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 serviceenvironments,which are significantly affected by surface integrity(SI)indexes(especially surface topography,residual stressσ_(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 compressiveσ_(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 theindeterminacy 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 furtherpredicted.The predicted FCI sites corresponded well with the experimental results,therebyverifying 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,thefatigue life of Inconel 718 samples could be improved by approximately 140%.

Surface Integrity of Inconel 738LC Parts Manufactured by Selective Laser Melting Followed by High-speed Milling

This study is concerned with the surface integrity of Inconel 738LC parts manufactured by selective laser melting(SLM)followed by high-speed milling(HSM).In the investigation process of surface integrity,the study employs ultradepth three-dimensional microscopy,laser scanning confocal microscopy,scanning electron microscopy,electron backscatter diffractometry,and energy dispersive spectroscopy to characterize the evolution of material microstructure,work hardening,residual stress coupling,and anisotropic effect of the building direction on surface integrity of the samples.The results show that SLM/HSM hybrid manufacturing can be an effective method to obtain better surface quality with a thinner machining metamorphic layer.High-speed machining is adopted to reduce cutting force and suppress machining heat,which is an effective way to produce better surface mechanical properties during the SLM/HSM hybrid manufacturing process.In general,high-speed milling of the SLM-built Inconel 738LC samples offers better surface integrity,compared to simplex additive manufacturing or casting.

Optimize Multiple Peening Effects on Surface Integrity and Microhardness of Aluminum Alloy Induced by LSP

Laser shock peening is a modernized surface enhancement performed methodically to improve fatigue life, enhance the hardness of the material and make coarse grains flat under the superficial layer. In this current study, the effect of varying optimized multiple laser shock peening (LSP) is studied on the surface integrity, microhardness, and mechanical properties. The results show that the LSP-treated specimens have visible signs of valleys, wavy and varying height distribution as well as dimples. However, the presence of non-uniformity and sharp protrusions was detected from the superficiality of the as-received specimen and this was so because of the SiC abrasive material used to polish the superficial layer of the specimen before the test experiment. Prior to LSP, the surface roughness was 2 μm, however, after LSP the roughness increased to 4 μm, 6 μm and 17 μm for 1, 2, and 4 impacts, respectively. High-density dislocation can also be observed close to the grain boundary because the grain boundary prevents the migration of dislocation which could lead to dislocation walls and dislocation tangles. The increase in impacts decrease the average grain size, nevertheless, the micro-strain increased after multiple impacts. Furthermore, coarse grains after LSP were transformed into finer grains. The increase in the number of impacts increases the micro-strain likewise the full-width half maximum (FWHM). Finally, the increase in microhardness increases as the LSP impacts increase.

ANALYSIS ON SURFACE INTEGRITY DURING HIGH SPEED MILLING FOR NEW DAMAGE-TOLERANT TITANIUM ALLOY

Surface integrity of a new damage-tolerant titanium alloy （TC21）, including surface roughness, microhardness and metallurgical structure is investigated when normal and high speed milling are used at different tool wear status. Results show that good surface integrity of TC21 can be obtained in high speed milling. In addition, even in acutely worn stages, there is no so-called serious hardening layer （or white layer） according to the studies on microhardness and metallurgical structure.

EXPERIMENT ON SURFACE INTEGRITY OF MILLING TOOL FOR HARDENED STEEL SKD11

To evaluate the new designed cutting tools for high-efficiency milling of the hardened die steel SKD11,surface integrities of millers with different geometric structures are analyzed, considering the surface roughness, micrograph of chips, surface microhardness, residual stress and metallurgical texture of the surface layer. The in fluences of geometric characteristics of different cutting tools and their wear characteristics on the surface integrity are studied. Results show that the milling tool with rake angle; 5 of the hardened diesteel. The generation of saw-tooth chips is depressed when a reasonable positive rake angle is selected. And the compressive residual stress is induced on the machined surface in milling the hardened die steel. The occurrence of surface softening is postponed by increasing the clearance angle and reducing the tool flank wear.

Surface Integrity of Ultrasonically-Assisted Milled Ti6Al4V Alloy Manufactured by Selective Laser Melting

The Ti6Al4V parts produced by the existing selective laser melting(SLM)are mainly confronted with poor surface finish and inevitable interior defects,which substantially deteriorates the mechanical properties and performances of the parts.In this regard,ultrasonically-assisted machining(UAM)technique is commonly introduced to improve the machining quality due to its merits in increasing tool life and reducing cutting force.However,most of the previous studies focus on the performance of UAM with ultrasonic vibrations applied in the tangential and feed directions,whereas few of them on the impact of ultrasonic vibration along the vertical direction.In this study,the effects of feed rate on surface integrity in ultrasonically-assisted vertical milling(UAVM)of the Ti6Al4V alloy manufactured by SLM were systemically investigated compared with the conventional machining(CM)method.The results revealed that the milling forces in UAVM showed a lower amplitude than that in CM due to the intermittent cutting style.The surface roughness values of the parts produced by UAVM were generally greater than that by CM owing to the extra sinusoidal vibration textures induced by the milling cutter.Moreover,the extra vertical ultrasonic vibration in UAVM was beneficial to suppressing machining chatter.As feed rate increased,surface microhardness and thickness of the plastic deformation zone in CM raised due to more intensive plastic deformation,while these two material properties in UAVM were reduced owing to the mitigated impact effect by the high-frequency vibration of the milling cutter.Therefore,the improved surface microhardness and reduced thickness of the subsurface deformation layer in UAVM were ascribed to the vertical high-frequency impact of the milling cutter in UAVM.In general,the results of this study provided an in-depth understanding in UAVM of Ti6Al4V parts manufactured by SLM.

Effect of Machined Surface Integrity on Fatigue Performance of Metal Workpiece:A Review

Fatigue performance is a serious concern for mechanical components subject to cyclical stresses,particularly where safety is paramount.The fatigue performance of components relies closely on their surface integrity because the fatigue cracks generally initiate from free surfaces.This paper reviewed the published data,which addressed the effects of machined surface integrity on the fatigue performance of metal workpieces.Limitations in existing studies and the future directions in anti-fatigue manufacturing field were proposed.The remarkable surface topography(e.g.,low roughness and few local defects and inclusions)and large compressive residual stress are beneficial to fatigue performance.However,the indicators that describe the effects of surface topography and residual stress accurately need further study and exploration.The effect of residual stress relaxation under cycle loadings needs to be precisely modeled precisely.The effect of work hardening on fatigue performance had two aspects.Work hardening could increase the material yield strength,thereby delaying crack nucleation.However,increased brittleness could accel-erate crack propagation.Thus,finding the effective control mechanism and method of work hardening is urgently needed to enhance the fatigue performance of machined components.The machining-induced metallurgical structure changes,such as white layer,grain refinement,dislocation,and martensitic transformation affect the fatigue performance of a workpiece significantly.However,the unified and exact conclusion needs to be investigated deeply.Finally,different surface integrity factors had complicated reciprocal effects on fatigue performance.As such,studying the comprehensive influence of surface integrity further and establishing the reliable prediction model of workpiece fatigue performance are meaningful for improving reliability of components and reducing test cost.

Influence and Optimization of Surface Roughness on Surface Integrity during Turning Using Grey Relational Analysis

Current machining studies have reported effects of prevalent and common factors,while ultra⁃high finish requires holistic approach to identify all factors and investigate their effects on machining of hard to machine materials.In this work,a less investigated yet important factor,roughness of the uncut surface,was studied,and its effects on the individual response,i.e.,surface finish of the machined part,were found to be significant.AISI 316,which is mainly applied in strategic areas,was selected and three effective turning factors,cutting speed(A),feed rate(B),and roughness of the uncut surface(C)on three output responses including surface roughness of the machined surface(Ra),microhardness(HV),and material removal rate(MRR),were reported.Further,single response optimization of the individual output response and multi⁃response optimization of all the three responses were carried out.Taguchi L9 orthogonal array based signal⁃to⁃noise(S/N)ratio method was used for individual response optimization,and grey relational analysis(GRA)was employed for multi⁃response optimization.Effects of the process factors on the output responses were evaluated through inclusive statistical analyses.The individual response optimization revealed that there was a considerable effect of roughness of the uncut surface on the machining performance.Results of the GRA illustrated that the speed during the cutting process and the feed rate had substantial trace on the surface integrity(indicated by Ra and HV)and production rate(indicated by MRR),while roughness of the uncut surface did not have a significant effect.

Improvement of titanium alloy TA19 fatigue life by submerged abrasive waterjet peening:Correlation of its process parameters with surface integrity and fatigue performance

Submerged abrasive waterjet peening(SAWJP)is an effective anti-fatigue manufacturing technology that is widely used to strengthen aeroengine components.This study investigated the correlation of SAWJP process parameters on surface integrity and fatigue life of titanium alloy TA19.SAWJP with different water pressures and standoff distances(SoDs)was conducted on the TA19 specimens.The surface integrity of the specimens before and after SAWJP with different process parameters was experimentally studied,including microstructure,surface roughness,microhardness,and compressive residual stress(CRS).Finally,fatigue tests of the specimens before and after SAWJP treatment with different process parameters were carried out at room temperature.The results highlighted that the fatigue life of the TA19 specimen can be increased by 5.46,5.98,and 6.28 times under relatively optimal process parameters,which is mainly due to the improved surface integrity of the specimen after SAWJP treatment.However,the fatigue life of specimens treated with improper process parameters is decreased by 0.55 to 0.69 times owing to the terrible surface roughness caused by the material erosion.This work verifies that SAWJP can effectively improve the surface integrity and fatigue life of workpieces,and reveals the relationship between process parameters,surface integrity,and fatigue life,which provides support for the promotion of SAWJP in the manufacturing fields.

Influence of transversal vibration on cutting performance and surface integrity during ultrasonic peening drilling of Al-Li alloys

Advanced hole-making process is of great importance to enhance the fatigue performance of Al-Li alloy part in aviation industry.Ultrasonic peening drilling(UPD),in which an ultrasonic transversal vibration is applied to the cutting tools,is a recently proposed hole-making method that integrates precision-machining and surface strengthening by single-shot operation.In the study,kinematics,material removal mechanism and strengthening mechanism for UPD of Al-Li alloy by helical fluted reamers are analyzed.The effect of transversal vibration on the cutting performance and surface integrity is studied through comparative experiments between UPD and conventional drilling(CD)of Al-Li alloy holes.The experimental results show that UPD exhibits superior cutting performance with a maximum reduction of 52.6%in thrust force and 52.3%in torque,respectively,compared to CD.Moreover,narrower dimensional tolerance is obtained in UPD due to the reduced transversal force and improved machining stability.Additionally,deeper plastic deformation,higher surface microhardness and residual compressive stress of machined holes are obtained by UPD.The electron back-scattered diffraction(EBSD)analysis confirms that deeper machined affect area and grain refinement are realized in UPD.Therefore,the results indicate that UPD is a feasible method for achieving high-precision and strengthened holes for Al-Li alloy.

Surface integrity evolution during creep feed profile grinding ofγ-TiAl blade tenon

Gamma titanium-aluminum(γ-TiAl)intermetallic compounds are increasingly used in manufacturing key hot-end components(e.g.,blade tenon)in aero engines due to their high specific strength and lightweight properties.Creep feed profile grinding(CFPG)as a crucial precision process that is applied to produce the final profile of the blade tenon.However,sudden surface burns and microcracks of machined c-TiAl blade tenon often occur because of its low plasticity and high strength during grinding processes,leading to poor surface integrity.In this work,CFPG experiments based on the profile characteristics ofγ-TiAl blade tenon were performed and an associated undeformed chip thickness model considering grain–workpiece contact condition was established to explore the evolution of the surface integrity.Subsequently,the surface integrity was analyzed at different positions of the blade tenon in terms of surface roughness and morphology,metallographic structure,microhardness,and residual stress.Results show that the profile characteristics of blade tenon have a significant influence on machined surface integrity because of the thermomechanical effect at various detecting positions.The residual stress was established based on the undeformed chip thickness model considering the profile structure,with a prediction error of 10%–15%.The thermomechanical effect is more obvious at the bottom area,where the surface roughness,work hardening degree,and subsurface plastic deformation range are the largest,while the values at the bevel area are the smallest.Based on the undeformed chip thickness model,a residual stress finite element simulation was conducted by employing thermomechanical coupled effects.In addition,the error between the simulation and the experiment was between 10%–15%.Strain and strain rate equations were established through the relationship between material displacement and depth.The average strain and strain rate of the ground surface when ap is 1.0 mm are 18.8%and 33.2%larger than when ap is 0.5 mm,respectively.This study deepens the understanding of surface integrity under the influence of CFPGγ-TiAl and provides a practical reference and theoretical basis for realizing high-quality profile grinding of other complex parts.

Experimental investigation of the relation between the surface integrity and bending fatigue strength of carburized gears

Bending fatigue is an essential parameter that needs to be considered in the improvement process of the power density and reliability of gear drives. Quantitative relations among the manufacturing parameters, surface integrities, and fatigue performance are not clear, which seriously limits the effectiveness of an anti-fatigue design. For this work, tooth-bending fatigue tests of carburized gears with different surface integrities were performed using a pulsator. The effects of the manufacturing parameters and surface integrities on the gear fatigue, such as surface hardness and residual stress, were investigated. The experimental results revealed that due to the improvement of surface integrities after shot peening, the nominal bending stress number(fatigue limit) increased by 6.3%–31.1%, with an amplitude range of 39–143 MPa. A supervised learning algorithm of a random forest was implemented to determine the contribution of the surface hardness and surface residual stress to the nominal stress number. An empirical formula was proposed to predict the nominal stress number considering the surface integrities. The prediction error was less than 7.53%, as verified by several gear-bending fatigue tests. This provided theoretical support for the modern, anti-fatigue design of the gears.

Collaborative manufacturing technologies of structure shape and surface integrity for complex thin-walled components of aero-engine:Status,challenge and tendency

Presently,the service performance of new-generation high-tech equipment is directly affected by the manufacturing quality of complex thin-walled components.A high-efficiency and quality manufacturing of these complex thin-walled components creates a bottleneck that needs to be solved urgently in machinery manufacturing.To address this problem,the collaborative manufacturing of structure shape and surface integrity has emerged as a new process that can shorten processing cycles,improve machining qualities,and reduce costs.This paper summarises the research status on the material removal mechanism,precision control of structure shape,machined surface integrity control and intelligent process control technology of complex thin-walled components.Numerous solutions and technical approaches are then put forward to solve the critical problems in the high-performance manufacturing of complex thin-wall components.The development status,challenge and tendency of collaborative manufacturing technologies in the high-efficiency and quality manufacturing of complex thin-wall components is also discussed.

Ironing effect on surface integrity and fatigue behavior during ultrasonic peening drilling of Ti-6Al-4V

Imposing compressive residual stress field around a fastening hole serves as a universal method to enhance the hole fatigue strength in the aircraft assembly filed.Ultrasonic Peening Drilling(UPD)is a recently proposed hybrid hole making process,which can achieve an integration of strengthening and precision-machining with a one-shot-drilling operation.Due to the ironing effect of tool flank surface,UPD introduces large compressive residual stress filed in hole subsurface.In order to reveal the strengthening mechanism of UPD,the influence of ultrasonic vibration and tool dynamic relief angle on ironing coverage rate and its corresponding effect on surface integrity in UPD were analyzed.The experiments were conducted to verify the influence of ironing effect on surface integrity and fatigue behavior of Ti-6Al-4V hole in UPD.The results indicate that the specimen features smaller surface roughness,higher micro-hardness,plastic deformation degree and circumferential compress residual stress under higher ironing coverage rate.The fatigue life increases with the raise of ironing coverage rate,and the fatigue source site in UPD shifts from surface to subsurface comparing with that without vibration assistance.The results demonstrates that a better strengthening effect can be obtained by reasonably controlling the ironing coverage rate in UPD.

Experimental study on surface integrity refactoring changes of Ti-17 under milling-ultrasonic rolling composite process

Ultrasonic rolling is an advanced non-cutting surface strengthening method that combines traditional rolling with ultrasonic vibration.In this research,the experiment of orthogonal end milling-ultrasonic rolling composite process has been carried out.The surface integrity refactoring changes and its mechanism of Ti-17 titanium alloy during the milling-ultrasonic rolling composite process has been studied and analyzed by the test and analysis of the surface geometric characteristics,residual stress,microhardness and microstructure before and after ultrasonic rolling.The residual stress and microhardness gradient distribution were characterized by cosine decay function and exponential decay function.All indicators of surface integrity were significantly improved after ultrasonic rolling.The study demonstrates that the reduction effect of the surface roughness by ultrasonic rolling process is inversely proportional to the initial surface roughness value.The ultrasonic rolling can only change the distribution form of the surface topography when the initial surface roughness is small.In addition,the improvement effect of ultrasonic rolling on surface compressive residual stress and microhardness decreased with the increase of initial milled surface roughness and surface compressive residual stress due to the factors such as energy absorption efficiency and mechanical properties changes of surface materials.A better ultrasonic rolled surface can be obtained by controlling the roughness and residual compressive stress of the initial milling surface to a small level.

Surface integrity of ball burnished bioresorbable magnesium alloy

Magnesium alloys are potential biodegradable and biocompatible implant materials because of their excellent biological properties. Recently, interest in these alloys as a promising alternative for temporary orthopedic implants has grown owing to their desirable biological, mechanical, and physical properties. However, the application of magnesium alloys is hindered by their rapid degradation and low corrosion resistance in physiological fluids, leading to the failure of implants. Thus, the current challenge is to enhance the corrosion resistance and control the degradation rate of magnesium under physiological conditions. The rapid degradation of magnesium alloys can be controlled by improving their surface integrity, such as surface roughness and microhardness. The present study aims to improve the surface integrity of the Mg Ze41A alloy by the ball burnishing technique. The surface roughness improved by 94.90% from 0.941 μm to 0.048 μm with a burnishing force of 50 N, burnishing speed of 1 300 r/min, burnishing feed of 130 mm/min, and three passes. Similarly, the microhardness improved by 50.62% from 75.2 HV to 113.27 HV with a burnishing force of 60 N, burnishing speed of 1 100 r/min, burnishing feed of 100 mm/min, and five passes. The variations in microhardness, which were observed up to 400 μm beneath the surface, exhibited a linear nature. These variations may be attributed to the movement of dislocations, formation of new dislocations, nanocrystal structures, metastable phases and subgrains, and lattice distortion or grain refinement. The surface features obtained from optical images demonstrated the fundamental mechanisms involved in the ball burnishing process. The concept of burnishing maps and zones will assist in the design of the ball burnishing parameters of a material with an equivalent yield strength of 140 MPa. The significant improvement in the surface integrity of the Mg Ze41A alloy by the ball burnishing technique is expected to improve its functional performance.

Grindability and Surface Integrity of Cast Nickel-based Superalloy in Creep Feed Grinding with Brazed CBN Abrasive Wheels

The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters （i.e. wheel speed, workpiece speed and depth of cut） on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride （CBN） abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardhess and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 ℃ is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm^3. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the bum-free and crack-free ground surface.

Dimension Accuracy and Surface Integrity of Creep Feed Ground Titanium Alloy with Monolayer Brazed CBN Shaped Wheels

Titanium alloy tenon is creep feed ground with monolayer brazed cubic boron nitride （CBN） shaped wheels. The dimension accuracy of the tenon is assessed and the results indicate that it completely meets the requirement of blade tenon of aero-engine. Residual stresses, surface roughness, microstructure and microhardness are measured on ground surfaces of the specimen, which are all compared with that ground with vitrified CBN wheels. Under all the circumstances, compressive residual stress is obtained and the depth of the machining affected zone is found to be less than 40 μm. No phase transformation is observed at depths of up to 100 lain below the surface, though plastic deformation is visible in the process of grain refinement. The residual stress and microhardness of specimens ground with brazed CBN wheels are observed to be lower than those ground with vitrified ones. The arithmetic mean roughness （Ra） values obtained are all below 0.8μm.

Boosting rate performance of layered lithium-rich cathode materials by oxygen vacancy induced surface multicomponent integration

The rapid development of electric vehicles and portable energy storage systems demands improvements in the energy density and cost-effectiveness of lithium-ion batteries,a domain in which Lithium-rich layered cathode(LLO)materials inherently excel.However,these materials face practical challenges,such as low initial Coulombic efficiency,inferior cycle/rate performance,and voltage decline during cycling,which limit practical application.Our study introduces a surface multi-component integration strategy that incorporates oxygen vacancies into the pristine LLO material Li1.2Mn_(0.6)Ni_(0.2)O_(2).This process involves a brief citric acid treatment followed by calcination,aiming to explore rate-dependent degradation behavior.The induced surface oxygen vacancies can reduce surface oxygen partial pressure and diminish the generation of O_(2)and other highly reactive oxygen species on the surface,thereby facilitating the activation of Li ions trapped in tetrahedral sites while overcoming transport barriers.Additionally,the formation of a spinel-like phase with 3D Li+diffusion channels significantly improves Li^(+)diffusion kinetics and stabilizes the surface structure.The optimally modified sample boasts a discharge capacity of 299.5 mA h g^(-1)at a 0.1 C and 251.6 mA h g^(-1)at a 1 C during the initial activation cycle,with an impressive capacity of 222.1 mA h g^(-1)at a 5 C.Most notably,it retained nearly 70%of its capacity after 300 cycles at this elevated rate.This straightforward,effective,and highly viable modification strategy provides a crucial resolution for overcoming challenges associated with LLO materials,making them more suitable for practical application.

An Exploration of Surface Integrity Remanufacturing for Aeroengine Components

Surface integrity is the major factor impacting on the operation quality, service life and reliability of the aeroengine components. The surface integrity of aeroengine component is damaged by the failures such as crack,deformation, oxidation, corrosion, erosion, and microstructural degeneration. It adopts advanced remanufacturing technologies to restore or improve the surface integrity and regenerate these high value parts. This paper firstly puts forward the concept, namely surface integrity remanufacturing for aeroengine components, and its connotation. The key remanufacturing technologies have been developed to repair the components with surface damages. Ultimately, some application examples of surface integrity remanufacturing technologies as well as their effects in aeroengine maintenance are introduced. The discarded components have been reused and their service lives have been extended and their reliability has been increased by implementing surface integrity remanufacturing. It has realized "The Repaired Components Outpacing the New Ones", material saving, energy saving, and emission reduction.