasion, and oxidation). It is found that tool wear rate is reduced, which in turn increases tool life, due to effective cooling and lubrication when nanofluid-based minimum quantity lubrication (NMQL) assisted machining is performed rather than dry and pure oil-based minimum quantity lubrication (MQL) conditions. Consequently, energy consumption in machining and surface quality of machined components are improved.

Enhancing Surface Integrity in Friction Stir Welding through Deep Rolling and Post-Weld Heat Treatment

This study aimed to investigate mechanical surface treatment through deep rolling (DR) and post-weld heat treatment (PWHT) to enhance the surface integrity of an AA7075-T651 aluminum alloy welded through friction stir welding (FSW). The surface integrity of the welded joint was evaluated by analyzing residual stress, microhardness, surface roughness, microstructure, and fatigue life. The experimental design comprised three sets: one set exclusively applied FSW, another set applied FSW followed by DR (FSW-DR), and the last set applied FSW followed by PWHT (FSW-PWHT). Fatigue testing (screening) was performed through a four-point bending test with a bending stress of approximately 300 MPa, test frequency of 2.5 Hz at room temperature, and stress ratio (R) of 0. The FSW parameters included a tool rotational speed of 1600 rpm, welding speed of 30 mm/min, immersion depth of 0.1 mm, dwell time of 15 s, and tool tilt angle of 0 °. The DR parameters included a rolling pressure of 150 bar and rolling speed of 1400 mm/min. The results revealed that the residual stress significantly influenced fatigue life. The fatigue test demonstrated that FSW workpieces treated with the DR process (FSW-DR) exhibited the highest fatigue life, showing a remarkable increase of 33.5% compared with that of untreated FSW workpieces. Moreover, the residual stress changed from tensile to compressive, accompanied by noticeable enhancements in microhardness and surface roughness. These results highlight that FSW followed by the DR process (FSW-DR) positively affects weld surface integrity, resulting in an extended service life for welded components.

Experimental investigation to assess the surface integrity in WEDM of Al-based hybrid composite material

Aluminum-based hybrid composites are used in various engineering applications due to their unique properties, such as high strength, good wear resistance, excellent corrosion resistance, and low density. Aluminum metal matrix (AMMC) composites reinforced with ceramic particles can be more difficult to machine than traditional aluminum alloys because of their increased hardness and abrasiveness. Wire electric discharge machining is a non-traditional machining process that uses a thin metal wire, typically made of molybdenum, brass or tungsten to cut through a workpiece using electrical discharge sparks. This process is useful for precision machining of complex shapes and profiles in hard or difficult to machine materials. WEDM is a commonly used process for cutting Al-SiC-ZrO2 HAMMCs due to their hardness and difficulty in machining using conventional techniques. The present study examines the relationship between machining parameters like pulse on time (TON), pulse off time (TOFF), peak current (IP) and wire feed (WF) and material removal rate (MRR) and surface roughness ( Ra) for Al-SiC-ZrO2 in WEDM. The Box-Beckham Design was used to plan the experiments, and response surface method was employed to develop the models. The pulse duration, TOFF, IP, and quadratic terms of [Formula: see text] and [Formula: see text] are the most influential factors of the MRR. The TON, IP and interaction term (TON × IP), and [Formula: see text] were the most significant factors for Ra. Multi-response optimization of process parameters was obtained using the desirability function approach. Furthermore, the machined samples were analyzed for surface integrity using SEM techniques. The prediction from this model validated the confirmation results.

Surface structure evolution and measurement analysis of Ti6Al4V titanium alloy by electric arc electrochemical machining

In this study, a theoretical model about the conversion mechanism of material removal by electric arc electrochemical machining (EAECM) was derived. The limiting conversion rate of ECM-EAECM was measured on this basis. The current waveform, surface integrity, shape accuracy and process indexes during machining were measured and evaluated. The results showed that when the limiting conversion rate of ECM was exceeded, the material removal consisted of alternating effects of electric arc machining (EAM) and ECM. The proportion of EAM increased and the surface structure evolved into discharge defects, verifying the correctness of the theory. In addition, parametric crossover experiments were performed to clarify the degree of parametric response to EAECM modulation. Finally, the optimal combination of parameters resulted in a material removal rate of up to 5452 mm3/min, a relative electrode wear rate of 1.39 %, and a surface roughness of only 4.62 μm.

Improving the surface quality of additive manufactured polyamide parts using conventional treatment methods

AbstractAdditive manufacturing processes have progressed in years past from not only being prototyping methods to also being end-product manufacturing methods. However, there are many challenges hindering higher industrial adoption rates of additive manufacturing such as low surface quality of the manufactured parts. Post-process surface treatment methods can play a key role in addressing this challenge. In this work, three mechanical methods were applied to selective laser-sintered polyamide 12 (PA12) parts with the aim of improving the surface quality. The effects of the methods regarding the surface integrity characteristics were evaluated. The results show improved surface roughness across all three methods: from initial Ra of 7.09 μm to 0.055 μm Ra, 0.28 μm Ra and 0.45 μm Ra by grinding, diamond turning and milling on the surfaces oriented upwards during fabrication respectively. Across the three methods, surface hardness was slightly reduced: with a maximum reduction of 2.5% by diamond turning.

Effect of surface high density twin microstructure induced by shot peening on the fatigue behavior of Ti-6Al-4V

A detailed analysis of the surface high density twin microstructure and fatigue resistance of the Ti-6Al-4V titanium alloy specimens treated with the different shot peening parameters was conducted, compared with the as-received samples. Experimental results revealed that a high-density twinned structure layer formed on the surface of the shot peened Ti-6Al-4V titanium alloy. The predominant twinning type was {10 1‾ 2} extension twins. The density of twins decreases with increasing depth from the surface, and this phenomenon has been proven to be related to the strain rate. A shot peening intensity of 0.3mmA and 200% coverage are suitable, yielding superior surface integrity. Furthermore, shot peening can improve the fatigue life of the Ti-6Al-4V titanium alloy. This enhancement stems from the synergistic effects of the high-density twinned structure, compressive residual stress, and surface work-hardening, which collectively inhibit surface fatigue crack initiation and shift the initiation region to the subsurface, also impeding crack propagation.

Temporal and spectral signatures of the interaction between ultrashort laser pulses and Bloch surface waves

The resonant excitation of Bloch Surface Waves (BSWs) in dielectric one-dimensional photonic crystals is becoming a realistic photonic solution for surface integration in many domains, from spectroscopy to local field management. Bringing BSWs to ultrafast and nonlinear regimes requires a deep knowledge of the effects that the photonic crystal dispersion and the resonant surface wave excitation have on the ultrashort laser pulses. We report on the experimental evidence of spectral and temporal modifications of the radiation leaving a planar one-dimensional photonic crystal after coupling to BSWs. In such a resonant condition, a characteristic long temporal tail is observed in the outgoing pulses. Observations are performed by employing both frequency-resolved optical gating and field cross-correlation techniques.

Surface Integrity Analysis of Si3N4 Under cryogenic assisted Femtosecond Laser Ablation

Femtosecond laser is suitable to process Si3N4, but heat effect forming during machining process could degrade the performance of specimen. To reduce heat damage, in this study, the effects of cryogenic assisted laser machining on the surface quality and micro-structures of Si3N4 was investigated. The femtosecond laser was employed to ablate Si3N4 at various low temperatures, accompanied with comprehensive analysis of the surface roughness, material removal rate and SEM topography. To further illustrate the formation mechanism of surface structure, finite element analysis was conducted. Results indicated that while low temperature exerted negligible effects in single-layer ablation, multi-layer laser machining benefits from improved surface quality. Low temperature mitigated thermal effects and reduced the recast layer area, resulting in decreased surface roughness. The lowest surface roughness was obtained during the machining of the specimen at -60°C of 1.072μm, representing a 54.6% reduction compared to ambient air machining. However, further decreasing the temperature below -60°C led to an increase in surface roughness. This was attributed to the combined effects of Gaussian beam energy distribution and low temperature, resulting in incomplete ablation of the surface region between two scanning pitches, thereby decreasing surface quality. This research provides valuable insights into the cryogenic assisted femtosecond laser machining.